Model answers Flashcards
0
Q
M- Slow twitch fibres
A
Contract more slowly
Less powerful
Adapted for endurance work
Adapted for aerobic respiration - to avoid build up of lactate
Lots of myoglobin and has a higher affinity for oxygen - appears darker
Good supply of glycogen, which is hydrolysed to glucose for respiration
Good supply of blood vessels to circulate oxygen and glucose ( and remove carbon dioxide)
Numerous mitochondria to produce ATP
1
Q
M- What is power stroke
A
when the myosin head moves and pulls the actin along
2
Q
M- DNA sequencing (Sanger method)
A
Determining the exact order of nucleotides in a DNA sequence
1. Four tubes set up containing single stranded DNA fragments (of the gene to be sequenced) - these act as a template for the synthesis of the complementary strand
- Mixture of nucleotides added (ATCG) plus a small quantity of modified nucleotides terminators added to each tube (A* to tube 1, T* to tube 2 etc)
- Primer added (as DNA polymerase only works on short sections of double stranded DNA) - the primer is labelled with a fluorescent dye or is radioactively tagged
- DNA polymerase added t synthesise new DNA
- Addition of a modified nucleotide to the sequence (which is a random process) truncates the synthesis and depending on where this happens, different size fragments are produced
- The fragments from tube 1 all have one thing in common - they all end in A (for example) and all the fragments in tube 2 end in T etc. Fragments can be identified due to the radioactive or fluorescent labelling
- The fragments are then separated using gel electrophoresis (based on density)
3
Q
M- PCR
A
DNA is heated to 95˚C to separate the strands
By breaking the hydrogen bonds
Mixture is cooled to 55˚C
Primers are added - lower temperature allows primers to anneal
Molecules are reheated to 72˚C (optimum for Taq polymerase)
Taq polymerase (DNA polymerase) joins nucleotides together
4
Q
Why is negative feedback important in maintaining a system at a set point?
A
If the information is not fed back once an effector has corrected any deviation and returned the system to the set point, the receptor will continue to stimulate the effector and an over-correction will lead to a deviation in the opposite direction from the original one.
5
Q
M- Effect of siRNA on gene expression
A
Sections of double stranded RNA are cut into smaller pieces of RNA by an enzyme dicer, which produces small interfering siRNA, one strand of the new single stranded RNA combines with an enzyme; the newly formed single stranded siRNA pairs with complementary bases on mRNA; enzyme cuts the mRNA into small sections; translation cannot occur so gene expression is blocked
6
Q
M- Regulation of blood glucose
A
blood glucose levels decreases which is detected by alpha cells (in the islets of Langerhans) in the pancreas
glucagon is produced
liver cells have receptors to glucagon and this activates an enzyme that converts glycogen to glucose ( glycogenolysis)
liver cells also increase the conversion of amino acids and glycerol into glucose (gluconeogenesis)
Raises in blood glucose causes alpha cell to reduce glucagon secretion (negative feedback)
blood glucose levels increases which is detected by beta cells ( in the islets of Langerhans) in the pancreas
insulin is produced
this causes increase cellular respiration, conversion of glucose to glycogen (glycogenesis), conversion of glucose to fat, absorption of glucose into cells
lowering of blood glucose causes beta cells to reduce insulin secretion (negative feedback)
adrenaline also raises blood glucose by activating an enzyme that causes the breakdown of glycogen to glucose in the liver (glycogenolysis) and by inactivating an enzyme that synthesises glycogen from glucose (glycogenesis)
7
Q
M- Using lipid molecule wrapping of the CFTR gene
A
CFTR genes isolated and inserted into bacterial plasmid vectors
Vectors are reintroduced into host cells and gene markers are used to detect successful recombinants
Bacteria are cloned to produce multiple copies of the CFTR gene
Plasmids extracted and wrapped in lipid molecules to form a liposome
Liposomes sprayed into nostrils as an aerosol and are drawn into the lungs
Liposomes pass across the phospholipid portion of the cell membrane of lung epithelial cells
8
Q
M- Two ways to get many copies of a gene
A
- PCR (in vitro cloning)
- In vivo cloning (inserting a gene into a plasmid and transforming bacteria) - this one get s you a desired protein product
9
Q
M- Regulation of body temperature in endotherms - response to warm environment/ increase in body temperature
A
- Vasodilation (shunt vessels constricts)
- Increased sweating
- lowering of body hair
- Behavioural mechanisms e.g. seeking shade
10
Q
M-Regulation of body temperature in endotherms - response to a cold environment/ decrease in core body temperature
A
- Vasoconstriction (shunt vessels dilate)
- Shivering
- Raising of hair
- Decrease in sweating
- Behavioural mechanisms e.g. huddling and sheltering
- Increased metabolic rate (N.B. this is a metabolic reason not physiological one)
10
Q
M- type 1 diabetes
A
where insulin is not produced and the disease is controlled by insulin injections
11
Q
M- Tropism definition
A
Growth movement of part of a plant in response to a directional stimulus
11
Q
M- Advantage to woodlice of moving away from a bright area
A
Prevents desiccation (drying out)
Helps to prevent against predation
Helps prevent temperature rising above optimum so enzymes are not denatured
(May also helps them to find food if their usual habitat is dark)
16
Q
M- Oestrus in animals
A
farmers can manipulate the oestrus cycle in animals by giving progesterone implants. When the implant is removed, the animals all come into season at the same time.
The advantage of this is two fold (both involve saving money) because the artificial insemination team/bull/ram only needs to be brought to the farm once and also lambs will be born at the same time
17
Q
M- Comparison of hormonal and nervous systems
A
in the hormonal system transition in by the blood whereas in the nervous system transmission is by neurones
Transmission is slow in the hormonal system but fast in the nervous system
response of hormonal system is widespread whereas response of the nervous system is localised
hormonal response is long lasting but nervous response is short lived
effects of hormonal system may be permanent and irreversible but effects if the nervous system are temporary and reversible
Hormones travel to all parts of the body but only target organs respond whereas nerve impulses travel to specific parts of the body
18
Q
M- Humans produce a large number of different hormones but only small number of different neurotransmitters. Explain the significance of this
A
Hormones reach all cells by the blood
Neurotransmitters secreted directly onto target cell
Different hormones are specific to different target cells
19
Q
M- type 2 diabetes
A
where target cell glycoprotein receptors lose their responsiveness to insulin (or inadequate insulin is releases from the pancreas) - this is usually regulated by controlling the diet (sometimes drugs can be given which stimulate insulin production)
20
Q
M- Explain the benefit of seedlings exhibiting positive phototropism
A
Growing shoots grow towards light
Chloroplasts absorb more light for photosynthesis
20
Q
M- Talk about experiments involving the use of mica and agar blocks.
A
Agar allows the diffusion of chemicals through it but does not conduct electrical impulses.
Mica conducts electrical impulses but it is impermeable to chemicals.
Results of these experiments have shown that IAA is transferred down the shade side of the shoot.
Experiments involving the shoot tip being cut have shown that IAA is produced only in the growing tip
20
Q
M- Kinesis definistion
A
The random non-directional movement of an organism in response to a stimulus in which the rate of movement depends on the intensity of the stimulus
20
Q
M- Cone cells
A
Respond to higher levels of light intensity ( as their pigment , iodopsin, requires more light to break down)
Cone cells respond to colour and are connected to single neurones so they have higher visual acuity.
Hence we can not see colours at night and we see much more detail in colour
20
Q
What are the two centres of the medulla oblongata?
A
A centre of that increases heart rate - link to sinoatrial node by the sympathetic nervous system
A centre that decreases heart rate- linked to sinoatrial node by the parasympathetic nervous system
21
Q
M- What role does IAA have in the shoot?
A
IAA stimulates growth
23
M- Control of heart rate by pressure receptors
Pressure receptors in the carotid arteries and aorta detect increase in blood pressure; nervous impulses sent to medulla; medulla sends more impulses down parasympathetic nerve to SAN to decrease heart rate
26
M- Taxis definition
A simple response to an external directional stimulus
27
M- Control of heart rate by chemoreceptors
Respiration produces an increase in carbon dioxide ; this decreases blood pH; which is detected by chemoreceptors; in the wall of carotid arteries and aortic bodies; increasing frequency of impulses sent from medulla oblongata along sympathetic nerve; to SAN increasing heart rate, the increase blood flow that this causes leads to more carbon dioxide being removed by the lungs and so carbon dioxide levels return to normal, as a consequence the pH of the blood rises to normal and the chemoreceptors in the wall of the carotid arteries and the aorta reduces the frequency of nerve impulses to the medulla oblongata, the medulla oblongata reduces the frequencies of impulses to the SAN which decreases heart rate to normal.
29
M- What is a reflex?
