enzymes

Question 1

what is enzyme?

Answer 1

Enzymes are organic catalysts or biocatalysts made up of proteins (except ribozyme) which increases the rate of biochemical reactions by lowering down the activation energy, but does not affect the nature of the final product.

Question 2

which are two enzymes that are not proteinaceous?

Answer 2

1) ribozyme: isolated from tetrahymena by Cech et al

2) ribonuclease:-p isolated from bacterial by Altman

Question 3

explain active site and substrate?

Answer 3

-the protein in enzymes has secondary and tertiary structures. in the tertiary structure, the backbone of the protein folds upon itself and the chain crisscrosses itself from crevices of pockets, this is called an active site.

• active is a crevice or pocket to which the substrate attaches to
• the substrate is a specific compound on which the enzyme is acting upon

Question 4

what are the characteristics of enzymes?

Answer 4

1) All enzymes are proteins, but all proteins are not enzymes, and they an organic and occurs in living cells
- enzymes are highly specific in their reaction
2) Enzymatic proteins consist of 20 amino acids.

3)All enzymes are tertiary and globular proteins (isoenzymes quaternary protein). Their tertiary structure is very specific and important for their biological activity
.
4)Enzymes accelerate the rate of reaction without undergoing any change in themselves.

5) Enzymes lower the activation energy of substrate or reactions.
6) they get damaged t a temperature over 40 degrees celsius
6) Enzymes have a complex molecular organization and are macromolecules of amino acids which are synthesized on ribosomes under the control of genes.

7) Molecular weight of enzymes are high and these are colloidal substances.
8) Enzymes are very sensitive to pH and temperature. The optimum temperature for enzymes is 20-35°C. Most of the enzymes are active at neutral pH, hydrolytic enzymes of lysosomes are active at acidic pH (5).

9) Enzymes are required in very minute amounts for biochemical reactions.
10) they are higly efficient

Question 5

eaxplin Michaelis Menten constant or km vlaue?

Answer 5

Km constant of an enzyme is the concentration of substrate at which rate of reaction of that enzyme attains half of its maximum velocity. It is given by Michaelis & Menten. The value of Km should be lower for an enzyme.

• Km exhibits catalytic activity of an enzyme.
• Km value differs from substrate to substrate because different enzymes differ in their affinity towards different substrates.
• A high Km indicates low affinity while a low Km shows strong affinity.
• Protease acts on different proteins. So its Km value differs from protein to protein.

km = 1/2*Vmax

V0 =Vmax(S)/ Km+(S)

Where Vo is the rate of initial reaction; Vmax is the maximum relative or the reaction rate with the excess substrate; Km is the Michaelis constant = K2+K3/K1; [S] is the substrate concentration.

The above reaction shows that the greater the affinity between an enzyme and its substrate, the lower the Km (in units moles per litre) of the enzyme-substrate reaction. Stated inversely, 1/Km is the measure of the affinity of the enzyme for its substrate.

• greater the affinity between an enzyme and its substrate, the lower the Km (in units moles per litre) of the enzyme-substrate reaction. Stated inversely, 1/Km is the measure of the affinity of the enzyme for its substrate.

Question 6

what is the turnover number?

Answer 6

The number of substrate molecules converted into products per unit time by one molecule of the enzyme in favourable conditions is called the turnover number. higher the turnover number higher the efficency

Question 7

what is catalytic power?

Answer 7

-Michaelis Menten constant or Km constant along with turn over number represents the catalytic power of an enzyme

Question 8

what are the characteristics of inorganic catalysts?

Answer 8

• usually small and simple like nickel and platinum
• do not occur in living cells
• not specific for any one reaction and can catalyse many
• they work efficiently at high temperatures
• they are comparatively less efficient

Question 9

what is an important quality of enzymes isolated from thermophilic organisms

Answer 9

thermophilic organisms who live in places with extreme temperatures like sulphur rings and hot vents retain their catalytic power at high temperatures (80-90 degrees Celcius), thus these enzymes are thermally stable.

Question 10

what is the velocity or rate of a chemical or physical process?

Answer 10

amount of product formed per unit time is the rate if the direction is specified it the velocity.

Question 11

explain the effect of temperature on reactions.

Answer 11

rate double or decreases by half at each change of 10degree celsius in either direction.

Question 12

what is the rate of production of carbonic acid with and without carbonic anhydrase (catalyst)?

