Energy and Enzymes

Question 1

How do you know if a reaction has positive or negative enthalpy?

Answer 1

• exothermic: negative because products have less potential energy than reactants)
• endothermic: positive because heat is taken up

Question 2

What is enthalpy and what is its letter?

Answer 2

• total energy in a molecule
• H

Question 3

What are the characteristics of enthalpy?

Answer 3

1. potential energy of the molecule
2. effect of the molecule on surrounding pressure and volume

Question 4

What is entropy and what is its letter?

Answer 4

• amount of disorder OR energy distribution/dispersal
• S

Question 5

If entropy is positive…

Answer 5

products are less ordered than reactants

Question 6

If entropy is negative…

Answer 6

products are more ordered than reactants

Question 7

What is Gibbs Free Energy and what is its letter?

Answer 7

• total energy in a rxn available to do work
• G

Question 8

If delta G is negative, the reaction is…

Answer 8

exergonic and spontaneous

Question 9

If delta G is positive, the reaction is…

Answer 9

endergonic and nonspontaneous

Question 10

If delta G = 0, the reaction is…

Answer 10

at equilibrium

Question 11

Gibbs Free Energy does not require….

Answer 11

the addition of external energy

Question 12

How do we determine delta G?

Answer 12

delta G = delta H - T x delta S

Question 13

As temperature increases…

Answer 13

rate and concentration also increase

Question 14

Nonspontaneous rxns are driven using…

Answer 14

chemical energy

Question 15

What is energetic coupling?

Answer 15

free energy released from an exergonic rxn drives an endergonic rxn

Question 16

What are the two ways energetic coupling occurs?

Answer 16

1. transfer of electrons
2. transfer of a phosphate group

Question 17

What is OIL RIG?

Answer 17

• Oxidation Is Loss
• Reduction Is Gain

Question 18

O2 is almost always the ______ agent EXCEPT with _______.

Answer 18

oxidizing
fluorine

Question 19

ATP transfers energy via ___________.

Answer 19

phosphate groups

Question 20

Energy is _________ when ATP is __________.

Answer 20

released; hydrolyzed

Question 21

Energy coupling uses _______ to rip off ____________.

Answer 21

ATP; phosphate groups

Question 22

On a graph, an endergonic rxn starts….

Answer 22

low to high

Question 23

On a graph, an exergonic rxn starts…

Answer 23

high to low

Question 24

What is a transition state?

Answer 24

intermediate point between breaking old bonds and forming new bonds (very unstable w/ very high energy)

Question 25

What is activation energy?

Answer 25

minimum energy required to form the transition state

Question 26

Enzymes are biological ________.

Answer 26

catalysts

Question 27

What is a catalyst?

Answer 27

speeds up a chemical rxn without being used up or changed in the process

Question 28

Reactants are also known as _______.

Answer 28

substrates

Question 29

Substrates bind a react in an __________.

Answer 29

active site

Question 30

What are the steps of an enzyme catalyzed rxn?

Answer 30

1. initiation: enzymes bring substrates together in a precise orientation
2. transition state facilitation: enzymes lower Ea by stabilizing transition state
3. termination: products have a low affinity for the active site and are released

Question 31

How do active sites hold substrates in precise orientation?

Answer 31

hydrogen bonds or other weak interactions

Question 32

What is induced fit?

Answer 32

upon binding substrates, enzymes change conformation (shape)

Question 33

Enzymes are able to stabilize…

Answer 33

transition states

Question 34

What do enzymes NOT change?

Answer 34

delta G and the energies of the reactants/products

Question 35

Enzymes can also work with…?

Answer 35

cofactors, coenzymes, and prosthetic groups

Question 36

What are cofactors?

Answer 36

metal ions (Zn2+, Mg 2+, Fe 2+)

Question 37

What are coenzymes?

Answer 37

organic molecules (NAD+, FAD, coenzyme-A)

Question 38

What are prosthetic groups?

Answer 38

atoms or molecules that are permanently attached to proteins

Question 39

What are some examples of prosthetic groups?

Answer 39

1. heme groups (hemoglobin- carry oxygen)
2. Retinal (vitamin A-basis of vision)

Question 40

At extreme conditions, what happens to enzymes?

Answer 40

denaturation

Question 41

What determines an enzyme’s optimal temp and pH?

Answer 41

location (environment helps optimize)

Question 42

Why does a curve eventually reach a plateau?

Answer 42

the enzymes run out/max out

Question 43

How can you increase the max speed of a rxn?

Answer 43

increase amount of enzymes

Question 44

How are enzymes regulated?

Answer 44

covalent modification (long-term)

Question 45

What is covalent modification?

Answer 45

1. cleavage of peptide bonds: can convert enzyme into its functional form (proenzyme)
2. addition of a phosphate group: enzyme changes shape, which changes function

Question 46

How are enzymes regulated (reversible)?

Answer 46

noncovalent interactions

Question 47

What are noncovalent interaction?

Answer 47

1. competitive inhibition
2. allosteric inhibition (noncompetitive)
3. allosteric activation

Question 48

What is competitive inhibition?

Answer 48

• other molecules compete for active site w/ substrate

Question 49

What is allosteric inhibition?

Answer 49

• “different structure”
• inhibitor binds to a different site on the enzyme

Question 50

What is allosteric activation?

Answer 50

makes active site more accessible to substrate

Question 51

What are catabolic pathways?

Answer 51

break down molecules, typically releasing energy (ex cellular respiration)

Question 52

What are anabolic pathways?

Answer 52

synthesize molecules, typically requiring energy (ex photosynthesis)

Question 53

How are metabolic pathways inhibited?

Answer 53

feedback inhibition

Question 54

What is feedback inhibition?

Answer 54

• product of a metabolic pathway inhibits an enzyme earlier in the pathway
• acts in reverse
• prevents the enzyme from starting