A rapid response to a stimulus which is automatic ( not under conscious control)
30
M- Reflex arc
Stimulus --> receptor --> coordinator --> effector --> response
the receptor sends an impulse to the coordinator along a sensory neurone. intermediate neurones link the sensory neurones to the motor neurones. Motor neurones carry an impulse to the effectors ( usually the muscle or glands)
31
M- Spatial summation
Different presynaptic neurones release neurotransmitter into the same cleft in order for the concentration to accumulate to exceed the threshold
32
M- Importance of reflex actions
Protect body from harmful stimuli and do not have to be learned (are present at birth)
Fast because neurone pathway is short and only one or two synapses (which are the slowest part)
Involuntary and do not require decision making powers to the brain and the brain is free to carry out more complex responses
33
HSW- Drugs can act on synapses in 2 ways
1. Stimulate by creating more action potentials
- mimic a neurotransmitter (have a similar structure and binds to receptors)
- stimulate the release of neurotransmitter
- inhibiting enzymes that breakdown neurotransmitters
- enhance the binding or neurotransmitter to its receptors e.g. valium enhances GABA, which inhibits action potential formation
2. Inhibit by creating fewer action potentials
- inhibit release of neurotransmitter
- block receptors on postsynaptic neurone e.g. morphine, codeine, heroin block receptors on pain pathways, reducing pain experienced
34
M- Fovea
Point directly behind the pupil, which receives the most light (only cone cells here)
35
M- Periphery of the retina
only rod cells are found
| peripheral vision tends to be more blurry
36
M- What will happen to heart rate if fewer impulses are sent down the sympathetic nerve?
decrease
37
M- Functions of pacinian corpuscle
In its normal resting state, the stretch mediated sodium channels of the membrane around the neurone of the pacinian corpuscle are too narrow to allow sodium ions to pass along them. In this sate, the neurone of the pacinian corpuscle has a resting potential
When pressure is applied to the pacinian corpuscle, it changes shape and the membrane around its neurone becomes stretched
This stretching widens the stretch mediated sodium channels in the membrane and sodium ions diffuse into the neurone
The influx of sodium ions changes the potential of the membrane- becomes depolarised- thereby producing a generator potential
the generator in turn creates an action potential (nerve impulse) that passes along the neurone then, via other neurones, to the central nervous system
38
What is the distance between adjacent z lines called?
Sarcomere
39
M- What is meant by metabolic heat gain
Body's reactions such as respiration rate
41
M- How connections of rod cells to neurones make it possible to see in dim light
Several rods have connection with one bipolar neurone; uses spatial summation (build up of neurotransmitters) - this is retinal convergence; to exceed threshold for action potential
42
M- Rod cells
Contain Rhodopsin, a pigment which can be broken down in low light intensity.
A consequence of retinal convergence is that light received by rod cells sharing the same neurone will only generate a single impulse, regardless of how many neurones are stimulated - this results in low visual acuity
43
M- Action potential
Energy of stimulus causes sodium voltage-gated channels to open
Na+ ions diffuse into axon along an electrochemical gradient
This triggers a reversal in the potential difference across the membrane (depolarisation) +40mv
Need to mention: positive feedback - this is where a small influx of sodium ions into the axon stimulates further inward diffusion
44
M- Comparison of DNA and RNA
DNA contains deoxyribose sugar , RNA contains ribose
DNA contains the base thymine whereas RNA contains uracil
DNA is double stranded, RNA is single stranded
Both contain bases cytosine, guanine and adenine
Both contains phosphate groups
Both contain pentose sugars
45
M- Blind spot
Part of the eye where the optic nerve attaches and contains no rod or cone cells
46
M- Transcription
DNA double helix unzips, hydrogen bonds are broken
Transcriptional factor binds promotor of gene
RNA polymerase binds to promotor
Free mRNA nucleotides complementary base pair with exposed DNA nucleotides (only on the template strand)
RNA polymerase seals the new backbone of mRNA - catalyses the formation of new phosphodiester bonds between adjacent nucleotides
When RNA polymerase reaches a stop condon it detaches and pre-mRNA is formed
DNA strands rejoin
47
M- Why conduction along an unmyelinated axon is slower than along a myelinated one
In myelinated axons, the fatty sheath is an electrical insulator and prevents action potential from forming
Action potentials can only form at gaps in the sheath - Nodes of Ranvier
Action potentials jump form node to node - saltatory conduction
48
M- What causes rigor mortis after death - where cross bridges remain firmly bound?
No respiration so no ATP produced so myosin head unable to detach from actin binding site and unable to revert myosin head group to original position so no reattachment
50
M- Repolarisation
Voltage-gated sodium channels close, which prevents further influx of Na+ ions and voltage-gated channels open
K+ diffuse out causing repolarisation
Temporary overshoot of electrical charge ( hyperpolarisation) causes K+ channels to close
Resting potential is reestablished
51
M- Factors affecting speed of impulse
The presence of a myelin sheath (saltatory conduction-impulse jumps from node to node)
The diameter of the axon (the greater the diameter, the faster the conductance, as there is less resistance and less leakage of ions in larger axons)
Temperature ( the higher the temperature the faster the impulse due to faster diffusion of ions, more kinetic energy, more movement ; also respiration rate is faster so more ATP is produced)
52
M- Refractory period
Where inward movement of Na+ ions prevented due to closure of the sodium voltage-gated channels - impossible to create a further action potential during this time ; ensures that action potentials are propagated in only one direction; produced discrete impulses; limits the number of action potentials
53
M- Control of the oestrus cycle
(day 1) Pituitary gland releases FSH and this stimulates development of follicles in the ovary
Growing follicles secrete small amounts of oestrogen causing the uterus lining to build up the inhibition of FSH and LH from the pituitary ( negative feedback)
More oestrogen is produced by growing follicles - this then stimulates the release of FSH and LH (around day 10) (positive feedback)
The surge in FSH and LH production causes ovulation (day 14)
LH stimulates the empty follicle to form the corpus luteum, which secretes progesterone and smaller amounts of oestrogen
Progesterone maintains the uterus lining and inhibits FSH AND LH (negative feedback)
If the egg is not fertilised then the Corpus luteum degenerates and no longer produces progesterone
Lower levels of progesterone mean that the uterus lining breaks down (menstruation) and FSH is no longer inhibited
54
M- Comparisons mRNA and tRNA
mRNA is a single helix linear molecule whereas tRNA is a clover leaf shaped molecule
mRNA is chemically unstable, tRNA is chemically more stable
Both have the same bases
Both contain the pentose sugar ribose
tRNA has areas of complementary base pairing, mRNA does not
tRNA has hydrogen bonding, mRNA does not
tRNA is a standard length, mRNA length is variable
tRNA has an amino acid attachment site, tRNA has an anticodon
55
M- Release and binding of acetylcholine
Energy from stimulus causes calcium ion channels to open and Ca2+ ions enter the synaptic knob; synaptic vesicles fuse with presynaptic membranes and release acetylcholine into the synaptic cleft; acetylcholine fuses with complementary receptors on the presynaptic neurone causing sodium channels to open and Na+ ions to diffuse in along a concentration gradient causing depolarisation and generating a new action potential in the postsynaptic neurone
56
M- Recycling of acetylcholine
Acetylcholinesterase hydrolyses acetylcholine and ethanoic acid, which diffuses back across the synaptic cleft into the presynaptic neurone; ATP used to recombine choline and ethanoic acid
57
M- Why recycle (breakdown) neurotransmitters
To avoid build-up of transmitter in the synaptic cleft
So the neurotransmitter can be re-used
To prevent the formation of continuous action potentials in the post synaptic neurone (as voltage-gated sodium channels would remain open so the axon would be permanently depolararised)
58
M- Temporal summation
The same presynaptic neurone releases neurotransmitter over time in order for the concentration to accumulate to exceed threshold
59
M- Why is the nervous transmission delayed at synapses?
It takes time for enough neurotransmitter to be accumulated to exceed threshold
60
M- Synapse inhibition
Cl- ion channels on postsynaptic neurone open, causing Cl- ions to diffuse into axon; charge in the axon is made more negative than at resting - hyperpolarizes; new action potential less likely to form
61
M- Definition of negative feedback
changes that result in a system returning to a specific set point
61
HSW- GABA
Some chemicals produced by the body e.g. GABA can cause inhibition to happen by binding to receptors causing the chloride channels to open (synapse inhibition is not necessarily a bad thing)
One form of epilepsy is caused by insufficient GABA - a drug called Vigabatrin has a similar molecular structure to GABA and therefore binds to receptors inhibiting nerve transmission
61
M- Acetylcholine must be broken down in the synaptic cleft. If it isn't, what happens?
