Lecture 4: Enzymes

Question 1

What are exergonic reaction

Answer 1

Reactants have a higher energy level than products, so it is usually catabolic, releasing energy

Question 2

What are endergonic reaction

Answer 2

Reactants have a lower energy than the products so large activation energy is required so usually anabolic

Question 3

Where is change in Gibbs free energy represented in the energy profile.

Answer 3

The difference between the energy of reactants and products (not including Ea)

Question 4

When will energy be released during an exergonic reaction

Answer 4

New bonds form to make the product

Question 5

What is the difference in energy between exergonic reaction with enzyme and without

Answer 5

Enzyme lowers the Ea without affecting the delta G.

Question 6

What are enzymes made of

Answer 6

Almost all are proteins with complex 3D structures. Some enzymes are made of RNA called ribozime

Question 7

What is the catalytic cycle of an enzyme

Answer 7

1. Substrates bind to the active site with weak bonds (H/ionic). forming the enzyme substrate complex
2. Enzyme destabilises the bonds in the substrate/ makes favourable microenvironment and allow them to reach transition state.
3. Bonds broken and new bonds are formed which are released from the active site leaving it available again

Question 8

What does the overall shape of the enzyme help with - small active site

Answer 8

The enzyme can clasp down on the substrate, forming additional H/ionic bonds. It makes sure the amino acids in the active site are correctly orientated for binding

Question 9

What are the main points about enzyme names

Answer 9

• ends with ase. They can describe the reaction they catalyse- can include substrate and type of reaction

Question 10

What do Ribonuclease and Deoxyribonuclease do vs RNA/DNA polymerase

Answer 10

hydrolyse RNA and DNA vs synthesising DNA / RNA

Question 11

What are cofactors

Answer 11

Non protein helpers for catalytic activity. Some enzymes need several cofactors.

Question 12

What are the two types of cofactors

Answer 12

Prosthetic groups: organic or inorganic molecules that tightly bond to the enzyme.
Coenzymes : small organic molecules that non covalently (weak) bond to enzyme.

Question 13

How does concentration influence reaction rate and the graph relationship

Answer 13

The concentration of enzymes is directly proportional to reaction rate (provided substrate increases at same rate), however only increasing substrate conc has a max rate of reaction as enzymes become saturated

Question 14

How does temperature and pH affect the reaction rate of enzymes and the differences in the graph

Answer 14

Reaction rate increases proportional to temperature up to an optimal temperature/pH which afterwards the enzyme denatures and reaction rate. drops off. For pH the graph is a bell shaped curve whereas temp is more assymetric, with quick drop off.

Question 15

How is enzyme activity regulated before they are made

Answer 15

The genes that code for particular enzymes can be turned on and off.

Question 16

Why do enzymes need to be regulated

Answer 16

Enzymes are part of metabolic pathways and so need to be able to turn off and on at specific times

Question 17

How is enzyme activity regulated after they are made

Answer 17

The inactive precursor of the active is made and activated when needed
The enzymes can be confined to specific organelles (eg lysosome)
The enzymes can oscillate between active and inactive forms - called allosteric regulation. depending on whether the cell produces an activator or inhibitor which binds away from the active site to fix it in the inactive or active state.

Question 18

How do allosteric regulatory molecules bond and how

Answer 18

They bind somewhere else from the active site. This binding is weak non covalent interaction which result in either stimulation or inhibition of enzyme activity

Question 19

What is an Allosteric feedback inhibition

Answer 19

This is when the final product of the metabolic pathway builds up and goes to bind to the early enzyme in the pathway to inhibit the enzymes pathway producing it. As the product decreases in conc, it is released from the first enzymes and then continues the cycle