Enzyme Structure and Function Flashcards
Define an enzyme:
Highly specific biological catalysts.
What is the purpose of an enzyme?
Increase the rate of a reaction without being changed at the end of the reaction.
What defines the precise specificity?
The 3D structure of the enzyme.
Give examples of proteases which undergo specificity.
Trypsin = cleaves after arginine or lysine residues. Thrombin = Cleaves between arginine and glycine only in particular sequences. Papain = Cleaves all peptide bonds irrespective of sequence.
Name the two types of co - factors:
Coenzymes - organic molecules derived by vitamins
Metal Ions - Mg2+ and Zn2+ and Cu2+.
What are co - enzymes?
Non - protein molecules which are required for enzyme // protein function.
What is the protein part (excluding the cofactor) called?
Apoenzyme
What is the protein - cofactor complex called?
Holoenzyme
What determines whether the reaction will occur spontaneously or not?
The free energy change of the reaction. (delta g)
In what state does (delta g) need to be in - in order for a reaction to occur?
(delta g) has to be in a negative state in order for a reaction to occur.
What is required to reach the transition state?
Activation energy is required to reach the transition state.
What factors affect enzyme activity?
1) Temperature
2) pH
3) Substrate / Enzyme Concentration
What is the lock and key model?
Active site has rigid shape and therefore the substrates have a matching fit.
What is the induced fit model?
Active site is flexible and therefore, the enzyme, active site and substrate adjust to maximise the fit.
How do the enzymes lower the activation energy?
By stabilising the transition state.
What are the interactions which stabilise the enzyme - substrate complex?
Electrostatic interactions
Hydrogen bonds
Van der Waals forces.
What happens to enzymes once they go above a certain temperature?
The enzymes will denature (unfold) and then become inactive - thus meaning it’s irreversible.
When does maximum activity occur?
When the enzyme is saturated.
What are allosteric enzymes?
These are enzymes with more than one binding site. They had 2 conformations - one active and one inactive.
Binding of a regulatory molecule (known as a ligand) changes activity by stabilising one of the two conformations.
What are activator ligands?
These bind at a regulatory binding site and thus stabilises the active conformation.
EG:
CTP - allosteric inhibitor
ATP - allosteric activator
In terms of the concerted model and sequential model what effect does positive effectors have?
They stabilise the high affinity form of the sub - units.
In terms of the concerted model and sequential model what effect does negative effectors have?
They stabilise the low affinity form of the sub - units.
Explain the concerted model.
When substrate binds to the T form it causes all sub - units to convert to R form.
R form has higher affinity for substrate than T form and thus, enzyme activity increases rapidly after each enzyme molecule has bound one substrate molecule.
Explain the sequential model.
When the substrate binds to T form it causes the sub - unit to which it binds to convert to R form.
Affinity increases once sub - unit has converted to R form and therefore, activity increases rapidly after protein has bound one substrate molecule.