If the acetylcholine isn't hydrolysed, the acetylcholine stays bound to the receptors on the postsynaptic membrane meaning that the sodium channels will be permanently open so there are continuous action potentials forming. This means (if it is a neuromuscular junction) that the muscle would be permanently contracted and cannot relax
62
M- Describe how nerve impulses arriving at a neuromuscular junction result in the shortening of myofibrils
Entry of calcium ions into the presynaptic membrane
Vesicles fuse with membrane (/exocytosis/release TS)
Neurotransmitter diffuses
Binds to receptors on postsynaptic membrane (/muscle membrane)
Depolarisation - sodium ions enter
Release calcium ions from within the muscle
removes tropomyosin and binds to troponin
Cross bridge formation as myosin binds
Myosin head moves and pulls the actin along
They detach then reattach
ATPase reactivated
63
M- How does a metabolic poison affect nerve transmission
Inhibits production of ATP during respiration therefore no energy for active transport so sodium ions cannot be pumped out of the axon/potassium ions cannot be pumped into the axon so resting potential cannot be achieved
64
M- What happens to the structure during a muscle contraction
```
sarcomere shortens
z line moves closer together
H zone is shorter
I band is shorter
A band remains the same size - because the size of myosin filaments does not change
```
65
M- Role of calcium ions in contraction of a myofibril
Calcium ions bind to troponin this reveals the binding site on the actin, this allows heads to bid to the actin forming a cross bridge, this then activates ATPase (energy is released from ATP)
66
M- Regulation of body temperature in ectotherms
* Basking/ solar reorientation
* Taking shelter
* Gaining warmth from the ground
* Generating metabolic heat
* Increase/decrease in physical activity
* Colour variation
* Thermal gaping
67
M- Examples of genetically modified plants
Tomatoes that do not soften (the enzyme causing softening has its expression blocked, as the mRNA cannot be translated)
Herbicide-resistant crops
Disease-resistant crops e.g. maize produces a toxin, killing the beetles that feed in it
Plants that produce plastics
Rice that expresses bta-carotene to avoid the deficiency problems in some Asian countries
68
M- Resting potential
Na+ actively transport out of the axon by sodium potassium pump
K+ actively transported into the axon by sodium potassium pump
Active transport of Na+ is greater than that of potassium ions so 3 sodium ions move out for every 2 potassium ions moving in
The outward movement of sodium ions is greater that the inward movement of potassium ions as a result there are more sodium ions in the tissue fluid surrounding the axon than in the cytoplasm, and more potassium ions in the cytoplasm rather than in the tissue fluid thus creating an electrochemical gradient
Na+ start to diffuse back into the axon
K+ start to diffuse back out
Sodium channels are closed so K+ ions are diffusing out faster
Equilibrium is established, as further movement of K+ ions becomes difficult as the outside of the axon becomes more positively charged so there is no net movement of ions
69
M- Three methods of isolating a DNA fragment
1. Identify the gene using a DNA probe and cut it out using restriction enzymes
2. Artificially synthesise the gene, after working out its base sequence from knowing the primary protein structure
3. Using mRNA and reverse transcriptase to produce cDNA
70
M- Control of tropisms by IAA
Cells in tip produce IAA
IAA initially transported to all sides as it moves down the shoot
Light causes movement of IAA from light to shaded side
Greater concentration of IAA builds up on shaded side
Cells on shaded side become elongated
Shaded side grows faster causing shoot to bend towards the light
71
M- Role of proto-oncogenes
Normal role is to stimulate cell division; mutation can cause formation of an oncogene; this can permanently activate the membrane receptor protein so cell division is switched on even in the absence of growth factor; or the oncogene may code for growth factor, which is produced in excessive amounts
72
M- Advantages of PCR (in vitro gene cloning)
Extremely rapid
Does not require living cells
73
M- In muscle contraction, ATP is needed for
Movement of myosin head
Reabsorption of Ca2+ by active transport
In aerobic conditions, ATP needs to be generated rapidly - phosphocreatine regenerates ATP - stored in muscle and acts as a reserve supply of phosphate - replenished from inorganic phosphate from the breakdown of ATP when muscles relax
75
M- Fast twitch fibres
Contract more rapidly
Powerful contractions over a short period
Adapted for intense exercise
Have thicker and more numerous myosin filaments
High concentration of enzymes involved in anaerobic respiration
Good store of phosphocreatine to generate ATP quickly from ADP to provide energy for muscle contractions
76
M- Define gene therapy
The replacement or supplementation of defective genes in an individuals with genes cloned from healthy individuals (or with dominant alleles in the case of gene supplementation - but only useful if the disease causing gene is a recessive allele
77
M- All or nothing principle
Below the threshold value, no action potential and therefore no impulse is generated (this is the nothing part); any stimulus above the threshold value will produce an action potential regardless of the strength or size of the stimulus (this is the all part)
79
M- Post-transcriptional modification of pre-mRNA - splicing
Pre-mRNA copies whole section of a gene including non-coding regions
Introns are removed (spliced) from the mRNA by enzymes
Functional exons are joined together
Mature mRNA molecules leave nucleus via a nuclear pore
80
M- Translation
Ribosome attaches to mRNA at start codon (AUG)
tRNA is activated in the cytoplasm by binding to a specific amino acid
This process requires ATP
tRNA with complementary anticodon sequence base pair with mRNA codons
Ribosome moves along the mRNA bringing together two tRNA at any one time
Two amino acids on the tRNA are joined by a peptide bond, this also requires ATP
tRNA is released from the amino acid and is recycled
Synthesis continues until the ribosome reached a stop codon
The polypeptide chain then detaches and is folded into a functional protein
81
M- example of proteins that rely on shape
```
enzymes
antibodies
antigens
receptors
protein channels
protein carriers
haemoglobin
```
82
M- effect of gene mutation
Changes the nucleotide base sequence of DNA; changes the sequence of mRNA codons; tRNA brings different amino acid to the ribosome; changes to the primary sequence of amino acids may change the tertiary structure of the protein; bonds form in different places and the folding pattern is different
83
M- Muscle relaxation
When stimulation ceases, Ca2+ ions actively transported into SR using ATP
Tropomyosin reblocks actin binding site
Myosin heads unable to bind actin - no cross bridges form so contraction ceases
84
M- Cystic fibrosis
Mutant recessive allele with 3 bases missing (deletion mutation)
Amino acid left out of protein for chloride ion channels (CFTR protein)
Chloride ions are not transported out of epithelial cells
So water does not move out of cells by osmosis (water potential gradient not produced)
So epithelial membranes dry out and produce a sticky mucus, which blocks the airways
85
M- Effect of oestrogen on transcription
Oestrogen is a lipid soluble hormone that can easily diffuse through the phospholipid bilayer into the cytoplasm, oestrogen combines with a receptor on the transcriptional factor molecule; due to it having a complementary shape; oestrogen changes the shape of the receptor molecule; and releases the inhibitor molecule form the transcriptional factor; transcriptional factor can now enter the nucleus and bind to the DNA; this stimulates transcription of the particular gene
86
M- Role of tumour suppressor genes
Normal role is to inhibit cell division; mutation can cause inactivation; cell division is no longer inhibited and becomes uncontrollable
87
M- Explain hoe a mutation in a tumour suppressor gene might lead to the development of a malignant tumour
Cell division by mitosis
Tumour cells growth abnormal/ uncontrolled
Tumour cells spread/ invade other tissues/ form secondary tumours/metastais
Via blood/ lymph system
88
M- Role of ATP and phosphocreatine in producing a muscle fibre contraction
ATP allows myosin to detach from actin; phosphocreatine allows regeneration of ATP by providing inorganic phosphate to combine with ADP under anaerobic conditions
89
M- Primers definition
Short single stranded molecules of DNA which complementary base pair with specific regions on the DNA molecules
90
M- Uses of siRNA
To identify the role of genes in biological pathways
| To block the genes that cause genetic diseases
91
M- Why primers are used in PCR
Primers prevent the single strands of DNA rejoining
| Provides a shot double stranded section of DNA for the attachment of Taq polymerase
92
M- Definition of totipotency
Cells that are able to differentiate into any body cell
93
at night it is often easier to see a star in the sky by looking slightly to the side of it rather than directly at it. suggest why.
light reaching earth from a star is of low light intensity
looking directly at a star, light is focused on the fovea, where there are only cone cells
cone cells respond only to high light intensities so they are not stimulated by the low light intensity for the star and it can not be seen
looking to one side of the star means that light for the star if focused towards the outer regions of the retina, where there are many rod cells. these are stimulated by low light intensity and therefore the star is seen.
94
M- Characteristics of stem cells
Pluripotent/ totipotent/undifferentiated/ have the ability to differentiate into any body cell; will replace themselves/keep dividing/replicating
94
M- Using reverse transcriptase to produce DNA fragments
A cell that readily produced the required protein is selected
The large quantities of relevant mRNA are extracted from the nucleus
Reverse transcriptase (isolated from retroviruses) enzyme catalyses the formation of cDNA from the mRNA
Via complementary base pairing
DNA polymerase is used to build up the complementary DNA nucleotides
95
M- Why is PCR not a good technique for cloning genes for use in human gene therapy
Not accurate
Can be errors made in the replication process
Could cause gene mutations and produce non functional proteins
97
M- What do ectotherms NOT have?
physiological cooling mechanism
98
M- What is the purpose of marker genes
to show that the desired gene has been taken up and will be expressed
99
M- What is In vivo gene cloning used for?
making lots of useful proteins like insulin and human growth hormones
99
M- Advantages of gene transfer (in vivo gene cloning)
Useful for delivering a gene into another organism
Involves no risk of contamination (due to matching of sticky ends)
Very accurate (mutations are very rare)
Cuts out specific genes
Produces transformed bacteria, which can be used to produce large quantities of gene products
100
M- In vivo gene cloning (gene transfer)
Required gene is identified from DNA strand using a DNA probe and is isolated by cutting at specific recognition sequences using restriction endonuclease
The same restriction endonuclease is used to cut the plasmid vector
To produce complementary palindromic sticky ends
DNA ligase is used to seal the DNA of the required gene into the plasmid vector; this produced a recombinant plasmid
Bacteria are then given an electric or thermal shock to encourage them to take up the recombined plasmid
Successful recombinants are identified using a marker gene e.g. antibiotic resistance, luciferin/GFP, lactase
Colonies containing bacteria possessing the recombined plasmid are selected and cultured in a batch fermenter ; the required protein is extracted and purified
100
M- Three types of marker genes
Antibiotic resistance e.g. ampicilline and tetracycline
Makes a fluorescent protein e.g. lucigerin/GFP
Produces an enzyme with an identifiable action e.g. lactase turns a particular substrate blue
101
M- Using a virus to deliver CFTR genes
Adenoviruses made harmless by interfering with a gene involved in their replication
Adenoviruses grown in epithelial cells along with recombinant plasmids containing the normal CFTR gene
Gene becomes incorporated into the DNA of the virus
Viruses are isolated from the epithelial cells and purified
Viruses containing the gene are introduced into the patients nostrils
Viruses inject their DNA into epithelial cells of the lungs
102
explain the response of bacteria to glucose and why
```
positive chemotaxis (moves towards region of high glucose concentration)
increase their chance of survival because glucose is their food source and needed for respiration
```
103
What is a stimulus?
