Paper 5 Flashcards
1
Q
Kinesis
A
A random movement away from a stimulus, without direction
2
Q
Taxis
A
A specific movement towards or away from a stimulus which has direction. Towards = positive taxis Away from = negative taxis Photo = light Geo = gravity Hydro = water Chemo = chemicals Thermo = heat
3
Q
How do taxes and kineses aid survival?
A
Increase chance of finding food
Avoid predators and conserve food and water better
Allows more time spent in conditions organism is best adapted to
4
Q
Tropism
A
A growth response in a plant to a stimulus
5
Q
IAA
A
Auxin (plant growth regulator) that causes cell elongation
6
Q
Somatic nervous system
A
Produces voluntary responses
7
Q
Autonomic nervous system
A
Produces involuntary responses
8
Q
Sympathetic nervous system
A
Stimulates effectors and speeds up activity - fight or flight response
9
Q
Parasympathetic nervous system
A
Inhibits effectors and slows down activity
10
Q
Reflex
A
A rapid and involuntary response to a stimulus
11
Q
Why are reflexes essentials for survival?
A
Effective from birth and do not have to be learned
Protect the body from harmful stimuli
12
Q
Reflex arc
A
Stimulus ➡️ receptor ➡️ sensory neurone ➡️ coordinator (intermediate neurone) ➡️ motor neurone ➡️ effector ➡️ response
13
Q
Control of heart rate due to increased metabolic activity
A
More CO2 in blood ➡️ blood pH lowered ➡️ chemoreceptors in walls of carotid arteries and aorta sense and increase frequency of impulses to medulla oblongata ➡️ sensory neurone ➡️ cardioacceleratory centre (cardioregulatory centre = coordinator) increases frequency of impulse to SAN ➡️ sympathetic nerves ➡️ heart rate incr ashes and CO2 concentration back to normal
14
Q
Control of heart rate due to increased blood pressure
A
Baroreceptors in walls of carotid arteries and aorta decrease the frequency of impulses to medulla oblongata ➡️ sensory neurone ➡️ cardiodeceleratory centre decreases frequency of impulses to SAN ➡️ parasympathetic nerves ➡️ heart rate decreases to lower the blood pressure
15
Q
Dendrites
A
Extensions of the cell body carry nerve impulses to cell body
16
Q
Cell body
A
Contains nucleus, large amounts of rough ER to produce neurotransmitters and proteins
17
Q
Myelin sheath
A
Made up Schwann membrane which produces myelin (lipid) m
18
Q
Node of Ranvier
A
The gap between myelinated areas 2-3 microm long and cop cur every 1-3mm
19
Q
Nerve impulse
A
A fast, self-propagating wave of electrical activity travelling across a plasma membrane
20
Q
Resting potential
A
Na+ ions out (3) K+ ions in (2) - actively transported by sodium-potassium pump
Open potassium ion channels allow some K+ ions to diffuse back out of axon into tissue fluid - negative charge inside axon of -65–70mV POLARISED MEMBRANE
21
Q
Action potential
A
Stimulus energy causes sodium voltage gated ion channels to open and sodium ions diffuse in along their electrochemical gradient. More open as Na+ diffuse in, greater influx of ions. DEPOLARISED MEMBRANE
Once an action potential of +40mV is established, Na+ ion channels close and voltage gated potassium ion channels open. K+ ions diffuse out and more channels open. REPOLARISED MEMBRANE
A temporary overshoot occurs - axon is more negative than usual - HYPERPOLARISATION
Potassium ion channels close and sodium-potassium pump restores the resting potential. REPOLARISED.
22
Q
All or nothing principle
A
Any stimulus that exceeds threshold results in depolarisation of the membrane.
Any stimulus below threshold will not cause an action potential
23
Q
Stimulus
A
A detectable change in the internal or external environment of an organism that produces a response in the organism.
24
Q
How does a myelin sheath affect the speed of propagation of an action potential?
A
An unmediated axon is slow as the whole length of the axon has to be depolarised
A myelin sheath acts as an electrical insulator and prevents passage of action potentials. The action potential can therefore jump from node to node in a process known as saltatory conduction.
25
Other factors that affect the speed of action potentials?
