Chapter 4

Question 1

What are enzymes?

Answer 1

biological catalysts that increase rate of chemical reactions
- proteins

Question 2

How do enzymes work?

Answer 2

lowers activation energy required for a reaction to proceed

Question 3

What is the structure of an enzyme?

Answer 3

3D shapes with pockets (active sites) where substrates fit

Question 4

What is the mechanism of enzymes?

Answer 4

• substrate fits in active sites
• enzyme-substrate complex forms
• reaction occurs
• products dissociate
• enzyme is unaltered

Question 5

What do phosphatases do?

Answer 5

remove phosphates

Question 6

What do kinases do?

Answer 6

adds phosphate groups

Question 7

What are cofactors?

Answer 7

metal ions necessary for normal activity of enzymes
- Ca++, Mg++, Mn++, Cu++

Question 8

What are coenzymes?

Answer 8

derived from vitamins to transport small molecules needed by enzymes
- taxi cabs

Question 9

How do cofactors work?

Answer 9

when it binds, it changes conformation of active site
- aids in temporary bonding between enzyme and substrates

Question 10

What is the relationship between product formation and substrate concentration?

Answer 10

directly related
- As product formation increases, substrate concentration increases
UNTIL reaction rate reaches a plateau

Question 11

Why does substrate concentration plateau?

Answer 11

enzyme is saturated

Question 12

What is the law of mass action?

Answer 12

reaction flows from higher concentration to lower concentration

Question 13

What are metabolic pathways?

Answer 13

sequences of enzymatic reactions that begin with initial substrate and progress through intermediates and end with a final product

Question 14

What is end-product inhibition?

Answer 14

when 1 product inhibits activity of the branch-point enzyme
- prevents final product accumulation
- causes reaction to favor alternate pathway

Question 15

How does end-product inhibition occur?

Answer 15

by allosteric inhibition
- product binds to enzyme causing it to change to an inactive shape

Question 16

When enzymes are produced, are they inactive or active?

Answer 16

inactive

Question 17

How are enzymes activated/inactivated?

Answer 17

activated: phosphorylation or ligands (2nd messengers)
inactivated: dephosphorylated

Question 18

How are receptors and enzymes related?

Answer 18

receptors = ligands (binding site)
enzymes = substrates (active site)
- both need to be regulated/controlled to manage reactions and procedures

Question 19

What are the 4 types of protein regulation?

Answer 19

• covalent modification
• allosteric modulators
• end-product inhibition
• competitive inhibition

Question 20

What is covalent modification? What response does it provide?

Answer 20

• phosphorylation of receptors or enzymes
• active/inactive response

Question 21

What are allosteric modulators? What is the response?

Answer 21

• cofactors bind to site other than active site
• can enable or inhibit reaction

Question 22

What is end-product inhibition?

Answer 22

special case of allosteric inhibition
- product binds to allosteric site of enzyme in earlier part

Question 23

What is competitive inhibition? What is the response?

Answer 23

binds to active site on enzyme or binding site of receptor
- inhibits activity

Question 24

What is bioenergetics?

Answer 24

flow of energy in living systems

Question 25

What is the first law of thermodynamics?

Answer 25

energy can be transformed but not created or destroyed

Question 26

What is the second law of thermodynamics?

Answer 26

energy transformations increase entropy
- disorganization/chaos of a system
- all living organisms require continued input of energy

Question 27

What is needed for work?

Answer 27

free energy
- systems go from higher free energy to lower free energy

Question 28

What are endergonic reactions?

Answer 28

requires input of energy to proceed
- products have more free energy than reactants

Question 29

What are exergonic reactions?

Answer 29

release energy as they proceed
- products contain less free energy than reactants

Question 30

What are coupled reactions?

Answer 30

endergonic + exergonic reactions together
- exergonic breaks down ATP

Question 31

What is a reducing agent? What is the action called?

Answer 31

donates electrons
- oxidizes

Question 32

What is an oxidizing agent? What is the agent called?

Answer 32

accepts electrons
- reduced

Question 33

NAD+ + 2H -> NADH + H+
In the equation above, what is the reduced form?

Answer 33

NADH is reduced
- more negative
(NAD+ = +1, NADH = 0)

Question 34

What is another example of a coupled reaction? What does it involve?

Answer 34

reduction + oxidation
- transfer of H’s instead of electrons
- coenzymes (NAD+ and FAD)