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biochemistry > Enzymes > Flashcards

Enzymes Flashcards

1
Q

Name an isomerase enzyme

A

Triose phosphate isomerase

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2
Q

The protein component in compound protein enzymes

A

Apoenzyme

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3
Q

The prosthetic group is termed as

A

Co-enzyme

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4
Q

Coenzymes may be involved in the transfer of hydrogen , eg:

A

NAD FAD FMN

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5
Q

Coenzymes involved in the transfer of groups other than hydrogen

A

Amino group by PLP , Hydroxyethyl group is transferred by TPP

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6
Q

Metal required for the activity of lipase

A

Calcium

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7
Q

State the Michaelis- Menten theory

A

That an enzyme combines with the substrate to form an enzyme substrate complex( reversible reaction )which breaks down to give the product (irreversible reaction .
Write as reversible and irreversible equation

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8
Q

Lock and key theory to explain the mechanism of enzyme action also called

A

Fischer’s template

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9
Q

Induced fit theory used to explain the mechanism of enzymes is also known as

A

Koshland’s induced fit theory

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10
Q

Define active site

A

Area of an enzyme where catalysis occurs

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11
Q

What are catalytic residues

A

Amino acid residues of the enzyme involve directly in the inning of the substrate

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12
Q

Enzyme activity is influenced by

A

Enzyme conc. , substrate conc.,temp , pH , presence of inhibitors

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13
Q

What does the km value denote

A

Affinity of the enzyme to the substrate

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14
Q

Relation of affinity and km value

A

Inversely proportional

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15
Q

Example of stereoisomerism

A

Lactate dehydrogenase

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16
Q

Explain , enzymes are diffusion limited

A

Rate of reaction is limited by the rate at which substrate molecules diffuse through solution and reach the active site of the enzyme

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17
Q

Examples of multi enzyme complexes

A

FAS (Fatty Acid Synthase
Pyruvate dehydrogenase
Alpha keto glutarate dehydrogenase
Acetyl coA carboxylase
Glycine cleavage system
Pyruvate carboxylase
Pyramiding nucleotide synthessi

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18
Q

NAD+ OR NADP+ Dependent enzymes are assayed by

A

Spectrophotometery

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19
Q

Why are NAD and NADP+ dependent enzymes assayed by spectrophotometer

A

As the reduced form of. These coenzymes will absorb light at a wavelength of 340nm
But oxidized forms will not absorb light

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20
Q

Enzyme activity is expressed as

A

Micro moles of substrate converted to product perminute under specifies assay conditions

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21
Q

Define the standard unit or international unit of enzyme activity

A

Amount of enzyme required to convert 1 micoromole of substrate per minute per litre of sample at 25°C

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22
Q

Glucose oxidase is absolutely specific to the high substrate

A

Beta -D-glucose

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23
Q

Urease hydrolyses urea to

A

Ammonia and co2

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24
Q

An example of bond specific peptide sets

A

Trypsin (hydrolysis binds formed by carboxyl groups of arginine or lysine residues in any protein

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25
Q

Define group specificity

A

One enzyme can cataclysm the same reaction on a group ofstructurally similar compounds

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26
Q

Name a group specific enzyme

A

Hexokinase - catalyze phosphorylation of glucose , galactose and mannose

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27
Q

Name a non protein enzyme and it’s enzyme activity

A

Ribozyme(RNA molecule with enzyme activity )
Which catalyzes cutting of nascent mRNA or primary transcript

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28
Q

Stereospecificity shown by human enzymes

A

Specific for L-amino acids and D-sugars

29
Q

Examples of stereospecific enzyme reactions

A

Lactate dehydrogenase acts on pyruvate to form “L-lactate !not D
Fumarse fumaric acid to malic acid , cis form male if acid not acted upon

30
Q

Salivary amylase show higher activity in the presence of which inorganic ion

A

Chloride

31
Q

Conversion of trypsinogen to active trypsin

A

By splitting a single peptide bond and removal of a small polypeptide chain . Results in unmasking of the active center

32
Q

The process of activation of chymotrypsinogen by trypsiongen

A
33
Q

Which law explains the effect of concentration of products

A

Law of mass action

34
Q

What happens when one enzyme of a metabolic pathway is blocked due to inborn metabolism

A

A +E1 —->B +E2—>C xE2—-> D
C will accumulate in the absence of E3 which will in turn inhibit E2 , in due time while pathway is blocked

35
Q

Lineweaver burk equation

A

V = vmas(s) /km+ (s)

36
Q

Shape of Curve of effect of temperature on enzyme activity

A

Bell shaped

37
Q

Define optimum temperature

A

The temp at which max amount of substrate is converted to product per unit ime

38
Q

How does increasing temp increase activity

A

Increases velocity of enzyme reaction so their collision probability is increased . More molecules get activation energy