- larger axon diameter is faster
| - greater temp is faster transmission due to more KE for faster diffusion
26
Synapse
A gap between neurones
Info is sent between neurones by chemical transmission of neurotransmitters across a synaptic clefts to trigger a new AP in the post-synaptic membrane
27
Cholinergic synapse
A synapse using acetyl choline as the neurotransmitter (CNS and neuromuscular junctions)
28
Cholinergic synapse action
AP in synaptic knob ➡️ Ca2+ ion channels open ➡️ Ca2+ causes vesicles containing NT to fuse with pre-synaptic membrane ➡️ vesicles release NT into synaptic cleft ➡️ acetylcholine diffuses across cleft and binds to receptors on sodium ion channels on post-synaptic membrane ➡️ ligand gated sodium ion channels open and NA+ ions diffuse across concentration gradient ➡️ depolarised and new AP generated if TH is overcome ➡️ enzyme acetylcholineterase hydrolyses acetylcholine to ethanoic acid and chloine which prevents continuous depolarisation of post-synaptic membrane ➡️ products actively reabsorbed through synaptic membrane and ATP provides energy to recombine NT and package into vesicles ➡️ Ca2+ pumped out, Na+ channels close ans synaptic knob repolarised
29
Effects of drug on synapses
antagonistic - reduce NT action
| agonistic - amplify NT effect
30
features of a synapse
unidirectional
excitatory or inhibitory
spatial summation = number of presynaptic knobs collectively release enough NT to exceed TH of post-synaptic membrane and trigger an AP
temporal summation = single presynaptic knob releases enough NT to trigger an AP due to many APs
31
What does the pacinian corpuscle do
Responds to changes in mechanical pressure and found deep under skin.
Frequency of impulses produced by receptor reflects the strength of the stimulus.
Acts as a transducer converting the energy of the stimulus into a form the body can interpret - a generator potential
32
What are lamellae?
The sensory nerve ending of the pacinian corpuscle is wrapped around layers of connective tissue - lamellae. These can slide past each other as they have a viscous gel between the layers.
33
How does the pacinian corpuscle work?
Pacinian corpuscle is stimulated and lamella are deformed and press on the sensory nerve ending. This stretches the stretch-mediated ️sodium channels in the sensory neurone's membrane to open and sodium ions to diffuse in, depolarising the membrane. If the generator potential produced exceeds the threshold, it triggers an action potential which is propagated along other neurones to the CNS.
34
Retina
Light sensitive layer at the back of the eye with both rods and cone cells
35
Fovea
Contains only cone cells
36
Blind spot
Contains no rods or cone cells
37
Optic nerve
The nerve that sends information from the eye to the brain
38
Where are rod cells found?
In the periphery of the retina
39
Where are cone cells found?
Concentrated at the fovea
40
Visual acuity of rod cells
Poor as many rods share a single connection to the brain by bipolar cells
41
Visual acuity of cone cells
High as there is a bipolar-neurone connection for every cone cell so the brain knows exactly which cone cell was stimulated
42
Sensitivity to light of rod cells
High due to spatial summation
43
Sensitivity to light of cone cells
Low as each individual cone cell must be stimulated to overcome threshold
44
Wavelength of light and pigment of rod cells
Black and white, night vision
| Rhodopsin
45
Wavelengths of light and visual pigment of cone cells
Colour, daytime vision
| Iodopsin
46
Chemical mediators
Active in their immediate viscinty, used at the cellular level to co-ordinate activities, released from certain mammalian cells
47
Histamines
Stored in white blood cells (mast and basophil) and released as a result of injury or in response to allergens.
Cause the dilation of small arteries and arterioles and increase permeability of capillaries leading to localised swelling, redness and itching (inflammation). InctI ashes blood to area to help get rid of allergen etc.
48
Prostaglandins
Found in cell membranes and cause dilation of small arteries and capillaries. Released following an injury and increase permeability of capillaries and blood pressure. Release neurotransmitters to intensify pain.
49
Hormones
Chemical communication in blood - slow.
Travel throughout body but only target cells respond.
Long lasting response - may be permanent and irreversible
50
Nervous system
Nervous communication by neurones - rapid
| Response is localised and short lived
51
Homeostasis
The maintenance of a constant internal environment in organisms despite external changes.
