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Biochemistry > BCH 201 Enzymes > Flashcards

BCH 201 Enzymes Flashcards

1
Q

What are the 2 fundamental conditions for life?

A
  1. An organism must be able to self-replicate
  2. It must be able to catalyze chemical reactions efficiently and selectively
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2
Q

Why is catalysis important?

A

Catalysis is very important for life to be sustained, without catalysis most reactions will not occur at the physiological conditions on a useful time scale and thus could not sustain life

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3
Q

Enzymes definition

A

Enzymes are catalysts of biological systems and are molecular device that determines the pattern of chemical transformations. They also meditate the transformation of one form of energy into another

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4
Q

All enzymes are protein except____

A

RIBOZYMES: Ribozymes are RNA molecules with catalytic ability

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5
Q

What is a zymogen/proenzyme and what is its role?

A

is an inactive precursor of an enzyme
some enzymes are synthesized in the inactive form, to prevent them from catalyzing reactions in the cell in which they are synthesized.

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6
Q

What must occur to a proenzyme to activate it?

A

The proenzyme must be cleaved in order to activate them, the cleavage changes the conformation of the enzymes and creates a binding site for the substrate

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7
Q

What must occur to a proenzyme to activate it?

A

The proenzyme must be cleaved in order to activate them, the cleavage changes the conformation of the enzymes and creates a binding site for the substrate

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8
Q

Examples of proenzymes

A

chymotrypsin is synthesized as chymotrypsinogen
Trypsinogen to trypsin and pepsinogen to pepsin are also examples

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9
Q

COFACTORS

A

These are additional non-protein or metallic ion components required by enzymes for their optimum activity

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10
Q

COENZYME

A

These are cofactors that are loosely bound to the enzyme. They are organic in nature

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11
Q

PROSTHETIC GROUP

A

These are non-protein components that are tightly bound to an enzyme.

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12
Q

APOENZYME

A

This is an enzymes without its cofactor

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13
Q

HOLOENZYME

A

A catalytically complete enzyme consisting of the enzyme and its cofactor

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14
Q

SUBSTRATE

A

The substrates of enzymes are the reactants that are activated by the enzymes

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15
Q

ACTIVE SITES

A

this is a region on the enzyme that binds the substrate. It is a special pocket or cleft that contains amino acid side chains that participate in substrate binding and catalysis. The substrate binds to the active site forming an Enzyme-Substrate (ES) complex

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16
Q

Turnover number (KCAT)

A

The number of substrate converted to product per enzyme molecule per second i

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17
Q

The specificity of an enzyme is determined by the_____

A

Active site

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18
Q

Specificity of an enzyme

A

SPECIFICITY: Enzymes are highly specific, interacting with one or a few substrates and catalyzing only one type of chemical reaction.

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19
Q

Regulation of enzyme activity

A

REGULATION: Enzymes activity can be regulated, i.e. increased or decreased, so that the rate of product formation responds to cellular need

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20
Q

Location of enzymes

A

LOCATION WITHIN THE CELL: Many enzymes are localized in specific organelles within the cell. Such compartmentalization serves to isolate the reaction substrate or product from other competing reactions. This organizes the thousands of enzyme present in the cell into purposeful pathways

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21
Q

Location of enzymes

A

LOCATION WITHIN THE CELL: Many enzymes are localized in specific organelles within the cell. Such compartmentalization serves to isolate the reaction substrate or product from other competing reactions. This organizes the thousands of enzyme present in the cell into purposeful pathways

22
Q

Catalytic efficiency of an enzyme

A

CATALYTIC EFFICIENCY: Enzyme catalyzed reactions are very efficient, proceeding from 103-108 times faster than uncatalyzed reactions.

23
Q

How to enzymes work?

A

ENZYMES make reactions easier to occur at
reasonable temperature by LOWERING the ACTIVATION ENERGY EA of the reaction

24
Q

What is the energy barrier, separating the reactants and the products?

A

Free energy of activation

25
Q

Define free energy of activation

A

is the energy difference between the energy of the reactant and high-energy intermediates that occur during the formation of a product.

