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    Could someone be ever so kind and explain to me the basics of the photochromes?! For some reason it's the one thing I cannot get my head around!


    This was posted from The Student Room's iPhone/iPad App
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    (Original post by ELB141)
    Could someone be ever so kind and explain to me the basics of the photochromes?! For some reason it's the one thing I cannot get my head around!


    This was posted from The Student Room's iPhone/iPad App
    if you go onto the previous page its discussed there it was the same with me XD
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    (Original post by wam-bam)
    heart muscle is myogenic, what is meant by myogenic (3 marks)
    Myogenic means that the heart iniciates it's own heart beat? The SAN sends electrical impulses causing the atriums to contract, the electrical impulse does not reach the ventircles due to the non-conductive tissue in the interventricle wall. The electric impulse then passess down the bundle of his and purkyne fibres so the ventricles contract simultaneously from the bottom up?

    Someone please correct me, I have a feeling that is extremely wrong.
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    (Original post by rocco94)
    Myogenic means that the heart iniciates it's own heart beat? The SAN sends electrical impulses causing the atriums to contract, the electrical impulse does not reach the ventircles due to the non-conductive tissue in the interventricle wall. The electric impulse then passess down the bundle of his and purkyne fibres so the ventricles contract simultaneously from the bottom up?

    Someone please correct me, I have a feeling that is extremely wrong.
    what you wrtoe is the process of heart activity !

    what is myogenic??

    the ability of cardiac muscle to contract on its own and initiate its own wave of depolarisation !
    SIMPLE 2 LINE ANSWER !
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    (Original post by rocco94)
    Myogenic means that the heart iniciates it's own heart beat? The SAN sends electrical impulses causing the atriums to contract, the electrical impulse does not reach the ventircles due to the non-conductive tissue in the interventricle wall. The electric impulse then passess down the bundle of his and purkyne fibres so the ventricles contract simultaneously from the bottom up?

    Someone please correct me, I have a feeling that is extremely wrong.
    Myogenic means it contracts and relaxes without receiving signals from Neurones
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    Hi guys! I have one question, its to do with Fast and Slow twitch muscles...

    I understand that fast twitch muscles have extensive sarcoplasmic reticulum, obviously so that there is enough Ca2+ to bind to troponin etc. and to cause muscle contraction.

    BUT, why do Slow twitch muscle fibres have little sarcoplasmic reticulum?

    Basically in my text book (different from SNAB) it says in a comparison table:

    Fast Twitch: Extensive sarcoplasmic reticulum
    Slow Twitch: Little sarcoplasmic reticulum

    Thnx in advance!
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    (Original post by ConnorB)
    Myogenic means it contracts and relaxes without receiving signals from Neurones
    ummm hi !
    sorry to be random
    but werent you blonde ??! lol
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    (Original post by Solidcancer07)
    Hi guys! I have one question, its to do with Fast and Slow twitch muscles...

    I understand that fast twitch muscles have extensive sarcoplasmic reticulum, obviously so that there is enough Ca2+ to bind to troponin etc. and to cause muscle contraction.

    BUT, why do Slow twitch muscle fibres have little sarcoplasmic reticulum?

    Basically in my text book (different from SNAB) it says in a comparison table:

    Fast Twitch: Extensive sarcoplasmic reticulum
    Slow Twitch: Little sarcoplasmic reticulum

    Thnx in advance!
    that detail IS NOT needed i think.
    cuz i didnt see any explanation of this in any book or rev guide .....
    so just learn what has more and what has less
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    (Original post by iesians)
    what you wrtoe is the process of heart activity !

    what is myogenic??

    the ability of cardiac muscle to contract on its own and initiate its own wave of depolarisation !
    SIMPLE 2 LINE ANSWER !
    its three marks so you could add to your answer saying it doesnt fatigue and the depolarisation of heart cells spreads like a wave depolarising cells next to each other

    and that the rate of depolarisation of cells (heart rate) can be adjusted accordingly by the medulla
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    (Original post by iesians)
    ummm hi !
    sorry to be random
    but werent you blonde ??! lol
    I'm mixed race. As of a result when my hair is in lots of light, it goes this weird reflective blonde colour It's actually very dark brown/black usually.

