Mock Questions Flashcards
Compare & contrast the structure and function of nicotinic receptors and voltage gated sodium channels
Both are permeable to sodium, cause depolarisation and action potential firing.
Nicotinic receptors are made of 5 protein subunits, each has 4 TMs. Where VG sodium channels is made of 1 protein with 4 domains, each domain has 6 TMs.
Nicotinic is ligand gated where sodium is gated by a change in voltage
How does agonist binding to a G protein- coupled receptor lead to increased production of cAMP
Ligand binding to the receptor causes the affinity of the G protein alpha subunit for GDP. GTP bound alpha subunit dissociates from beta gamma subunits, GTP-bound alpha subunit and beta-gamma subunit now free to engage with downstream effectors, change levels of second messenger cAMP
Briefly describe the function of SNARE proteins
SNARE proteins are involved in vesicle fusion. They form a coiled-coil structure between vesicles and target membranes forcing membrane merger
What is telomerase and why is it essential for cell viability
Telomerase is a specialised DNA polymerase which specifically synthesises multiple copies of a simple sequence hexameric repeat, which are called telomeres, found at the ends of linear eukaryotic chromosomes. Telomeres prevent gradual loss of DNA sequences at the ends of chromosomes in proliferating cell populations, which would otherwise occur due to the removal of RNA primer sequences from the Okazaki fragment at each end of a recently replicated chromosome
Explain how pyrimidine dimers are removed from DNA and how the damaged DNA is repaired, naming the 4 main enzymes involved
And excision nuclease cleaved the damaged DNA strand on either side of the pyrimidine dimer, several nucleotides away from the dimer. DNA helicase removes the fragment of single stranded DNA containing the pyramidine dimer, leaving an approx 12 nucleotide gap. DNA polymerase then repairs the gap with new DNA synthesis from the primer template junction. DNA ligase seals the nick
Define kinetochores, describe their function and how they maintain stability
Kinetochores are the protein complexes that bind to centromeric DNA sequences in chromosomes and microtubules within mitotic spindle, and thus ensure that one copy of each chromosome is faithfully segregated into each daughter cell during anaphase
The deamination of a cytosine base leads to a transversion mutation. True or false
False. Deamination of a cytosine base involves the removal of an amine group, converting cytosine to uracil, which remains as a purine. A transversion is the conversion of a purine to a pyramidine. Therefore this process leads to an unchanged strand via transition rather than a transversion mutation.
How are the activities of small GTPases regulated in the cell
The natural hydrolysis of bound GTP by a GTPase is regulated by accessory proteins. GAPs promote the hydrolysis of GTP to GDP + Pi, and the retention of GDP inactivates the GTPase. GEFs facilitate both the release of GDP that is bound to GTPase and the binding of a new molecule of GTP, which then activates the GTPase once more
How does autophagy protect against cancer?
Autophagy acts as a tumour suppressor. It does this by removing damaged organelles, protein toxicity and ROS which reduces oxidative stress and DNA damage. Accumulation of DNA damage can lead to mutations and consequently cancer
Describe the proteins directly involved in vesicle fusion during secretion and their unique properties. What methods would you use to study their properties?
SNARE proteins are small membrane associated proteins that drive membrane fusion, SNARE proteins interact by the SNARE domains and form stable complexes. SNARE proteins on the target membranes, (SNAP25 and syntaxin) and the vesicle VAMP2 biochemically interact to form a snare complex which drive synaptic vesicles fusion. The function of these proteins can be studied using a range of approaches, such as liposome fusion assays to study ability of SNAREs to drive membrane fusion, and transgenic mice in combination with electrophysiology to measure synaptic activity
How can you determine the size of a protein by western blot analysis?
Whole protein lysates are mixed with a loading dye and loaded into a polyacrylamide gel. A current is applied and the proteins migrate towards the anode, which separates out the proteins. The rate of migration is determined by their size. After transfer and immunoblotting. The side of protein of interest is in compared to standard protein known size.
Which second messenger does adenyl cyclase activate?
cAMP
Describe the structure in terms of protein domains of a GPCR
7 transmembrane domains connected by 3 extracellular and 3 intracellular loops. The N-terminal is on the extracellular side, and is where the ligand binds. The C terminal is in the cytoplasm where an additional helix domain allows the G-protein to bind
How many subunits make up P2X receptors?
There are 3 subunits that make up the trimeric P2X receptor
Which three stimuli called platelet activation
- Basal lamina
- Thrombin
- ADP
