ENZYMES ITS STRUCTURE AND FUNCTIONS:
Q.No.1
a) What are enzymes? Briefly discuss their structure and functions.
b) Explain co-factor, actÃvator, prosthetic group.co-enzyme, apoenzyme and holoenzyme.
Answer:
ENZYMES:
Enzymes are the most important group of proteins, which are biologically active They are also called biological catalysts. The substance on which the enzyme acts is called the substrate.
Importance:
They tremendously increase the efficiency of a biochemical reaction and are specific for each type of reaction. Without these enzymes the reaction would proceed at a very slow speed making life impossible.
Structure of enzymes:
Enzymes are composed of hundreds of amino acids joined together and coiled upon themselves to forma globular structure The catalytic activity is restricted to a small portion of the structure known as the active site. The substrate is attached to the active site consisting of only a few amino acids, while rest of the bulk of the amino acids maintains the globular structure of the enzyme.
Functions of enzymes:
Many enzymes are simply dissolved in the cytoplasm. Other enzymes are tightly bound to certain sub-cellular organelles. They are produced by living cells for use in or near the site of their production. The enzymes important in photosynthesis are found in the chloroplasts and enzymes involved in cellular respiration are found in the mitochondria. Some of the enzymes, which are involved in the synthesis of proteins, are integral part of ribosomes. Some enzymes are potentially damaging if they become active in the wrong place For example, Pepsin is a powerful protein digesting enzyme and is quite capable of destroying a cell's internal structure and thus is produced in active Pepsinogen form by the cell enclosed in membrane-bounded bodies called lysosomes.
CO-FACTOR:
Some enzymes also have a non-protein part known as a co- factor, which is essential for the proper functioning of the enzymes. The cofactor usually acts as "bridge" between the enzyme and its substrate; often it contributes directly to the chemical reactions, which bring about catalysis .
Activator:
Sometimes the co-factor provides a source of chemical energy, helping to drive reactions, which would otherwise be difficult or impossible. Some enzymes use metal ions as co-factors like Mg2+, Fe2+ & Cu+ Zn2+ etc. The detachable co-factor is known as an activator if it is an inorganic ion.
Diagram: Substrate molecules will not fit correctly at the active center and there will be catalytic action unless the cofactor molecule is also present.
Prosthetic Group:
If the non-protein part is covalent bonded to the enzyme, that part is known as a prosthetic group.
Co-enzyme:
If non-protein part is loosely attached to the protein part it is known as coenzyme. Vitamins represent the essential raw materials from which coenzymes are made. Only small quantities of vitamins are needed because, live enzymes, co-enzyme substances can be reused again and again.
Apoenzyme:
An enzyme with its coenzyme, or prosthetic group, removed is designated as apoenzyme. Adding the correct, concentrated coenzyme to the apoenzyme will restore enzyme activity.
Holoenzyme:
An activated enzyme consisting of polypeptide chain and a cofactor is known as holoenzyme.
Q.no.2
Describe different characteristics of enzymes.
Answer:
CHARACTERISTICS OF ENZYMES:
Enzymes, the biochemical catalysts posses the following important characteristics:
1. All enzymes are globular proteins.
2. They increase the rate of reaction without themselves being used up.
3. Their presence does not affect the nature or properties of end products.
4. Even a small amount of an enzyme can bring about the change in a large amount of the substrate.
5. They are very specific in their action; generally a single enzyme catalyzes only a single substrate or a group of related substrates.
6. They are sensitive to even a minor change in pH, temperature and substrate concentration.
7. Some enzymes require a co-factor for their proper functioning.
8. They lower the activation energy of the reactions:
Q.no. 3
How enzymes catalyses the chemical reaction?
Or
What is the mechanism of enzyme action. Explain with the help of models.
Answer:
MECHANISM OF ENZYMES ACTION(CATALYSIS).
An enzyme is a three dimensional globular protein that has specific chemical composition due to its component amino acids and a specific shape. Every enzyme by virtue of its specificity recognizes and reacts with a special chemical substance called substrate. Any enzyme, therefore, reacts only with its specific substrate and transforms it into product(s). It is then released unaltered and thus can be used again and again.
An enzyme and its substrate react with each other through definite charge bearing sites called active sites. The active site of an enzyme is a three- dimensional cavity bearing a specific charge by which the enzyme reacts with its substrate.
The charge and shape of the active site is formed by some amino acids present in the polypeptide chain of the enzyme. These amino acids are brought closer and are arranged in a specific way by coiling and folding of the polypeptide chain within the globular symmetry of the enzyme.
Role of Active site in Enzyme Action:
The active site of the enzyme is made up of two definite regions.
1. The binding site and
2. The catalytic site.
The binding site helps the enzyme in the recognition and binding of a proper substrate to produce an ES complex. This reaction activates the catalytic site. Activated catalytic site catalyzes the transformation of the substrate into product(s). Thus the enzyme after catalysis detaches itself from the products unchanged. Enzyme require aqueous medium for its activity. Mechanism óf enzyme action can be understood through models very easily.
LOCK & KEY MODEL:
Emil Fischer (1890) proposed a Lock and Key model to visualize substrate and enzyme interaction. According to this model, as one specific key can open only a specific lock, in the same manner a specific enzyme can transform only one substrate into products(s).
According to this model the active site is a rigid structure. There is no modification or flexibility in the active site before, during or after the enzyme action and it is used only as a template. Later studies did not support this model in all reactions.
INDUCE FIT MODEL:
On the basis of new evidences, Koshland (1959) proposed modified form of Lock & Key Model. He argued that when a substrate combines with an enzyme, it induces changes in the enzyme structure. The change in structure enables the enzyme to perform its catalytic activity more effectively.
Pre-medical ist year biology notes.
0 Comments