Enzymes

Question 1

What is the function of an enzyme?

Answer 1

They catalyse reactions by lowering the activation energy

Question 2

What are 3 characteristics of an enzyme?

Answer 2

Soluble in water
Globular protein
Specific 3D tertiary structure
Affected by temperature, pH and salt
Contain an active site
Specific to one type of substrate

Question 3

How does an enzyme catalyse a reaction?

Answer 3

They will randomly collide with a substrate molecule and hold the substrate in a way that a product will be formed

Question 4

Explain the lock and key hypothesis of enzyme action

Answer 4

The substrate binds to the active site of an enzyme due to it being complementary, the enzyme then splits the substrate into two products

Question 5

Explain the induced fit hypothesis and why it is more widely accepted

Answer 5

The substrate collides with the active site of an enzyme, the active site then slightly changes shape to better fit with the substrate, the enzyme then puts pressure on the bonds in the substrate so that the reaction is catalysed and product is released.

It is more widely accepted because it gives a better explanation as to how the bonds in the substrate are broken and the products are produced

Question 6

Define the terms, Intracellular and Extracellular

Answer 6

Intracellular-Catalyse reactions inside cells

Extracellular-Catalyse reactions outside cells

Question 7

Define activation energy

Answer 7

The amount of energy that must be applied for a reaction to happen

Question 8

Explain how temperature affects rate of reactions

Answer 8

Increasing temperature will increase the rate of reaction due to higher amounts of kinetic energy

At a certain point (optimum) the reaction will reach its peak rate and any temperature after that will lower the rate of reaction due to enzymes denaturing and having their active sites changed

This happens because at high temperatures the bonds that hold the tertiary structure together will break

Question 9

Explain how vibrations lead to denaturing

Answer 9

More kinetic energy results in more vibrations which puts strain on the bonds in the tertiary structure which can break weaker bonds like ionic or Hydrogen

Question 10

What is the equation for the temperature coefficient (Q10)

Answer 10

Rate of reaction at X+10 degrees C
divided by
Rate of reaction at X degrees C

Question 11

What is pH and how is it measured?

Answer 11

pH is the concentration of H+ ions

A higher concentration of H+ ions results in a lower pH value which means acids have a high concentration of H+ ions

High pHs have a low concentration of H+ ions and a high concentration of OH- ions

Question 12

How does pH affect bonds and active sites?

Answer 12

Due to H+ ions being positively charged they attract -charged molecules

Tertiary structures are held together by lots of H bonds and ionic bonds

H+ ions will interfere with these bonds

Increasing the concentration of H+ or OH- ions can change the active site

Question 13

What is used to control pH in practical’s?

Answer 13

A buffer

Question 14

What is the definition of V max?

Answer 14

The point in a reaction where the rate can no longer increase due to a limiting factor

Question 15

What is an inhibitor?

Answer 15

A substance or molecule that slows down the rate of an enzyme controlled reaction by affecting the enzyme

Question 16

What are the 4 types of inhibitors?

Answer 16

Competitive

Non competitive

Permanent

End product

Question 17

How do competitive inhibitors slow down a reaction?

Answer 17

They have a similar shape to the substrate and so they occupy the active site and form an enzyme-inhibitor complex

This means the substrate cannot fit into the active site

Question 18

How does a competitive inhibitor affect ROR on a graph?

Answer 18

The ROR goes up consistently and plateaus at the same point as if without an inhibitor

Question 19

How do non competitive inhibitors slow down a reaction?

Answer 19

They bind to an area away from the active site called the allosteric

Then they distort the 3D structure and change the shape of the active site

This means the substrate can no longer fit the active site

Question 19

How do non competitive inhibitors affect rate of reaction on a graph?

Answer 19

ROR increases to a low point and then plateaus very quickly

Question 19

How do permanent inhibitor slow reactions?

Answer 19

They tend to be non competitive inhibitors because they permanently denature the enzyme when they change the active site

Question 19

How do end product inhibitors slow down reactions?

Answer 19

The end product of the substrate acts as a non-competitive inhibitor for the first enzyme in the process

This prevents a build up of end products

Question 19

What are cofactors?

Answer 19

They are inorganic ions that increase the rate of enzyme controlled reactions

They combine with the enzyme or substrate so the enzyme-substrate complex can form easier

This happens as it can change charge distribution and sometimes the shape

Question 20

What are 3 characteristics/functions of coenzymes?

Answer 20

Small organic and non protein
Often vitamins
Often carry chemical groups between enzymes for metabolic pathways
Take part in the reaction
Can be used repeatedly

Question 20

What is a prosthetic group?

Answer 20

A permanent part of an enzyme that contributes to the shape and overall size