Answer 12

without carbonic anhydrase: 200 molecules/hour
with carbonic anhydrase: 600000 molecules/hour

enzymes accelerate a reaction about 10million times

Question 13

what is a metabolic pathway?

Answer 13

it is a multistep chemical reaction, and each step is catalysed by the same or different enzyme.
eg: in glycolisis glucose is converted to pyruvate(2 pyruvic acids) with ten different catalysed metabolic reactions

in skeletal muscles :
a) anaerobic: pyruvate(2 pyruvic acids) converted to 2lactic acid
b)anaerobic: pyruvate converted to acetyl CoA wich is then converted to H20 and CO2
in yeast:
a)anaerobic: pyruvate(2 pyruvic acids) converted to alcohol (2ethanol and CO2)(fermentation)

Question 14

how were enzymes discovered?

Answer 14

in 1875 Eduard Buchner found a compound in yeast present in a conal flask with sugar solution and called it enzyme.

Question 15

explain the nature of enzyme action?

Answer 15

1) In 1913, Michaelis and Menten proposed that for a catalytic reaction to occur it is necessary that the enzyme and substrate bind together to form an enzyme-substrate complex. (ES), this is a transient phenomenon and takes a short time and forms the transition state structure
2) there can be many altered structural states between stable substrate and product. these intermediate structural states are unstable and stability depends upon the energy of the molecules or structure

3) the substrate undergoes many chemical changes and turns ES TO EP
4) finally product is released from the active sites

Question 16

how do enzymes work?

Answer 16

Enzymes act by decreasing the activation energy so that the number of activated molecules is increased at lower energy levels. If the activation energy required for the formation of the enzyme-substrate complex is low, many more molecules can participate in the reaction than would be the case if the enzymes were absent.

Question 17

what is activation energy?

Answer 17

Energy is required to convert the inert molecules into the activated state. The amount of energy required to raise the energy of molecules at which a chemical reaction can occur is called activation energy.

Question 18

explain the relationship between the energy of the substrate, product and the type of reaction product

Answer 18

1) endothermic reaction: the energy in the substrate is lower than the energy in the product as energy is absorbed.
2) exothermic reaction: the energy in the substrate is higher than the energy in the product as energy is released in the form of heat.

Question 19

explain the different modes of enzyme action?

Answer 19

(1) LOCK & KEY THEORY OR TEMPLATE THEORY
- given by Emil Fischer.
- active sites of enzymes serve as a lock into which the reactant substrate fits like a key.
- Enzymes have specific sites where a particular substrate can only be attached.
- This model accounts for enzyme specificity.

(2) ENZYME - SUBSTRATE COMPLEX THEORY
In 1913, Michaelis and Menten proposed that for a catalytic reaction to occur it is necessary that the enzyme and substrate bind together to form an enzyme-substrate complex.

(3) INDUCED FIT THEORY
- proposed by Koshland (1959).
- -the active site is not static but it undergoes a conformational change which is induced by the specific substrate
- the site that has undergone change is called buttressing site or group and its meant for supporting the substrate
- the catalytic group is meant for the reaction

Question 20

factors affecting enzyme action?

Answer 20

10temprature:

• 37 degree celsius is the optimum temperature for humans, below it they are preserved in an inactive state and above optimum temperature the kinetic energy of the molecules increases and break free pf the hydrogen bond of the tertiary protein structure and lose catalytic power, thus they denature and cannot be brought back
• the optimum temperature of thermaus aquatiuses is 72 - 95 degree celsius

2) hydrogen ion concentration or PH value:
Enzymes are very sensitive to pH. Each enzyme shows its highest activity at optimum pH. they become inactive below and denature above the optimum value.
eg:pepsin:- 1.3 - 1.5, salivary amylase:-6.1- 6.2 , trypsin:- 8.5 - 9.2

3) substrate concentration: increase in substrate concentration increases the activity of enzymes until all the active sites of the enzyme have been filled with the substrate after which it becomes constant.
4) product concentration: overproduction will bring down the velocity of the reaction.

Question 21

explain the inhibition of enzyme activity?

