Enzymes for Exam 1

Question 1

Meta-Stable State

Answer 1

Reaction is spontaneous, but needs energy (activation energy) to break down

Question 2

Reaction Progression

Answer 2

• Overcome Activation Energy
• Transition State
• Products

Question 3

Heat’s Effect on Reaction Rate

Answer 3

Heat advances reaction of molecules…move toward activation energy

Question 4

High Activation Energy Importance

Answer 4

The high Ea is important for life, w/o it, all reactions would proceed quickly to equilibrium

Question 5

To overcome activation energy:

Answer 5

• Increase average content of all molecules

- Lower activation energy

Question 6

Catalysts

Answer 6

• Substance which speeds up a reaction but is chemically unchanged at the end of the reaction
• Catalysts ONLY CHANGE SPEED of reaction
• Usually metals
• Catalysts remain unchanged after reaction

Question 7

Inorganic Catalysts

Answer 7

• Do not have specificity, catalyzing anything it can

- RARELY used by biological systems

Question 8

Organic Catalysts (Enzymes)

Answer 8

HAVE GREAT SPECIFICITY, have very specific substrates it will bind to

Question 9

Active Site

Answer 9

• Region of enzyme that binds to the substrates and carries out the reaction
• Amino acids here are brought together with Tertiary and Quaternary structure
• All enzymes have active sites
• Some contain prosthetic groups
• Tend to be very small

Question 10

Prosthetic Group

Answer 10

Atoms which are bound (metal cofactor or coenzyme) to the enzyme which aids the catalyst

Question 11

-ase

Answer 11

Enzyme

Question 12

Six Classes of Enzymes

Answer 12

1) Oxidoreductases (oxidation-reduction reactions)
2) Transferases (Transfer of function groups from one molecule to another)
3) Hydrolases (Hydrolytic cleavage of one molecule into two molecules)
4) Lyases (Removal of a group from, or addition of a group to, a molecule with rearrangement of electrons)
5) Isomerases (Movement of a functional group within a molecule)
6) Ligases (Joining of two molecules to form a single molecule)

Question 13

Temperature and Enzymes

Answer 13

Increase in temp greatly increases reaction rate to a certain point, then causes it to fall quickly

Question 14

pH and Enzymes

Answer 14

• Not all enzymes share optimum pH

- Enzymes are pH specific

Question 15

Enzyme Sensitivity to Factors

Answer 15

• Inhibitors: bind to an enzyme and prevent the substrate from binding to the active site
• Activators: bind to an enzyme and increase its catalytic activity
• Alternative substrates create competition
• Ionic strength affects H-bonding and enzyme/substrate interaction

Question 16

Substrate Binding

Answer 16

• Binding (initial contact) depends on random collision
• One substrate is in groove of active site, it is bound to the specific amino acids
• Binding involves H-bonds and/or ionic bonds
• Bond strength between 3 - 12 kcal/mol

Question 17

Induced Fit

Answer 17

Active site of enzyme rearranges to fit substrate

Question 18

Suicide Inhibitor

Answer 18

Substrate permanently bonds (usually to active site) to enzyme, rendering it useless

Question 19

High Affinity Bonding vs Low Affinity Bonding

Answer 19

• High: Substrate is almost always bound

- Low: Substrate is bound as little as possible

Question 20

Lock and Key Model for Enzymes

Answer 20

• Incorrect

- Does not explain temp, pH, inhibitor, etc… sensitivity

Question 21

Induced-Fit Model

Answer 21

• Flexible active site
• Binding of substrate to active site induces a conformation change in the enzyme and substrate
• Stabilizes the transition state
• Substrates move from meta-stable to transition states

Question 22

Substrate Activiation

Answer 22

• Enzyme conformation distorts bonds of substrate
• Enzyme may accept/donate protons, increasing reactivity of substrate by altering charge
• Enzyme may accept/donate electrons, temporarily forming covalent bond with substrate

Question 23

Enzyme Kinetics

Answer 23

• Investigation of how enzymes bind substrates and turn them into products
• Increased reaction rate can be cause by increased concentration of substrate or enzyme

Question 24

Reaction Rate

Answer 24

product formed / minute

Question 25

Substrate Saturation Curve

Answer 25

Curve from set of experiments saying that as substrate concentration increases, the reaction rate increases

Question 26

Vmax

Answer 26

Vmax means all enzymes are being used

Question 27

Km

Answer 27

• Km is the substrate concentration that results in 1/2 Vmax
• Low Km means HIGH AFFINITY of enzyme for substrate
• High Km means LOW AFFINITY of enzyme for substrate

Question 28

Lineweaver-Burk Double-Reciprocal Plot

Answer 28

• Yaxis is 1/v
• Xaxis is 1/[S]
• Xintercept is -1/Km
• Yintercept is 1/Vmax
• Slope is Km/Vmax

Question 29

Reversible Enzyme Inhibitors

Answer 29

• Bind to enzyme in a noncovalent, dissociable manner

- Two most common are Competitive and Noncompetitive

Question 30

Competitive Inhibitors

Answer 30

Bind to the active site of the enzyme (compete with substrate for binding) and reduce the activity of the enzyme

Question 31

Noncompetitive Inhibitors

Answer 31

Bind to the enzyme surface at location other than the active site, causing a conformational change in enzyme causing active site to act more slowly or not at all