Enzymes 1 Flashcards
What is an enzyme?
- Globular protein
- Biological catalyst
What does an enzyme do?
- Catalyses very high reaction rates
- Shows great reaction specificity
- Work in mild temp/pH conditions
- Can be regulated
Ribozyme
Catalytic RNA molecule with no protein component
Cofactor
Non-protein component needed for activity
Coenzyme
Complex organic molecule, usually produced from a vitamin
Prosthetic group
Cofactor covalently bound to the enzyme or very tightly associated with the enzyme
Apoenzyme
The protein component of an enzyme that contains a cofactor
Holoenzyme
The apoenzyme plus the cofactor(s)
Substrate
Molecule acted on by the enzyme
Active Site
Part of the enzyme in which the substrate binds and is acted upon
Class 1
Oxidoreductases
Transfers e
Class 2
Transferases
Group transfers
Class 3
Hydrolases
Hydrolysis
Class 4
Lyases
Form, or add groups to double bonds
Class 5
Isomerases
Transfer groups within molecules
Class 6
Ligases
Formation of C-C, C-S, C-O, and C-N bonds
What do enzymes not do?
- Move reaction equilibria
- Make a non-spontaneous reaction spontaneous
What can enzymes do?
- Increase rate of spontaneous reaction
- Lower the activation energy of biochemical reactions
- Accelerate movement towards reaction equilibrium
What is Gibbs free energy?
Useful energy generated from cellular reactions
What is true of spontaneous reactions?
They must have -ve ΔG value as they will decrease enthalpy and/or increase entropy
What is the energy barrier equal to?
Energy required to position chemical groups correctly
What does the transition state represent?
The moment that chemical bonds are formed and broken
Binding energy
When enzymes for non-covalent bonds with substrate molecules allowing them to take the reaction through a different path of reaction intermediates
What must the active site be complementary to in order for a reaction to take place?
Transition state
What 3 ways do enzymes reduce activation energy?
- Entropy reduction
- Desolvation
- Induced fit
How does entropy reduction reduce activation energy?
- Molecules in free solution will only react by bumping into one another
- Enzymes force the substrate to be correctly orientated by binding them in the formation they need to be in for the reaction to proceed
How does desolvation reduce activation energy?
Weak bonds between the substrate and enzyme essentially replace most or all of the H bonds between substrate and aqueous solution
How does induced fit reduce activation energy?
Conformational changes occur in the protein structure when the substrate binds
How can an enzyme by analysed?
- Enzyme kinetics
- Mutagenesis
- 3D structure
Why does Vmax occur when you increase the amount of substrate?
All of the enzyme active sites are saturated with substrate
What is critical to the Michaelis-Menten equation?
Formation of an enzyme-substrate complex
What does the model state?
- The first part of the reaction (to produce ES) occurs reversibly
- Second part of the equation (to produce E and P) occurs more slowly than the first part
What assumptions are made with the Michaelis-Menten equation?
- If 2nd part is slower it must limit the rate of the overall reaction so the overall rate of reaction must be proportional to the amount of ES
- More ES would give a higher overall reaction rate and less would give a slower overall reaction rate
What is the M-M equation?
Vo= Vmax[S]
————
Km+ [S]
What is the M-M equation consistent with?
The experimentally observed dependence of Vo on [S] with the curves shape depending on Vmax/Km at low [S] and depeding on Vmax at high [S]
Define Km.
Km is equivalent to the substrate concentration at which the initial reaction rate is half of the maximum reaction rate
What do larger Km values indicate?
A less stable ES complex
What do smaller Km values indicate?
A more stable ES complex
