Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Cellular Composition > Enzymes > Flashcards

Enzymes Flashcards

1
Q

What is Kcat?

A

Kcat is equivalent to the number of substrate molecules a single molecule of enzyme can bind and convert to product every second (when substrate is unlimited)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Enzyme activity can be measured by determining one of which 3 things?

A
  • rate of production of product
  • rate of loss of substrate
  • rate of production of loss or cofactor involved in the reaction
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is an enzyme activity unit?

A

The amount of enzyme which transforms 1 micromole of substrate per minute at 25°C

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the specific activity of an enzyme?

A

The number of enzyme units per milligram of protein

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the function of triose phosphate isomerase?

A

Catalyses the interconversion of DHAP and G3P in glycolysis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the units of Km?

A

Same as the units of substrate concentration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is on the y axis of a Lineweaver-Burk plot?

A

1/V (rate of reaction)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is on the x axis of a Lineweaver-Burk plot?

A

1/[Substrate]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the y intercept on a Lineweaver-Burk plot?

A

1/Vmax

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What does the x intercept on a Lineweaver-Burk plot represent?

A

-1/Km

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is Vmax?

A

Rate of reaction when an enzyme is saturated with substrate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is Km?

A

The concentration of substrate which permits the enzyme to achieve half Vmax

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Why is enzyme inhibition important biologically?

A

Acts as a mechanism for controlling enzyme catalysed reactions in vivo

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How do drugs inhibit HIV protease?

A

They mimick the natural peptide substrate and blocks the active site

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Does prescence of a competitive inhibitor affect Km?

A

Yes, it increases it

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Does prescence of a competitive inhibitor affect Vmax?

A

No

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Does prescence of a non-competitive inhibitor affect Vmax?

A

Yes, it reduces it

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Does prescence of a non-competitive inhibitor affect Km?

A

No

19
Q

Give an example of an inhibitor used to regulate enzyme activity

A

Pancreatic trypsin inhibitor

20
Q

What is the structure of COX enzymes?

A

Dimer with haem group at active site

21
Q

How can competitive and non-competitive inhibitors be easily distinguished kinetically?

A
  • Compare the Lineweaver-Burk plot for reaction in prescence and abscence of inhibitor
    *
22
Q

Outline 6 main contributions to the catalytic activity of enzymes

A
  • Enhanced reactivityof side chains in amino acids in active site
  • Proximity and orientation effects
  • Acid-base catalysis
  • Covalent catalysis
  • Stabilisation of transition state
  • Utilisation of metal ions in catalysis
23
Q

How is proximity and orientation important in the catalytic activity of enzymes?

A
  • binding of substrate orients it with respect to catalytic groups of enzyme (esp. important for stereospecificity)
  • electrostatic steering of substrate towards active site
24
Q

What is the function of L-lactate dehydrogenase?

A

Stereospecific conversion of pyruvate to L-lactate under anaerobic conditions

25
Q

What is the structure of L-lactate dehydrogenase?

A

Tetrameric enzyme

26
Q

What cofactor is required by L-lactate dehydrogenase?

A

NADH

27
Q

Outline the mechanism of L-lactate dehydrogenase

A
  • Ternary complex formed
  • Hydride transfer from NADH
  • Protonation of pyruvate C=O by His
  • Stereospecific L-lactate produced
  • Active site loop closure
28
Q

How does the stereospecificty of L-lactate dehydrogenase arise?

A

Pyruvate binds in the active site in a very specific orientation due to groups in side chain of active site

29
Q

Which 3 amino acids are involved in the catalytic triad in serine proteases?

A
  • Serine
  • Histidine
  • Aspartate
30
Q

What kind of amino acids can the chymotrypsin specificity pocket accomodate?

A

Large hydrophobic amino acids

31
Q

What kind of amino acids can the trypsin specificity pocket bind to?

A

Positively charged amino acids due to a negative charge in the pocket

32
Q

How does L-lactate hydrogenase have stereospecificity?

A

Pyruvate is held in the active site in such an orientation hydride can only enter from one side

33
Q

Name an example of a serine protease

A

Chymotrypsin

34
Q

What is the evidence for the mechanism of serine proteases?

A
  • The rate of the reaction seems to occur in 2 phases which suggests a covalent intermediate is formed
  • Chymotrypsin is inactivated by DIPF which specifically reacts with ser195 whilst the rest of the serines do not, suggesting that ser195 has enhanced reactivity
35
Q

What is the function of the oxyanion hole?

A

Stabilises the negative charge on the oxygen as the NH groups point downwards and stablise the O-

36
Q

How is chymotrypsin activated?

A

By proteolysis of trypsin

37
Q

How does trypsin activate chymotrypsin?

A
  • In the preform of chymotrypsin the active site is strained and not fully formed
  • Trypsin cleaves a peptide bond which produces a working active site
38
Q

What activates all serine proteases?

A

Trypsin

39
Q

What activates trypsin?

A

Enteropeptidase

40
Q

What inactivates trypsin?

A

Pancreatic trypsin inhibitor

41
Q

Give an example of a serine protease which was formed due to convergent evolution

A

Carboxypeptidase II

42
Q

Outline how divergent evolution has led to different forms of serine proteases

A
  • ancient gene coding for the catalytic triad is duplicated through a gene duplication process
  • there are now 2 genes coding for the same enzyme
  • this allows one to mutate whilst the other maintains function
43
Q

Why is it important to measure the initial rate of an enzyme catalysed reaction?

A

Rate of reaction begins to tail off, especially at high concentrations of enzyme

Cellular Composition (15 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions