Mol Lecture #27

Question 1

Activation energy:

Answer 1

• reactions often require a small input of energy to start even with a -ΔG.
• AE is the small input of energy required to go from reactants to products.

Question 2

Enzymes

Answer 2

• We use catalysts in systems where we cannot use heat to overcome the activation energy (like cells).
• Catalysts are chemical agents that accelerate the rate of a reaction by reducing the activation energy

Question 3

Most common enzymes in cells

Answer 3

• protein enzymes
• also ribozymes

Question 4

When using enzymes rate is…

Answer 4

• altered but free energy (overall- net) of the reaction is not.

Question 5

Substrate:

Answer 5

• the reactant(s) bound by an enzyme in a region called the active site.

Question 6

Enzyme specificity

Answer 6

• enzymes can usually catalyze 1 or a few closely related reactions (in 1 active site)

Question 7

Enzyme binding

Answer 7

• Enzymes will bind the substrate(s), accelerate the reaction (altering activation energy), and be released unchanged. (Therefore, the enzyme can continue to catalyze with new iterations of substrate molecules)

Question 8

Co-factors

Answer 8

• Some enzymes use cofactors, which are non-protein components that help with catalysis.

Question 9

Active site:

Answer 9

• identity of shapes, specific amino acid side-chains (allowing it to interact and perform reactions) are important in the active site.

Question 10

2 rules of enzymes:

Answer 10

• Do not change thermodynamic properties of a rxn
• Are not consumed or modified in reaction

Question 11

Transition Sites

Answer 11

• Enzymes lower the activation energy by stabilizing energetically unfavorable transition states.

Question 12

Factors that Affect Enzyme Activity

Answer 12

a) pH
b) Temperature
c) Concentrations of substrate
d) Substrate concentration
e) Activators and inhibitors

Question 13

Activators and inhibitors

Answer 13

• Important for how you can poison enzymes and how cells regulate enzymes activity with their own activity

Question 14

2 ways to inhibit an enzyme:

Answer 14

• Competitive inhibition mechanism
• Noncompetitive inhibition

Question 15

competitive inhibition mechanism:

Answer 15

• inhibitors compete directly with the substrate for binding to the active site. Highly sensitive to substrate concentration ([ ]).

Question 16

Noncompetitive inhibition:

Answer 16

• Inhibitors can bind to enzyme somewhere other than the active site. Insensitive to substrate concentration ([ ]).
  –> Subtly changing the fold so that the active site is not so open to the substrate.

Question 17

Allosteric Regulation

Answer 17

• Regulation of an enzyme by binding of a regulatory molecule to a site other than the active site.
  → Changing enzyme function by causing conformation shifts in the overall fold of the protein.

Question 18

Feedback inhibition

Answer 18

• Isoleucine inhibits through the allosteric mechanism and halts its own activity.
• The product of this pathway feeds back into its own production.

Question 19

Chemical Modification

Answer 19

• Chemical modification can alter enzyme activity in a manner similar to allosteric regulation.
  →One way: Phosphorylating a protein to produce an active enzyme that can interact.

Question 20

Carbon cycle and energy

Answer 20

• Photosynthesis: through the process we release oxygen and produce glucose
• Cellular respiration: requires oxygen, give off the same inputs for photosynthesis and charge up ADP into ATP.