Model answers Flashcards
M- Slow twitch fibres
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
M- What is power stroke
when the myosin head moves and pulls the actin along
M- DNA sequencing (Sanger method)
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)
M- PCR
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
Why is negative feedback important in maintaining a system at a set point?
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.
M- Effect of siRNA on gene expression
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
M- Regulation of blood glucose
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)
M- Using lipid molecule wrapping of the CFTR gene
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
M- Two ways to get many copies of a gene
- 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
M- Regulation of body temperature in endotherms - response to warm environment/ increase in body temperature
- Vasodilation (shunt vessels constricts)
- Increased sweating
- lowering of body hair
- Behavioural mechanisms e.g. seeking shade
M-Regulation of body temperature in endotherms - response to a cold environment/ decrease in core body temperature
- 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)
M- type 1 diabetes
where insulin is not produced and the disease is controlled by insulin injections
M- Tropism definition
Growth movement of part of a plant in response to a directional stimulus
M- Advantage to woodlice of moving away from a bright area
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)
M- Oestrus in animals
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
M- Comparison of hormonal and nervous systems
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
M- Humans produce a large number of different hormones but only small number of different neurotransmitters. Explain the significance of this
Hormones reach all cells by the blood
Neurotransmitters secreted directly onto target cell
Different hormones are specific to different target cells
M- type 2 diabetes
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)
M- Explain the benefit of seedlings exhibiting positive phototropism
Growing shoots grow towards light
Chloroplasts absorb more light for photosynthesis
M- Talk about experiments involving the use of mica and agar blocks.
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
M- Kinesis definistion
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
M- Cone cells
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
What are the two centres of the medulla oblongata?
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
M- What role does IAA have in the shoot?
IAA stimulates growth
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
M- Taxis definition
A simple response to an external directional stimulus
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.
M- What is a reflex?
A rapid response to a stimulus which is automatic ( not under conscious control)
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)
M- Spatial summation
Different presynaptic neurones release neurotransmitter into the same cleft in order for the concentration to accumulate to exceed the threshold
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
HSW- Drugs can act on synapses in 2 ways
- 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 - 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
M- Fovea
Point directly behind the pupil, which receives the most light (only cone cells here)
M- Periphery of the retina
only rod cells are found
peripheral vision tends to be more blurry
M- What will happen to heart rate if fewer impulses are sent down the sympathetic nerve?
decrease
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
What is the distance between adjacent z lines called?
Sarcomere
M- What is meant by metabolic heat gain
Body’s reactions such as respiration rate
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
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
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
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
M- Blind spot
Part of the eye where the optic nerve attaches and contains no rod or cone cells
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
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
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
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
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)
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
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
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
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
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
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)
M- Temporal summation
The same presynaptic neurone releases neurotransmitter over time in order for the concentration to accumulate to exceed threshold
M- Why is the nervous transmission delayed at synapses?
It takes time for enough neurotransmitter to be accumulated to exceed threshold
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
M- Definition of negative feedback
changes that result in a system returning to a specific set point
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
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
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
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
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
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)
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
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
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
M- Three methods of isolating a DNA fragment
- Identify the gene using a DNA probe and cut it out using restriction enzymes
- Artificially synthesise the gene, after working out its base sequence from knowing the primary protein structure
- Using mRNA and reverse transcriptase to produce cDNA
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
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
M- Advantages of PCR (in vitro gene cloning)
Extremely rapid
Does not require living cells
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
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
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
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)
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
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
M- example of proteins that rely on shape
enzymes antibodies antigens receptors protein channels protein carriers haemoglobin
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
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
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
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
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
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
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
M- Primers definition
Short single stranded molecules of DNA which complementary base pair with specific regions on the DNA molecules
M- Uses of siRNA
To identify the role of genes in biological pathways
To block the genes that cause genetic diseases
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
M- Definition of totipotency
Cells that are able to differentiate into any body cell
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.
M- Characteristics of stem cells
Pluripotent/ totipotent/undifferentiated/ have the ability to differentiate into any body cell; will replace themselves/keep dividing/replicating
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
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
M- What do ectotherms NOT have?
physiological cooling mechanism
M- What is the purpose of marker genes
to show that the desired gene has been taken up and will be expressed
M- What is In vivo gene cloning used for?
making lots of useful proteins like insulin and human growth hormones
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
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
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
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
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
What is a stimulus?
A detectable change in the external or internal environment of an organism that produces a response
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.
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
M-Problem with gene therapy
- Patients could become resistant to the viral vector
- Patients immune system could recognise the viral vectors as non-self antigens and destroy them
- Viral vectors may cause infections
- Protein may not be expressed
M- Why is the treatment for SKID not a viable long term treatment?
T cells only live for 6-12 months
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)
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)
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
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
what are changes in heart rate controlled by?
Medulla oblongata
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
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
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
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
M- What will happen to heart rate if fewer impulses ass down the parasympathetic nerve?
increase
Means of communication between receptors and effectors
hormones - slow - in animals and plants
nervous system - rapid - in animals
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