A detectable change in the external or internal environment of an organism that produces a response
106
cone cells
three different types- responding to different wavelengths of light- colour
own seperate bipolar cell connecting to a sensory neurone-harder to exceed threshold potential and so creates a generator potential- therefore only responds to high light intensity
contain iodopsin - requires high light intensity for breakdown and to create a generator potential
high visual acuity - each cone cell has a connection to their own single bipolar cell , if two cone cells are stimulated means that the brain recieves two seperate impulses- can distinguish between two seperate sources of light.
107
M- Treatment of SKID
Defective gene coding for adenosine deaminase (ADA) - this enzyme destroys toxins that kill white blood cells, so white blood cells are affected and are unable to produce antibodies
Normal ADA gene isolate from human tissue and cut using restriction endonuclease
ADA gene inserted into a retrovirus
Retroviruses are grown with host cells in the lab to increase their number of copies of the ADA gene
Retroviruses mixed with patients T cells
Retroviruses inject a copy of the normal ADA gene into the T cells
T cells are reintroduced into the patients blood to provide the genetic code needed to make ADA
108
M-Problem with gene therapy
1. Patients could become resistant to the viral vector
2. Patients immune system could recognise the viral vectors as non-self antigens and destroy them
3. Viral vectors may cause infections
4. Protein may not be expressed
109
M- Why is the treatment for SKID not a viable long term treatment?
T cells only live for 6-12 months
110
What does the sympathetic nervous system do?
Stimulates effectors and speeds up activity
Helps us to cope with stressful situations by heightening our awareness and preparing us for activities (flight or flight)
111
M- Using antibiotic resistance marker genes (replica plating)
Bacteria are cultured on a plate containing ampicillin - those that survive are known to have taken up the recombinant plasmid
A sterile gauze is used to transfer the colonies onto a second plate containing tetracycline
The colonies of bacteria containing the recombinant plasmid will not survive on the second plate
As the gene for tetracycline resistance will have been disrupted due to insertion and subsequent ligation of the required gene
The colonoies transferred are in the same position as the originals
So comparison of the plates can identify the required colonies (i.e. the colonies that appear on the first plate but not on the second plate)
112
M- Second messenger model - the role of adrenaline in increasing blood glucose
The hormone adrenaline is the first messenger and it binds to specific receptors on the membrane of target cells to form a hormone-receptor complex; this activates an enzyme (adenylate cyclase) inside the membrane; this enzyme converts ATP to cyclic AMP; which acts as a second messenger by activating other enzymes e.g. that converts glycogen to glucose - glycogenolysis
112
M- What is a gene probe?
A DNA probe is a short (up to 20 base pairs long) single stranded section of DNA that has a radioactive or fluorescent label
Bases of the probe are complementary to a portion of DNA sequence in the target gene
Can be used to screen for genetic diseases
114
what are changes in heart rate controlled by?
Medulla oblongata
115
Schwann Cells
Surround the axon, protecting it and providing electrical insulation
Carry out phagocytosis ( removal of cell debris)
Play a part in nerve regeneration
They wrap themselves around the axon many times so that layers of their membranes build up around it
116
M- Genetic fingerprinting
DNA is extracted from the sample and restriction endonuclease cut the DNA into fragments, this is inserted into wells in an agar jelly
Fragments are separated using gel electrophoresis where an electrical charge is applied to the gel
DNA moves to the positive end as it is negatively charged
Smaller, lighter fragments move the furthest up the gel
Southern blotting occurs to transfer the DNA fragments from the gel to a nylon membrane
DNA probes are added to radioactively labelled fragments
The membrane is placed onto an xray film and developed - a banding pattern is revealed
117
What is a receptor?
transform the energy of a stimulus into some form of energy that can be processed by the organism that can lead to a response
118
Explain the response of plant shoot to light and why
```
Positive phototropism ( grows towards light)
Their leaves are in more favourable positions to capture light for photosynthesis
```
120
M- What will happen to heart rate if fewer impulses ass down the parasympathetic nerve?
increase
121
Means of communication between receptors and effectors
hormones - slow - in animals and plants
| nervous system - rapid - in animals
122
Explain the response of single celled algae to light and why
```
Positive phototaxis (Moves towards light)
Increase chance of survival because of being photosynthetic because they need light to manufacture their own food
```
122
Explain the response of earthworms to light and why
```
Negative phototaxis ( moves away from light)
increase chance of survival because it takes them into the soil where they are better able to conserve water, find food and avoid predators
```
123
Explain the response of plant roots to light and gravity and why
```
Negative phototropism ( roots grow away from light)
Positive geotropism (grows towards gravity)
Increases the probability that roots will grow into the soil where they are better able to absorb mineral ions and water
```
124
Explain the response of plant roots to water and why
```
Positive hydrotropism (moves towards water)
Root systems will develop where there is most water
```
125
Rod cells
Cant distinguish between different wavelengths of light- therefore only images in black and white
More numerous than cone cells
Many rod cells share a single sensory neurone therefore respond to low light intensity - this is because the threshold value has been exceeded so a generator potential is created in the bipolar cells
Number of rod cells attached to a single bipolar neurone - retinal convergance- greater chance threshold value exceeded
rhodopsin has to be broken down to create a generator potential - low light intensity is sufficient
low visual acuity - a single bipolar cell is receiving light from many rod cells so only generates a single impulse therefore cant distinguish between separate sources of light
126
What are the two divisions of the nervous system and explain them?
the central nervous system (CNS) - made up of the brain and the spinal cord.
the peripheral nervous system (PNS) - made up pairs of nerves that originate from either the brain or the spinal cord
127
Two main coordination systems in mammals
Nervous system
| hormonal system
128
M- Different modes of heat loss
* Evaporative heat loss - the action of a fluid evaporating on the skin surface or tongue has a cooling effect
* Radiative heat loss - the action of losing heat by radiation to an organisms environment
128
the peripheral nervous system is divided into...explain.
sensory neurones- carry nerve impulses from receptors towards the central system
motor neurones- carry nerve impulses away from the central nervous system to the effectors
128
the motor neurone can be sub divided into ...explain.
voluntary nervous system- carries nerve impulses to body muscles and is under voluntary (conscious) control
autonomic nervous system- carries nerve impulses to glands, smooth muscle and cardiac muscle and is not under voluntary control (involuntary-subconsious)
128
where is a reflex arc found?
in the spinal cord
132
explain the main stages of a spinal reflex arc when withdrawing your hand from a hot object
the stimulus- heat from the hot object
receptor- temperature receptors in the skin on the back of the hand which creates a nerve impulse in a sensory neurone
sensory neurone - passes the nerve impulse to the spinal cord
intermediate nerone- links the sensory neurones to the motor neurone in the spinal cord
motor neurone- carries the nerve impulse for the spinal to cord to a muscle in the upper arm
effector- the muscle in the upper arm which is stimulated to contract
response - pulling the hand away from a hot object
133
Two divisions of the autonomic nervous system
Sympathetic nervous system
| Parasympathetic nervous system
134
the nerve connecting the carotid artery to the medulla oblongata of a person is cut. this person then undertakes some strenuous exercise. suggest what might happen to the persons blood carbon dioxide concentration
blood carbon dioxide concentration increases as a result of increase respiration during exercise.
135
What is the relationship between sympathetic and parasympathetic?
antagonistic -oppose each other
135
what happens when blood pressure is lower than normal?
pressure receptors which occur in the walls of carotid arteries and aorta transmit a nervous imouse to the centre in the medula oblongata that increases heart rate. this centre sends imoulses via the sympathetic nervous system to the SAN whic increases the rate
136
Two types of receptors which stimulates one of the two centres of the medulla obongata
Chemical changes in the blood
| pressure changes in the blood
137
the nerve connecting the carotid artery to the medulla oblongata of a person is cut. this person then undertakes some strenuous exercise. suggest what might happen to the persons heart rate.
heart rate remains as it was before taking exercise- after exercise, blood pressure increases and carbon dioxide concentration of blood rises causing blood pH to be lowered. the changes are detected by pressure and chemical receptors in walls of carotid arteries. as the nerve from here to the medulla oblongata is cut no nerve impulse can be sent to the centres that control heart rate.
138
M- What role does IAA have in the roots?
