Content I missed Flashcards
How is light absorption maximised in chloroplasts?
Antenna proteins are non-covalently bound to proteins and provide a large spatial cross section for absorption
What happens in cyt b6f?
Bifurated electron transfer:
When a PQH2 molecule is oxidised, two protons move into the lumen, creating a proton gradient. One electron is stored on haem C and another electron reduces Pc.
What is the redox potential across PSI?
P700+/P700 redox couple is +480mV
This can reduce free floating 4Fe-4S clusters which reduce 2Fe-2S clusters on feerodoxin (-420mV). Pc oxidation is +370mV
-790mV
What is the energy budget of linear electron transfer compared to cyclic electron transfer?
Linear- 1.28ATP per NADPH
Cyclic- 1.5ATP per NADPH
What is the speed of internal conversion between S2 and S1 compared to S1 and S0?
S2 –> S1 10^-12S
S1 –> S0 10^-9S
How are C type haems linked to cyt b6f?
Covalent bonds
How are B type haems linked to cyt b6f?
Coordination bond with Fe ions
What do α subunits in ATP synthase do?
Play a structural role
What do β subunits in ATP synthase do?
Catalyse ATP production and releasing it
What does thioredoxin detect?
Changes in redox state of the stroma due to reduction of Fd and NADP+.
What does thioredoxin regulate?
Calvin cycle enzymes
How does CO2 react with RuBP?
CO2 reacts with the lysine residue in rubisco which forms a carbonate ion. This is attracted to Mg2+ which activates RuBP.
Why are thioester bonds favourable in group carriers?
They are less stable than ester bonds so are ideal for donating groups. E.g in Coenzyme A
Which isozyme subunit of lactate dehydrogenase is inhibited by pyruvate?
H form as the M form is more favourable under aerobic conditions
Outline the alanine transaminase reaction?
Glutamate + Pyruvate <-> Alanine + α-ketoglutarate
What stimulates the pentose phosphate pathway?
Low NADPH and low ribulose
What cofactors do the link reaction have?
pyrophosphate, thiamine, lipoic acid, FAD, CoA, NAD
Outline pyrimidine synthesis
Bases are assembled by adding amino acids to ribulose from PPP. Ribose is then attached
Outline purine synthesis
Rings assembled onto ribose and groups added bit by bit
Ribose activation is very intense: 2 ATP to activate bicarbonate and add it onto ribose
How is phophatetidylethanolamine structured and where does it usually sit in cell membranes?
Small phosphate head, allowing curvature and it is usually in the inner monolayer
How is phosphatidylserine moved in plasma membranes in response to apoptosis?
PS moves to the surface of plasma membranes signals to macrophages to phagocytose and digest the dead cell.
1. Phospholipid translocators transport PS to the inner monolayer. These are deactivated
2. Scramblase is activated, allowing phospholipids to transfer to both sides of the membrane non-specifically
Outline a Gq protein coupled response
- A Gαq subunit stimulates phospholipase C
- Phospholipase C cleaves phosphatidylinositol phospholipid (PIP2) in the cytoplasmic monolayer of the plasma membrane
- This splits into protein kinase C and IP3. PKC remains in the membrane and IP3 stimulates Ca2+ release from the endoplasmic reticulum
What increases plasma membrane fluidity?
Cis fatty acids
Phospholipids
Cholesterol squashing against fatty acids
Shorter fatty acids
What are the 5 main ways of changing membrane curvature?
Changing lipid composition
Amphipathic helix insertion
Indirect scaffolding
Actin cytoskeleton pushing the membrane out
Microtubule motors
Which phospholipids facilitate positive membrane curvature?
PI and PC
Which phospholipids facilitate negative membrane curvature?
PE
Give 4 functions of membrane rafts
Concentrate proteins for signal transduction
Organising the start of endocytosis
T cell activation
Bridging gaps between differently sized membranes
How do voltage gated Na+ channels open and close?
They have a plug which has voltage-sensing α-helices which move up or down depending on the side they are attracted to
How is a G protein switch turned off?
GAP hydrolyses GTP to GDP which is bound to a phosphate.
This binds Thr35 and Gly60 to closes switches 1 and 2 respectively
What is a similarity between rhodopsin and β-adrenergic receptor
Locations of 11-cis retinal
Which residues flip water dipoles in aquaporins?
Asn76 and Asn192
What does the NPA motif do in aquaporins?
Prevents ions moving through the middle of the channel
What does histidine do in aquaporins?
Makes a size restriction to prevent water moving through
What does arginine do in aquaporins?
Keeps protons out of the aquaporin with electrostatic respulsions
Which residues carry the proton in bacteriorhodopsin?
Asp96
Retinol- Lys216 schiff base
Asp85
How does rhodopsin wave absorption compare to that of transient receptor potentials (TRPs)?
The extinction coefficient is 100 times greater
How is the positive charge of the protonated schiff base on retinal in rhodopsin compensated for?
Glutamate counterion on helix 2
Outline the order of the rhodopsin cycle
Retinal (11-cis retinal, red)
Bathorhodopsin (all-trans retinal)
Lumirhodopsin
Metarhodopsin I
Metarhodopsin II
Free-all trans retinal (white)
Name some properties of detergents
Amphiphilic- crucial for ejecting proteins
More water soluble than lipids
Alter surface tension
What are the main limitations of cryo-em?
Limited to large particles (>500kDa)
Resolution limited to 10Å, unless the molecule has high symmetry
