Unit 7: Enzymes — Short Questions

Metabolism
Definition
Metabolism is the sum of all chemical reactions that occur within an organism to sustain life.

Catabolism
Definition: It involves the breakdown of complex molecules into simpler ones. This process releases energy in the process.
Example:
i) Cellular respiration i.e. oxidation of food (glucose) into CO₂and H₂O to get energy.
ii) Lipolysis i.e., break-down of lipids (fats) into fatty acids and glycerol, which can be used for energy production.

Anabolism
Definition: Involves building up complex molecules from simpler ones. This process consumes energy.
Examples:
i) Photosynthesis i.e. conversion of carbon dioxide and water into glucose and oxygen using sunlight.
ii) Protein synthesis i.e., formation of proteins from amino acids, which are vital for cell structure and function.

Anabolism demands input of energy. Photosynthesis i.e., conversion of carbon dioxide and water into glucose and oxygen using sunlight.

Definition
Enzymes are biological catalysts that speed up chemical reactions in living organisms without being consumed in the process.
They are primarily proteins and highly specific to their substrates.
Role
Enzymes play an important role in controlling cellular metabolism. An enzyme functions by lowering the activation energy of a chemical reaction inside the cells. Activation energy is the minimum amount of energy needed to form or break chemical bonds and convert reactants to products.

Only a small portion of enzyme molecule is directly involved in catalysis. This catalytic region is known as active site. It recognizes and binds substrates and then carries out biochemical reactions.

The enzyme protease (which breaks peptide bonds in proteins) will not work on starch (which is broken down by an enzyme amylase).

Enzymes are sensitive to hydrogen ion concentration (pH) of the fluid in which they work. They show maximum activity at a specific pH called their Optimum pH.
Affect of change in pH
Change in pH can affect the ionization of the amino acids at the active site of enzyme. It slows down enzyme activity or blocks it completely. Different enzymes have different optimum pH values. For example, Pepsin (working in stomach) works in acidic medium (pH 1.5 to 2.0) while trypsin (working in small intestine) works in alkaline medium (7.8).

Pepsin (working in stomach) works in acidic medium (pH 1.5 to 2.0) While trypsin (Working in small intestine) works in alkaline medium (7.8).

Optimum temperature
Each enzyme works at maximum rate at a specific temperature called optimum temperature. The optimum temperature for most of human enzymes in 37°C.
Optimum pH
Optimum pH is a measure of how acidic or basic a substance or solution is. It is measured on pH scale of 0 to 14 with 7 being neutral.
Enzymes show maximum activity at a specific pH, called their optimum pH.

Definition
Non-competitive inhibitors do not attach to the active site of an enzyme. Rather, they attach to some other location of enzyme.

i. Competitive Inhibition
Introduction
Some inhibitors resemble the enzyme's substrate. They compete with the substrate to attach to the active site of enzyme. When the inhibitor is attached to the active site, it blocks it and does not allow the substrate to attach.
Examples
Examples of competitive inhibitors are antibiotics. The antibiotic molecules compete with the substrates of bacterial enzymes. They attach to bacterial enzymes and inhibit them.

ii. Non-Competitive inhibition
Introduction
Some enzyme inhibition do not have similarity to the substrate. They do not attach to the active site of enzyme. Rather, they attach to some other location of enzyme. This attachment changes the overall shape of enzyme and active site. So, this changed active site does not fit substrate and enzyme is inhibited.
Examples
Heavy metals like mercury and certain drugs used in cancer therapy.

Enzymes are known as biocatalysts because they speed up and regulate the metabolic pathways in living organisms. Enzymes are mostly proteins that catalyze a chemical reaction in our body. They function as a catalyst that speed up the reaction by lowering the activation energy.

Each enzyme is specific to a chemical reaction as it contains an active site which is the area of an enzyme that has a specific shape which differs from one enzyme to another.

Because enzymes have high capability to convert giant quantities of substrate into product. Enzymes increase the rate of reaction and remain unaffected by reaction which is being catalyzed.

Some enzymes require non-protein molecules or ions to work, these molecules or ions are called cofactors. Cofactors can either be inorganic e.g. metal ions or organic e.g. Flavin and haem

When all the active sites of the enzymes are occupied (at high substrate concentration) and adding more substrate molecule do not find free active sites, this state is called saturation of active sites and the reaction rate does not increase.

a) Catalyst and Enzyme
Catalyst: Catalyst is a substance that increases rate of a chemical reaction without itself undergoing any permanent chemical change.
Enzyme: Enzymes are proteins that speed up biochemical reactions and are not changed during the reaction.

b) Intracellular and extracellular enzymes.
Intracellular Enzymes: Enzymes which remain inside the cell to speed up the reaction are called intracellular enzymes. Example: Enzymes of glycolysis working in cytoplasm.
Extracellular Enzymes: Enzymes that work outside the cell are called extracellular enzymes. Example: Pepsin enzyme working in the stomach cavity.

Enzymes are very specific for the substrate. One enzyme can act on a particular substrate because active sites possess specific geometric shapes that fit with specific substrates. According to induced fit model, the active site is slightly flexible but not flexible enough that any substrate can attach with active site.

Emil Fischer proposed the lock and key model of enzyme action. The active site has particular rigid shape into which the specific substrate fits exactly. The substrate is imagined being like a key whose shape is complementary to the enzyme or lock. Once the product is formed no longer fits into the active site and escapes into the surrounding medium. The active site is free to combine again with another substrate molecule.

(1) Temperature
(2) Substrate Concentration
(3) pH

At very low temperature (below 0°C) enzyme remain inactive due to fall in available activation energy.

Pepsin is a protein digesting enzyme which functions in acidic medium.