Lecture 5: Enzymes

Question 1

Enzymes are proteins

Each enzyme has a specific?

Answer 1

-shape
-electrical charge
-structure
-function (specific catalysis)
Almost all cellular reactions are controlled by enzymes

Question 2

What do you base an enzymes name on?

Answer 2

• what it reacts with
• how it reacts
• ASE ending

Question 3

Classification of enzymes:
What are the 6 classifications of enzymes? And what are each of their reaction types?

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Answer 3

1. Class:
   Oxidoreductases: Oxidation-reduction reactions eg oxidase
   Transferases: transfer of functional groups from one molecule to another eg kinase
   Hydrolases: causes hydrolysis eg phosphatase
   Lyases: removal of a group from, or addition of a group to, a molecule with rearrangement of electrons eg decarboxylase
   Isomerases: movement of a functional group within a molecule eg mutase
   Ligases: joining of two molecules to form a single molecule eg ligase

Question 4

What are the 4 general properties of enzymes?

Answer 4

1. They are all proteins
2. They have enormous catalytic power
3. They are highly specific- single enzyme performs single function
4. They accelerate the rate of getting equilibrium without affecting the equilibrium itself

Question 5

How do enzymes function?

Answer 5

There is a minimum amount of energy (activation energy) that reactants must have before collisions between the occur to create he product. Reactants therefore need to reach a transition state, which has higher energy level than the reactants or the products.
Enzyme accelerate reactions by reducing Ea

An enzyme- substrate complex is formed

• substrate binds to a small region on the enzyme known as the Active site.
• bonds are then made or broken
• the greater the Ea the slower the reaction
• the smaller the Ea the bigger the reaction

Question 6

What are the factors that effect the rate enzymes catalyse a reaction? Explain how

Answer 6

1. Enzyme concentration- if substrate is not limiting there is a linear relationship between the amount of substrate/minute and enzyme concentration
2. Temperature- as temp is increased, more molecules have enough activation energy, thus reaction rate will increase with increasing temp. If temp increases beyond a certain poin denaturation occurs and reaction rate ceases
3. Substrate concentration: if we plot substrate concentration and and enzyme catalysis reaction then we end up with a MICHAELIS-MENTEN CURVE. Vmax is maximum velocity and Km is the michaelis constant. It is when the substrate concentration which produces half the maximum velocity and is constant for a given enzyme.
4. pH- electrostatic charges are important in stabilising an enzymes tertiary structure. The charge distribution is totally dependant on the pH. Changing the pH changes the distribution of electrostatic bonds, changes the tertiary structure, and thus the shape of the enzyme altering its activity.

Question 7

How is enzyme activity regulated?

Answer 7

Enzyme is stored in an inactive form and activated when required.
1. Eg pepsinogen is activated by H+ in the stomach giving active pepsin. Or they are activated by hormones
2. Controlled by feedback inhibition
Eg a > b > c > d > e
As the end product E accumulates, it may bind to the first enzyme in the sequence and inhibit it , thus preventing further synthesis of E when it is inadequate concentration for cells needs. This is ‘feedback inhibition’
The place in which E binds to change enzymes active site shape is called ‘allosteric enzymes’

Question 8

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Answer 8

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Question 9

What do proteolytic enzymes do?

Give example and their functions

Answer 9

-break peptide bonds
-proteins are the substrate
-involved in digestion
Examples:
Subtilisin (bacterial): breaks any peptide bond
Chymotrypsin (gut): breaks peptide bond AFTER aromatic OR bulky aliphatic aa
Trypsin (gut): breaks peptide bond AFTER lysine OR arginine
Thrombin (blood clotting): breaks peptide bone BETWEEN Arginine AND lysine