Essential due to enzymes.
Set point ➡️ receptor ➡️ controller ➡️ effector ➡️ response ➡️ feedback loop
52
Negative feedback
A deviation from the normal level which causes a return to the normal level. Occurs when the feedback loop causes the corrective measures to be turned off.
53
Positive feedback
Increases original change detected by receptors - the corrective mechanisms remain turned on.
54
Methods of gaining heat
Production of heat from metabolism of food during respiration
Gain of heat from the environment by conduction convection and radiation
55
Methods of losing heat
Evaporation of water eg sweating, panting
| Loss of heat to the environment by conduction convention and radiation
56
Ectotherms and their adv/disadv
Animals that as cold blooded and rely on the external environment for temperature control instead of generating their own body heat.
Use less food in respiration, need to eat less, can use more energy from food for growth
Less active in cooler temps - may not be capable of activity during winter so hibernation is key to survival
57
How ectotherms regulate their temperature
(Predominately behavioural)
Exposing themselves to the sun - basking
Taking shelter to prevent overheating when the suns radiation is at its peak
Gaining warmth from the ground - conduction
Generating metabolic heat - respiration
Colour variations - darker colours absorb more heat, lighter colours reflect heat
58
Endotherms and their adv/disadv
Animals that are warm blooded and produce their own body heat through metabolism (35-440C)
Constant temp, active in cold temps, can inhabit colder and warmer locations
Lots of energy used to regulate body temp, less energy from food goes into growth so more food is needed
59
How endotherms regulate temperature when it's cold
(Predominately physiological)
Vasoconstriction - diameter of arterioles neat skin surface reduces, reducing volume of blood reaching surface through capillaries. Blood passes beneath fat so less heat is lost to the environment.
Shivering - involuntary rhythmic contractions that produce metabolic heat due to muscle respiration and friction
Raising of hairs - hair erector muscles in the skin contract, raining hairs and trapping a thick layer of still air for insulation.
Increased metabolic rate - hormone increase respiration and heat is produced.
Sweating reduced or ceases
Behavioural - shelter from wind, bask in sun, huddle together
60
How endotherms regulate their temp when it's hot
(Predominately physiological)
Vasodilation - diameter or arterioles near skin surface increases, allowing warm blood to pass close to skin surface through capillaries and heat radiates away
Increased sweating to evaporate water from the skin surface in the form of heat. Mammals with fur pant through mouth and tongue to evaporate water.
Lowering of body hair - hair erector muscles relax and hairs flatten against body to reduce thickness of insulating layer and more heat is lost.
Behavioural mechanisms - avoid heat of day by sheltering in the shade to prevent body temperature rising
61
Detection of temp and location of heat loss centre
Hypothalamus
62
Hormone
A regulating chemical produced by an endocrine gland and is carried in the blood to the target cells on which it acts
Effective in small quantities
Transported in blood plasma
Can use a second messenger to bring about chemical changes
63
Why is glucose essential and what is the normal level in the blood
Main substrate for respiration
Too low - cells deprived of energy and die
Too high - water potential of blood lowered
Normal is 4.5-5.5mmol
64
If glucose level rises...
Detected by beta cells of Islet of Langerhans in the pancreas ➡️ insulin released into the blood and binds with complementary receptors on the liver and muscle cells ⬅️ glucose transport proteins open and glucose enters cells: enzymes are stimulated to convert glucose into glycogen (glycogensis), glucose is converted to triglycerides, rate of respiration is increased: blood glucose level falls
65
If blood glucose level falls....
Detected by alpha cells of Islet of Langerhans in the pancreas ➡️ glucagon released into the blood and binds to complementary receptors on liver cells only: glucogenolysis and gluconeogenesis: glucose enters the blood by facilitated diffusion and blood glucose level rises
66
Glucose
Sugar used in reparation
67
Glycogen
A polymer of glucose for storage
68
Glycogensis
Converting glucose into glycogen
69
Glycogenolysis
Converting glycogen to glucose
70
Gluconeogenesis
Making new glucose from glycerol and amino acids
71
Glucagon
Hormone released when blood sugar levels are low
72
Insulin
Hormone released when blood sugar levels are high
73
How does insulin decrease blood sugar levels
Insulin binds to receptor
Causes vesicle of glucose carrier proteins to move to plasma membrane, fuse and add carrier proteins to the cell so that glucose enters the cell
74
Diabetes symptoms
```
Increased thirst and hunger
Need to urinate excessively
Tiredness
Weight loss
Blurred vision
```
75
Type 1 diabetes causes
Body unable to produce insulin due to an autoimmune response in which the immune system attacks the beta cells of Islet of Langerhans.