    I'm a genetic freak
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    Can someone please briefly the spirometer practical to me?? what would i write for a response to them 6marker practical questions?? Any links to videos/websites would be helpfull azwell! thanks
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    (Original post by iesians)
    lol. i think the brown looks lovely on you.
    sorry for interfering in your hair colour ! thought id ask cuz you are one of the few people here who put there own pic as display pic. so it always gravitates me lol
    Thank you
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    (Original post by Hanz_a93)
    Can someone please briefly the spirometer practical to me?? what would i write for a response to them 6marker practical questions?? Any links to videos/websites would be helpfull azwell! thanks
    - fill the tank with oxygen
    -insert a mouthpiece into someons mouth (lol ofcourse)
    - place a nose clip on their nose.
    -allow them to breathe through the mouthpiece for a while to acclimatise.
    -connect the mouthpiece tot he oxygen chamber and turn on the kymograph rotation.
    -allow them to breathe calmly for a minute and then advice them to breathe in as fully as possible followed by max forced exhalation.
    - stop the rotating drum.
    -the pen would have marked a spirometer trace for you.
    -read off the tidal volume and vital capacity form the trace.


    OH YEAHH !! also calibrate the chart beforehand to read off the volume !

    HOPE IT HELPS !!
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    (Original post by Cleoleo)
    what is the phospholipid bilayer permeable to again?
    Lipids and small molecules e.g. H20 I think, but not 100% sure!
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    (Original post by bertiejess)
    Lipids and small molecules e.g. H20 I think, but not 100% sure!
    H2O is not a small molecule
    and it is also polar so membrane isnt permeable to it !
    it passes through specialised protiens called aqua porins (this isnt needed)
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    I seriously don't understand Rod cells when exposed to light and exposed to darkness.

    Could someone "Enlighten" me please"

    ...Revision does crazy **** to people.
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    (Original post by DarrenDM)
    Could you post the rest please?
    Hey all, I've completed a series of responses to questions on the unit 5 article given earlier in this thread. I've made a few modifications to the original questions and have underlined what i feel are key ideas in most points. Let me know if you have any suggestions for any of the points or if you think I've misinterpreted the question.
    Hope these ideas are helpful.

    Unit 5 Biology: Question 7 Article Focus Ideas – W/ Answers
    Paragraphs in the article where I have pulled data from are given by eg: 3)

    1. Using specific examples; discuss whether there is a correlation between the media and amount of body dissatisfaction.
    Examples For:
    • 5) University of Central Florida study; approx. half of 3 – 6 year old girls in the study said they were concerned with being fat. (No direct link- but media images could be influencing) Idea of diet pill usage increase (100% increase) in 15-17 year olds being an indicator of increased body dissatisfaction.
    • 6) 80% increase in young girls admitted to hospital with anorexia.
    • 7) Meta-analysis of 25 studies (likely to be reliable) concluded ‘body image was significantly more negative after view thin media images’.
    • 10) Hiroshima University study on healthy women: all subjects showed mPFC activation (associated with self-reflection/sub conscious thoughts) when presented with overweight images.
    • 12) Hiroshima study showed healthy women have PFC and amygdala (emotional reaction processing) ‘signicantly activated’ when presented with a self ‘fat image’.
    • 15/16) Harvard Medical School study evaluating the impact of television (main visual media source) on body satisfaction and disordered eating in adolescent girls.
    o Idea of traditional preference for full figure; low 12.7% with pathological scores for eating disorders, low/no dieting in adolescent females (implied; 15) ‘rare’), no self-induced vomiting
    o --- Increase in all above measures in 3 years since introduction of television suggests strong correlation. Eg; 16.5% increase in pathological eating disorders, 66% of subjects concerned with body image (not just limited to females), girls openly citing thin media figures as desirable / eqv, increase in self-induced vomiting to 11.3%.
    • 17) British study found ¼ UK adults is trying to lose weight either due to body dissatisfaction obesity.
    Against:
    • 11) Men showed no significant mPFC activation when [resented with overweight/ thin male images.
    • 13) Men have activated mPFC (amygdala deactivation also implied) when presented with unpleasant word stimuli concerning ‘heavy’ body image.