IAA inhibits growth
138
Features of pacinian corpuscle
specific to a single type of stimulus- mechanical pressure
Produces a generator potential by acting as a transducer (transducers convert one form of energy into another) - all receptors convert the energy of the stimulus into a nervous impulse known as generator potential- pacinian corpuscle transduces mechanical energy into a generator potential
139
Myelin Sheath
Forms a covering to the axon and is made up of membranes of the Schwann cells. These membranes are rich in a lipid known as myelin.
Neurones with a myelin sheath are called myelinated neurones
Some neurones lack a myelin sheath and are called unmyelinated neurones.
Myelinated neurones transmit nerve impulses faster than unmyelinated neurones.
140
M- What is phosphocreatine?
store of inorganic phosphate found in muscles
| doesnt limit ATP production because it is recycle constantly
143
What are motor neurones?
Transmits nerve impulses from an intermediate or sensory neurone to an effector, such as a gland or muscle
They have a long axon and many short dendrites
144
Structure of pacinian corpuscle and where they occur
respond to mechanical stimuli
deep in the skin - most abundance on fingers, soles of feet and external genitalia - ,joints, ligaments and tendons
Single sensory neurone of a pacinian corpuscle is at the centre of layers of connective tissue each separated by viscous gel
Stretch mediated sodium channels on its plasma membrane
145
What enzyme breaks down acetylcholine?
acetylcholinesterase
146
How is the movement of ions controlled across the axon membrane?
Phospholipid bilayer of the axon plasma membrane prevents sodium and potassium ions diffusing across it
Intrinsic proteins - some are voltage gated channels
Some intrinsic proteins actively transport potassium ions into axon and sodium ions out of axon in sodium potassium pump
147
Light receptors in the eye are found...
on its inner most layer: the retina
148
How do both rod and cone cells act as transducers?
They convert light energy into electrical energy of a nerve impulse
149
chemical mediators
Complement nervous and hormonal system in coordination
the chemical s are released from certain mammalian cells and have effects on cells in their immediate vicinity
Typically released from infected or injured cells - cause small arteries and arterioles to dilate - causes rise in temperature and swell in infected area
150
Two types of chemical mediators and what they do
Histamine - Stored in certain white blood cells and released following injury or response to an allergen - causes dilation of small arteries and arterioles and increased permeability of capillaries - leading to localised swelling, redness and itching
Prostaglandins - found in cell membranes causes dilation of small arteries and arterioles. released following injury which increases permeability of capillaries. Also affects blood pressure and neurotransmitters (substances involved in the transmission of nerve impulses) - affects pain sensation
151
How do plants respond to external stimuli?
Plant hormones - actually called plant growth factors
152
explain why brightly coloured objects often appear grey in dim light.
only rod cells are stimulated by low intensity light
rod cells can not distinguish between different wavelengths/ colours of light, therefore the object is perceived only in a mixture of black and white i.e. grey
153
What do plant growth factors do?
They exert their influence by affecting growth
Unlike animal hormones they are made by cells located throughout the plant rather than in particular organs
Unlike animal hormones, some plant growth factors affect the tissues that release them rather than acting on distant organs
Produced in small quantites
154
Example of plant growth factor
IAA - indoleactic acid
155
suggest two advantages of a plant of having roots responding to gravity by growing in the direction of its pull
Response ensures that roots grow downwards into the soil therefore anchoring the plant firmly
Brings them closer for water which is needed for photosynthesis
156
What is mammalian neurone made up of?
```
Cell body
Dendrons
Axon
Schwann cells
Myelin sheath
Nodes of Ranvier
```
157
What are muscles?
Effector organs that respond to nervous stimulation by contracting and so bring about movement
158
cell body
contains a nucleus and large amounts of rough endoplasmic reticulum
This is associated with proteins and neurotransmitters
159
In myelinated axon, sodium and potassium ions can only be exchanged in certain points along it: What effect does this have on the way an action potential is conducted along the axon?
It moves along in a series of jumps from one node to the next
161
How can the size of the stimulus be perceived?
The number of impulses passed in a given time - the larger the stimulus the more impulses are generated in a given time
Different neurones with different threshold values
162
dendron
Small extensions of the cell body which sub divide into small branched fibres called dendrites that carry nerve impulses towards the cell body
163
When walking along a street we barely notice the background noise of traffic however we often respond to louder traffic noises such as the sound of a horn. From your knowledge of summation, explain this difference.
The relatively quiet background noise of traffic produces a low level frequency of action potentials in the sensory neurones of the ear.
The amount of neurotransmitters released into the synapse is insufficient to exceed the threshold in the post synaptic neurone and to trigger an action potential and so the noise is ignored.
Louder noises create a greater frequency and the amount of neurotransmitter released is sufficient to trigger an action potential in the post synaptic neurone and so there is a response.
This is an example of temporal summation.
(An explanation in terms of spatial summation is also valid: many sound receptors with a range of thresholds -> More receptors respond to louder noises -> more neurotransmitters -> response)
164
Nodes of Ranvier
Gaps between adjacent Schwann cells where there is no myelin sheath
165
Neurones can be classified according to their function. What are the three types of neurone?
Sensory neurone
Motor neurone
Intermediate neurone
166
What are sensory neurones?
Transmit nerve impulses from a receptor to an intermediate or a motor neurone
They have one dendron that carries the impulse towards the cell body and one axon that carries it away from the cell body
167
Is the inside of an axon negatively or positively charged?
NEGATIVE
| -65
168
What are intermediate neurones?
Transmit impulses between neurones for example sensory to motor neurone
They have numerous short processes
169
Axon
A single, long fibre that carries nerve impulses away from the cell body
169
Neurones are adapted to carry electrochemical charges caller 1. Each neurone comprises a cell body that contains a 2 and large amounts of 3, which is used in the production of proteins and neurotransmitters. Extending from the cell body is a single long fibre called an axon and smaller branched fibres called 4. Axons are surrounded by 5 cells, which protect and provide 6 because their membranes are rich in a lipid known as 7. Their are three main types of neurone. Those that carry nerve impulses to an effector are called 8 neurones. Those that carry nerve impulses from a receptor are 9. Those that link the other two types are called 10 neurones
1. Nerve impulse/ action potentials
2. Nucleus
3. rough endoplasmic reticulum
4. dendrites
5. Schwann cells
6. insulation
7. myelin
8. motor
9. sensory
10. intermediate
169
passage of a action potential along an unmyelinated axon
At resting potential the concentration of sodium ions outside the axon membrane is high relative to the inside, whereas that of the potassium is high inside the membrane relative to the outside. The overall concentration of positive ions is, however, greater on the outside, making this positive compared to the inside. The axon membrane is polarised.
A stimulus causes a sudden influx of sodium ions and hence a reversal of charge on the axon membrane. this is the action potential and the membrane is depolarised.
Thee localised electrical circuit established by the influx of sodium ions cause the opening of sodium voltage gated channels a little further along the axon. the resulting influx of sodium ions in this region causes depolarisation. Behind this new region of depolarisation, the sodium voltage gated channels close ad the potassium ones open. Potassium ions begin to leave the axon along the electrochemical gradient.
The action potential (depolarisation) os propagated in the same way further along the axon. The outward movement of potassium ions has continued to the extent that the axon membrane behind the action potential has returned to its original charged state (positive outside, negative inside) ie. it has been repolarised.
Repolarisation of the axon allows sodium ions to be actively transported out, once again returning the axon to its resting potential in readiness to a new stimulus if it comes.
171
What is a nerve impulse?
A self propagating wave of electrical disturbance that travels along the surface of the axon membrane
172
explain how temperature affects the speed of which the action potential travels along the axon
Affects rate of diffusion - higher temperature the faster the rate of nerve impulse
The energy for active transport comes from respiration - respiration and sodium potassium pump are controlled by enzyme function move rapidly at higher temperatures until they are denatured - when they are denatured the enzyme fails to conduct at all
173
In myelinated axon, sodium and potassium ions can only be exchanged in certain points along it: what name is given to this type of conduction?
Saltatory
174
Passage of an action potential along a myelinated axon
In a myelinated axon the fatty sheath of the myelin around the axon acts as an electrical insulator, preventing action potentials from forming. At the nodes of ranvier, action potentials occur. The localised circuits therefore arise between adjacent nodes of ranviers and the action potentials, so in effect they jump from node to node - saltatory conduction.
Action potential passes along myelinated axon faster than an unmyelinated axon.
175
In myelinated axon, sodium and potassium ions can only be exchanged in certain points along it: what is the name given to these points?
Nodes of Ranvier
175
In myelinated axon, sodium and potassium ions can only be exchanged in certain points along it: Explain why ions can only exchange at these points.
The remainder of the axon is covered by myelin sheath that prevents ions being exchanged or prevents potential difference being set up
175
In myelinated axon, sodium and potassium ions can only be exchanged in certain points along it: How does this affect the speed which the action potential is transmitted compared to unmyelinated axon
It is faster than an unmyelinated axon
176
What is acetylcholine made up of?
Acetyl (ethanoic acid)
| Choline
177
Explain how the myeline sheath affects the speed of an action potential
Acts as an electrical insulator preventing an action potential forming in part of the axon covered in myelin
Jumps from node to node of ranvier - saltatory conduction
Increases the speed of conductance in a myelinated neurone
178
what are the light bands called?
I bands - isotropic - actin and myosin do not overlap
179
Name factors in which affect the speed in which an action potential travels
Myelin sheath
Diameter of the axon
Temperature
182
What is the parasympathetic nervous system?