26
Q

First step in enzymatic catalysis

A

Formation of an enzyme-substrate (ES) complex is the first step in enzymatic catalysis
The substrate is bound through multiple NON-COVALENT interactions at the active site of the enzyme forming an enzyme-substrate (ES) complex which is subsequently converted to product and free enzyme
E + S ——>ES —-> E + P

27
Q

MODELS OF SUBSTRATE BINDING TO THE ACTIVE SITE

A
  1. Lock and key model or rigid template model of Emil Fisher.
  2. Induced fit model or hand-in-glove model of Daniel E Koshland
28
Q

What was Daniel E Koshland’s postulation in 1958 about enzymes and substrates

A

Daniel E Koshland in 1958 postulated that enzymes are flexible and shapes of the active site can be modified by the binding of the substrate.

29
Q

Describe the induced fit model

A

In the induced fit model, the substrate induces a conformational change in the enzyme, in the same manner in which placing a hand (substrate) into a glove (enzyme) induces changes in the glove’s shape. Therefore, this model is also known as hand-inglove model.

30
Q

Describe to lock and key model

A

This model was proposed by Emil Fisher in 1890
This model is called lock and key model, because in this model the substrate fits into the active site in much the same way that a key fits into a lock.

31
Q

Classify enzymes according to their IUB system

A
  1. EC-1 : Oxidoreductases
  2. EC-2 : Transferases
  3. EC-3 : Hydrolases
  4. EC-4 : Lyases
  5. EC-5 : Isomerases
  6. EC-6 : Ligases
32
Q

EC-1

A

EC-1:Oxidoreductases :Lactate dehydrogenase (LDH), Glucose 6-phosphate dehydrogenase(G-6-PD), Cytochrome oxidase

33
Q

EC-2

A

EC-2: Transferases:
Those enzymes that catalyze the transfer of a group such as, amino, carboxyl, methyl or phosphoryl, etc. from one molecule to another are called transferases.

Eg. Aspartate aminotransaminase(AST), Alanine aminotransaminase (ALT), Hexokinase

34
Q

EC-3

A

EC-3: Transferases
Enzymes of this class catalyze the cleavage of C-O, C-N, C-C and some other bonds with the addition of water. These can be illustrated as follows
A – B + H2O ——-> A-OH + B-H
Some common enzymes in this category are:
Acid phosphatase, All digestive enzymes like α-amylase, pepsin, trypsin, chymotrypsin, etc

E.gHydrolases: Lipase, α-Amylase, Trypsin, Lactase, Sucrase, Pepsin

35
Q

EC-4

A

EC-4: Lyases:
Lyases catalyze the cleavage of C-O, C-C and C-N bonds by means other than hydrolysis or oxidation, giving rise to compound with double bonds or catalyze the reverse reaction, by the addition of group to a double bond.
In cases where reverse reaction is important, then synthase

Eg..Aldolase, Argininosuccinase, Carbonic anhydrase

36
Q

EC-5

A

EC-5: Isomerases:
Isomerases catalyze intramolecular structural rearrangement in a molecule.
They are called epimerases, isomerases or mutases, depending on the type of isomerism involved. This reaction can be illustrated as follows:

e.g.Phosphoglucomutase, Triphosphate isomerase, Phosphohexose isomerase

37
Q

EC-6

A

EC-6: Ligases:
Ligases catalyze the joining of two molecules coupled with the hydrolysis of ATP.

E.g Glutamine synthetase, Pyruvate carboxylase, DNA ligases

38
Q

Allosteric enzymes and modulators

A

Allosteric enzyme is a regulatory enzyme, they have active site for binding of the substrate but they also have one or more regulatory (or allosteric) sites for binding regulatory metabolites which is called modulator.

