enzymes Flashcards
(40 cards)
what is enzyme?
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.
which are two enzymes that are not proteinaceous?
1) ribozyme: isolated from tetrahymena by Cech et al
2) ribonuclease:-p isolated from bacterial by Altman
explain active site and substrate?
-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
what are the characteristics of enzymes?
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
eaxplin Michaelis Menten constant or km vlaue?
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.
what is the turnover number?
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
what is catalytic power?
-Michaelis Menten constant or Km constant along with turn over number represents the catalytic power of an enzyme
what are the characteristics of inorganic catalysts?
- 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
what is an important quality of enzymes isolated from thermophilic organisms
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.
what is the velocity or rate of a chemical or physical process?
amount of product formed per unit time is the rate if the direction is specified it the velocity.
explain the effect of temperature on reactions.
rate double or decreases by half at each change of 10degree celsius in either direction.
what is the rate of production of carbonic acid with and without carbonic anhydrase (catalyst)?
without carbonic anhydrase: 200 molecules/hour
with carbonic anhydrase: 600000 molecules/hour
enzymes accelerate a reaction about 10million times
what is a metabolic pathway?
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)
how were enzymes discovered?
in 1875 Eduard Buchner found a compound in yeast present in a conal flask with sugar solution and called it enzyme.
explain the nature of enzyme action?
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
how do enzymes work?
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.
what is activation energy?
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.
explain the relationship between the energy of the substrate, product and the type of reaction product
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.
explain the different modes of enzyme action?
(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
factors affecting enzyme action?
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.
explain the inhibition of enzyme activity?
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
explain competitive inhibitors?
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.
explain non-competitive inhibitors?
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.
nomenclature oh enzymes?
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
