lecture 9 - allosteric regulation of energy metabolism Flashcards
what is a ligand?
substrates, hormones or compounds that regulate protein activity
what is a ligands function?
to catalyse (lock and key), recognise (cell surface receptor signal molecule binding) and transport
what is an induced fit model?
it is moved so that it fits
what does a sigmoidal kinetic show?
gradual and slow activity until vmax , at start of reaction – low rate, low conc of substrate available so it can only really bind to one sub unit of PK
when is there rapid activation?
when there is more subunits
what are the characteristics of proteins showing sigmoidal kinetics?
- Composed of 2 or more subunits
- The subunits can exist in 2 diff shapes
- When the first conc of substrate molecule binds to its binding site in one of the sub units it increases its affinity of the second sub unit for the second molecule so that the 2nd molecule binds more easily to its binding site
- This is described as cooperative binding or cooperativity
- It gives rise to the sigmoidal curve
what are allosteric proteins?
- Show cooperativity and sigmoidal kinetics with regard to their substrate
- The enzyme subunits are also able to bind ligands that aren’t their substrates
- These ligands called effectors and bind at the effector building sites separate form the active site
- Binding effectors influencs affinity of the protein subunits for the ligand
- Pos effectors increase affinity
- Neg effectors decrease affinity
what does a positive modulator allow for?
binds to some enzymes
what does more effectors mean?
easier for the substrate to bind to the 2nd subunit and so the energy increases rapidly
what is the effect of a positive effector?
- Rate of activation is much steeper but vmax is the same – higher velocity and rate of enzyme
what is the effect of a negative effector?
- Prevent or slow the rate at which a substrate will bind to iys enzyme – need a higher substrate conc – rate is slower and shallower but vmax will still be the same, gradient is shallower
- Lower velocity for the same amount of substrate than when there is no effector present
what is monod-wyman-changeux’s concerted model?
- Subunits of an enzyme can exist in two forms – tense and relaxed
- Cant have mixed molecules – either t or r
- T form has low affinity for the substrate
- R form has high affinity for the substrate
- Cooperativity – when the substrate binds to t form it causes all subunits to convert to r form
- positive effectors stabilises the R form
what is koshland’s sequential model?
- Sub units can exist in 2 forms – t and r
- Can have mixed molecules
- T has low affinity for the substrate
- R has high affinity for the substrate
- Binds to the relaxed form
- pos effectors stabilises the R form
if a cell has high energy stores what will it do?
- Store energy in the form of ATP
- Store energy in the form of glycogen or lipid
if a cell needs energy what will it do?
- Release energy generating nutrients from stores
- These will go through the energy generating pathways to yield ATP
