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effect of decreased acetylation of histones
DNA not accessible to transcription factors
effect of increased methylation on transcription
inhibits transcription
how does increased methylation inhibit transcription
prevents binding of transcriptional factors
attracts proteins that condense DNA-histone complex
what happens when a gene is switched off
DNA blocked by an inhibitor, so RNA polymerase cant bind
oestrogen role
lipid soluble so diffuses across the phospholipid bilayer, forms oestrogen-receptor complex, acts as a transcriptional factor
how can a gene be inhibited even after transcription
siRNA
how does siRNA work
binds to complementary sequence of mRNA, causing it to become double-stranded, viewed as abnormal, so broken down by enzymes
Hardy Weinberg
p2 + 2pq + q2 → 1
p+q = 1
conditions needed for Hardy- Weinberg to be true
no mutations, so no new alleles created
no immigration/emigration so no new alleles are introduced
no selection so no alleles are favoured or eliminated
mating is random, so alleles are mixed randomly
define what is meant by epigenetics
heritable changes in gene function
without changes to base sequence of DNA
explain how increased methylation can lead to cancer
methyl groups could be added to tumor suppressor gene
transcription of tumor suppressor genes is inhibited
leads to uncontrolled cell division
Exercise causes an increase in heart rate. Describe the role of receptors and of the nervous system in this process. (4)
Chemoreceptors detect rise in CO2
Send impulses to medulla
More impulses to SAN;
By sympathetic nervous system
When the heart beats, both ventricles contract at the same time. Explain how this is coordinated in the heart after initiation of the heartbeat by the SAN
Electrical activity only through Bundle of His
Wave of electrical activity passes through both ventricles at the same time
why is there a delay before the AVN sends waves of electrical activity down the bundle of His
to allow the ventricles to fill with blood
describe how the heart controls and coordinates the contraction of the atria and ventricles (5)
impulse goes from SAN to AVN to purkyne fibres
wave of electrical activity passes over the atria
atria contract
non-conducting tissue between atria and ventricles
delay at AVN allows for the ventricles to fully fill with blood
ventricles contract from the apex upwards
describe how a pacinean corpuscle produced a generator potential when stimulated (4)
pressure causes membrane to become deformed
stretch mediated sodium ion channels open
greater pressure, more channels open
depolarisation generates an action potential
what is the effect of a stronger stimulus on action potentials
results in a more frequent action potential
rods and cones sensitivity and visual acuity
rods are more sensitive, but have a lower visual acuity
cones are less sensitive and have a higher visual acuity
what do rods contain
rhodopsin
what do cones contain
iodopsin
why do cones have higher visual acuity
each cone forms a synapse with an individual bipolar neurone
why do rods have higher visual sensitivity
more than one rod forms a synapse with a single neurone
visual acuity meaning
the ability to tell apart objects that are close together
explain how the fovea of a hawk having high concentration of cone cells makes the hawk more able to catch its prey
high number of cone cells, high visual acuity
each cone is connected to a single neurone
cones send seperate impulses to the brain through optical nerve
give some features of slow twitch muscle fibres
myoglobin
lots of mitochondria
lots of blood vessels
fast twitch muscle fibres location
eye movement/sprinting
fast twitch muscle fibres features
stores of phosphocreatine
white as lack of blood vessels and myoglobin
Stages of succession
Initial colonisation by pioneer communities
Alteration of conditions by pioneer species
Settlement by intermediate communities
Diversification of intermediate communities
Development of climax communities
The scientists then compared the length of time that the control mice and the trained mice could carry out prolonged exercise. The trained mice were able to exercise for a longer time period than control mice. Explain why.
More aerobic respiration produces more ATP
Anaerobic respiration delayed
Less or no lactate
Describe how the mark-release-recapture method could be used to determine the population of A. aegypti at the start of the investigation
Capture sample, mark and release
Leave time for mosquitoes to disperse before second sampling
Population number in first sample × number in second sample divided by number of marked in second sample
what happens when the sarcomere contracts
H band and I band decrease
A band stays the same
In fruit flies, males have the sex chromosomes XY and the females have XX. In fruit flies, a gene for eye colour is carried on the X chromosome. The allele for red eyes, R, is dominant to the allele for white eyes. Male fruit flies are more likely than female fruit flies to have white eyes. Explain why.
males have one allele
females need two recessive allels/ homozygous for gene to be expressed
function of tumor suppressor genes
produce proteins that inhibit cell division and cause apoptosis
function of proto-oncogenes
lead to production of proteins that stimulate cell division
what does hypermethylation of tumor supressor genes lead to
prevents transcription of tumor suppressor genes, meaning it cannot produce the protein for controlling mitosis and apoptosis, mitosis becomes uncontrolled
what happens to proto-oncogenes that leads to uncontrolled cell division
become oncogenes
hypomethylation causes increased and uncontrollable cell division
explain how alterations in tumor suppressor genes can lead to cancer (3)
hypermethylation
means tumor suppressor genes are not transcribed
results in uncontrolled cell division
MM is caused by a faulty receptor protein in cell-surface membranes. Cells in MM tumours can be destroyed by the immune system. Suggest why they can be destroyed by the immune system. (4)
Faulty protein recognised as an antigen
T cells will bind to faulty protein
T cells will stimulate clonal selection of B cells
release of antibodies against faulty protein.
