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Medical Biochemistry > 7-Enzymes > Flashcards

7-Enzymes Flashcards

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USMLE® Step 1 flashcards
1
Q

In which classes are enzymes divided?

A
  1. Oxidoreductases
  2. Transferases
  3. Hydrolases
  4. Lyases
  5. Isomerases
  6. Ligases
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2
Q

What Oxidoreductases do?

A

Oxidoreductases catalyze oxidation/reduction reactions; transfer of H and O atoms or electrons from one substance to another

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3
Q

What Transferases do?

A

Transferases catalyze the transfer of functional groups from one substance to another

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4
Q

What Hydrolases do?

A

Hydrolases catalyze formation of two products from a

substrate by hydrolysis (splitting using water)

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5
Q

What Lyases do?

A

Lyases catalyze non-hydrolytic addition or removal of
groups from substrates
C-C, C-N, C-O or C-S bonds may be cleaved

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6
Q

What Isomerases do?

A

Isomerases catalyze intramolecule rearrangement,

i.e. isomerization changes within a single molecule

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7
Q

What Ligases do?

A

Ligases join together two molecules by synthesis of
new C-O, C-S, C-N or C-C bonds with simultaneous
breakdown of ATP

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8
Q

What a Cofactor is?

A

Cofactor = a non-protein substance that is

necessary for the activity of an enzyme

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9
Q

What a co-enzymes are?

A

Organic cofactors that are not firmly attached to the enzyme

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10
Q

What prosthetic groups are?

A

Organic cofactors that are firmly attached to the enzyme

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11
Q

What isoenzymes are?

A

Describes enzymes with different protein structures that catalyse the same reaction

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12
Q

What Ezyme Kinetics are and which is its purpose and in which factors does this purpose depend on?

A

-The study of the rate of an enzyme
catalysed reaction

The rate of a catalyzed reaction depends on :

  • Substrates Concentration
  • Effects of inhibitors
  • Effects of pH
  • Effects of cofactors
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13
Q

How do competitive inhibitors block the enzyme’s activity?

A

Competitive inhibitors block the enzyme active site

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14
Q

How do Non-competitive inhibitors block the enzyme’s activity?

A

Non-competitive inhibitors interfere in some other

way with the catalytic mechanism

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15
Q

How competitive enzymes alter Vmax and Km?

A

Competitive inhibitors increase apparent Km

They do not alter Vma

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16
Q

How Non-competitive enzymes alter Vmax and Km?

A

Non-competitive inhibitors decrease Vmax

They do not alter Km

17
Q

Which are the enzymes that insulin activate in order to maintain glucose levels?

A

❑Glucokinase
❑Phosphofructokinase
❑Pyruvate kinase

18
Q

Are phosphorylated enzymes always active?Any examples?

A

No, the can be either active( glycogen phosphorylase) or inactive (glycogen synthase).

19
Q

Which substrates(amino acids) can be phosphorylated and from which molecules?

A

Addition or removal of phosphate from Ser, Thr, Tyr, His residues by kinase and phosphatase

20
Q 
Some inorganic elements that act as
cofactors for enzymes:
-Cu2+
- Mg2+
- Zn2+
- Fe2+/3+
A

— Cytochrome c oxidase (electron transport chain)
— Hexokinase, DNA and RNA polymerase
— Alcohol dehydrogenase
— Catalase

21
Q

Are isoenzymes found in the same tissues or compartments?

A

– Different isoenzymes often found in different cellular compartments (cytosol or mitochondria), or different amounts in different tissues

22
Q

What is the reaction rate when substrate concentration is low?

A

At low substrate concentration, the reaction rate is directly proportional to the substrate concentration

23
Q

What is the reaction rate when substrate concentration is high?

A

At high substrate concentration, the reaction rate is independent of substrate concentration

24
Q

How does Aspirin function?

A

Aspirin irreversibly inhibits cyclooxygenase by covalent modification of active site
– Inhibits inflammatory response

25
Q

How does ACE (Angiotensin-converting enzyme) function?

A

ACE (Angiotensin-converting enzyme) inhibitors block production of angiotensin
– reduce blood pressure
– treat heart failure and hypertension

26
Q

With which 3 ways can enzyme activity be regulated?

A

-Allosteric enzymes

-Covalent modification by other enzymes
[Phosphorylation (kinases) or
dephosphorylation (phosphatases)]

-Induction or repression of enzyme
synthesis

Medical Biochemistry (7 decks)

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