39
Q

What is temperature coefficient

A

Factor by which the rate of catalysis is increased for a a rise in 10°C
Generally rate will be doubled

40
Q

Why is the curve of temp bell shaped

A

Temp is more than 50°C , heat desaturation and loss of tertiary structure of protein occurs , so enzyme activity his decreased

41
Q

Optimum temp for human enzymes

A

37 degree Celsius

42
Q

Certain bacteria have optimum temp

A

100°C living in hot springs

43
Q

Effect of pH on catalysis , graph is

A

A bell shape curve

44
Q

How does the pH effect the catalytic activity

A

pH decides the net charge on the amino acid residues at the active site . The net binding and catalytic activity . The net charge on the enzyme protein would influence substrate binding and catalytic activity. They are ampholytes with charges , alters enzyme activity by altering the dissociation activity

45
Q

Optimum ph may vary with

A

Temperature
Concentration of substrate
Presence of ions

46
Q

Optimum pH of enzymes

A

6 to 8

47
Q

Exceptions of optimum pH of enzymes

A

Pepsin(pH 1-2)
Alkaline phosphatase (optimum pH 9- 10
Acid phosphatase (optimum pH 4-5)

48
Q

Km for glucokinase

A

10mmol/L

49
Q

Km value of hexokinase

A

0.05 m mol/L (therefore 50% molecules of hexkinase are saturated even at a low conc of glucose )

50
Q

What does the difference in Km of glucokinase and hexokinase tell us

A

Hexokinase has more affinity for glucose than. Glucokinase

51
Q

What is km value

A

Affinity of the enzyme to the substrate ,
Is the substrate con at half-maximal velocity .
It denotes that 50% of enzyme molecules are bound with substrate molecules at that particular substrate concentration

52
Q

What is the km value independent of

A

Enzyme conc.
When enzyme conc. is doubled , max doubles . But 1/2vmax remains same
(That is irrespective of the enzyme conc , 50% molecules are bound to substrate at the particular substrate conc

53
Q

Coenzyme that acts as a cosubstrate

A

Pyruvate converted to lactate in the presence of lactate dehydrogenase and NADH +H+ To NAD+

54
Q

Example of an end product assay

A

Disodium phenyl phosphate (substrate ) in the presence of alkaline phosphatase to form phenol + 4amino pyrine

55
Q

The more intense color in end point assay shows

A

More amount of chemical reaction or enzyme activity

56
Q

If velocity is plotted against substrate conc , a what type of curve is achieved

A

A typical curve ,

57
Q

If velocity is plotted against substrate conc , a typical curve is achieved . Why

A

As substrate conc increases in the initial phases ,velocity also increases but the curve flattens afterwards

58
Q

What does the maximum velocity obtained represent

A

Represents the maximum reaction rate attainable in presence of excess substrate (at substrate saturation level )

59
Q

Relation btw enzyme conc and rate of reaction /velocity

A

Directly proportional when sufficient substrate is present

60
Q

Velocity of reaction is increased proportionately with the concentration of enzyme, provided substrate concentration is unlimited . This property is used for

A

Determining the level of particular enzyme in plasma , serum or tissues (sample ).
Known volume of serum is incubated with substrate for a fixed time , then reaction is topped and product quantified (end point method )since product formed proportional to enzyme con , latter will be assayed

61
Q

Cofactor is

A

Collective term for coenzymes and cofactors

62
Q

Active center of an enzyme contains with amino acid residue

A

Serine residue

63
Q

Mistake of Fisher’s template theory

A

Envisaged a rigid structure for enzymes , could not explain flexibility shown by enzymes

64
Q

What does koshland’s induced fit theory state

A

Conformational changes occur at the active site of enzymes which leads to more secondary binding and conformational changes

65
Q

Catalytic or active site of ribonuclease

A

Lies within the hydrophobic cleft .
With 7th and 41st lysine on one side , other side 12th and 119th histidine on the opposite side of the binding ofuridylic acid acid .

66
Q

Active groups are brought to specific orientation by

A

Tre

67
Q

Example of uncompetitive inhibition

A

Inhibition of placental alkaline phosphatase (Regan iso-enzyme) by phenylalanine b

68
Q

Examples of non competitive inhibition

A

Cyanide inhibits cytochrome oxidase.
b. Fluoride will remove magnesium and manganese ions and so will inhibit the enzyme, enolase, and
consequently the glycolysis.
c. Iodoacetate would inhibit enzymes having -SH
group in their active centers.
d. BAL (British Anti-Lewisite; dimercaprol) is used
as an antidote for heavy metal poisoning. The heavy

biochemistry (10 decks)

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