Stock Answers Flashcards
Enzymes with increasing temperature
• As the temp increases, kinetic energy increases
• Increases successful collisions/Enzyme substrate complexes
• More product formed per unit time.
• Above a certain temperature, increased vibrations break H bonds
• Change the shape of the specific tertiary structure of enzyme and hence the active site
• No longer complimentary to the substrate so no longer forms ESCs
• Denatured.
Effect of mutation
• A change in DNA base sequence
• Changes the mRNA codons
• Changes the sequence of A acids/ primary structure of the polypeptide
• Changes the H, ionic, disulphide bonding between R groups of A acids
• Changes the specific shape and structure of the tertiary protein
• This leads to a non-functional protein/ enzyme with altered active site shape- no longer complimentary to substrate
Structure and function of DNA
• Sugar-phosphate (backbone) helix provides strength and protects hydrogen bonds;
• Long molecule – stores a lot of information
• Helical so compact
• Base sequence allows information to be stored for amino acid sequence
• Double stranded so replication can occur semi-conservatively with both strands acting as templates for complementary base pairing for accurate replication
• (Weak) hydrogen bonds for strand separation but many hydrogen bonds so stable.
Transcription
• DNA strands separated using DNA helicase to break H bonds exposing bases
• Free RNA nucleotides bind to complementary bases: U-A, A-T, C-G and G-C (name bases)
• RNA polymerase joins RNA nucleotides to growing RNA strand forming phosphodiester bond of the sugar-phosphate backbone
• Reaches the stop codon and detaches from the DNA coding strand
• Pre RNA spliced to remove the introns and form mRNA which leaves the nucleus via pores.
Translation
• mRNA binds to ribosome in the cytoplasm
• tRNA molecules bring specific A acids and bind to the codons on the mRNA with their complementary anticodon
• Two tRNA molecules bind to each of two binding sites on the ribosome
• The amino acids undergo a condensation reaction to produce a peptide bond between the two and extend the polypeptide chain
• The mRNA moves on one codon.
- Active Immunity
- Vaccine contains antigen from pathogen/ pathogen enters blood
• Phagocyte engulfs it and presents antigen on its surface
• B cell with complementary receptor on surface binds to antigen: is sensitised
• T helper cell activates B cell causing it to replicate by mitosis
• And differentiate to produce plasma cells which secrete large amounts of specific antibody
• Also produce memory cells which stay in the blood
• These produce plasma cells/ antibodies rapidly when exposed to the same antigen in the
future
- Cellulose structure and function
• Long and straight chains of β-glucose monomers joined by 1,4 glycosidic bonds.
• Become linked together by many hydrogen bonds to form fibrils.
• (Provide strength to cell wall so that) they withstand turgor pressure
- Translocation in phloem
• Sucrose actively transported into the phloem/sieve tubes via companion cells in source.
• This lowers the water potential in the sieve tube, so water moves in (from xylem) by osmosis
down the water potential gradient.
• Increasing hydrostatic pressure
• At the sink, sucrose is removed from the phloem for use/storage and water moves out
reducing the pressure.
• Sucrose moves from source to sink by mass flow down the pressure gradient
- Adaptations of tissues in lungs for transport
• Many alveoli provide a large surface area.
• Many capillaries provide a large surface area.
• Alveoli or capillary walls are thin.
• Made of squamous epi/ endothelium.
• So short diffusion pathway
• Ventilation maintains a concentration gradient
• THINK FICK’S LAW
- Cell fractionation and ultra-centrifugation to separate mitochondria
• Cells homogenised to break open cells
• Filter to remove (large) debris / whole cells
• Use isotonic solution to prevent damage to organelles by osmosis
• Ice cold to prevent / reduce damage by enzymes
• Buffer to prevent protein / enzyme denaturation
• Centrifuge to separate nuclei in pellet
• Re-spin supernatant at higher speed to get mitochondria in pellet
- Translation
• mRNA binds to ribosome in the cytoplasm
• tRNA molecules bring specific A acids and bind to the codons on the mRNA with their
complementary anticodon
• Two tRNA molecules bind to each of two binding sites on the ribosome
• The amino acids undergo a condensation reaction to produce a peptide bond between the
two and extend the polypeptide chain
• The mRNA moves on one codon
- Describe what a P value of <0.05 in a Chi^2 test means
• You are required to know when to use Chi squared, student T test and correlation
coefficient. You need to be able to work out the degrees of freedom for each and look
up the critical value in a table. When the value for any of these is above the critical
value (for P at 0.05 unless otherwise stated), the difference/ correlation is significant.
• A significant difference for Chi2
result: where the P value is < 0.05 and / or the Chi2
value is > the critical value.
• This means we need to reject the null hypothesis as the probability of the difference
being due to chance alone is less than 5%.
• State what you would conclude in the context of the question
- Oxygen dissociation curves
• A shift to the left shows an increased affinity for oxygen. This means that oxygen will
associate more easily and will dissociate less easily. This is required for organisms living in
low oxygen environments since they need to pick up what little oxygen there is available.
• A shift to the right shows a decreased affinity for oxygen. This means that oxygen will
associate less easily and will dissociate more easily. This is required for organisms with high
metabolic rate since the haemoglobin will release more oxygen at any given pp oxygen and
they need to release as much oxygen as possible to the respiring tissues
- Effect of habitat
loss /
deforestation
• Reduction in number of plant species
• Reduces habitats/niches
• Reduces variety of food sources available (both plant types and consequently fewer prey
species for predators)
(Can be used to write the converse argument when supporting the extension of wild areas)
- Natural selection
Natural selection is the process that leads to speciation, but you need to decide
whether which the question is asking for. Natural selection will occur where new alleles have
appeared or where the environment is changing. It does not require a divide in the population.
New alleles produced by random mutation
• Variation within a species
• Certain phenotypes and therefore alleles are beneficial in the environment and
those with this live longer, reproduce more and pass on this allele to their
offspring (differential reproductive success)
• The allele frequency in the population increases
- Non- competitive inhibition
• Inhibitor binds to site on enzyme other than active site (allosteric)
• Changes shape of active site
• Cannot be overcome by higher substrate concentrations as active sites no longer available
- ATP properties
• Releases relatively small amount of energy → little danger of thermal death of cells
• One step process to release energy (happens instantaneously) → energy is readily available
• Phosphorylates other compounds, making them more reactive
• Can be rapidly re-synthesised
- sociable so can move within cell but cannot leave
- Osmosis
• State where and/or why the water potential is lower
• “water moves from A→B by osmosis down the water potential gradient”
• State the biological significance of this/ what this means in the context of the question
- Properties of
water and how
they are
important for
living things
• A metabolite in condensation/hydrolysis/ photosynthesis/respiration
• A solvent so (metabolic) reactions can occur/so allows transport of substances
• High heat capacity so buffers / reduces/ slows changes in temperature
• High latent heat of vaporisation so provides a cooling effect (through evaporation)
• Cohesion between water molecules so supports columns of water (in plants)
• Cohesion between water molecules so produces surface tension supporting (small)
organisms