where does anaerobic respiration take place
cytoplasm
where does aerobic respiration occur
mitochondria
what is the net gain of ATP in anaerobic respiration
2
net gain of ATP in aerobic respiration
28-32
what is pyruvate converted to anaerobic respiration animals
lactic acid
what is pyruvate converted to anaerobic plants
yeast
why is it important that pyruvate is converted to lactic acid anaerobic animals
so that NAD can be produced, so glycolysis can continue to occur
what is meant by the term phenotype (2)
expression of characteristic due to genetic constitution, characteristic due to environment
in genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios, suggest reasons why (4)
random fertilisation of gametes
small sample size
epistasis
sex linkage
a student investigated the monohybrid inheritance of eye shape in fruit flies. Two fruit flies with bar eyes were crossed. Of the offspring, 1538 had bar eyes, 462 round eyes. Using suitable symbols explain the phenotypes of the parents (2)
both heterozygous- Nn
both parents have bar eyes, but have some offspring with round eyes, so parents must be carriers of recessive allele for round eyes
what is meant by codominant alleles
if both alleles are present, both are expressed in the phenotype
in fruit flies, the genes for body colour and wing length are linked. Explain what this means. (1)
genes on the same chromosome
which statistical test should the scientist use to determine whether his observed results were significantly different from the expected results
chi squared
categorical data
mitochondrial disease causes muscle weakness. explain why.
less ATP produced from aerobic respiration
less force between actin and myosin in muscle contraction
fatigue from lactate from anaerobic respiration
suggest how the change in the anticodon of tRNA leads to mitochondrial disorder
Change to tRNA leads to wrong amino acid being incorporated into protein
Tertiary structure change
Protein required for oxidative phosphorylation so less ATP made
what is a tumor
clump of abnormal cells
give examples of physical defences in organisms
skin, mucus
examples of non-specific immunity
physical barriers and phagocytosis
examples of specific immunity
cell mediated and humoral response
what are the 4 things that cloned T cells do
develop into memory cells
stimulate phagocytosis
stimulate plasma B cells
activate cytotoxic T cells
what causes T cells to clone
T helper cell binds to antigen presenting cell
where do B- lymphocytes mature
bone marrow
what is a monoclonal antibody
one specific type of antibody that has been produced from a cloned plasma cell
what is clonal selection
producing one type of B cell that produces one type of antibody that is specific to one type of antigen
what does P value less than 0.05 mean
there is a less than 5% probability that the results are down to chance
structure of an antibody
2 heavy chains, 2 light chains
4 polypeptide chains
held together by disulfide bonds
purpose of agglutination
causes pathogens to clump together, making phagocytosis more efficient as more than one pathogen can be engulfed at once
describe how a pregnancy test works
monoclonal antibodies linked to a coloured compound and complementary to hCG
hCG-antibody-colour complex will move along the test strip until it binds to a another antibody which is fixed in position
how are monoclonal antibodies produced
mouse injected with an antigen
B cell of mouse start producing antibodies, which are extracted
B cells mixed with myeloma cells
B cells and myeloma cells will be fused forming hybridomas
large volumes of antibody produced in a given time
why are cancer cells used in combining with monoclonal antibodies
divide readily outside the body
why can an antibody against HIV not be produced
high antigenic variability/ lots of mutations
explain why each of the following means that a vaccine might not be effective against HIV:
HIV rapidly enters host cells
HIV shows a lot of antigenic variability
HIV enters cells before antibodies can bind to it, antibodies cannot enter cells to destroy HIV
antigen on HIV changes/mutates
specific antibody no longer binds to new antigen
HIV replication
binds to CD4 receptor on T helper cell
capsid fuses with T helper cells membrane and RNA
along with reverse transcriptase enters
reverse transcriptase converts HIV RNA to DNA
HIV enters nucleus and is integrated into host cells DNA
cell proteins used to transcribe and produce more HIV proteins
budding occurs, where HIV exits the cell, taking with it a part of the cell membrane
describe ELISA test to test for HIV
1- fix HIV antigens to a plate
2- add a sample of patient’s blood, if HIV positive, blood will contain antibodies specific to HIV antigen and bind
3- add a second antibody that is complementary to the HIV antibody and has an enzyme linked to it
4- wash to remove unbound antibodies
5- add a substrate that will change colour if the enzyme is present