    2. Analyse and interpret the possible link between obesity and health issues, such as diabetes, CVD and cancer.
    • 3) ‘Obesity defined as a surplus of body fat which is detrimental to health’ around the waist/abdomen
    o Idea that if energy intake from food is greater than energy expenditure person will gain weight. (normally, fat –stored in the form of triglycerides)
     Reference to BMR (Basal Metabolic rate)
     Reference to PAL (physical activity level) needing to be taken into account
    • Idea that type 2 diabetes is caused long term high blood glucose levels
    o Relation to higher energy input than expenditure; leading to increased blood glucose levels.
    o Idea that insulin controls blood glucose levels
    o Idea body cells do not produce enough insulin/ cells do not respond to insulin /eqv
    • Idea that CVD is a multifactorial condition.
    o So obesity is only one factor.
    o Triglycerides can form fatty acid plaques in the arteries
     Possibly leading to CVD / blood clots /death
     Or raising blood pressure and leading to atherosclerosis
    o Obese people unlikely to have appropriate diet; may have high blood cholesterol levels due to a diet high in saturated fats. Unlikely to be exercising an appropriate amount.
    o Idea that LDLDL ratio is a good indicator of CVD risk
    • Idea that body weight shouldn’t have a causal relationship with cancer
    o As cancer is caused by DNA mutation, caused by factors such as UV light/ Asbestos / X Rays / Carcinogens (eg in tobacco) (Environmental factors)
    • Idea that obesity is likely to be correlated with an unhealthy life style, people may also smoke/drink alcohol heavily.
    o These are factors that influence CVD and also cancer

    3. Lipids are biological molecules that are insoluble in water, but soluble in organic solvents, like ethanol. Triglycerides are lipids made out of three fatty acids and one molecule of glycerol joined via an ester bond. The glycerol molecules are all the same. Recall the variation between the fatty acids.
    • Fatty acids may be saturated/ unsaturated (presence of double bonds in the long carbon chain)
    • Lipids can be mono, di or tri-glycerides.
    4. When a triglyceride is broken apart by hydrolysis, how many components are found as products? Name them.
    • 3 fatty acids and 1 glycerol molecule

    5. Suggest reasons why it is likely that gender plays a role in susceptibility to eating disorders.
    • 23) Women may have evolutionary adaptations to try to acquire figures which seem to be attractive to males (subcutaneous fat /fat deposits around buttocks/hips – ideal for sexual selection). Hence, they could be more likely to look at the figures of other seemingly successful females, (eg media figures) as ideal for attracting a mate and improving chances of reproducing and passing genes on.
    • However, women may have different preferences in men (eg ability to provide for offspring) and hence, maintaining an ideal waist to hip ratio may not be as important for sexual selection in men. (This idea is backed up by lack of mPFC activation in men (11))
    o So women are more likely to take steps to change their figure and so would be more susceptible to developing an eating disorder.
    6. List key features of a good study used to determine health risk factors. Refer to examples in the text.
    • Use of a control group/individuals: 10) Study shows women images of both overweight and thin models; to see mPFC activation. This means mPFC activation when looking at overweight models can be attributed to the models being overweight and not another factor (eg knowledge that they are models) as otherwise looking at the thin models would also cause mPFC activation.
    • Epidemiological studies
    o Large sample size. eg 15) Harvard Group use the Fijian population (– no exact figure given) This gives more meaningful results.
    o Longitudinal studies: Harvard group only considers the changes in a 3 year period.
    • Methodology must be repeatable. Eg 7) multiple studies on the effect of experimental presentation of thin media images on body satisfaction
    7. Analyse and interpret data about the threats of eating disorders.
    • Occurrence of eating disorders on the rise (in England): 6) 80% rise in the last decade in number of girls admitted to hospital with anorexia.
    o Mortality rate of 10-20%. Anorexia causes death due to heart complications. Eg. Bradycardia, where the heart beats abnormally slowly (<60Bpm). This is because the heart muscles are starved of certain electrolytes due to a reduction in fluid and mineral levels. A precise electrolyte balance is needed to maintain correct electrical currents for heartbeat.
    • Eating disorders that restrict calories to under 1200kcal/day (18)) increase total cortisol output in females. This leads to a number of threats including; higher blood pressure, suppressed thyroid function, impaired immunity, increased abdominal fat which further lead to conditions such as cancer, CVD and diabetes.
    • 52) Anorexia prevalent in the UK, 1.4M females with eating disorder 10% anorexia.
    o Any logical argument about how this is a significant proportion of the total UK population (Approx 62M)
    • Logical argument about how perceived risk and actual risk are different. Eg. People may not understand the biological effects of severe dietary restriction.
    8. Recall how brain activation patterns are used to determine the influence of exposure to media images to ones sense of self.
    • Functional magnetic resonance imaging (fMRI)
    o fMRI used to monitor O2 uptake in different brain areas during a task
     Oxyhaemoglobin more opaque to radio waves than deoxyhaemoglobin
    • More oxyhaemoglobin in active areas of the brain due to increased blood flow. Detected by change in radio wave absorbance.

