enzymes part1 Flashcards
What is an enzyme?
A protein molecule that catalyzes chemical reactions without itself being destroyed or altered
How do biological catalysts differ from chemical?
Catalyses very high reaction rates
Shows great reaction specificity
Work in mild temperature/pH conditions
Can be regulated
What do oxidoreductases do?
transfer electrons
What do transferases do?
group transfers
What do hydrolases do?
hydrolysis
what do lyases do?
form or add groups to double bonds
what do isomerases do?
transfer groups within molecules
what do ligases do?
formation of C-C, C-S, C-O and C-N bonds (coupled to ATP cleavage)
What is a co factor?
non protein component needed for the reaction
What is a co enzyme?
heat-stable substance that can aid enzyme reactions
What is an isoenzyme?
enzymes that catalyse the same reaction but vary in structure and other chemical properties
What happens in basic reaction (shown as equation)
E + S –ES—-EP—-E + P
What do enzymes do to speed up rate of reaction?
lower activation energy
How do enzymes lower the activation energy?
Entropy reduction
Enzymes “force” the substrate(s) to be correctly orientated by binding them in the formation they need to be in for the reaction to proceed
Desolvation
Weak bonds between the substrate and enzyme essentially replace most or all of the H-bonds between substrate and aqueous solution
Induced fit
Conformational changes occur in the protein structure when the substrate binds
What does V , Vo, V max , [S] , Km stand for ?
V= velocity (rate)
Vo= initial reaction velocity
V max=maximum reaction velocity
[s]= substrate conc
Km=the substrate conc when the reaction is at half the maximum velocity
What do Km and Vmax tell us ?
Km – how specific the enzyme is for the substrate
Low value = good fit
High value = poor fit i.e. takes a lot of substrate to get to ½ Vmax
Vmax – how fast a reaction is proceeding when the enzyme is saturated with substrate
What is the x intercept of the lineweaver- burk plot?
1/ V max
What is y intercept of lineweaver- burk plot?
-1/Km
What can affect enzyme reactions?
Enzyme conc – increasing the enzyme concentration will speed up the reaction so long as there is substrate available
Substrate conc – the more substrate that’s available the quicker the enzymes collide and bind with them
Temperature – as the temperature rises the number of collisions between the enzymes and substrates speeds up.
pH – as with temperature it’s important to remember that enzymes are proteins so there are limits to the conditions that they can function at.
Inhibitors – two main forms of inhibition are competitive and non-competitive.
Describe competitive inhibition?
Vmax unchanged
Km increases because it takes more substrate to overcome the inhibition
Describe non competitive inhibition?
