Ch. 4 Enzymes and Energy

Question 1

What are enzymes?

Answer 1

Class of proteins that serve as biological catalysts

Question 2

What is the enzyme exception?

Answer 2

Ribozymes are made of RNA

Question 3

What do enzymes do?

Answer 3

Increase rate of reaction
Not changed by reaction (can be used again)
Do not change nature of reaction - reaction could have occurred w/o enzyme, just much slower
Lowers activation energy of reaction

Question 4

What is activation energy?

Answer 4

Energy required for reactants to engage in a reaction

–a barrier we have to overcome

Question 5

Most molecules ____ the activation energy for a reaction.

Answer 5

Lack

Question 6

Adding ____ increases the likelihood of a reaction occurring.

Answer 6

Heat

–increases rate of reaction, yet has some negative effects on cells.

Question 7

____ help the reaction occur at lower temperatures.

Answer 7

Catalysts

Question 8

Why do we have enzymes?

Answer 8

Because heat isn’t a great option in physiology to speed up a reaction

Question 9

The function of an enzyme is dictated by its ____.

Answer 9

Structure

Question 10

Describe the shape of enzymes.

Answer 10

Characteristic 3D shape or conformation, has pockets that serve as active sites in the enzyme

Question 11

Enzyme reactants are called ____.

Answer 11

Substrates

Question 12

Lock-and-key model

Answer 12

Substrates fit into the active site like a key to a lock

Question 13

Induced-fit model

Answer 13

The initial fit is not always exact, but will change as the substrate moves into the active site

Question 14

All enzymes end with the suffix ____.

Answer 14

-ase

Question 15

Phosphatase?

Answer 15

Remove phosphate groups

Question 16

Synthetase and Synthase?

Answer 16

Catalyze dehydration synthesis

Question 17

Hydrolase?

Answer 17

Promote hydrolysis

Question 18

Dehydrogenase?

Answer 18

Removes hydrogen atoms

Question 19

Kinase?

Answer 19

Add phosphate groups

Question 20

Isomerase?

Answer 20

Rearrange the atoms

Question 21

Does an enzyme that does the same job in two different organs have the same name?

Answer 21

Yes

–names are given to enzymes based on function

Question 22

What are isoenzymes?

Answer 22

Molecules that may be slightly different (in areas outside the active site)

Question 23

How is enzyme activity measured?

Answer 23

By the rate at which substrate is converted to product

Question 24

What influences enzyme activity?

Answer 24

• Temperature (heat makes reaction occur faster)
• pH (different enzymes activate at different pH levels)
• Cofactors and coenzymes
• Enzyme activation
• Substrate concentration (adding more substrate = reaction occurs faster)
• Possible stimulatory or inhibitory effects of products on enzyme function

Question 25

Most enzymes work really well at what temperature?

Answer 25

37ºC (our core body temperature)

Question 26

Enzymes exhibit peak activity within a ____ pH range.

Answer 26

Narrow

Question 27

pH changes will result in what?

Answer 27

Enzyme conformational changes

Question 28

True or False: Optimum pH reflects the pH of the fluid the enzyme is found in.

Answer 28

True

Question 29

What are coenzymes?

Answer 29

Organic molecules derived from water-soluble vitamins

Larger molecules, many enzymes require these to function properly

Question 30

What do coenzymes transport?

Answer 30

Hydrogen atoms and other small molecules between enzymes

Question 31

What are cofactors?

Answer 31

Help form the active site through a conformational change of the enzyme or help in enzyme-substrate binding.

Much smaller than coenzymes

Question 32

What types of ions are cofactors?

Answer 32

Metal ions such as Ca2+, Mg2+, Mn2+, Cu2+, Zn2+

Question 33

Can cofactors bind at different sites?

Answer 33

Yes

Question 34

What is zymogen?

Answer 34

Enzymes, particularly of the digestive system, are often produced in an inactive form called a Zymogen that is activated when needed

Make enzymes, store them, release when needed
–ex: pepsinogen –> pepsin

Question 35

Enzyme inhibition can be controlled through what?

Answer 35

Turnover, by which enzymes are degraded

Question 36

Enzyme activation often requires ____ ____ to phosphorylate or dephosphorylate the molecule.

Answer 36

Additional enzymes

Question 37

As the substrate concentration ____, so will the rate of the reaction until the enzyme becomes ____.

Answer 37

Increases; saturated

Question 38

What is meant by saturated?

Answer 38

Every enzyme in the solution is being used

Question 39

Will adding more substrate (in already saturated enzymes) increase the rate of the reaction?

Answer 39

No, if it’s saturated (all enzymes are being used), the reaction can’t increase

Question 40

Reversible Reactions

Answer 40

Sometimes a single enzyme can drive a reaction in two directions, depending on the concentration of substrate/product

When one side gets higher, the other reaction reverses; the law of mass action
–wants to be in equilibrium

Question 41

What are metabolic pathways?

Answer 41

Reactions linked together in a chain (or web)
–begin with an initial substrate and end with a final product, with many enzymatic steps along the way

Coupling a bunch of reactions together = metabolic pathway

Question 42

Are few metabolic pathways branched or linear?

Answer 42

Few are linear

Most include branches where several products can be produced

Question 43

End product inhibition

Answer 43

Branch points are often inhibited by a form of negative feedback in which one of the final products inhibits the branch point enzyme

Question 44

Allosteric Inhibition

Answer 44

The product binds to the enzyme at a location away from the active site and changes the 3D conformation of the enzyme
–influencing activity, but influencing it away from the active site (still gives us structural changes)

Question 45

End product in inhibition keeps the final product from ____.

Answer 45

Accumulating

Question 46

Endergonic Reactions

Answer 46

Chemical reactions that require an input of energy

Products contain more free energy than the reactants (trap some energy in products)

ex: glucose –> glycogen (synthesis reaction)…stored energy in our cells

Question 47

Exergonic Reactions

Answer 47

Releasing energy

Chemical reactions that produce energy. Products will have less free energy than the reactants.

Energy is used to make ATP for use in other endergonic reactions in the body.

ex: breaking glucose down into CO2 and water produces energy

Question 48

Coupled Reactions

Answer 48

Energy from the environment (food) is broken down in exergonic reactions to drive the endergonic reactions in our bodies.

Energy must be stored in a usable form, ATP

Use exergonic reactions to drive endergonic reactions