Inhibits effectors and slows down activity
n normal resting conditions
conserves energy and replenishes body reserves
183
How does diameter of the axon affect the speed of which an action potential passes along the axon
The greater the diameter of an axon, the faster the speed of conductance. This is due to less leakage of ions from a large axon (leakage makes membrane potentials harder to maintain)
184
What is the purpose of the refractory period?
Action potentials are propagated in one direction only
Produces discrete impulses - a new impulse can not be formed directly behind the first one and ensures that the action potentials are separated from each other
Limits the number of action potentials
184
Neurones are separated by a small gap called...
synaptic cleft
185
The neurone that releases the neurotransmitter is called...
Pre-synaptic neurone
186
What is found in the presynaptic membrane and why?
Mitochondria and large amounts of endoplasmic reticulum
| They are required in the manufacture of the neurotransmitter
188
Once made, where are the neurotransmitters kept?
In the synaptic vesicles
189
Why is splicing of pre-mRNA important?
Splicing is necessary because pre-mRNA has nucleotide sequences derived from introns in DNA. These introns are non-functional and if left on the mRNA, would lead to the production of non-functional polypeptides or no polypeptides at all. Splicing removes these non-functional introns from the pre-mRNA.
190
Adaptations of fast twitch fibres
thicker and more numerous myosin filaments
high concentration of enzymes involved in anaerobic respiration
store of phosphocreatine, a molecule that rapidly generate ATP from ADP in anaerobic conditions and so provide energy for muscle contractions
191
When walking along a street we barely notice the background noise of traffic however we often respond to louder traffic noises such as the sound of a horn. Suggest an advantage to responding to high lever stimuli but not to low level ones.
Reacting to low level stimuli (background traffic noise) that present little danger can overload the (central) nervous system and so organisms may fail to respond to more important stimuli. High level stimuli (horn) need a response because they are more likely to represent danger.
191
Two important proteins found in a muscle?
troponin- globular protein involved in muscle cotraction
| tropomyosin - fibrous strand around the actin filament
192
Explain why hyperpolarisation reduces the likelihood of a new action potential being created.
As the inside of the membrane is more negative than at resting potential, more sodium ions must enter, to reach the potential difference of an action potential ie. it is more difficult for depolarisation to occur. Stimulation is less likely to reach the threshold level needed to reach an action potential.
193
Explain why maintaining a constant blood glucose concentration is important in mammals
Maintaining a constant blood concentration is important in ensuring a constant water potential. Changes to the water potential of the blood and tissue fluids may cause cells to shrink and expand (even to bursting point), due to water leaving or entering by osmosis. In both instances the cells cannot operate normally. A constant blood glucose concentration also ensures a reliable source of glucose for respiration by cells
194
If a neurone is stimulated in the middle of its axon, an action potential will pass both ways along it to the synapses at each end of the neurone. However, the action potential will only pass along the synapse at one end. Explain why.
Only one end can produce neurotransmitter and so this end alone will create an action potential in the neurone on the opposite side of the synapse. At the other end there is no neurotransmitter that can be released t pass along the synapse and so no new action potential can be set up.
196
What is a cholinergic synapse's neurotransmitter?
Acetylcholine
197
suppose the parasympathetic nerve connection from the medulla oblongata to the SAN is cut. Suggests what might happen if a persons blood pressure increases above normal.
blood pressure remains high because the parasympathetic system is unable to transmit nerve impulses o the SAN which decreases heart rate and so lowers blood pressure.
197
Where are cholinergic synapses most commonly found?
In a vertebrate animal where they occur in the central nervous system and at neuromuscular junctions.
198
Why is it necessary for acetylcholine to be hydrolysed by acetylcholinesterase?
To recycle the choline and the ethanoic acid
Prevent acetylcholine continuously generating a new action potential in the post synaptic neurone
199
three type of muscles in the body
Smooth - involuntary - in walls of blood vessels and the gut
cardiac - involuntary - heart
skeletal - voluntary - in a vertebrate attached to bone
200
Myofibrils are made up of two different types are proteins filaments which are?
actin- thinner and consists of two strands twisted around each other
myosin- thicker and consist of long rod shaped fibres with bulbous heads
202
Why do myofibrils appear stripped?
They have alternated light and dark bands
203
What are the dark bands called?
A bands - anisotropic - appear darker because actin and myosin overlap
204
At the centre at anisotropic band, there is a lighter region called?
H zone
204
Trained sprinters have high levels of phosphocreatine in the muscles . Explain the advantage of this
Phosphocreatine stores the phosphate that is used to generate ATP from ADP in anaerobic conditions. A sprinters muscles often work so strenuously that the oxygen supply cannot meet the demand. The supply of ATP from the mitochondria during aerobic respiration therefore ceases. Sprinters with the most phosphocreatine have an advantage because ATP can be supplied to their muscles for longer, and so they perform better.
205
What is a neuromuscular junction?
Where motor neurone meets a skeletal muscle fibre
206
At the centre of each isotropic band there is a line called?
Z line
207
Explain why a large, compact mammal will probably require less food per gram of body mass to maintain its body temperature in a cold climate than a small, less compact mammal
Food is a source of heat produced by its metabolism in the body. A large, compact mammal will have a smaller surface area to volume ratio than a smaller, less compact one. Because heat is lost from the surface and produced in the volume, the larger mammal will both produce more heat and lose less heat per gram of body mass compared to the smaller mammal. It will therefore need less food in order to maintain its body temperature
208
M- Definition of positive feedback
Changes that results in a system deviating further away from a specific set point
209
What are the two centres in the hypothalamus?
Heat gain centre - activated by a fall in blood temp and controls the mechanisms that increase body temperature
Heat loss centre - activated by a rise in blood temperature and controls the mechanisms that decrease body temp
210
What happens to the sarcomeres when the muscle contracts?
Sarcomere shortens and pattern of light and dark changes
210
Suggest a reason why there are numerous mitochondria in the sarcoplasm
Muscle requires much energy for contraction
Most of this energy is released during the Krebs cycle and the electron transport chain in respiration
Both of these take place in the mitochodria
211
If you cut across the myofibril at certain points, we see only thick myosin filaments. Cut at a different point we see only thin actin filaments. At yet other points we see other types of filaments. explain why?
The actin and myosin filaments lie side by side in a myofibril and overlap at the edges where they meet. Where they overlap, both filaments can be seen. Where they do not overlap, we see one or the other filament only.
212
Adaptations of slow twitch fibres
Large store of myoglobin - stores oxygen
Supply of glycogen to supply source of metabolic energy
Rich supply of blood vessels to deliver oxygen and glucose
Numerous mitochondria to provide ATP
213
What is the evidence for the sliding filament mechanism?
There will be more actin and myosin overlapping in a contracting muscle than a relaxed one.
215
The main features of the genetic code
Each amino acid in a protein is coded for by a sequence of three nucleotide bases on mRNA i.e. a codon
A few amino acids have a single codon
The code is a degenerate code. This means that most amino acids have more than one codon
Three codons do not code for any amino acids. These are called stop codons and mark the end of a polypeptide chain.
The code is non overlapping, that is, each base in the sequence is read only once.
It is a universal code - the same codon codes for the same amino acid in all organisms
216
What are the changes in the sarcomere when the muscle contracts?
```
The I band becomes narrower
Z lines move closer
Sarcomere shortens
H zone becomes narrower
A band remains the same width
```
217
What is myosin made up of?
Two proteins;
A fibrous protein arranged into a filament made up of several hundred molecules (the tail)
A globular protein formed into two bulbous structures at one end (the head)
219
Structure of actin
globular protein
| molecules are arranged into a long chain that are twisted around one another to form a helical strand
219
Structure of tryopomyosin
forms long thin threads that are wound around the actin filament
220
what three processes take part in the sliding filament theory?
muscle stimulation
muscle contraction
muscle relaxation
221
symptoms of diabetes
```
high blood glucose level
presence of glucose in the urine
increased thirst and hunger
need to urinate excessively
genital itching and episodes of thrush
tiredness
weightloss
blurred vision
```
222
M- muscle stimulation
An action potential reaches many neuromuscular junctions simultaneously, causing calcium ion channels to open and calcium ions to move into the synaptic cleft
The calcium ions cause the synaptic vesicles to fuse with the presynaptic membrane and release their acetylcholine into the synaptic cleft
acetylcholine diffuses across the synaptic cleft and binds with receptors on the postsynaptic membrane, causing it to depolarise
223
During the contraction of a muscle sarcomere, a single actin filament moves 0.8µm. If the hydrolysis of a single ATP molecule provides enough energy to move an actin filament 40nm, how many ATP molecules are needed to move an actin filament 0.8µm?
A single ATP molecule is enough to move an actin filament of 40nm.
Total distance moved by actin filament is 0.8µm = 800nm.
Number of ATP molecules required is 800/40=20
224
Name precisely the structure that produces the hormone:
a) LH
b) Progesterone
c) Oestrogen
a) Pituitary gland
b) Corpus Luteum in the ovary
c) Follicles in the ovary
225
What happens to the size of an action potential as it moves along the axon
stays the same
226
M- Muscle contraction
The action potential travels deep into the fibre through the system of T-tubules that branch throughout the cytoplasm of the muscle (sarcoplasm)
The tubules are in contact with the endoplasmic reticulum of the muscle (sarcoplasmic reticulum) which has actively absorbed calcium ions from the cytoplasm of the muscle.