    9. The energy you need in a day depends on your Basal Metabolic Rate (BMR) and level of activity. BMR varies with gender, age and body mass. Discuss this statement.
    • BMR is minimum amount of energy to maintain basic metabolic processes everyday
    • PAL is a modifying factor used to take into account physical activity levels when determining BMR
    • Gender: Men have a higher BMR mainly due to greater body weight than females and different body compositions, eg higher muscle mass, generally lower body fat levels. Muscle tissue is more metabolically active (than fat tissue) so requires more energy/day to maintain the same mass.
    • Body mass: Greater body mass is associated with more metabolically active tissue and hence more energy is needed per day to maintain it.
    Page 4

    1. How can restricting calories to 1200 calories per day affect cortisol and its subsequent effects on the body (para 18)?
    • 18)‘Increases total output of cortisol in females’
    o Regulates behaviour and functions eg glucose metabolism/inflammatory process
    • Prolonged exposure to high levels can lead to:
    o Higher blood pressure
    o Suppressed thyroid function
    o Impaired immunity
    o Increased intra-abdominal fat
     Contributes to heart disease/diabetes/cancer
    2. In paragraph 20, the brains of rats have been studied to see the effect of ‘yo-yo dieting’. Why are rats considered a good model for study and describe the ethical issues involved in the use of animals in a trial of this kind?
    • Good model because:
    o Easy to obtain
    o Easy to breed
    o Have short life cycles
    o Small adult size (can be stored in lab)
    o Similarity to humans (mammals)
    • Ethical objections:
    o Trial of this kind; Animal suffering/rats likely to feel pain
     Idea that rats have a ‘good sense of pain’ as opposed to use of sea slugs/ simple invertebrates
     Any logical argument using evidence from paragraph 20/22
    • 20) Eg; May be long/short term pain/effects due to ‘stress reactions ‘
    • 22) Argument based on weight cycling eg. That in human’s changes averaging only 2.5kg strongly linked to CVD /death. Hence mice likely to suffer longer term due to study.
    o Idea of weighing the effect on animals with the potential for improvement in human life/ does the end justify the means
     Idea that this research could save lives/ is not for cosmetics
    o Specific point on animal rights ‘Is it acceptable for the rats to be kept captive in laboratory cages’
    o Idea of animal welfare ‘there isn’t non-animal alternative’

    3. Describe the waist-hip ratio and one other measure of physique or obesity.
    • Waist hip ratio:
    o Waist circumference divided by hip circumference.
    o Measure of WAT/BAT levels
     Idea that a low ratio suggests better health
    • Body Mass Index
    o BMI= (mass/kg)/((height/m)^2)
    o Idea that BMI is only suitable for inactive people of normal body composition
    o Idea that BMI does not take into account difference between muscle/fat
    Page 5