Allosteric enzymes may be inhibited or stimulated by their modulators
Modulators that inhibit enzyme activity are termed negative modulators. Whereas those that increase enzyme activity are called positive modulators

The allosteric site is specific for its modulators. Allosteric enzymes are generally larger and more complex than those of simple enzymes

39
Q

Significance of Km

A
  1. Km provides a measure of the substrate concentration required for significant catalysis to occur.
  2. It is a measure of the of the ES complex or a measure of affinity of the enzyme for its substrate, a high Km indicates weak binding and a
    \ low Km indicates strong binding with its substrate
40
Q

Significance of Vmax

A

Vmax reveals the turnover number of an enzyme (the number of substrate molecules converted into products by an enzyme molecule in a unit time when enzyme is fully saturated with substrate)

The Vmax of a reaction is an index of the catalytic efficiency of an enzyme. The Vmax is useful in comparing the activity of one enzyme with that of another

41
Q

Lineweaver-Burk Plot or Double-Reciprocal Plot

A

Lineweaver-Burk plots are used to obtain values for Vmax and Km. A more accurate method of determining values for Vmax and Km uses Lineweaver-Burk equation shown below. This equation is obtained by taking the reciprocal of the Michaelis-Menten equation.

When 1/V0 is plotted against 1/[S], a straight line is obtained, with a slope equal to Km/Vmax.
The point, at which line intersects the y-axis, is numerically equal to 1/Vmax.
The point at which the line intersects the x-axis is numerically equal to –1/Km.
This plot is useful to determine the mechanism of action of enzyme inhibitors.

42
Q

Feedback Allosteric Inhibition

A

In some multienzyme systems, the first enzyme of the sequence is the regulatory enzyme and has distinctive characteristics.
It is inhibited by the end product of the multienzyme system whenever the end product of such metabolic reaction is produced in excess of the cells needs.
The end product of the pathway acts as a specific inhibitor of the first or regulatory enzyme in the pathway
The whole enzyme system thus slows down to bring the rate of production of its end product back into balance with the cell’s needs
E.g., δ-aminolevulenic acid synthase is an allosteric enzyme in heme synthesis is inhibited by its end product heme

42
Q

Clinical significance of enzymes

A

For the diagnosis of the disease
As therapeutic agents
As analytical reagents

43
Q

ENZYMES OF CLINICAL SIGNIFICANCE

A
44
Q

ALT

A

Alanine transaminase (ALT): formerly as glutamate pyruvate transaminase (GPT). The plasma ALT normal value for adult is 10 to 40 U/L. ALT level is elevated in liver diseases (viral or toxic hepatitis), jaundice and cirrhosis of liver.

45
Q

AST

A

Aspartate transaminase (AST): It was known formerly as glutamate oxaloacetate transminase (GOT). The plasma AST normal value for adults is 10 to 30U/L.
Increased AST level occurs after myocardial infarction. The plasma AST level starts increasing after 6 to 8 hours after the onset of chest pain with peak values 18 to 24 hours and the values fall to normal level by the fourth or fifth day.
It is moderately elevated in liver disease.

46
Q

ALP

A

Alkaline phosphatase (ALP): ALP hydrolyzes organic phosphate at alkaline pH. Normal serum level for adults is 3-13 KA units/dl. It is elevated in certain bone and liver disease
Very high levels may be noticed in obstructive
jaundice, bone diseases such as Paget’s disease, rickets, osteomalacia, carcinoma of bone and
hyperparathyroidism.

47
Q

ACP

A

Acid phosphatase (ACP): It hydrolyzes phosphoric acid ester at pH 5 to 6. Normal serum value for ACP is 0.5 to 4 KA units/dL.
* Prostatic acid phosphatase enzyme is useful for the
diagnosis and prognosis of prostate cancer. ACP is
therefore an important tumor marker

48
Q

Amylase

A

Amylase: It catalyzes hydrolysis of starch and glycogen.
* Normal serum value is 50-120 U/L.
* The activity of serum amylase is increased in acute
pancreatitis.
* Elevated activity of amylase is also found in urine of the patient of acute pancreatitis.
* Increase in serum levels are also seen in chronic
pancreatitis, mumps and obstruction of pancreatic duct.

48
Q

Lactate Dehydrogenase

A

Lactate dehydrogenase (LDH): Significant elevation of LDH1 and LDH2 (LDH1>LDH2) occurs within 24 to 48 hours after myocardial infarction.
* Predominant elevation of LDH2 and LDH3 occur in leukemia. LDH3 is the main isoenzyme elevated due to the malignancy of many tissues.
* Elevation of LDH5 occurs after damage to the liver or skeletal muscle.

Biochemistry (8 decks)

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