Common in children with a family history of type 1 diabetes.
76
Type 2 diabetes causes
Glycoprotein receptors on body cells lose their responsiveness to insulin or inadequate supply of insulin from pancreas.
People over 40 at risk, but developing in adolescents.
Overweight, unearthly diet, lack of excercise are contributing factors in developing type 2 diabetes
77
Treatment and control of type 1 diabetes
Controlled by insulin injections 2-4 times a day. Must exactly match glucose intake - monitored using biosensors. Carbohydrate and exercise must also be monitored carefully.
78
Type 2 diabetes treatment and control
Regulate carbohydrate intake and match to amount of exercise - lifestyle changes
May be supplemented by insulin or use of drugs stimulating production of insulin or slow rate at which body absorbs glucose from the intestine.
79
Sugar, bases and number of strands in DNA
Deoxyribose, adenosine/thyamine, cytosine/guanine, 2 chains
80
Sugar, bases and number of strands in RNA
Ribose sugar, adenosine/uracil, cytosine/guanine, single stranded
81
mRNA
Messenger RNA
Originates in the nucleus and moves to cytoplasm during protein synthesis
Single polynucleotide
Groups of 3 adjacent bases = a codon
82
tRNA
Transfer RNA
Found in to cytoplasm
Carries amino acids used to make proteins to ribosomes
Single stranded, but folds back on itself in a very precise way.
Anticodon is 3 unpaired bases on the anticodon loop that are complementary to a triplet of bases on the mRNA and code for a specific amino acid.
83
Transcription
The mechanism by which the base sequence of a section of DNA (a gene) is converted into the complementary base sequence of mRNA using one strand of DNA as a template.
1) DNA helicase breaks the hydrogen bonds between the bases, causing the two strands to separate - exposing bases on the DNA in the region of the gene.
2) RNA polymerase moves along one exposed strand (template strand) causing nucleotides in this strand to join with the complementary nucleotides from the pool present in the nucleus.
3) Phosphoester bonds join between free nucleotides and DNA re-joins behind it
4) Once the RNA polymerase reaches a stop triplet on the DNA, the pre-mRNA molecule detaches from the DNA
5) In eukaryotic cells, DNA and pre-mRNA contain introns - sections that do not code for proteins. These must be removed by splicing in post-transcriptional processing.
6) The mature mRNA molecule then leaves the nucleus via a nuclear pore
84
Translation
The mechanism by which the sequence of bases in the mRNA molecule is converted into a sequence of amino acids in a polypeptide chain.
1) A ribosome attaches to the start codon at one end of the mRNA molecule
2) The tRNA molecule with the complementary anticodon sequence moves to the ribosome and pairs up with the sequence on the mRNA. This tRNA carries a specific amino acid.
3) A second tRNA molecule attaches itself to the next codon on the mRNA in the same way.
4) Each ribosome can hold two tRNA molecules at a time. At the ribosome, a peptide bond forms between the two amino acids using an enzyme and ATP.
5) The first tRNA molecule moves away, leaving its amino acid behind. A third tRNA molecule binds to the next codon, it's amino acid forms a peptide bond with the first two and the second tRNA molecule moves away.
6) This process continues with up to 50 ribosomes passing behind the first to form identical polypeptide chains.
7) The synthesis continues until a stop codon is reached, where the ribosome, mRNA and last tRNA separate and the polypeptide chain is complete.
85
The genetic code is a triplet code
It's read in groups of 3 bases which code for 1 amino acid
86
The genetic code is non-overlapping
Each base is read only once
87
The genetic code is degenerate
Most amino acids have more than one codon
88
Termination or stop codons
Eg UAA do not code for a particular amino acid, but instead act as stop signals to mark the end of a polypeptide.
