1.4 Biological reactions are regulated by enzymes

Question 1

What are enzymes?

Answer 1

Globular proteins with tertiary structure.

Question 2

What are intercellular enzymes?

Answer 2

Enzymes that can act inside the cell.
e.g. ATP synthase, DNA helicase which unwinds the helix, DNA polymerase involved in catalysing the
formation of bonds, lysosome which carry enzymes.

Question 3

What are extracellular enzymes?

Answer 3

Enzymes that can be secreted by cells. e.g. e digestive enzymes secreted by the cell

Question 4

What does the 3D shape of the enzyme create?

Answer 4

an active site

Question 5

What determines the shape of the active site?

Answer 5

The sequence of amino acids in the polypeptide

Question 6

What name is given to the whole when the substrate binds to the enzyme?

Answer 6

Enzyme substrate complex

Question 7

What conditions affect enzyme production?

Answer 7

• temperature
• pH
• substrate concentration

Question 8

What is the name of the energy needed for enzyme reaction to take place?

Answer 8

Activation energy

Question 9

What is the Lock and Key hypothesis?

Answer 9

• active site (lock) and only one substrate (key) can fit together
• active site is a fixed shape
• enzyme not affected by reaction and can be reused

Question 10

What is anabolism?

Answer 10

When two substrate molecules are combined to form a single product molecule

Question 11

What is catabolism?

Answer 11

Breaking down molecules into two or more product molecules

Question 12

What is the Induced Fit hypothesis?

Answer 12

• as the substrate enters the active site forces of attraction between the substrate and the polar atoms of amino acids in active site are formed
• the shape of the active site changes and stronger bonds are formed with substrate
• this weakens bonds so activation energy is lower
• when product is released the active site returns to its original shape

Question 13

How does enzyme concentration effect the rate of enzyme-controlled reactions?

Answer 13

• the rate of reaction increases as enzyme concentration increases as there are more active sites for substrates to bind to
• increasing the enzyme concentration beyond a certain point has no effect on the rate of reaction
• more active sites than substrates, substrate concentration becomes the limiting factor

Question 14

How does Substrate concentration effect the rate of enzyme-controlled reactions?

Answer 14

• concentration of substrate increases, rate of reaction
  increases
• more enzyme-substrate complexes are formed
• beyond a certain point the rate of reaction no longer increases
• enzyme concentration
  becomes the limiting factor

Question 15

How does Temperature effect the rate of enzyme-controlled reactions?

Answer 15

– rate of reaction increases up to the optimum temperature
- more energy means more frequent collisions
- rate of reaction decreases beyond the optimum temperature.

Question 16

How does pH effect the rate of enzyme-controlled reactions?

Answer 16

– in the case where the pH is more acidic than the optimum pH, H+
ions disrupt
the enzyme-substrate binding and decrease the rate of reaction.
- In the case where
the pH is more alkaline than the optimum, the OH- ions disrupt the binding, also leading to a decrease in product formation.

Question 17

What is an inhibitor?

Answer 17

a substance which slows down or stops a reaction by affecting the binding of substrate to the enzymes. Inhibitors can either be reversible and irreversible

Question 18

What are competitive inhibitors?

Answer 18

• similar in structure to substrate so they bind to active site
• amount of product formed remains the same but the rate decreases largely

Question 18

What are reversible inhibitors?

Answer 18

They bind to the active site through hydrogen bonds and weak ionic interactions therefore they do not bind permanently. Reversible inhibitors can either be
competitive or non-competitive

Question 19

What is a non-competitive inhibitor?

Answer 19

• substance has no structural resemblance to a substrate molecule so does not bind to active site
• instead it binds to an area called the allosteric site
• this changes the 3D structure of the active site so feweer enzyme-substrate complexes are made

Question 20

What does immobalisation of an enzyme do?

Answer 20

By placing enzymes in an inert substace the ability of the polypeptide chain to move reduces which means temperature and pH have less effect on the 3D shape

Question 20

What are immobilised enzymes’ uses in industry?

Answer 20

• recovered and reused to reduce cost
• lower/higher temperatures can be used and still have higher yeilds
• e.g Lactase can produce lactose free milk

Question 21

What are immobilised enzymes’ uses in medicine?

Answer 21

• Biosensors or analytical reagents as they are specific
• e.g. Glucose oxidase electrode that is used by diabetics to detect blood glucose levels