Block C Lecture 1 - Enzymes and Kinetics Flashcards
Why are catalysts important?
As they increase the rate of a reaction without themself being changed or consumed in the overall process - meaning they can be used in future reactions
(Slide 10)
How do enzymes / catalyses increase the rate of a reaction?
By lowering the activation energy of a reaction
(Slide 11)
Do enzymes affect energetics or the equilibrium of a reaction?
No
(Slide 12)
What 2 things are enzymes highly specific for?
A substrate (i know thats obvious), but also a reaction! (as long as it doesn’t have side reactions)
(Slide 13)
What is a side reaction?
an unintended chemical reaction that occurs alongside the main reaction
(Slide 13)
Why do all enzymes end in “ase”?
Diastase was the first enzyme discovered, with the word coming from the greek work diastasis, meaning to separate
(Slide 16)
What is an EC number?
A numerical classification system for enzymes based on the chemical reactions they catalyse. They follow a four-digit format.
(Slides 17 and 18)
What do the 4 digits of an EC number mean?
The first digit represents the general type of reaction which is catalysed by the enzyme
The second and third digits are the enzymes sub-class and sub-sub-class respectively and describe the reaction with respect to the compound, group, bond or product involved in the reaction
The final digit, also known as a serial identifier, zeros in on specific metabolites and cofactors involved
Note: There’s a good example on this slide idk how to put into flashcards without it taking a lot of space
(Slide 18)
What are all the possible values of the first digit of an EC number and what do these represent?
EC 1 - Oxidoreductases (Catalyse oxidation-reduction (redox) reactions by transferring electrons between molecules.)
EC 2 - Transferases (transfer functional groups from one molecule to another)
EC 3 - Hydrolases (Break chemical bonds using water via hydrolysis reactions)
EC 4 - Lyases (breaks bonds without water or redox reactions)
EC 5 -Isomerases (Catalyses the structural rearrangement of molecules (isomerization))
EC 6 - Ligases (Joins two molecules together, usually using energy from ATP)
(Slide 17)
What is the equation of enzyme catalysis?
E+S <> E — S <> E+P
E= Enzyme , S = Substrate, P = Product
(Slide 20)
What interactions do enzyme active sites usually rely on to bind the substrate?
Weak bonds
Hydrogen bonds
Van der wall forces
Hydrophobic interactions
(Slide 20)
What are 2 examples of small non-protein molecules which enzymes contain which can participate in catalysis?
Prosthetic groups and coenzymes
(Slide 21)
What are prosthetic groups?
Tightly bound, permanent non-protein components which are usually bound to the enzyme covalently
(Slide 21)
What are coenzymes?
Organic molecules which are loosely bound to enzymes, and usually bind temporarily, with most being derivatives of vitamins
(Slide 21)
What is free energy (G)?
Energy which is released which is available to do work
Change in free energy during a reaction is referred to as ΔG
(Slide 24)
What do reactions with a negative ΔG and a positive ΔG mean?
Reactions with a negative ΔG release free energy whereas those with a positive ΔG require energy
(Slide 24)
What is the activation energy?
The energy which is required to bring all molecules in a chemical reaction into the reactive state. Catalysis is usually required to breach this barrier
(Slide 25)
How do enzymes reduce the activation energy of a reaction?
- The substrate binds
- The enzyme holds the substrate in an orientation that aligns reactive groups, then specific amino acids in the active site apply strain on certain bonds, making them easier to break.
- They stabilise the transition state, which lowers its Gibbs energy
(Slide 29)
What is the transition state?
This is the highest-energy, least stable point in a reaction found at the top of the energy barrier, which is sometimes referred to as the “activated complex”
(Slide 30)
What may the transition state have in comparison to substrates or products?
Partly or fully broken bonds
Distorted shape
Any other number of extra changes
(Slide 30)
What is a racemisation reaction?
A reaction which flips a molecule into its mirror image
(Slide 31)
What is the full Michaelis-Menten equation?
k1 k2
E + S ⇌ ES → E + P
k-1
k1 = forwards rate constant for this step
k-1 = backwards rate constant for this step
k2 = rate constant for this step
(Slide 36)
How is the initial rate calculated?
By plotting product concentration (X axis) against time (Y axis), this should give an initial straight line before slowing down, generating a curve. Initial rate is the gradient of the straight line portion
(Slides 37 and 38)
What are 3 possible causes for the rate of a reaction slowing down after the initial rate?
Substrate concentration falling
Inhibition by an accumulating product
Inactivation of the enzyme
(Slide 37)