Answer 21

1) inhibitors are substances that inhibit or slows down a catalytic reaction
2) reversible inhibition: this occurs when the inhibitor forms a covalent bond with the enzyme but enzymes return to their normal state after the dissociation of the bond

3) irreversible inhibition: this occurs when the inhibitor forms a covalent bond with the enzyme but enzymes do not return to their normal state after the dissociation of the bond.
eg: the neurotoxic effects of insecticides are due to the irreversible binding of inhibitors on the site of the catalytic enzyme acetylcholinesterase

the two types of inhibitors are:

1) competitive
2) non-competitive

Question 22

explain competitive inhibitors?

Answer 22

1) the inhibitor resembles the substrate
2) inhibitor competes with the substrate for the active site
3) effect on Vmax: remans the same
4) effect on Km : increases

eg: 1)Malonate oxaloacetate is a competitive inhibitor of the enzyme succinate dehydrogenase and prevents the formation fumarate.
2) Sulfonamides(antibiotic) inhibit multiplication of bacteria by acting as competitive inhibitors of p-aminobenzoic acid in the folic acid metabolism cycle and prevents the formation of floic acid.

Question 23

explain non-competitive inhibitors?

Answer 23

1)inhibitor binds with the allosteric site of the enzyme
2) then changes the shape of the active site of the enzyme, thereby inhibiting the substrate binding and the reaction.
3)it is a type of irreversible inhibition
4) non-competitive inhibition cannot be overcome thus decreasing Vmax.
5) non-competitive inhibition does not affect the Km
eg:

Cyanide all bind to cytochrome c oxidase inhibiting the protein from functioning and prevents oxidative reaction leading to low O2 levels in the body., azide, and carbon monoxide does the same thing too.

Question 24

nomenclature oh enzymes?

Answer 24

1)Émile Duclaux suggested that suffix ‘ase’ to enzymes
2) nomenclature by using the living organisms it was isolated from.
eg: papaya = papain
ficus = ficin

3) the international union of biochemistry used the reaction the enzymes catalyze for nomenclature
4) his lead to the making of six classes of enzymes

Question 25

what are the 6 classes of enzymes?

Answer 25

OTHLIL

1) Oxidoreductase: catalyses oxidation reactions.
- transfer either protein or electron from the substrate to the product
- eg: catalase-peroxidase, cytochrome c oxidase, succinate dehydrogenase, alcohol dehydrogenase

2) transferases: catalyze the transfer of functional group from a substrate to product
- transaminase: transfer of an amino group
- transketolase :transfer of ketose group
- subclass: kinases - transfer of a phosphate group usually from ATP
eg: hexokinase
- glucose and ATP give Glu6PO4 and ADP in the presence of hexokinase

3)Hydrolasescatalyse splitting of the substrate by addition of water
- most digestive enzymes
-sucrose and water splits sucrose into fructose and glucose in the presence of sucrase/invertase
-maltose and water splits maltose into 2glucose molecules in the presence of maltase
-lipases : hydrolyzes fat
-proteinases : hydrolyzes protein
ribonucleases:hydrolyzes RNA
deoxyribonucleases :hydrolyzes DNA

4) Lyases: catalyzes the splitting of substrates without the addition of water
- eg: aldolase, carbonic anhydrase, Citrate synthase

5) Isomersase; catalyses molecular rearrangement in the substrate
- eg:phosphohexoisomerase
- GLU6PO4 givesFRU6PO4 in the presence of phosphohexoisomerase

6) Ligases: catalyses the formation of bonds by the expenditure of ATP
- DNA ligases, rubisco, Ubiquitin Ligases (C-N bond),PEPco

Question 26

what is the function of succinate dehydrogenate?

Answer 26

Succinate dehydrogenase enzyme catalyzes the oxidation of succinate by removal of its two hydrogen atoms and forms fumarate. The removed hydrogen atoms reduce the FAD into FADH2

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Question 27

the function of cytochrome c oxidase?

Answer 27

Cytochrome c oxidase (CcO) is a respiratory energy-transducing enzyme. It catalyzes the electron transfer from cytochrome c to molecular oxygen, conserving the released energy as a charge and proton gradient across the membrane in which it is located

Question 28

what are co-factors?

Answer 28

1)enzymes are composed of several polypeptide chains, they conduct their catalytic activity in the presence of several non-protein substances called co-factors. the protein portion of these enzymes is called apoenzyme.
catalytic activity stops when the co-factor is removed from the enzyme

Question 29

explain the three types of co-factors?