AUG - methionine - acts as an initiation codon
89
The genetic code is universal (ubiquitous)
The same triplets code for the same amino acids in all organisms
90
FSH
Follicle stimulating hormone
Produced by pituitary gland in brain
Stimulates follicle maturation (egg)
Stimulates follicles in ovaries to produce oestrogen
91
Oestrogen
Produced by follicle in ovary
Stimulates rebuilding of uterus walk after menstruation
Stimulates pituitary gland to produce LH
Inhibits production of FSH when increasing and stimulates FSH and LH production when falling
92
LH
Leutenising hormone
Produced by pituitary gland in brain
Stimulates follicle to burst and release ovum - ovulation
Stimulates ruptured follicle to convert into corpus leuteum and produce progesterone.
93
Progesterone
Produced by corpus leuteum in ovary.
Maintains lining of uterus wall to receive fertilised egg
Promotes glycogen storage
Increases blood supply in uterus lining
Inhibits production of FSH and LH in large quantities.
94
Three types of muscles
Cardiac - only in heart
Smooth - walls of blood vessels
Skeletal muscle
95
I bands
Light and contain only actin
96
A bands
Dark - overlap of actin and myosin
97
H zone
Light - only myosin
98
Z line
- distance between = sarcoma re
99
Myofilaments
Actin and myosin
100
Actin
Myofilament that is thinner. Two stands are twisted around each other
101
Myosin
Myofilament that is thicker. Long rod shapes fibres with bulbous heads
102
Why are muscle cells joined into fibres?
Stronger.
| Share nuclei, sarcoplasm, mitochondria and rough sarcoplasmic reticulum.
103
Slow twitch fibres
Weak, slow, long contraction time, aerobic respiration, large myoglobin store (O2 supply), large glycogen store, few and thinner myosin filaments, many mitochondria, rich supply of blood vessels - red in apparance
104
Fast twitch fibres
Fast, strong, short contraction time, anaerobic respiration, large phosphocreatine store converting ️ADP + Pi to ADP building up lactic acid and causing fatigue, more and thicker myosin filaments, less mitochondria, fewer capillaries and paler in colour.
105
Neuromuscular junction
Cholinergic synapse
| Threshold potential in sarcolemma causes Ca2+ ions to be released from the sarcoplasmic reticulum
106
When contraction occurs
```
Sliding filament mechanism
Sarcomere shortens
I band narrows
H band narrows
A band same width
Actin and myosin slide past one another
```
107
How does reverse transcriptase isolate DNA fragments?
Retroviruses contain RNA as genetic material, but can synthesise DNA using reverse transcriptase enzyme.
Single-stranded DNA complementary to RNA made.
DNA polymerase converts to double stranded cDNA
Genetic engineers take mature mRNA from host cell. Reverse transcriptase then converts to DNA - intron free.
A primer is needed
108
How do restriction endonucleases isolate DNA fragments?
Enzymes used to cut DNA molecules in specific places - destroy DNA of infective viruses in bacteria.
Act in specific base sequences, cutting at recognition or restriction sites 4-6 bases long.
Sequences must be palindromic.
Cuts with blunt or sticky ends.
Gene can be chopped out without destruction.
Any 2 strands of DNA chopped by the same restriction endonuclease will hybridise as they have the same sticky ends.
109
How does the polymerase chain reaction (PCR) work?
Rapid simple procure used to amplify DNA by in vitro cloning.
Need:
1) DNA fragment to be copied
2) DNA polymerase to join nucleotides - extracted from bacteria living in volcanic hot springs - thermostable due to extremes in temp in PCR
3) primers - short sequences of complementary nucleotides to ends of fragments
4) free nucleotide DNA bases
5) thermocycler - varies temp precisely over a set time
1) 95 degrees - separation of DNA strand
2) 35-66 degrees - annealing of primers
3) 68-72 degrees - synthesis of DNA using DNA polymerase
110
How is a gene inserted into a plasmid (vector)?
Plasmids are small circle of cytoplasmic DNA found in bacteria. They are capable of replicating independently.
Plasmid cut open by a restriction endonuclease. Same enzyme used to cut donor DNA so sticky ends are complementary.
DNA fragment inserted into plasmid and circle is reformed. DNA lipase joins sugar-phosphate groups together.
