Lecture 2 - Quiz 1

Question 1

What are enzymes?

Answer 1

Proteins (except peptidyl transferase) that act as biocatalysts to increase the rate of a chemical reaction but is not changed in the reaction

Question 2

What uses enzymes to assist in diagnosis?

Answer 2

Diagnostic enzymology

Question 3

How much faster is a catalyzed reaction?

Answer 3

10^4-10^16

Question 4

What does the enzyme work upon and what does is the result?

Answer 4

substrate, products

Question 5

What does the active site of the enzyme contain?

Answer 5

The substrate binding site and catalytic site

Question 6

What does the substrate binding site produce?

Answer 6

substrate specficity

Question 7

What does the catalytic site produce?

Answer 7

Reaction specificity

Question 8

What is the allosteric site?

Answer 8

An additional site used for regulation of other sites and is not at the active site - binding here can cause conformational change

Question 9

What are isoenzymes?

Answer 9

Isoenzymes are enzymes that catalyze the same reaction but differ slightly in amino acid composition since they arise from different genetic loci

Question 10

Why are isoenzymes helpful diagnostically?

Answer 10

Different organs can have different proportions of isoenzymes so checking levels in blood can show damage to a specific tissue type - isoenzymes also have different charge and can be electrophoretically separated

Question 11

What is the creatine kinase reaction?

Answer 11

Creatine + ATP –CK–> creatine-phosphate + ADP

Question 12

What is the makeup of creatine kinase (CK)?

Answer 12

dimer with M subunit (muscle) and B subunit (brain) and highest concentration found in muscle

Question 13

What is the composition of brain (bowel) CK isoenzymes?

Answer 13

CK1 BB

Question 14

`What is the composition of myocardium CK isoenzymes and used to track heart attacks?

Answer 14

CK2 MB

Question 15

What is the composition of skeletal muscle and some myocardium CK isoenzymes?

Answer 15

CK3 MM

Question 16

Which CK isoenzyme has the most positive and most negative charge?

Answer 16

positive = MM, negative = BB

Question 17

What is an active enzyme?

Answer 17

The protein and all of its other factors

Question 18

What is an apoenzyme?

Answer 18

Just the protein part of an enzyme

Question 19

What are cofactors?

Answer 19

Small inorganic molecules that participate in the reaction - metal ions like iron, zinc, cobalt, calcium, copper, magnesium

Question 20

What is a holoenzyme?

Answer 20

The apoenzyme + coenzyme - the functionally active enzyme

Question 21

What are coenzymes?

Answer 21

Small organic molecules that participate in the reaction like water soluble vitamins

Question 22

Where do cofactors and coenzymes bind?

Answer 22

close to or at the active site by apolar interaction with protein, covalent bonding or coordinative binding

Question 23

How do enzymes work as a reaction?

Answer 23

An enzyme takes the substrate and converts it to products
S P
S1 + S2 P1 + P2
S P1 + P2

Question 24

Do enzymes change the equilibrium of a reaction?

Answer 24

No - they only accelerate the speed by lowering activation energy

Question 25

How could you increase the rate of a chemical reaction?

Answer 25

Temperature

Question 26

What are international units (IU) of enzyme activity?

Answer 26

umol S/min - either umol of substrate lost or product formed

Question 27

What are Katal units of enzyme activity?

Answer 27

mol S/s - loss of a mol of a substrate per second

Question 28

What is specific activity of an enzyme?

Answer 28

activity divided by the mass of the protein - specific activity increases as the enzyme is purified

Question 29

What is the catalytic constant or turnover number?

Answer 29

mol P/s/mol of enzyme how fast does it convert? Allows comparison of relative catalytic activity between enzymes -- normalized by molar concentration

Question 30

What is the induced fit model?

Answer 30

A slight conformational change makes a tighter fit

Question 31

What are some serine proteinases?

Answer 31

Trypsin, chymotrypsin, elastase are processed this way by breaking serine bond at the catalytic site to convert and break peptide bond - R groups cause substrate specificity - interact with serine residue

Question 32

What is the enzyme kinetics reaction?

Answer 32

E + S ES --> E + P

Question 33

When is V0?

Answer 33

When less than 5% of product was made

Question 34

What is velocity?

Answer 34

The slope of the line demonstrating the change in concentration of substrate or product per unit time

Question 35

What is Vmax?

Answer 35

When all enzyme molecules are saturated as S concentration is increased - usually theoretical and not reached

Question 36

How does S and P change over time during an enzymatic reaction?

Answer 36

Indirectly proportional - as s decrease, P increases

Question 37

How does ES and E change over time during an enzyme reaction?

Answer 37

Substrate saturates the enzyme - ES slightly increases and then plateaus (in steady state) and E slightly decreases and plateaus

Question 38

What is the michaelis-menten constant?

Answer 38

Km = {k2 + k3} / k1

Question 39

What is v0 equation in michaelis menten?

Answer 39

Vo = vmax x [s] / km + [s]

Question 40

What does Km demonstrate?

Answer 40

the substrate concentration at which the enzyme works with half of it's Vmax

Question 41

What is the relationship between Km and binding efficiency

Answer 41

The lower the Km the more efficient the enzyme is in binding the substrate = higher affinity

Question 42

How do you make a Lineweaver-Burk plot?

Answer 42

1/V0 - where slope = Km/Vmax - y intercept is 1/Vmax and x intercept is -1/Km

Question 43

What kind of curve does MM and LineBurk give you?

Answer 43

MM gives hyperbolic curve, LineBurk gives linear

Question 44

What can influence catalytic activity?

Answer 44

pH - effect charge on side chain and binding - charge on enzyme and cause conformational change Ionic strength - interfere with charges, change conformation Temperature - starts to denature

Question 45

What is enzymatic rate determined by?

Answer 45

Availability of substrate/cofactor

Question 46

What controls the rate of synthesis of enzymes and their turnover?

Answer 46

Genetic control

Question 47

How are enzymes modified covalently?

Answer 47

Irreversible covalent modifications by zymogen activation (by removal by proteolytic action) or inactivation (by chemically modifying the active center by routes like poison) or reversible covalent modifications like attachment of chemical group to enzyme (like phosphorylation that can be taken off or put on)

Question 48

How are enzymes modified by non-covalent modification?

Answer 48

inhibition by binding specific molecules to the active center of the enzyme either competitively or noncompetitively

Question 49

What is competitive inhibition?

Answer 49

Inhibitors are structurally similar to substrate and bind at substrate binding site

Question 50

What removes a competitive inhibitor?

Answer 50

Increasing substate concentration - cause apparent increase in Km

Question 51

What is noncompetitive inhibition?

Answer 51

When an inhibitor binds at the catalytic site

Question 52

What does a noncompetitive inhibitor binding result in?

Answer 52

Decreased Vmax - Km does not change

Question 53

What are allosteric enzymes regulated by?

Answer 53

Conformational change

Question 54

What kind of line do allosteric enzymes produce?

Answer 54

Sigmoidal, positive move curve toward higher velocity, negative lower, and positive move curve toward lower [S] in K class and negative move curve toward higher [S] in K class