Biomolecules: Biological Importance of Carbohydrates and Proteins (For CBSE, ICSE, IAS, NET, NRA 2022)

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Biological Importance of Carbohydrates

  • Carbohydrates act as storage molecules. For example, they are stored as starch in plants and as glycogen in animals.
  • D-Ribose and 2-deoxy-D-ribose are the constituents of RNA and DNA, respectively.
  • Cell walls of bacteria and plants are made up of cellulose. It may be of interest to note that human digestive system does not have the enzymes required for the digestion of cellulose, but some animals do have such enzymes.
  • Some carbohydrates are also linked to many proteins and lipids. These molecules are known as glycoproteins and glycolipids, respectively. These molecules perform very specific functions in organisms.

Proteins

Proteins are the most abundant macromolecules in living cells. The name protein is derived from the Greek word ‘proteins’ meaning ‘of prime importance’ . These are high molecular mass complex amino acids.

Classification of Proteins

Proteins are classified on the basis of their chemical composition, shape and solubility into two major categories as discussed below.

Simple Proteins

Simple proteins are those which, on hydrolysis, give only amino acids. According to their solubility, the simple proteins are further divided into two major groups fibrous and globular proteins.

  • Fibrous Proteins: These are water insoluble animal proteins e. g. collagen, elastin՚s, keratins are good examples of fibrous proteins. Molecules of fibrous proteins are generally long and thread like.
  • Globular Proteins: These proteins are generally soluble in water, acids, bases or alcohol. Some examples of globular proteins are albumin of eggs, globulin (present in serum) , and hemoglobin.

Conjugated Proteins

  • Conjugated proteins are complex proteins which on hydrolysis yield not only amino acids but also other organic or inorganic components. The non-amino acid portion of a conjugated protein is called prosthetic group.
  • Unlike simple proteins, conjugated proteins are classified on the basis of the chemical nature of their prosthetic groups.

These are:

  • Nucleoproteins (protein + nucleic acid)
  • Mucoproteins and glycoproteins (protein + carbohydrates)
  • Chromoproteins (proteins + a colored pigment)
  • Lipoproteins (proteins + lipid)
  • Metalloproteins (metal binding proteins combined with iron, etc.)
  • Phosphoproteins (proteins attached with a phosphoric acid group) .

Structure of Proteins

Protein molecules are polymers of different sizes and shapes with different physical and chemical properties. The monomer units for proteins are amino acids. All the amino acids that are found in proteins have an amino group on the carbon atom adjacent to carbonyl group, hence are called amino acids.

Structure of Proteins

The actual structure of a protein can be discussed at four different levels.

  • Primary structure: Information regarding the sequence of amino acids in a protein chain is called its primary structure. The primary structure of a protein determines its functions and is critical to its biological activity.
  • Secondary structure: The secondary structure arises due to the regular folding of the polypeptide chain due to hydrogen bonding between and group. Two types of secondary structures have been reported. These are α – helix when the chain coils up and β-pleated sheet when hydrogen bonds are formed between the chains.
  • Tertiary structure: It is the three-dimensional structure of proteins. It arises due to folding and superimposition of various a-helical chains or b- plated sheets.
  • Quaternary structure: The quaternary structure refers to the way in which simple protein chains associate with each other resulting in the formation of a complex protein.

Biological Importance of Proteins

  • Proteins are structural components of cells.
  • The biochemical catalysts known as enzymes are proteins.
  • The proteins known as immunoglobins serve in defense against infections.
  • Proteins participate in growth and repair mechanism of body tissues.
  • A protein called fibrinogen helps to stop bleeding.

Lipids

Those constituents of the cell which are insoluble in water and soluble in organic solvents of low polarity (such as chloroform, ether, benzene etc.) are termed as lipids.

Nucleic Acids

It has been discovered that chromosomes are composed of nucleic acids. These are named so because they come from the nucleus of the cell and are acidic in nature. Two types of nucleic acids exist which are called DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) .

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