111
How are plasmids inserted into the host cell?
Directly by bacterial cells by transformation. Mixed with plasmids at low temps in the presence of Ca2+ ions. Cell membranes become leaky so plasmids can be absorbed.
Now transgenic - contain a gene from a different organism
112
Why does only about 1% of the bacterial cells take up the plasmid containing recombinant DNA?
Some cells will not have taken up any plasmids
| Some cells will have taken up plasmid without desired gene - self-ligated
113
How can a transgenic host cell be identified using antibiotic resistance ?
2 genes for antibiotic resistance.
Donor DNA inserted into centre of antibiotic resistance gene 1, so the enzyme breaking down antibiotic 1 will not be produced.
Bacteria is grown on antibiotic 2. Those that have survived have taken up a plasmid. Then grown on antibiotic 1. Plates replicated before by spreading thinly on nutrient agar plates. Bacteria that survive have not transformed the transgenic plasmid.
114
How do fluorescent markers allow identification of transgenic host cells?
A gene from jellyfish for the production of green fluorescent protein (GFP) is engineered into the plasmid. Gene is then transplanted into the centre of the GFP gene. Therefore, bacterial cells with specific plasmid will not fluoresce as the GFP gene has been cut.
115
How do enzyme markers allow the identification of transgenic host cells?
Eg enzyme lactase acts on a particular colourless substrate to produce a blue product. If the gene for lactase is disrupted by inserting DNA into the centre, enzyme will not be produced and substrate won't change colour.
116
How are proteins extracted form bacteria?
Removed from agar plate and grown in a fermenters.
If secreted by bacteria, can be extracted from the medium.
If protein not secreted, bacteria must be broken up to allow extraction of protein. Must be purified and packaged before selling by downstream processing.
117
Uses of recombinant DNA technology (genetic modification)
Increasing yields, improving nutrient content, introducing resistance to disease and pests, making crops tolerant to herbicides, tolerance to environmental conditions eg drought, making vaccines, producing medicines.
Eg insulin for diabetics now produced by bacterial cells rather than cows or pigs. Less side effects, no modification and no killing animals.
Eg GM tomatoes have a gene sequence complementary to gene producing enzyme responsible for softening of tomatoes. Combine to form a double strand and enzyme is not produced.
Eg gene for production of rare and expensive proteins in human medicine inserted into fertilised egg cell of goat. Eg anti thrombin to prevent blood clotting. Extracted from goats milk.
118
In vitro vs in Vivo cloning methods
PCR can use partly broken down, only small amounts needed and does not need to be isolate.
However base sequence needs to be known (primers), cannot produce protein, will only reliably copy up to 1000bp compared to 2Mbp in bacteria, and have no corrective mechanism.
119
Risks of recombinant DNA technology
```
May transfer gene to other organisms eg herbicide resistance to weeds
Spread antibiotic resistance
Don't know long term consequences
Wrong hands
Is cost justified?
Immoral to tamper with genes?
```
120
Benefits of recombinant DNA technology
Produce a range of substances
Helpful to farmers- more tolerance, higher nutritional content, higher yields, help prevent certain diseases eg rise with gene for vitamin A productions
121
DNA probe
Short, single-stranded section of DNS with label to make it identifiable: radioactive label of 32P or fluoro event label.
Complementary to section of DNA want to find - DNA separated, mixed with probe, DNA hybridisation, identification. Need to know base sequence.
122
How is DNA sequencing carried out using the Sanger method?
Set up four test tubes, each containing:
1) many single-stranded fragments of DNA to be sequenced - template
2) mix of free DNA nucleotide bases - A, T, C, G
3) primer to start protein synthesis with label
4) DNA polymerase
5) modified (dideoxyribonucleotides) terminating bases - either A, T, G or C in each tube.
Allow DNA to be synthesised in each tube. DNA synthesis stops when terminator inserted. Different lengths.
Separated using gel electrophoresis - labelled and a chart made.
123
How does gel electrophoresis work?
Sample of DNA undergoes PCR
DNA fragments inserted into a gel covered in buffer solution
Electrical current passes through - DNA negative so moves to the positive end.
Smaller fragments move faster.
