Answer in Brief
Long answer question.
Describe classes of proteins with their importance.
On the basis of structure, proteins are classified into three categories:
- Simple proteins:
- Simple proteins on hydrolysis yield only amino acids.
- These are soluble in one or more solvents.
- Simple proteins may be soluble in water.
- Histones of nucleoproteins are soluble in water.
- Globular molecules of histones are not coagulated by heat.
- Albumins are also soluble in water but they get coagulated on heating.
- Albumins are widely distributed e.g. egg albumin, serum albumin, and legumelin of pulses are albumins.
Importance: They are involved in structural components; they also act as a storage kind of protein. Some are associated with nucleic acids in nucleoproteins of cells.
- Conjugated proteins:
- Conjugated proteins consist of a simple protein united with some non-protein substance.
- The non-protein group is called the prosthetic group e.g. haemoglobin.
- Globin is the protein and the iron-containing pigment haem is the prosthetic group.
- Similarly, nucleoproteins have nucleic acids.
- Proteins are classified as glycoproteins and mucoproteins.
- Mucoproteins are carbohydrate-protein complexes e.g. mucin of saliva and heparin of blood.
- Lipoproteins are lipid-protein complexes e.g. conjugate protein found in the brain, plasma membrane, milk etc.
Importance: They are involved in structural components of cell membranes and organelles. They also act as a transporter. Some conjugated proteins are important in the electron transport chain in respiration.
- Derived proteins:
- These proteins are not found in nature as such.
- These proteins are derived from native protein molecules on hydrolysis.
- Metaproteins, peptones are derived proteins.
Importance: They act as a precursor for many molecules which are essential for life.
Concept: Biomolecules in the Cell
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