lecture 9 - allosteric regulation of energy metabolism

Question 1

what is a ligand?

Answer 1

substrates, hormones or compounds that regulate protein activity

Question 2

what is a ligands function?

Answer 2

to catalyse (lock and key), recognise (cell surface receptor signal molecule binding) and transport

Question 3

what is an induced fit model?

Answer 3

it is moved so that it fits

Question 4

what does a sigmoidal kinetic show?

Answer 4

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

Question 5

when is there rapid activation?

Answer 5

when there is more subunits

Question 6

what are the characteristics of proteins showing sigmoidal kinetics?

Answer 6

• 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

Question 7

what are allosteric proteins?

Answer 7

a protein whose activity at one site is affected by the binding of a molecule (ligand or effector) at another site, distinct from the primary binding site

Question 8

what does a positive modulator allow for?

Answer 8

binds to some enzymes

Question 9

what does more effectors mean?

Answer 9

easier for the substrate to bind to the 2nd subunit and so the energy increases rapidly

Question 10

what is the effect of a positive effector?

Answer 10

• Rate of activation is much steeper but vmax is the same – higher velocity and rate of enzyme

Question 11

what is the effect of a negative effector?

Answer 11

• 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

Question 12

what is monod-wyman-changeux’s concerted model?

Answer 12

• 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

Question 13

what is koshland’s sequential model?

Answer 13

• 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

Question 14

if a cell has high energy stores what will it do?

Answer 14

Store energy in the form of ATP, glycogen or lipid

Question 15

if a cell needs energy what will it do?

Answer 15

• Release energy generating nutrients from stores
• These will go through the energy generating pathways to yield ATP