DNA either viewed under UV light to see bands or using auto radiography - southern blotting of gel (fragile) - nylon membrane and paper towels to absorb liquid. UV light sets.
124
How does restriction mapping work?
Restriction endonucleases cut at recondition sites
Produced different length fragments - separated using gel electrophoresis
Distance between sites discovered and a map of DNA can be drawn
125
How does automation of DNA sequencing and restriction mapping work?
Labelled with fluorescent dye - electrophoresis - scanned and sequenced. Fast.
126
How does genetic screening work?
Complementary fragments to known faulty gene is produced and labelled - DNA probe.
PCR
DNA extracted from patient's blood, amniotic fluid or umbilical cord
Strands separate and probes added
Probe binds of sequence is present - photographic plate of X-Ray film shows up
Hundreds of probes may be attached to gals slide - to test for many genetic disorders at once
Can also test for oncogenes for cancer diagnosis
127
Why may genetic counselling be needed?
It advice patients and relatives about risks of genetic disorders. Also explaining of results and advising of options
128
How does DNA fingerprinting work?
Introns contain repeating sections that differ in length in every person.
1) extraction - DNA extracted from blood, hair follicle, semen etc. DNA separated and PCR.
2) digestion - cut into fragments using restriction endonucleases- cut close to specific sequence of introns - different lengths
3) separation using gel electrophoresis
4) southern blotting
5) hybridisation - immersed in DNA probes - bind to complementary sequences
6) development - X-ray film radiation
Match DNA
Used in forensics, population and evolutionary studies and paternity testing
129
Gene therapy aims
Involves altering defective genes inside cells to treat genetic disorders and cancer by transfection
130
How should gene therapy be used?
If the disorder is caused by 2 mutated recessive alleles, supplement a working dominant allele to mute the recessive effect.
If the disorder is caused by a mutated dominant allele, the effect Dan be silenced by putting a DNA sequence in the middle of the allele
131
How can new, healthy genes be inserted into the body?
Cloned from healthy human genes
Inserted using plasmid vectors: adenoviruses (inject DNA into epithelial cells for diseases such as cystic fibrosis), retroviruses (SCID - Tcells) , plasmids or liposomes (spheres of lipid contain plasmid which diffuse along phospholipid bilayer better)
132
Somatic gene therapy
Altering of genes (alleles) in specific body cells (the cells most affected) eg epithelial cells in lungs for CF. Although not in gametes so not passed on
133
Germ-line gene therapy
Altering of alleles in sex cells - fertilised egg but illegal due to moral issues and what may come of it (designer babies)
134
Advantages of gene therapy
Prolong lives
Better q of l for genetic disorder sufferers
Conception of babies without genetic disorders
Decrease in number of sufferers
135
Disadvantages of gene therapy
```
May be short lived (somatic)
Multiple treatments needed (somatic) unless in bone marrow - risk of cancer
Difficult in specific cells
Immune response against vectors
Wrong place can lead to more problems eg cancer
Over expression of gene
Multiple gene disorders is difficult
Immune
Cause infection (viruses)
Ethical issues
```
136
Gene mutation
Any change to one or more nucleotide bases, or rearrangement in DNA
- during formation of gametes may be inherited (discontinuous variation)
137
Substitution of bases
A different base is inserted into the sequence but the number of bases does not change
138
Nonsense mutation
A substitution of bases that has resulted in the formation of a stop codon, marking the end of a polypeptide chain. Causes the production of the polypeptide to stop prematurely resulting in a non-functional protein
139
Mis-sense mutation
Substitution of bases resulting in a different amino acid being coded for - affects tertiary structure
140
Silent mutation
Substitute base produces a triplet that codes for the same amino acid as before (degenerate code). Polypeptide not altered.
141
Deletion/addition of bases
Alter every set of 3 bases that follows - frame shift. Protein that forms is complement,y different. May be useless of a stop triplet could be made.
142
Causes of mutations
Spontaneous
Rare - 1-30 mutations per million gametes
Rate can be increased by mutagenic agents or mutagens - high energy radiation eg UV, X-Ray, chemicals eg in tobacco.
Most disadvantageous - but promote genetic diversity eg antibiotic resistance.
143
Proto- oncogenes
Growth factors attach to receptor protein on membrane - switch on genes for DNA replication.