    1. The electron transfer chain leads to ATP synthesis. How is this explained by the chemiosmotic theory?
    • Energy is released as electrons pass along the ETC. This energy is coupled to active transport of H+ ions (from glycolysis) from the mitochondrial matrix, across the inner mitochondrial membrane, into the intermembrane space.
    • Electrochemical gradient created across inner mitochondrial membrane
    • H+ ions diffuse back across the inner mitochondrial membrane
    o Through protein channels in stalked particles
    o H+ ions cause a conformational shape change in ATPase’s active site.
    o Allowing ADP/Pi to bind and releasing ATP after phosphorylation
    2. Suggest how UCP-1 may disrupt respiration at the Electron Transfer level and prevent the production of some ATP.
    • ‘Uncouples’ the process by dissipating the hydrogen ion concentration gradient.
    o By allowing H+ ions to cross the inner mitochondrial membrane via facultative diffusion.
    o So not all H+ ions pass through stalked particles/ATPase.
    o 28)So ‘energy from respiration is lost as heat, rather than being stored’
    3. Explain how transcription factors work.
    • Idea that transcription factors can work in 2 ways;
    o By binding to and causing a conformational shape change in repressor molecules attached to promoter region.
     Hence, enabling are RNA polymerase to bind and transcribe DNA
    • RNA polymerase binds to the promoter region adjacent to gene
    • Or Formation of transcription initiation complex
    o transcription factor complexes with RNA polymerase allowing transcription
    4. Outline the process by which peptide hormones can affect gene transcription.
    • Peptide hormones are unable to pass through the cell membrane.
    o Bind to receptors on the cell surface membrane
    o membrane bound complex activate a second messenger in the cell cytoplasm which further triggers a cascade of activation of proteins (signal pathway)
    o until a final protein enters the nucleus
    o acts as a transcription factor affecting gene expression/transcription an
    5. Explain how BAT is able to regulate both core body temperature and body weight.
    • BAT (Brown adipose tissue) cells contain ‘large numbers of mitochondria which are packed with a specialised protein: uncoupling protein 1’
    • idea that uncoupling protein 1 helps to regulate core body temperature by disrupting respiration, by dissipating the electrochemical gradient as heat(thermogenesis)
    • idea that if respiration is disrupted, energy from uptake of free fatty acids and glucose is not used to produce ATP
    • hence more fatty acids and glucose must be respired
    • so less available for storage/so less bodyweight
    6. Explain how PET scans work.
    • Positron Emission Tomography (PET)
    • patients injected with radioactively labelled glucose molecule
    • 18F-flurodexoyglucose taken up by metabolically active tissue
    • and becomes trapped in the first step of metabolism
    • radioactive isotope decays and emissions can be detected externally
    • metabolically active tissues include cancer cells (tumours) and the brain and heart which use large amounts of glucose
    7. Suggest why heart and brain need to absorb large amounts of glucose.
    • Idea that neurons in the brain require a lot of ATP before active transport of ions across the cell surface membrane (Na/K+ pump)
    • idea that neurotransmitter synthesis in the synaptic knob uses ATP
    • Idea that heart is (cardiac muscle/tissue) and requires ATP for muscular contraction (e.g. atrial/ventricular contractions)
    • suggestion that ions may be actively transported during repolarisation of tissue, which may require ATP
    • idea that both tissues are very metabolically active, and it is important they have enough ATP/comment on consequences of lack of ATP
    Page 6

    1. How does BAT deposition differ in rodents and humans (para 34)?
    • In adult humans, BAT is mainly deposited above the collar bones and around the neck, however in rodents BAT is mainly deposited between shoulder blades.