Answer 29

1) prosthetic group: they are compounds d= tightly bound with apoenzyme.
- heam is a prosthetic group present in peroxidase and catalase and they help in the dissociation of hydrogen peroxide into water and oxygen. heam is part of the active site of the enzyme.

2) co-enzymes: they are organic compounds but their association with enzymes is for a short period.
- their main components are mostly vitamins
- coenzyme nicotinamide adenine dinucleotide(NAD) and NADP contain vitamin niacin

3) metal ions: metal ions play an essential role in regulating the activity of enzymes by forming coordination bonds with side chains at the active site and at the same time form one or more coordination bonds with the substrate
- zinc is a co-factor for proteolytic enzyme carboxypeptidase

Question 30

terms related to enzymes?

Answer 30

–Endoenzymes: Enzymes which are functional only inside the cells.
–Exoenzymes : Enzymes catalysed the reactions outside the cell. E.g., enzymes of digestion, some enzymes of insectivorous plants, zymase complex of fermentation.
–Proenzyme/Zymogen: These are precursors of enzymes or inactive forms of enzymes.
E.g., Pepsinogen, Trypsinogen, etc.
-Iso-enzymes: Enzymes having similar action, but little difference in their molecular configuration are called isoenzymes. 16 forms of α-amylase of wheat and 5 forms of LDH (Lactate dehydrogenase) are known. These all forms are synthesised by different genes.
–Inducible enzymes: When the formation of the enzyme is induced by substrate availability. E.g., Lactase, Nitrogenase, β-galactosidase.
–Bio detergents: Enzymes used in washing powders are known as bio-detergents, e.g., amylase, lipase, proteolytic enzymes.
–Housekeeping / constitutive enzymes: These enzymes are always present in constant amounts and are also essential to cells.

Question 31

explain the vitamin nicotinamide?

Answer 31

nucleotide: nicotinamide adenine dinucleotide(NAD) r or NAD+ nicotinamide adenine dinucleotide phosphate or NADP+

components: nicotinamide-ribose-phosphate-phosphate -ribose-adenine
nicotinamide-ribose-phosphate-phosphate–phosphoribose-adenine.

Question 32

explain the vitamin riboflavin.

Answer 32

nucleotide: flavin mononucleotide or FMN flavin adenine dinucleotide or FAD

components: riboflavin - phosphate
riboflavin -phophate-PHOSPHATE-ribose-
adenine

Question 33

what does riboflavin and nicotinamide do?

Answer 33

they act as coenzymes for oxidising enzymes

Question 34

explain commission number.

Answer 34

given by the international union of biochemistry(IUB).
enzyme number has 4 digits and they represent:
1st digit: class(1-6)
2nd digit: subclass
3rd digit: subdivision
4th digit: individual enzyme

Question 35

what are the rate of carbonic anhydrase and the formation of h2co3?

Answer 35

carbonic anhydrase: 600000 molecules per second

h2co3 ; 200 molecule per hour.

Question 36

what are the two types of enzymes?

Answer 36

1) intracellular enzyme or endocellular enzyme:
- inside the cell
- all the 11 enzymes required to convert glucose to lactic acid can be extracted from the water of ground-up liver cells
- they can be dissolved in the cytoplasm
- sometimes they are bound to particles like mitochondria, chloroplast, ribosomes etc.
- enzymes required for converting lactic acid into co2 and water is bound to mitochondria

2) extracellular or exoenzyme :
- function outside the cell
- usually in digestive enzymes- eg: salivary amylase; pancreatic lipase. gastric pepsin
- lysosomes in tears and nasal secretion
- catalytic action retain even after the extraction from the cell.
- rennet, the tablet contains rennin from the calf’s stomach which used coagulate milk for the formation of cheese.

• applications :
  
  • amylases and proteases in detergent,=amylases in dish wash
• they help in breaking own protein or substances from food that may stain clothes
• dairy digestive supplement contains lactases
• baby food has trypsin to partially pre-digest the food
• onion has sulphur compounds called amino acid sulphoxide that results in the flow of lacrimal fluid

Question 37

explain iso- enzymes.

Answer 37

LEARN FROM TB LEVEL 2

Question 38

explain allosteric enzyme?

Answer 38

LEARN FROM TB LEVEL 2

Question 39

explain inhibition in allosteric enzymes?

Answer 39

LEARN FROM TB LEVEL 2

Question 40

explain the qualitative test for biomolecules?

Answer 40

LEARN FROM TB LEVEL 2