Types of protein
Proteins are complex nitrogenous organic compounds.
Protein consists of carbon, oxygen, hydrogen, nitrogen and sometimes sulphur, phosphorous, iron and other elements in varying amounts.
They are building blocks of body tissues.
They are composed of different amino acids joined by peptide linkage (bond).
Dietary proteins are broken down to amino acids which are absorbed from the gastrointestinal tract.
Depending upon chemical complexity, Types of protein are of three. They are:
Types of protein
1. Simple proteins :
These proteins are formed of amino acids linked by peptide bonds.
e.g. albumin and globulin etc.
2. Conjugated proteins
(e.g. haemoglobin, casein and membrane proteins etc)
are proteins present with other compounds like carbohydrates (glycoprotein) and lipids (lipoprotein) etc.
3. Derived proteins
These proteins are obtained by partial hydrolysis of proteins.
e.g. peptides and proteases etc.
The human body requires twenty different amino acids for the synthesis of human proteins.
The amino acids are the basic units of protein.
Depending upon the capacity of formation of protein in the body,
The amino acids are classified as essential and non-essential amino acids.
a. Essential amino acids
The human body can not produce 10 out of 20 amino acids at an adequate rate. So, these amino acids must be present in our diet and these amino acids are known as essential amino acids.
Essential amino acids include leucine, isoleucine, lysine, valine, phenylalanine, tryptophan, methionine and threonine.
Two amino acids (arginine and histidine) are essential only during rapid tissue growth periods. (e.g. during childhood and recovery from illness).
b. Non-essential amino acids
Non-essential amino acids are the amino acids, that produces inside the human body.
They may or may not be present in the diet.
They include glycine, alanine, serine, tyrosine, cysteine, aspartic acid, asparagine, glutamic acid, glutamine and proline.
Dietary sources of proteins
1. Animal sources
It includes milk, meat, egg, and fish, etc.
They contain all essential amino acids in adequate amounts.
2. Plant sources
It includes pulses, cereals, beans and nuts, etc.
They do not contain all essential amino acids.
Soybean is the richest source of plant protein.
Daily requirements of proteins
Healthy adults should consume 50-60 grams of protein per day.
The RDA for protein is 0.8 gram per kg body weight for adults,
1 gram per kg body weight for athletes and 2 gram per kg of body weight for children.
Pregnant women require 30 gram per day in addition to their basal requirements.
Functions of proteins
Proteins are the most important compounds of the body with diverse functions.
The functions of proteins are as follows:
1. They are building blocks of body tissues.
2. They help in the growth and development of our body.
3. Proteins like collagen and proteoglycan are the structural components of different body tissues.
4. When carbohydrates and fats are not available, proteins can provide energy to our body.
5. Blood clotting factors (e.g. thrombin and fibrinogen) are the proteins which prevent haemorrhage.
6. They also perform storage function (e.g. ferritin and myoglobin).
7. They transport insoluble components in the blood.
8. They are necessary for movement and locomotion.
Deficiency of protein
Deficiency of protein causes malnutrition which includes marasmus and kwashiorkor.
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