The action potential open the calcium ion channels on the endoplasmic reticulum and the calcium ions flood into the muscle cytoplasm down a diffusion gradient.
The calcium ions cause the tropomyosin molecules that were blocking the binding sites on the actin filament to pull away.
The ADP molecule attached to the myosin heads means they are now in a state to bind to the actin filament and form a cross bridge.
Once attached to the actin filament, the myosin heads change their angle, pulling the actin filament along as they do so and releasing a molecule of ADP.
An ATP molecule attaches to each myosin head, causing it to become detached from the actin filament.
The calcium ions then activate the enzyme ATPase, which hydrolyses the ATP to ADP. The hydrolysis of ATP to ADP provide the energy for the myosin head to return to its original position.
The myosin head, once more with an attached ADP molecule, then reattaches itself further along the actin filament and the cycle is repeated as long as nervous stimulation of the muscle continues.
226
What does progesterone do?
Produced by the ovaries.
Maintains the uterus lining in readiness to receive the fertilised egg and inhibits the production of FSH from the pituitary gland.
227
What is conduction?
Gaining or losing heat from the environment ie the ground (solids)
Heat causes particles to vibrate and gain kinetic energy and the energy i transferred to adjacent particles.
228
What is convection?
Gaining or losing heat from the environment (ie the air or water...gases and liquids)
Transfer of heat through the movement of warm matter
230
M - What is homeostasis?
Maintenance of a constant internal environment at a set point
231
What are islets of langerhans
groups are hormone producing cells
Two types:
alpha cells - which are the larger and produce the hormone glucagon
beta cells- which are smaller and produce the hormone insulin
232
Control of body temperature
Stimulus > receptors (thermoreceptors) > coordinator/hypothalamus > effector (skin) >response
233
Four structures in the skin which are involved with thermoregulation in mammals
sweat gands
hair muscle ( piloerector muscles)
fat tisues
arterioles (shunt vessels)
234
Suggest an explanation for why tiredness is a symptom of diabetes
Diabetes is a condition in which insulin is not produced by the pancreas. This leads to fluctuations in the blood glucose level. If the level is below normal, there may be insufficient glucose for the release of energy by cells during respiration. Muscle and brain cells in particular may therefore be less activie, leading to tirdness
235
When insulin binds with glycoprotein receptors, what happens?
Change in tertiary structure of the glucose transport protein channels, causing them to change shape and open, allowing more glucose into cells
Increase in the number of carrier molecules on the cell surface membrane
Activation of the enzymes that convert glucose to glycogen and fat
235
Advantage of negative feedback?
Has greater homeostatic control
236
What cells can insulin and glucagon bind to?
Insulin can bind to any glycoprotein receptors on any cells
Glucagon can only bind to receptors in the liver
237
Distinguish between positive and negative feedback.
Positive feedback occurs when the corrective measures to remain turned on. In doing so, it causes the system to deviate even further away from the original set point.
Negative feedback occurs when the feedback causes corrective measures to be turned off. In doing so, it returns the system to its original set point.
239
The chemical energy in glucose is released by cells during the process known as 1. It is therefore important that the blood glucose level is maintained at a constant level because if it falls too low cells are deprived of energy and 2. cells are especially sensitive in this respect. If it gets too high 3 problems occurs that may cause dehydration. Blood glucose is formed directly from 4 in the diet or from the breakdown of 5 which is stored in the cells of the liver and 6. The liver can also increase blood glucose levels by making glucose from other source, such as glycerol and 7, in a process known as 8. Blood glucose is used up when it it absorbed into cells, converted into fat or 9 for storage, or used up during 10 by cells. In order to maintain a constant level of blood glucose the pancreas produces two hormones from clusters of cells within it called 11. The beta cells produce the hormone 12 which causes the blood glucose level to fall. The alpha cells produce the hormone 13 which has the opposite effect. Another hormone called 14 can also raise blood glucose levels
1. respiration
2. brain
3. osmotic/water potential
4. carbohydrates
5. glycogen
6. muscles
7. amino acids
8. gluconeogenesis
9. glycogen
10. respiration
11. islets of langerhans
12. insulin
13. glucagon
14. adrenaline
240
What does FSH and LH stand for?
FSH- follicle stimulating hormone
| LH- luteinising hormone
240
What is a mis-sense mutation?
A substitution reaction
When the base change results in a different amino acid being coded for.
will affect the polypeptide if the amino acid changed is responsible for a bonding or for the shape of the protein or the enzyme
241
What are totipotent cells?
Cells with the ability to develop into any other cell of the organism
242
A strand of mRNA has 64 codons but the protein produced only has 63 amino acids, Suggest a reason for this difference.
One of the codons is a stop codon that indicates the end of polypeptide synthesis. Stop codons do not code for any amino acid so there is one less amino acid than there are codons.
243
What does FSH do?
Produced in the pituitary gland.
Stimulates the development of follicles in the ovary, which contains eggs, and stimulates the follicles in the ovaries to produce oestrogen.
244
Features of synapses
Unidirectional- can only pass impulses in one direction- from pre to post synaptic neurone
Summation- spatial or temporal
Inhibition - inhibits the proteins on post synaptic membrane causing ions to flood in (not the sodium ones we want ) so hard to generate new action potential.
245
What does LH do?
Produced in the pituitary gland.
causes the ovulation to occur, and stimulates the ovary to produce progesterone from the corpus luteum.
247
Describe an example of negative feedback in oestrous cycle
More oestrogen -> more inhibition of FSH production -> less FSH -> less stimulation of oestrogen production -> less oestrogen
more progesterone -> more inhibition of LH production -> less LH -> less stimulation of progesterone production -> less progesterone
248
What does oestrogen do?
Produced in the ovaries.
causes the rebuilding of the uterus lining after menstruation and stimulates the pituitary glands to produce LH.
248
When a female human reaches menopause, she has very few follicles left in her ovaries. Suggest a reason why levels of FSH in the blood rise in women reaching the menopause
Oestrogen is produced in developing follicles. Menopausal women have few follicles left so produce less oestrogen. Oestrogen inhibits the production of FSH so the reduction of oestrogen means that there is less inhibition of FSH. Therefore more FSH is produced.
249
Some female farm animals were given progesterone in their diet. When the progesterone was withdrawn from their diet, they all ovulated a few days later. Suggest an explanation for this
High progesterone levels inhibit the production of FSH and LH. When progesterone is withdrawn from the diet, its level falls and so the production of FSH and LH resumes. FSH causes the follicles to develop in the ovary and LH causes the egg to be released
250
Name three substitution mutations
Silent mutation
Mis-sense mutation
Nonsense mutation
251
Distinguish between a codon and an anticodon
A codon is the triplet of bases on messenger RNA that codes for an amino acid
An anticodon is the triplet of bases on transfer RNA molecule that is complementary to the codon
252
M- Comparison of PCR and DNA replication
PCR uses heat to separate the strands whereas DNA replication involves the enzyme helicase
PCR uses primers but DNA replication does not
PCR uses Taq polymerase with a higher optimum temperature
Both involve the breaking of hydrogen bonds
Both involve polymerase polymerase enzyme
Both involve complementary base pairing
253
What is splicing?
Where introns are removed and exons join together
254
What is the other enzyme involved in transcription other than RNA polymerase, and what is its role?
DNA helicase
This acts on a specific region of the DNA molecule to break the hydrogen bonds between the bases, causing the two strands to separate and expose the nucleotide bases in that region.
255
How is a generator potential generated?
When a nervous system receptor is in its resting state (not being stimulated) there is a difference in voltage between the inside and outside of the cell. the difference in voltage across the membrane is called the potential difference.
The potential difference when a cell is at rest is called its resting potential.
When a stimulus is detected, the cell membrane is excited and becomes more permeable, allowing more ions to move in and out of the cell- altering the potential difference. The change in potential difference, due to a stimulus, is called the generator potential.
256
Name the cell organelle involved in translation
Ribosome
257
How does the distribution of totipotent cells in animals differ from that in plants?
In animals, only a few are totipotent. In humans these are known as stem cells and are found in the embryo, the inner lining of the intestine, skin and bone marrow.
In plants, many of the cells throughout a plant are totipotent
258
What is the role of a vector during in vivo cloning?
Transfers gene (DNA) from one organism into another
259
What is frameshift?
Deletion mutation
When a nucleotide is lost from the normal DNA sequenceThe amino acid sequence may be completely different because the genetic code is read in units of 3 bases (triplet). The reading frame that contains each three letters of the code has been shifted left by one letter. The gene is now read in the wrong three base groups and the genetic message is altered.
260
How is the shape of the myosin molecule adapted to its role in muscle contraction?
Myosin is made up of two proteins. The fibrous protein is long and thin in shape, which enables it to combine with others to form a long thick filament along which the actin filament can move. The globular protein forms two bulbous structures (the head) at the end of a filament (the tail). This shape allows it to exactly fit recesses in the actin molecule, to which it can become attached. Its shape also means it can be moved at an angle. This allows it to change its angle when attached to actin and so move it along, causing the muscle to contract
261
Describe the role of tRNA in the process of translation
A tRNA molecule attaches an amino acid at one end has a sequence of 3 bases, called an anticodon, at the other end. The tRNA molecule is transferred to a ribosome on an mRNA molecule. The anticodon on tRNA pairs with the complementary codon sequence on the mRNA> Further tRNA molecules, with amino acids attached, line up along the mRNA in the sequence determined by the mRNA bases. The amino acids are joined by peptide bonds. Therefore the tRNA helps to ensure the correct sequence of amino acids in the polypeptide.
