Coenzymes + Cofactors Flashcards
deltaG’o
the difference between the free energy (G) of the substrates and the products
A catalyst cannot effect the position and direction of equilibrium. True or false?
True
Enzymes + activation energy
~ enzymes enhance the rate of reaction by lowering the activation energy
E + S =….
E + S ES EP E + P
~ numerous weak interactions between
E & S (enzyme and substrate) are optimised in the transition state
Cofactor
a non-protein component required by enzymes
Coenzymes
organic cofactors
Co-substrates
coenzymes that are loosely associated with their enzyme
e.g. NAD/NADP
Prosthetic groups
tightly associated cofactors
e.g. flavin group
Metal cations
~ type of cofactor
~ multiple oxidation sates are often important
e.g. Na+ Mg2+
Co-enzymes participate in…
group transfer reactions
~ transient carriers of info
~ activated carrier
Apoprotein/apoenzyme
protein/enzyme without its tightly associated cofactor
Holoprotein/holoenzyme
protein/enzyme bound to its tightly associated cofactor = active enzyme
List co-enzymes and the vitamins they are derived from.
NAD+/NADP = Vitamin B3
FMN/FAD = Vitamin B2
Coenzyme A = Vitamin B5
Pyridoxal phosphate = Vitamin B6
NAD stands for…
nicotinamide adenine dinucleotide
NAD + NADP (4)
~ function in 2e- transfer reactions
~ a.k.a. pyridine nucleotides
~ contain a nicotinamide ring
~ can also accept H- = 1 proton and 2e-
NAD+ function
~ oxidation of alcohol and aldehydes
~ alcohol/aldehyde dehydrogenase
Transdeamination
~ catalysed by glutamate dehydrogenase
~ uses NADH/NADPH as coenzymes
~ rare example
High levels of NAD/NADH or NADP/NADPH favours…
hydride transfer from substrate
How do enzymes lower the activation energy?
~ substrate binding = decrease in freedom of movement/rotation
~ they distort their substrate towards the transition state
~ the multiple weak ads between substrate and active site can offset/pay activation energy
Flavin group
e.g. FAD/FMN
~ prosthetic group
~ participate in e- tranfers
~ reactive part = isoalloxazine ring
Coenzyme A
active carrier of acetyl and acyl groups
The Rossman fold
a classic nucleotide binding motif found in all NAD(P)-dependent dehydrogenases and used to bind the cofactor