Matric Notes Class IX Biology Proteins

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Proteins

Proteins are very important organic compounds found in all organisms. Proteins contain carbon, hydrogen, oxygen and nitrogen and sometimes some amount of sulphur. There is no 2:1 ratio between hydrogen and oxygen. A protein molecule is composed of many building units linked together to form a chain. A chain of amino acids is called polypeptide. Amino acids are building units of a protein molecule. About twenty different amino acids occur in nature that combines in different manners to make different type of proteins. Proteins are structural part of the cell membrane. Some proteins are fibrous. They form different structures in the body like muscles, bones and skin. They also occur in our blood and cells. The enzymes which control different chemical reactions in the body are also proteins in nature. As a result of protein catabolism, energy is released. One gram of protein produces 4.3 kilo cal of energy which is used to synthesize ATP.

Amino Acids

Plants can synthesize all the amino acids they need from carbohydrates, nitrates and sulphates but animals can not synthesize all amino acids. Amino acids are the building units of proteins.

There are about twenty different types of amino acids which are used in the synthesis of protein found in the human body.

Non-Essential Amino Acids

There are many amino acids which a human body can synthesize within the body. These are called non-essential amino acids.

Essential Amino Acids

There are approximately ten amino acids, which human beings cannot make. These are called essential amino acids and can be obtained directly from proteins in the diet.

Sources of Proteins

Following are the sources of proteins:

Animal Sources e.g. meat, fish, chicken, milk and cheese.

Plant Sources e.g. legumes, pulses, dry fruit and cereals.

Importance of Proteins in Human Body

1. Proteins are essentially required for growth and development.
2. Growing children ,pregnant women and lactating mothers need a lot of proteins.
3. An adult requires 50-100 gms of proteins daily.
4. Protein deficiency in children and cause a disease called Kwashiorkor.
5. Proteins play an important role in the building of cellular protoplasm.
6. They also play an important role in the building of muscles and connective tissues.
7. Many proteins are required for making enzymes, hormones and antibodies.
8. If proteins are eaten in excess than needed by body, the excessive amino acids are converted into carbohydrates by the liver, which are either oxidized to release energy and converted into glycogen and fat and stored.