What are the 3 structures of enzymes?
Three-dimensional structure of enzyme:
The enzymes are globular proteins. The specificity of enzymes comes from their unique three-dimensional structure. The tertiary structure of a protein or any other macromolecule plays an important role in their proper functioning.
The simple protein consists of only one long polypeptide chain e.g., ribonuclease consists of 124 amino acids. The kind of amino acids and the sequence in which they are arranged determines the three-dimensional structure of an enzyme.
Enzyme Cofactors:
Some enzymes do not need additional components to show full activity. However, most of the enzymes require non-protein molecules called cofactors to be bound for activity. Cofactors can be either inorganic metal ions or organic compounds like flavin or heme.
These cofactors serve many purposes e.g., metal ions help in making enzyme-substrate complexes either by molding the active site or shape of the substrate. The organic substances may be co-enzymes which are released from the enzyme's active site during the reaction.
They are loosely attached to enzymes. Prosthetic groups are tightly bound with the enzyme hence the permanent part of the enzyme. Most vitamins are co-enzymes or components of co-enzymes. That is why vitamins are needed in our daily lives.
3.2 Mechanism of Enzyme Action Reaction.
Enzymes must bind their substrate before they can understand the mechanism of enzyme action
Lock and Key Model:
This model was developed by German chemist Emil Fischer in 1894. catalyze any chemical models that have been proposed. The specific action of the enzyme with a single substrate can be explained using a lock and key analogy.
In this analogy, the lock is the enzyme and the key is the substrate. Only the correctly sized key is the substrate fits into the keyhole which is the active site of the lock that is the enzyme. The same enzyme can be used to catalyze hundreds of the same substrates.
The enzymes that work on this mechanism are called nonregulatory enzymes e.g., lipase, amylase, etc. This model explains the specificity of enzymes but does not say anything about the change in the active site.
Induced-Fit Hypothesis (Model):
In 1958 Daniel Koshland suggested a modification to the lock and key model. According to the induced-fit model, the active site of the enzyme is a flexible structure. Enzyme
molecules are in an inactive form. To become active, enzymes must undergo slight conformational changes in the structure to accommodate the substrate. A suitable analogy would be that of hand and gloves.
The hand corresponds to the substrate and glove as the enzyme is shaped by the insertion of the hand. Enzymes that follow the induced-fit mechanism are called regulatory or allosteric enzymes e.g. hexokinase.
3.3 Factors Affecting The Rate of Enzyme Action
The activity of enzymes is affected by the following factors.
Temperature:
Heat increases molecular motion. As the temperature rises from "zero" reacting molecules of substrate and enzyme will get more and more kinetic energy. This increases the chance of a successful collision and so the rate of reaction increases. For every 10°C rise in temperature, the rate of enzyme is approximately.
There is a specific temperactivity doubles at which an enzyme catalytic activity is fastest and
this is known as optimum temperature. The optimum temperature for enzymes found in humans is 37°C. After this point, the rate of enzyme activity will decrease at 45-50°C.
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