Lecture 1. Enzyme Essentials Flashcards
Carbonic anhydrase increases the forward rate of which reaction?
CO₂ + H₂O ⇌ HCO₃⁻ + H⁺
Without carbonic anhydrase, how fast is the forward rate of reaction?
0.1 molecules per second
With carbonic anhydrase, how fast is the forward rate of reaction?
1,000,000 molecules per second
What are the names of RNA molecules that operate as enzymes?
Ribozymes
What can catalytic power be demonstrated by?
The ‘turnover number’ or ‘catalytic constant’ kcat
What does kcat mean?
Number of molecules of ‘substrate’ that one enzyme molecule can convert in 1 second
What are the reactants in an enzyme-catalysed reaction known as?
Substrates
What are substrates converted to in an enzyme-catalysed reaction known?
Products
What are cofactors?
Small molecules not part of the enzyme but which are
required for activity
Examples of cofactors
Metal ions, organic molecules, co-enzymes and prosthetic groups
What is an apoenzyme?
An enzyme lacking an essential cofactor
or coenzyme
What is the complete machinery of an enzyme and its cofactors called?
Holoenzyme
How many classes of enzyme are there?
6
What are EC 1 enzymes and what do they do?
Oxidoreductases - oxidation/reduction
What are EC 2 enzymes and what do they do?
Transferases - transfer of a group
What are EC 3 enzymes and what do they do?
Hydrolases - water cleaves a bond
What are EC 4 enzymes and what do they do?
Lyases - Non-hydrolytic cleavage, addition or removal of groups
What are EC 5 enzymes and what do they do?
Isomerases - intramolecular rearrangement
What are EC 6 enzymes and what do they do?
Ligases - join two molecules
Example of an oxidoreductase
Lactate dehydrogenase
Example of a transferase
Hexokinase
Example of a hydrolase
Glucose-6-phosphate
Example of a lyase
Carbonic anhydrase
Example of an isomerase
Triose-phosphate isomerase
Example of a ligase
Amino-acyl tRNA synthetases
What does specificity imply?
Enzymes recognise and bind substrates in an enzyme
What proteinases are not highly specific?
Papain and savinase
What does trypsin hydrolyse and where?
Trypsin hydrolyses peptide bonds at the C-terminal side of lysine or arginine
What does chymotrypsin hydrolyse and where?
Chymotrypsin hydrolyses peptide bonds at the C-terminal side of phenylalanine, tyrosine or tryptophan
What does thrombin hydrolyse?
Thrombin hydrolyses the arginine-glycine bond
What is the name of the part of the enzyme that interacts with the substrate?
The active site
What determines the activity and specificity of the enzyme?
The structure and the chemistry of the active site
What is the current model used by scientists to represent the active sites?
The induced fit model
What does the active site bind to?
Transition states
What is a transition state?
The highest energy state
What is the activation barrier?
The difference in energy between the reactant(s) and the transition state
What do enzymes lower?
The activation barrier speeding up reactions
What is the enzyme-substrate complex also known as?
The Michaelis complex