Gene mutation - oncogenes.
Permanently activated - tumour
144
Tumour suppressant genes
Inhibit cell division and promote apoptosis - programmed death of cells and damaged DNA
Mutated = inactivated and mutated DNA can replicate etc
145
Housekeeping genes
Genes expressed in all cells eg respiratory enzymes
146
Totipotent
Cells not yet differentiated and are capable of expressing any of its Genes eg fertilised human egg cell
147
Stem cells
Divide and renew themselves over long periods
Unspecialised
Can develop into other specialised types of cell
148
Pluripotent
Can develop into most of body's cell types eg embryonic stem cells
149
Multipotent
Can develop into a limited number of body tissues eg adult stem cells from bone marrow
150
How is transcription controlled?
Promoter region 100bp upstream of gene had a transcription factor (protein) bind to it. Causes RNA polymerase to attach to start of target gene, stimulating transcription.
When not expressed, promoter region is blocked by an inhibitor.
151
How does oestrogen affect transcription?
A hormone produced by ovaries - steroid so lipid soluble
Diffuses easily through plasma membranes to cytoplasm
Binds with a site on a specific receptor molecule - ER- alpha.
When bound, oestrogen changes shape of receptor molecule and releases inhibitor from DNA binding site on the transcriptional factor.
Transcription factor the enters nucleus through a nuclear pore and combines with the promoter region to stimulate transcription.
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What is siRNA?
Small interfering RNA - double stranded RNA molecules
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How can translation be controlled?
RNA-dependent RNA polymerase catalyses production of complementary RNA stand - double stranded RNA (dsRNA)
dsRNA broken up by dicer enzyme = siRNA 23bp long
Another enzyme combines to form a protein complex (requires ATP)
One of the siRNA strands is destriyed.
Protein complex binds to original mRNA.
Enzyme cuts mRNA into smaller sections which can no longer be translated and therefore not expressed
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Sliding-filament theory of muscle contraction
1. Nerve impulse arrives at neuromuscular junction
2. Ca2+ floods into axon
3. Neurotransmitter in vesicles empty into synaptic cleft (exocytosis)
4. Neurotransmitter diffuses to receptor sites on sarcolemma
5. Na+ flood in to sacrcoplasm and sarcolemma depolarised
6. Wave of depolarisation spreads through sarcolemma and T-tubules
7. Wave spreads to SR
8. Ca2+ channels open and Ca2+ floods out of cisternae of SR into muscle myofibrils
9. Ca2+ binds with troponin molecules on actin filaments
10. Troponin changes shape
11. This makes tropomyosin molecules move, exposing the myosin binding sites on the actin filament
12. Myosin head with ADP+Pi bound to it joins to binding site on actin > actin-myosin cross-bridge
13. It now tilts through 45 degrees and pulls the actin along
14. As myosin tilts it released ADP and Pi
15. A new ATP can now fit into the myosin head, it is hydrolysed by ATPase in the head into ADP+Pi and energy
16. The energy detaches the actin and myosin
17. The head flips back to its original position and joins to the next binding site on the actin, pulling it along further
18. This continues until the muscle is no longer stimulated by action potentials
19. Ca2+ channels in SR close
20. Ca2+ bound to troponin are released
21. Ca2+ are pumped back into the cisternae by active transport
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What is ATP needed for in muscle contraction?
To move myosin heads and actively transport Ca2+ ions back into SR
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Sources of ATP for muscle contraction:
1. Stored ATP in sarcoplasm
2. Stored phosphocreatine - transfers phosphate to ADP to rapidly generate ATP using the enzyme creatine kinase
3. Stored glycogen in muscle > glucose > respiration
4. Fatty acids in muscle > respiration
5. Anaerobic respiration > 2 ATP (causes muscle fatigue and lactic acid which is transported to liver in blood where it is metabolised with oxygen - oxygen debt)
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Troponin
Protein on actin filaments that Ca2+ binds to
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Tropomyosin
Protein in actin filaments that is moved to expose myosin binding sites on actin filament when Ca2+ is bound to
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Muscle structure
Whole muscle > Bundle of muscle fibres (with nerves and capillaries) > Single muscle fibre (with striations and nuclei) > myofibril > sarcomere > myofilaments
