Enzymes Flashcards
No questions on multisubstrate mechanisms
What is significant about enzymes being globular proteins?
It means they are generally soluble
What is a cofactor?
Non-protein component needed by the enzyme to work
What is a coenzyme?
Complex organic molecule
Takes part in the reaction but is not the enzyme
Coenzymes are usually produced from…
Vitamins
Define a prosthetic group.
Non-protein group covalently bonded/tightly bound to an enzyme
True/False
A prosthetic group is a type of cofactor?
True
PG’s are covalently bonded cofactors
What is the Apoenzyme?
Protein component of enzyme that contains a cofactor
What is the Holoenzyme?
Whole enzyme
Apoenzyme + any cofactors
True or false
There is 6 classes of enzymes based on the location of the enzyme.
False
6 classes based on the type of reaction the enzyme carries out
What is a Ligase Enzyme?
Formation of C-C, C-S, C-O, C-N bonds
Bond making/breaking enzyme
What is the significance of whether G is positive or negative?
Shows spontaneity
Negative = Spontaneous
What is the free energy equation?
/\G = /\H - T*/\S
True or false
If E= ‘energy barrier’ is applied to molecule in its ground state, then it will undergo a reaction and change to product.
False :(
It will reach transition state
Can either react to form product, OR revert back
How do enzymes reduce activation energy?
Entropy reduction
Desolvation
Induced fit
Kachow or Kerchoo
M-M equation assumed that K2 is slower than K1/K-1 so the RDS is:
ES —> E + P
Kachow
Thus rate is proportional to [ES]
Give the word definition of the Michaelis constant.
Substrate concentration when initial reaction velocity is half of Vmax
Give the numerical definition of the Michaelis constant.
Km = K(-1) / K(1)
What does a low Km value indicate?
Enzyme has high affinity for Substrate
What does a high Vmax indicate?
Very fast enzyme
Describe an enzyme with high Km and high Vmax.
Very fast enzyme that is very bad at grabbing the substrate
How are the Lineweaver-Burk plot and Michaelis-Menten equation linked?
L-B is double reciprocal plot of M-M equation
Vo = (Vmax*[S]) / (Km + [S])
L-B or M-M?
M-M
What is an Isoenzyme?
Two different enzymes that catalyse the same reaction
Blow your load or Hit the road
Hexokinase is actually Glucokinase IV.
Hit the road
Glucokinase is a type of hexokinase enzyme
Hexokinase IV
Glucokinase is found where?
Liver
Describe why Glucokinase having a high Km + Vmax and hexokinase having a low Km + Vmax allows the body to respond to fluctuating [Glc].
- After meal - [Glc] goes up
- Hkase already working at Vmax
- Gkase able to respond proportionally as extra Glc is left for it
What reaction do Glucokinase and Hexokinase catalyse?
Glc + ATP —> G-6-P + ADP
What effect does phosphorylation of Glc have?
Traps Glc
Transporters don’t recognise G-6-P
What experimental method can be used to study isoenzymes or separate complex mixtures of enzymes?
Electrophoresis
What is a ternary complex?
When both substrates are in the same complex
E + S’ + S” <==> ES’S”
What is an Allosteric enzyme?
Multiple active sites
Gucci gang or itchy wang
Cooperative binding: one substrate binding to one active site causes change in the other active sites, allowing more substrates to join
Gucci gang gucci gang gucci gang gucci gang
What is the difference between an Un-competitive and a non-competitive inhibitor?
NC - binds onto allosteric site causing change in AS
UC - binds on after substrate and prevents interaction from taking place (as efficiently)
What is the advantage of transition state analogues?
Easier for enzyme to bind to molecule in transition state shape than normal shape
What 2 forms of inhibition can enzymes use to regulate their pathways?
Feedback inhibition
Allosteric inhibition
How does feedback inhibition work?
Product of a pathway, or key stage, can inhibit enzyme at start
Stops more of the product being made
True or false
Allosteric control of enzymes always involves inhibition of the enzyme.
False
Effectors can either be activators or inhibitors
Why are many enzymes phosphorylated?
Fine tunes enzyme function
Adaptation to cellular conditions
What is proteolytic cleavage?
Cleavage of inactive proenzyme to form active enzyme
Why is proteolytic cleavage useful?
Prevents enzymes damaging cells or generally fucking stuff up
Eg: Digestive enzymes
What 3 ways are enzyme molecules modulated/controlled?
Proteolytic cleavage
Covalent modification (phosphorylation)
Allosterically
