2.4 Enzymes

Question 1

Describe the lock + key hypothesis

Answer 1

• Enzymes have a active sites and the substrate molecule has a complementary shape
• An enzyme-substrate complex in temporarily formed, the R groups of the amino acids in the active site interact with the substrate
• The interaction of the substrate with the active site breaks the substrate apart. The product molecules leave the active site, leaving enzyme molecule unchanged and ready to bind with another substrate molecule

Question 2

What are examples of intracellular enzymes?

Answer 2

Ribosomes
DNA helicase
RNA polymerase
Catalase

Question 3

What are examples of extracellular enzymes?

Answer 3

Amylase
Pepsin
Fungi

Question 4

Describe the induced fit hypothesis

Answer 4

• States that the active site is not rigid but is flexible so that the shape change slightly when the substrate enters it
• Once the product(s) has been released the active site returns to its original shape

Question 5

What group are enzymes in

Answer 5

Proteins

Question 6

What is activation energy?

Answer 6

Energy required to initiate the reaction

Question 7

What does catalase do?

Answer 7

Hydrogen peroxide (H2O2) is the toxic by-product of several cellular reactions. If left to build up, it can kill cells.

Catalase is an enzyme that works inside cells to catalyse the breakdown of hydrogen peroxide to harmless oxygen (O2) and water (H2O)

Question 8

What is the effect of pH on the rate of enzyme reaction?

Answer 8

Above and below the optimum pH, the H+ and OH- ions found in acids and alkalis can mess up the ionic bonds and hydrogen bonds that hold the enzymes tertiary structure in place. This makes the active site change shape, so the enzyme is denatured.

Question 9

What is the effect of temperature on the rate of enzyme reaction?

Answer 9

The rise in temperature makes the enzyme’s molecules vibrate more.
If the temp goes above a certain level, this vibration breaks some of the bonds that hold the enzymes in shape.
The active site changed shape and the enzyme and substrate no longer fit together. (Denatured)

Question 10

What is the effect of concentration on the rate of enzyme reaction?

Answer 10

If the amount of substrate is limited, there comes a point when there’s more than enough enzyme molecules to deal with all the available substrate, so adding more enzymes has no further effect.

Question 11

Explain the need for cofactors in some enzymatic reactions

Answer 11

Some enzymes will only work if there is another non-protein substance bound to them (cofactors). Some cofactors are inorganic molecules/ions work by helping the enzyme + substrate bind together, don’t directly participate in reaction so are not used up.

Question 12

Explain the need for coenzyme in some enzymatic reactions

Answer 12

Some cofactors are organic molecules and they participate in the reaction and are changed by it (act as carriers, moving chemical groups between different enzymes, are continually recycled during the process.

Question 13

Explain the need for prosthetic groups in some enzymatic reactions

Answer 13

If a cofactor is tightly bound to an enzyme, it is a prosthetic group. The prosthetic group are a permanent part of the enzyme’s active site.

Question 14

Explain the effects of inhibitors in the rate of enzyme-controlled reactions

Answer 14

Enzyme activity can be prevented by enzyme inhibitors. Inhibition can be competitive or non competitive.
Competitive inhibitor molecules have a similar shape to substrate molecules. Block active site.
Non-competitive inhibitor molecules bind to enzyme away from active site, bind to site known as allosteric site. Causes active site to change shape so substrate cannot bind to it.

Can be reversible or not