Enzymes

Question 1

What is an enzyme?

Answer 1

A globular protein molecule that acts as a biological catalyst and increases the rate of biochemical reactions

Question 2

How do enzymes increase the rate of reactions?

Answer 2

it forms enzyme-substrate complexes which lowers the activation energy of the reaction it catalyses which means that the reaction requires less energy to start and therefore makes it quicker

Question 3

What is the active site?

Answer 3

an area of depression in the enzymes’ shape caused by folds due to the enzymes tertiary structure

Question 4

What is the substrate?

Answer 4

the molecule that the enzyme acts on

Question 5

Explain and describe the lock and key hypothesis.

Answer 5

• it’s an earlier model used to explain how enzymes work
• the enzyme’s structure is fixed so the active site is specific to the substrate
• the substrate is a perfect fit for the enzyme

Question 6

Explain and Describe the induced fit model.

Answer 6

• a more recent model used to explain how enzymes work
• the tertiary substrate changes as the subatrate approaches
• as the bonds begin to form the tertiary structure of the active site molds itself around the substrate
• this ensures that the substrate fits perfectly

Question 7

Why is the enzyme specific to the substrate according to the lock and key theory?

Answer 7

because the enzyme has a fixed structure therefore it’s active site is only complementarty to one substrate

Question 8

Why is the enzyme specific to the substrate according to the induced fit hypothesis?

Answer 8

• if the substrate isn’t complementary it can’t form the correct bonds with the correct amino acids in the active site
• this means the tertiary strcuture can’t change to become the perfect fit and catalyse the reaction

Question 9

How does temperature affect enzyme controlled reactions?

Answer 9

• the kinetic energy of enzyme atoms increase
• this increases the rate of reaction first until the optimum temperature
• then the vibrations break the hydrogen bonds
• changes the shape of the protein and therefore the active site
• the active site is no longer complementary with the substrate so rate decreases

Question 10

What factors affect the rate of enzyme controlled reactions?

Answer 10

1. temperature
2. pH
3. concentration of enzymes
4. concentration of substrate
5. concentration of competitive inhibitors
6. concentration of non-competitive inhititors

Question 11

How does pH affect enzyme controlled reactions?

Answer 11

• acids and alkalines contail H+ and OH- ions respectively
• these interfrere with the hydrogen and ionic bonds that create the tertiary structure of the active site/enzyme
• this reduces the active site’s ability to bind with the substrate as the shape is no longer complementary
• this causes the rate of reaction to decrease

this happens above the optimum pH

Question 12

How does enzyme consentration affect enzyme controlled reactions?

Answer 12

• as the concentration increases so does the rate of reaction
• this is because there are more active sites for the substrates to form enzyme-substrate complexes with
• however after a certain point there are more enzymes than substrate so the rate of reaction stays the same
• substrate concentration is now the limiting factor

Question 13

How does substrate concentration affect enzyme controlled reactions?

Answer 13

• as the concentration increases so does the rate of reaction
• this is because there are more enzyme-substrate complexes forming
• however after a certain point there are more substrates than enzymes this means all the enzymes are occupied
• so the rate of reaction stays the same
• enzyme concentration is now the limiting factor

Question 14

How does competitve reversible inhibitors concentration affect enzyme controlled reactions?

Answer 14

• it occupies the active site of an enzyme
• this means that the substate can’t form enzyme-substrate complexes which slows down the rate of reaction

Question 15

What does Vmax represent?

Answer 15

the max rate of reaction

Question 16

How do competitive reversible Inhibitors work?

Answer 16

• they are molecules that have a similar shape to the substrate of an enzyme
• this means it can attach to the active site of an enzyme and then it eventually detatches
• this means that it occupies the enzyme for a period of time instead of the substrate

Question 17

How can the affect of competitive reversible Inhibitors be decreases?

Answer 17

by increasing the concentration of the substrate it means that the inhibitor is less likely to occupy the active site

Question 18

How do competitive irreversible Inhibitors work?

Answer 18

• it perminantly attaches to the active site of an enzyme
• this means that once on the active site it never leaves
• this also means that increasing the substrate concentration is inaffective as the active site is perminantly occupied

Question 19

How does non-competitve reversible inhibitors concentration affect enzyme controlled reactions?

Answer 19

as the concentration of non-competitve reversible inhibitors increase, the rate of reaction decreases as the shape of the active site is altered and therefore no longer able to catalyse the reaction

Question 20

How do non-competitve reversible inhibitors work?

Answer 20

• it binds to an alternative site (allosteric site)
• this changes the tertiary structure of an enzyme which changes the active site
• substrate is no longer complementary with the substrate so enzyme-substrate complexes can’t form
• which decreases rate of reaction

Question 21

Why does increasing substrate concentration not affect non-competitve reversible inhibitors?

Answer 21

even if you increase the consentration, the substrate is still no longer complementary with the altered active site