    2. Why have thyroid hormones and other drugs that stimulate the SNS (Sympathetic Nervous System) been used then abandoned?
    • Unpleasant side effects were encountered; therefore the thyroid hormones and drugs were abandoned.
    • E.g. line nurse blood disorders death
    • due to uncontrollable heat production
    3. Describe the effects of fucoxanthin from seaweed (paragraph 38).
    • Increase the production of UCP-1 in White Adipose Tissues.
    • Comment on function of UCP-1/effects of increased UCP-1
    o Eg. reduced amount of abdominal fat in rodents

    4. Explain why studies of fucoxanthin involving humans might be necessary?
    • General argument that other animals are dissimilar to humans, therefore it is necessary to test fucoxanthin on humans to observe its effectiveness and any possible side effects.
    • comment on use of rodents-not the most similar model (eg chimpanzees more similar)
    5. Describe the clinical trial process/modern drug testing process that would be needed if fucoxanthin were to be licensed for human trials.
    • Phase 1 trials, researchers test an experimental drug or treatment in a small group of people (20-80) for the first time to evaluate its safety, determine a safe dosage range, and identify side effects.
    • Phase 2 trials, the experimental study drug or treatment is given to a larger group of people (100-300) to see if it is effective and to further evaluate its safety.
    • Phase 3 trials, the experimental study drug or treatment is given to large groups of people (1,000-3,000) to confirm its effectiveness, monitor side effects, compare it to commonly used treatments, and collect information that will allow the experimental drug or treatment to be used safely.
    • Idea of phase 1-3 trials must be successfully passed before approval by national authority for use of general population
    • Idea of (Phase 4 trials, post-marketing studies to find additional information, including the drug's risks, benefits, and optimal use.)
    6. Use your scientific knowledge to describe the process by which mice could be genetically engineered to produce high levels of PRDM16 proteins (para 40).
    • Germ line engineering
    • Specific gene must be located in donor cell
    • Gene must be isolated in a piece of donor DNA
    o Use of restriction endonucleases to cleave DNA at specific sequences (Do not allow ‘molecular scissors’)
    • idea that gene must be transferred into embryo cell
    • via a vector
    o mention of use of DNA ligase to join sections of isolated DNA to plasmids (loops of DNA)
    • Plasmid can recombine with host DNA once it has entered the host’s nucleus producing recombinant DNA.
    • Mention of harmless viruses or liposomes (severe is formed from a lipid bilayer) being used to deliver DNA into cytoplasm
    • idea that duplicate gene(s) in DNA may increase gene expression
    • idea that when embryos develop, all cells will have the gene (if vector is successful)
    Page 7

    1. Paragraph 40 suggests that PRDM16 is a protein that controls development of brown adipose tissue and that lack of it causes abnormal (BAT) development. Explain how they could ‘transform stem cells’ (paragraph 41) with PRDM16.
    • Idea that transcription factors control cell determination
    • Idea that PRDM16 is a transcription factor.
    • And normally controls cell differentiation from a progenitor cell
    o suggestion of multipotent/pluripotent stem cell
    • idea that PRDM16 causes a cascade of reactions in a signal pathway (mechanism of peptide hormones) leading to change in gene expression

