Enzymes - w3

Question 1

What is the job of enzymes?

Answer 1

lowers the activation energy (but doesn’t change net energy for the reaction)

Question 2

What are the four catalytic strategies of enzymes?

Answer 2

proximity and orientation of substrates, metal ions, acid-base catalysis, covalent catalysis

Question 3

Which catalytic strategy acts as electron-attaching groups?

Answer 3

metal ions (zinc and acetaldehyde)

Question 4

Which catalytic strategy has active sites that may contain residues which can cause hydrogen ion transfer?

Answer 4

histidine, chymotrypsin

Question 5

What is the optimum temperature for most human enzymes?

Answer 5

35-40 C

Question 6

What is the optimum pH for enzymes?

Answer 6

varies depending on the enzyme

Question 7

What is the clinical way to classify enzymes?

Answer 7

systematic naming system and four-digit classification number

Question 8

What are the two main types of cofactors?

Answer 8

inorganic (metal ions) and organic/co-enzymes (vitamins)

Question 9

What is the lock and key model type of binding?

Answer 9

complementarity between enzyme and substrate by hydrogen bonds or electrostatic interactions

Question 10

What is the induced-fit model of bonding?

Answer 10

binding induces conformational change in the active site

Question 11

What do we call the intermediate change at binding, and has unstable high-energy?

Answer 11

transition state complex

Question 12

Which type of enzymes catalyzes redox reactions?

Answer 12

oxidoreductase

Question 13

Which type of enzymes catalyzes the transfer of C, N, or P-containing groups?

Answer 13

transferase

Question 14

Which type of enzymes catalyzes the cleavage of bonds by the addition of water (+ H20 ->)

Answer 14

hydrolase

Question 15

What type of enzymes catalyzes the SPLITTING of C-C,S,N bonds?

Answer 15

lyase/synthase (decarboxylase)

Question 16

What type of enzymes catalyzes the rearrangement of optical or geometric isomers?

Answer 16

isomerase

Question 17

What type of enzymes catalyzes the FORMATION of bonds between carbon to O,S,N using ATP?

Answer 17

ligase

Question 18

What does the rate of formation of the substrate dependent on?

Answer 18

the concentration of the substrate

Question 19

What is the constant concentration of the enzyme-substrate (ES)?

Answer 19

steady-state concentration

Question 20

What is the rate-limiting step of enzyme kinetics?

Answer 20

decomposition of the ES complex into E + P

Question 21

What is the Km formula?

Answer 21

[E] [S] / [ES]

Question 22

Why is Km a first order reaction when [S] is lower than Km?

Answer 22

the V (velocity) of the reaction is proportional to the substrate concentration

Question 23

What do we call the straight line obtained if 1/Vo is plotted against 1/[S]?

Answer 23

Lineweaver-Burk plot (Km/Vmax)

Question 24

What is the use of the Lineweaver-Burk plot?

Answer 24

to determine the mechanism of action of enzyme inhibitors

Question 25

What are the two reversible enzyme inhibitors?

Answer 25

competitive and noncompetitive

Question 26

What is enzyme competitive inhibition?

Answer 26

inhibitor binds to the SAME site as the substrate (analogue)

Question 27

How can we reverse the effect of competitive inhibition?

Answer 27

increasing substrate concentration

Question 28

How does competitive inhibition affect enzyme kinetics?

Answer 28

increases Km, but doesn't affect Vmax

Question 29

What is the enzyme in the liver that methanol (bad) and ethanol (good) compete for?

Answer 29

alcohol dehydrogenase

Question 30

What is enzyme non-competitive inhibition?

Answer 30

inhibitor binds to a different site on the enzyme and doesn't interfere with substrate binding?

Question 31

How does non-competitive inhibition affect enzyme kinetics?

Answer 31

Km remains unchanged, Vmax is reduced

Question 32

What is the inhibitor of angiotensin converting enzyme, reducing high blood pressure?

Answer 32

captopril

Question 33

What are the three irreversible enzyme inhibitors?

Answer 33

covalent/suicide inhibitors / transition state analogues / heavy metal toxicity

Question 34

What do covalent/suicide inhibitors do?

Answer 34

form strong bonds with functional groups in the catalytic active site

Question 35

What type of compounds cause acetylcholinesterase inhibition?

Answer 35

organophosphorus compounds (malathion)

Question 36

What do transition state analogues do?

Answer 36

tightly binds to the active site, mimicking the transition state -> inhibiting the enzyme from binding to its normal substrate

Question 37

How does penicillin act as a transition state analogue?

Answer 37

it inhibits bacterial enzyme from crosslinking the bacterial cell wall peptidoglycan strands

Question 38

What is the transition state analogue part of penicilin?

Answer 38

its lactam ring (binds with a serine residue at the active site

Question 39

How can heavy metals inhibit enzyme reactions?

Answer 39

they bind to a functional group in an enzyme (lead and mercury inhibit -SH groups)

Question 40

What are enzymes that are regulated by effectors and bind to sites other than the active site?

Answer 40

allosteric enzymes

Question 41

What kind of bonds do allosteric enzymes make with its sites?

Answer 41

non-covalent

Question 42

What kind of curve does an allosteric enzyme make?

Answer 42

sigmoid (not Km curve)

Question 43

What is the main purpose of allosteric enzymes?

Answer 43

show positive cooperativity (binding to one subunit promotes binding to another subunit)

Question 44

What is the T (tense) conformation of allosteric enzymes?

Answer 44

lowers affinity for binding to inhibitors

Question 45

What is the R (relaxed) conformation of allosteric enzymes?

Answer 45

raises affinity for binding to activators

Question 46

What catalyzes phosphorylation?

Answer 46

protein kinases (uses ATP to get a phosphate)

Question 47

Which enzymes cleave/split phosphate groups (dephosphorylation)?

Answer 47

phospho-protein phosphatases

Question 48

During cell death where do their intracellular enzymes get secreted into?

Answer 48

the blood!

Question 49

What are normal blood enzymes called?

Answer 49

zymogens (precursors for coagulation)

Question 50

Liver damage increases the count of what enzyme in the blood?

Answer 50

alanine aminotransferase

Question 51

Acute pancreatitis increases the count of what enzymes in the blood?

Answer 51

amylase and lipase

Question 52

The presence of what enzyme can be used to diagnose myocardial infarctions?

Answer 52

creatine kinase