262
What is a nonsense mutation?
A substitution mutation
Occurs if the change in base sequence results in the formation of one of the three stop codons that mark the end of a polypeptide chain
The final protein would almost certainly be significantly different and the protein could not perform its normal function.
263
M- Examples of genetically modified animals
Disease resistance
Transfer of growth hormone gene to increase yield e.g. salmon
Sheep/goats with modified milk that can express useful proteins e.g. spider silk or anticoagulants such as facto IX (antithrombin)
264
Cell division is controlled by genes. Most cells divide at a fairly constant rate to ensure that dead or worn out cells are replaces. In normal cells, this rate is tightly controlled by two gene- which are?
Proto-oncogenes that stimulate cell division
Tumour suppressor genes that slow down cell division
265
Symptoms of cystic fibrosis
mucus congestion in the lungs leading to a much higher risk of infection because the mucus which traps disease causing organisms can not be removed.
Breathing difficulties and less efficient gas exchange
Accumulation of thick mucus in the pancreatic ducts- prevents pancreatic enzymes from reaching the duodenum and leading to the formation of fibrous cysts
Accumulation of thick mucus in the sperm ducts in males possibly leading to infertility
266
Two ways that oncogenes affect cell division
1. The receptor protein on the cell surface membrane can be permanently activated, so that cell division is switched on even in the absence of growth factors
2. The oncogene may code for a growth factor that is then produced in excessive amounts, again simulating excessive cell division
The result is that cells divide too rapidly and a tumour or cancer develops
267
Explain why a mutation that is transcribed on to mRNA may not result in any change to the polypeptide that it codes for
The mutation may result from the substitution of one base in the mRNA with another. Although the codon affected may be different, the amino acid may not necessarily be different because of the genetic code being degenerate. The polypeptide will be unchanged and there will be no effect.
268
Errors in transcription occur a lot more more than errors in replication. Explain why errors in DNA replication can be far more damaging than errors in transcrition.
These errors may be inherited and may therefore have a permanent affect on the whole organism. Errors in transcription usually affect only specific cells, are temporary and not inherited. They are therefore less damaging.
269
Two ays in which genes are prevented from being expressed include...
1/ preventing transcription and hence preventing the production of mRNA
2/ breaking down mRNA before its genetic code can be translation
270
What is the role of transcription factor?
Stimulates transcription of a gene
271
state two roles of a primers used in the sanger method of sequencing of DNA
starts the process of DNA synthesis by making the DNA double stranded ( DNA polymerase only works on double stranded DNA)
Carries the radioactive label for identification of fragments in later use
272
What are the gene markers?
Resistant to antibiotics- replica plating
Make a fluorescent protein that is easily seen - GFP( green fluorescent protein)
Produce an enzyme whose action can be identified - lactase turns a colourless substrate blue
273
The process of making a protein using the DNA technology of gene transfer and cloning involves a number of stages, which are...
Isolation of the DNA fragment that have the gene for the desired protein
Insertion of the DNA fragment into a vector
Transformation- transfer of DNA into suitable host cells
Identification of the host cells that have successfully taken up the gene by use of gene markers
Cloning/growth of the population of host cells
274
Where the DNA of two different organisms is combined, the product is know as 1. DNA. One method of producing DNA fragments is to make the DNA from RNA using an enzyme called 2. This enzyme initially forms a single strand of DNA called 3. DNA. To form the other strand requires an enzyme called 4. Another method of producing DNA fragments is to use enzymes called 5. which cut up DNA. Some of these leaves fragments with two straight edges called 6. ends. Some of these leave ends with uneven edges called 7. ends. IF the sequence of bases on one of these uneven ends is GAATTC then the sequence on the other end, if read in the same direction will be 8.
1. Recombinant
2. Reverse transcriptase
3. complementary DNA (cDNA)
4. DNA polymerase
5. Restriction endonucleases
6. Blunt
7. Sticky
8. CTTAAG
275
Why are gene markers necessary in in vivo cloning?
To show which cells ( bacteria) have taken up the plasmid (gene)
276
Give one advantage of using fluorescent gene markers rather than antibiotic gene markers. Explain
Results can be obtained more easily and quickly
Because with antibiotic resistant markers the bacterial cells with the required gene are killed so replica plating is necessary to obtain the cells with the gene.
With fluorescent gene markers the bacterial cells are not killed and so there is no need to carry out replica plating.
277
Why are two different primers required?
Because the sequences at the opposite strands of DNA are different
278
Genetic modifications can benefit humans in many ways like...
Increasing yield from animal or plant crop
Improving nutrient content of food
Introducing resistant to disease and pests
Making crop plants tolerant to herbicides
Developing tolerance to environmental conditions- extreme temperatures and drought
Making vaccines
Producing medicines for treating disease
279
Bright light causes circular iris muscles in an animals eye to contract, which constricts the pupil and protects the eye
a) Suggest why this response uses nervous communication rather than hormonal communication (1 mark)
b) Describe and explain the roles of receptors and effectors for this response (5 marks)
a) Nervous communication is more suitable because electrical impulses travel faster than hormones, so the (protective), response is quicker
b) receptors detect the stimulus [1] e.g light receptors (photoreceptors) in the animals eye detect the bright light [1]. The receptor sends impulses along neurones via the CNS to the effectors [1]. The effectors bring about a response [1] e.g. the circular iris muscles contract and protect the eyes [1]
280
It is important in PCR that the fragments of DNA used are not contaminated with any other biological material. Suggest why.
Biological contaminants may contain DNA and this DNA would also be copied.
281
Treatment of cystic fibrosis
Gene replacement- defective gene replaced with a healthy gene
Gene supplementation- one or more copies of the healthy gene are added alongside the defective gene, as the other genes have dominant alleles the effect of the other genes are masked
282
Problems with delivering the cloned CFTR genes by using a harmless virus or wrapping the gene in a lipid molecule
Adenoviruses may cause infections
Patients may develop immunity to the adenoviruses
Liposome aerosol may not be fine enough to pass through the tiny bronchioles in the lungs
Even where the CFTR gene is successfully deceived to the epithelial cells very few are actually expressed
283
Why does somatic gene therapy fail to provide a permanent cure for cystic fibrosis?
Somatic gene therapy targets just the infected tissues
Additional gene is not present in sperm or eggs and therefore not passed onto future generations
As the cells of the lung tissues are continually dying and being replaced the treatment has to be repeated periodically
284
Outline the process of genetic screening for a disease such as sickle cell anaemia
Determine the order of nucleotides on the mutated gene by DNA sequencing
Produce a fragment of DNA that has complementary bases to the mutated portion of that gene
Label the fragments to form a DNA probe
Make multiple copies of the DNA probe using PCR techniques
Add the probe to DNA fragments to the DNA being tested
If the donor has a mutant allele the probe will bind to the complementary bases on the donor DNA
These fragments will now be labelled and can be distinguished from the rest of the DNA
285
M - Mutagenic agents (mutagens)
High energy radiation that can disrupt the DNA molecule
Chemicals that alter the DNA structure or interfere with transcription
286
Genetic screening shows that a person has one mutant allele of the tumour suppressor gene. How might this person use this information revealed by genetic screening?
Change their lifestyle to reduce the risk of cancer e.g. give up smoking, lose weight, eat healthily, avoid mutagens as far as possible, check more regularly for early symptoms of cancer, choosing to under go gene therapy
287
Five steps of genetic fingerprinting
1. Extraction of DNA
2. Digestion - DNA cut into fragments using DNA endonucleases
3. Separation - gel electrophoresis under electrical voltage - double strands to single strands
4. Hybridisation - labelled DNA probes used to bind with core sequences
5. Development - X ray film if radioactively labelled/ visually located if fluorescent markers used
288
Uses of DNA fingerprinting
Forensics
Paternity tests
Determining genetic variability in a population
289
M - what is a codon
Three mRNA bases coding for one amino acid
290
M- what is degenerate
Amino acid that have more than one codon coding for them
291
What does non overlapping mean
Each base is read only once
292
How is the strength of a stimulus measured?
Action potentials are all one size so the strength of the stimulus is measured by the frequency of action potentials.
293
What is a silent mutation?
A substitution mutation
Occurs when the substituted base, although different, still codes for the same amino acid as before.
This is due to the degenerate nature of the genetic code- most amino acids are coded for by more than one codon.
294
What is a universal code?
Same codons code for the same amino acids in all organisms
295
What happens at the end of a neurone?
Once the electrical impulse has reached the end of one neurone, chemicals called neurotransmitters take the information across to the next neurone which can then send an electrical impulse
297
Describe the role of RNA polymerase in transcription
The enzyme RNA polymerase moves along the template DNA strand causing the bases on this strand to join with the individual complementary nucleotides from the pool that is present in the nucleus. The RNA polymerase adds the nucleotides one at a time, to build a strand of pre mRNA until it reaches a particular sequence of bases on the DNA that it recognises as a stop codon