    2. ‘Tenmodulin’ (paragraph 44) is a transmembrane glycoprotein. Explain the post-transcriptional modifications that are made and the processes that occur before the glycoprotein reaches its final destination.
    • After transcription mRNA is spliced
    • introns are removed
    • exon sequence may be rearranged/some exons not included
    • spliced mRNA is translated into protein at ribosomes (/rough endoplasmic reticulum RER) from a three amino acids
    • idea that it is a glycoprotein so must be modified in the Golgi body/apparatus
    • idea that vesicles pinch of the rough endoplasmic reticulum and fuse with the Golgi body to form flattened sacs
    • idea that carbohydrate is added to protein to form glycoprotein
    • idea that glycoprotein is transported via endoplasmic reticulum network to cell membrane
    Paragraph 45 states that mRNA codes for various proteins. Explain how mRNA templates are used to specify the chemical structure of a protein.
    • Translation
    • mRNA attaches to the surface of a ribosome
    • mRNA codons face tRNA binding sites on ribosome
    • one side of a tRNA molecule is a triplet base sequence called an anticodon
    • tRNA molecules with complementary anticodon to the mRNA codon bind
    • specific tRNA molecules attach to specific free amino acids in the cytoplasm
    • idea of start codon
    • idea that ribosome holds mRNA tRNAs amino acids and associated enzyme in place while a peptide bond forms between amino acids
    4. Paragraph 46 mentions the ‘dopaminergic system’. Name and describe a disease where dopamine secretion is affected and describe the main symptoms.
    • Parkinson's disease
    • Mention of substantia nigra/basal ganglia
    • idea that dopamine secreting neurones die
    • idea that dopamine normally released into motor cortex
    • idea that motor cortex receives little dopamine and there is loss of control of muscular movements
    • symptoms:
    o stiffness of muscles
    o tremor of the muscles
    o slowness of movement
    o poor balance
    o walking problems
    • allow symptoms including depression, difficulties with speech, breathing
    5. Paragraph 45 mentions the protein ‘interleukin-6’, which is an anti-inflammatory protein. Suggest the impact of anorexia on the immune system.
    • 45) reduction in interleukin-6 level due to reduced mRNA expression.
    • Any logical argument explaining reduced and immune system function using specific examples from knowledge of immune system function
    o e.g. reduced B/T lymphocytes/ levels resulting in reduced ability to combat infection
    o or e.g. reduced inflammatory response/reduced phagocytosis of foreign matter/pathogens due to decreased neutrophils/macrophages
    o reduced B-cell clone division (not enough nutrients for more cells to function/be created).
    o Reduced antibody production
    • idea that nutrients are required for development and functionality of immune system cells
    o idea that anorexics may not be consuming RDA of necessary nutrients/minerals
    • idea that anorexics are also unlikely to consume many calories per day
    • 18) ‘restricting calories to 1200 kcal per day increases total output of cortisol’
    o suggestion that increased cortisol levels impair community
    6. Epigenetic changes’ are where the DNA base sequence remains the same, but changes are made to other parts of the DNA structure. This may affect gene expression. Using your knowledge of DNA structure and protein synthesis, suggest how ‘DNA methylation’ may ‘alter gene expression’ (paragraph 46).
    • Idea that DNA methylation may prevent DNA transcription by some structure change
    o credit mention/idea of histone proteins being a ‘scaffolding’ for DNA//idea that ‘scaffolding’ changes
    • idea that RNA polymerase cannot attach to DNA
    • so reduced mRNA synthesis/gene expression
    o hence less protein synthesis
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    (Original post by ConnorB)
    I seriously don't understand Rod cells when exposed to light and exposed to darkness.

    Could someone "Enlighten" me please"

    ...Revision does crazy **** to people.
    when light strikes rod cells rhodopsin bleaches and breaks into opsin and retinal.
    retinal closes the Na channels on the outeer region but the inner region continues to actively transport Na ions out of the cell (its crazy it cannot be stopped)
    so the membrane becomes hyperpolarised ! due to more negative charge inside and so the inihbitory neurotransmitter glutamate is NOT released. thus the bipolar cell depolarises as it isnt inhibited anymore and so an action potential is triggered and bran interprets this.

    THE OPPOSITE HAPPENS IN dark.
    the inner region STILL continues to pump Na ions out but as outer region Na channels arent closed so they again come in and result in depolarisation of the ROD CELL this time.

    HOPE IT HELPS
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    (Original post by Dixie)
    dyu know what raw mark you got??
    and i really dont know how to revise for the pre release coz theres so many questions on here that people have suggested but ive got limited time and so kinda confused about the best way to revise and get the best grade, lol i need like 113 in this exam :/
    I am not really sure about what raw marks I got - probably above 70%.

    Read all of the predicted questions with answers today evening itself. I mean it is very important so reading all questions with answers is worth the time especially if they are by Sir V. Redden because he is very good in predicting. Don't panic about what's the best way to revise - just revise the way you feel most comfortable about. You have to become familair with the article so read it every now and then and understand how one part links with the other and in what ways. Also make your own question bank with short questions and try to answer them whenevr you ahve time. Read the textbook and the notes that I will link you to (I will quote you soon) to understand the spec. and hopefully you will be sorted out for the exam. Good luck.
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    BACKFLIP IS DA MAAAAN !!!
 
 
 
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