Topic 3 - Enzymes

Question 1

What does an enzyme do?

Answer 1

• lowers activation energy needed to initiate a reaction

- speeds up the rate of reaction

Question 2

What is the name of the substrate specific region on an enzyme?

Answer 2

• the active site

Question 3

TRUE or FALSE: the active site amino acids come from different parts of the primary sequence.

Answer 3

• TRUE

Question 4

Where are active sites found on a 3D enzyme and why?

Answer 4

• in crevices, folds and clefts

- because it can hide from water to avoid the complications water brings to reactions

Question 5

What are the concepts behind complementary enzyme - substrate interaction?

Answer 5

• lock and key model: the enzyme active site is complementary in shape to the incoming substrate which slots right in
• induced fit model: the approaching substrate induces a change in the active site shape which makes it complementary to itself and so it can slot in.

Question 6

How are substrates bound to enzymes? And why?

Answer 6

• multiple weak interactions: h bonds and other non covalent interactions.
• because allows substrate to bind and product to be released fairly freely.

Question 7

What does Vo notation mean?

Answer 7

• initial rate of reaction

Question 8

What is Km?

Answer 8

• the Michaelis constant

- the substrate conc that gives half of the max rate

Question 9

What is Vmax?

Answer 9

• Maximum rate

- all enzyme is saturated with substrate

Question 10

What is the relation between the rate of an enzyme catalysed reaction to the conc of enzyme?

Answer 10

• proportional
• 2x conc of enzyme = 2x rate of reaction
• keep in mind that the rate will be 1:1 if it’s standardised for example per litre.

Question 11

What does the lineweaver-Burk plot do with the mm equation?

Answer 11

• Converts it into a straight line graph form

- y=mx+c form

Question 12

What are competitive and non-competitive inhibitors?

Answer 12

Competitive:
- Binds at active site and blocks the substrate from binding
- reduces proportion of enzyme bound to a substrate
Non Competitive:
- Binds at alternate site and changes active site shape so substrate cannot bind
- decreases conc of functional enzyme

Question 13

What does competitive inhibition do to Km and Vmax?

Answer 13

• Km increases

- Vmax unaffected (comp inhibitor can be outcompeted by infinite substrate)

Question 14

What does non-competitive inhibition do to Km and Vmax?

Answer 14

• Km unaffected

- Vmax decreases

Question 15

What is the unit of enzyme activity?

Answer 15

The amount of enzyme that produces 1micromole of product per minute
1micromole/min(/litre/gram)

Question 16

What does it mean if a substance has a lower Km?

Answer 16

• lower Km means higher affinity of substrate for binding to the enzyme
• it takes less substrate conc to get to half of Vmax

Question 17

How can you determine values for Km and Vmax from a substrate and velocity graph?

Answer 17

• Vmax is the highest value of V that occurs

- Km is the x intercept

Question 18

Why is it unsuitable to try to change the amino acid sequence to make a cell produce an enzyme in a human? Give the better alternative.

Answer 18

• only that cell would have coding for the enzyme

- alternative is that you can use gene expression to encourage enzyme production