Enzymes And Biological Reactions 1.4

Question 1

What are enzymes?

Answer 1

Biological catalysts that lower activation energy through the formation of enzyme-substrate complexes.

Question 2

What is activation energy?

Answer 2

The minimum amount of energy needed to start a chemical reaction.

Question 3

Describe the lock and key hypothesis

Answer 3

• active site is complementary in shape to the substrate
• the substrate is specific to the active site and fits into it.
• an enzyme-substrate complex is formed by temporary bonds
• products are released and enzyme remains unchanged and reusable.

Question 4

Why can an enzyme only catalyse one type of chemical reaction?

Answer 4

The enzyme has a unique shape

Question 5

How does the induced fit hypothesis differ to the lock and key model?

Answer 5

• the active site will change shape slightly to accommodate the substrate
• this puts a strain on the bonds in the substrate to lower its activation energy (as these bonds must be broken)

Question 6

Give an example of an enzyme which supports the induced fit hypothesis

Answer 6

Lysozyme (an antibacterial enzyme found in human mucus saliva and tears.

Question 7

What is metabolism?

Answer 7

All chemical reactions that occur in the body.

Question 8

What are metabolic pathways?

Answer 8

The sequence of chemical reactions controlled by enzymes. This includes anabolic and catabolic reactions.

Question 9

What is an anabolic reaction?

Answer 9

The building up of molecules

For example protein synthesis

Question 10

What is a catabolic reaction?

Answer 10

Breaking down of molecules

For example digestion.

Question 11

What are the properties of enzymes?

Answer 11

Biological catalysts so made of living cells.

Tertiary proteins with a globular structure

Soluble as it as the hydrophilic R-group in the outside.

Particular sequence of amino acids.

Question 12

What are the three sites of enzyme action?

Answer 12

Extra cellular
Intercellular membrane bound
Intercellular in solution

Question 13

Where do extracellular enzyme actions occur?

Answer 13

Outside the cell as they are secreted throughly exocytosis. For example amylase in digestion.

Question 14

Where do intracellular /in solution enzymes work ?

Answer 14

I’m Inside the cell like in the stroma of chloroplasts catalyse the synthesis of glucose.

Question 15

Where do intracellular /membrane bound enzymes work?

Answer 15

Inside the cell attached to a membrane. Like the cristae of mitochondria and grana of chloroplasts.

Question 16

Why are enzymes soluble?

Answer 16

The hydrophilic R-group is on the outside of the enzyme

Question 17

What bonds are present in enzymes.

Answer 17

• disulphide
• ionic
• hydrogen
• hydrophobic
• polypeptide

Question 18

What factors affect the rate of enzymes reactions?

Answer 18

Substrate concentration

Temperature and PH

Question 19

How does substrate concentration affect the rate of enzymes reactions?

Answer 19

Up to levelling off the higher the substrate concentration the higher the number of collisions between the enzyme and substrate so the rate increases.

Then it reaches saturation point and continues at a constant level as all active sites are occupied so maximum turn over rate has been reached for those conditions.

Question 20

How does temperature affect the rate of enzyme action?

Answer 20

Rate increases as temperature increases until optimum temperature. This is because they have more kinetic energy so enzymes and substrate collide more frequently.

Above optimum temperature hydrogen bonds are broken so the shape of the active site changes cause inflation the enzyme to denature.

Question 21

How does temperature affect the rate of enzyme action?

Answer 21

The rate of an enzyme catalysed reaction will vary with PH levels. Small changes in PH will cause small reversible changes in the enzymes structure causing inactivation. Extreme changes in PH will cause permanent changes to the enzyme structure causing it to denature.

Question 22

How is enzyme action and enzyme concentration described as?

Answer 22

Directly proportional.

Question 23

What is enzyme inhibition?

Answer 23

It is the decrease in the rate of an enzyme controlled reaction by an inhibitor.

Question 24

What are the differences between competitive inhibition and noncompetitive inhibition?

Answer 24

Competitive inhibition is when the inhibitor goes into the active site and the active stays the same shape.

No competitive inhibition is when the inhibitor enters the allosteric site and changes the shape of the active site so that the substrate will no longer fit.

Question 25

What is competitive inhibition? Describe it.

Answer 25

• inhibitor has a complementary shape to the active site so competes with the substrate to fit into it.
• the higher the competitive inhibitor concentration the bigger the decrease in rate of enzymic reaction.

Question 26

What is non competitive inhibition. Describe it.

Answer 26

• the inhibitor bonds to the allosteric site. This affects the bonds in the enzyme W causing it to change the overall shape and the active site. This prevents the enzyme-substrate complexes forming.
• the more inhibitors the more enzymes are denatured but even at high substrate concentrations the noncompetitive inhibitor will ALWAYS reduce the rate of reaction.

Question 27

What does inert mean?

Answer 27

Unreactive substance

Question 28

What are immobilised enzymes?

Answer 28

Enzymes that have been bound to an inert matrix.

Question 29

What are the uses of immobilised enzymes.

Answer 29

• fermentation
• lactose free milk
• biosensors
• HFCS

Question 30

Give two examples of immobilising an enzyme

Answer 30

Algenate beads (micro encapsulation)

Cellulose microfibrils (entrapment)

Question 31

Why are enzymes put into a. Inert matrix?

Answer 31

So that threes are no unwanted reactions only the substrate => product reaction.

Question 32

What are the advantages of immobilised enzymes

Answer 32

• increased stability over a wide range of temp & PH
• products are not contaminated with the enzyme
• enzymes are easily recovered for reuse making them cheaper
• greater control over the process as the enzymes can be added or removed.
• a sequence of enzymes with different optimum PH and temperature can be used together in the same process

Question 33

How can the rate of reaction be measured?

Answer 33

Measure how fast the product is produced.