BMS 108 Ch. 04 Enzymes

Question 0

Where does the substrate fit? What might be needed to fully activate the enzyme?

Answer 0

One the activation site; cofactors and coenzymes

Question 1

What is an enzyme? What is the mechanism by which it does its job?

Answer 1

A protein that speeds up a chemical reaction; works by lowering the energy of activation

Question 2

What forces can easily destabilize an enzyme?

Answer 2

Changes in pH and body temperature

Question 3

What is conformation?

Answer 3

Highly ordered three dimensional shapes of enzymes.

Question 4

What is a conformational change?

Answer 4

Change in the three dimensional shape of a protein

Question 5

What does it mean to denature a protein?

Answer 5

Change in the structure of a protein

Question 6

What is the difference between a competitive and noncompetitive inhibitor? What is it called when a protein is inhibited by its own product? What is the mechanism?

Answer 6

Competitive - competes with the substrate for active sites
Noncompetitive - binds to regulatory sites (not necessarily active sites)

Feedback inhibition; Activity is blocked by the product of the reaction that was catalyzed by the enzyme

Question 7

What is the action of phosphatases and kinases?

Answer 7

Phosphatases are enzymes that remove phosphate groups from substrates; kinases transfer phosphates from ATP to specific substrates.

Question 8

How and why does a coenzyme binding to a regulatory site change the activity of the enzyme?

Answer 8

Coenzymes form an ionic bond with the enzyme causing a conformational change that changes the shape of the active sites of the enzyme.

Question 9

The ability of enzymes to lower energy requirement is due to its __________.

Answer 9

structure

Question 10

Enzymes contain pockets called _______ ______ into which __________ (reactants/ligands) fit.

Answer 10

Active sites; substrates

Question 11

Enzymes act by bringing ________ close together so they can react.

Answer 11

substrates

Question 12

Describe the mechanism of enzyme action.

Answer 12

1. Substrates fit into the active sites
2. Enzyme-substrate complex is formed
3. Reaction occurs
4. Products dissociate
5. Enzyme is unaltered

Question 13

Most enzymes end with ______.

Answer 13

-ase

Question 14

What do phosphatases do?

Answer 14

removes phosphate groups

Question 15

What two things effect the optimal range for enzyme activity?

Answer 15

Temperature and pH

Question 16

What are cofactors? and coenzymes?

Answer 16

molecules necessary for normal enzyme activities

metal ions; small biological molecules such as vitamins

Question 17

How do cofactors and coenzymes work?

Answer 17

Cofactor/coenzymes binding changes conformation of active site, which aids in temporary bonding between enzymes and substrates.

Question 18

How are enzymes activated and deactivated?

Answer 18

Many are activated by phosphorylation (with phosphatases) and dephosphorylation (with kinase).
- others are activated by 2nd messenger (diffusable intracellular molecules or ion carrying a message)

Question 19

Enzymes are also regulated by ______ of enzymes - breakdown and re-synthesis of enzymes therefore allowing genes to alter enzyme activitiy as conditions change.

Answer 19

turnover

Question 20

What are the three types of enzyme inhibitors?

Answer 20

1. Competitive - compete with substrates for active sites
2. Noncompetitive - bind to regulatory sites (not necessarily active sites)
3. Feedback - activity is blocked by a product of the reaction that was catalyzed by the enzyme

Question 21

What does it mean when we say an enzyme is “rate-limiting” in a chemical reaction?

Answer 21

Rate of product formation increases as substrate concentration increases until reaction rate reaches a plateau. This is where the enzyme is said to be saturated.

Question 22

What is the law of mass activation?

Answer 22

The principle that reversible reactions will be driven from the side of the equation where the concentration is higher to the side where the concentration is lower.

Question 23

What is a metabolic pathway?

Answer 23

Sequences for enzymatic reactions that begin with initial substrate, procedes through intermediates and end with a final product.

Question 24

What is end-product inhibition?

Answer 24

It occurs when one product in a divergent pathway inhibits activity of the branch point enzyme.

• prevents final product accumulation
• causes the reaction to favor alternate pathway
• occurs by noncompetitive/allosteric inhibition whereby product binds to enzyme causing it to change to an inactive shape