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Cell Molecules Part 3 - Proteins

Cell Molecules Part 3 - Proteins:

Structure of protein:

  • Proteins are made up of amino acids which are joined together by peptide bonds.
  • Amino acids are amphoteric in nature as it contains an amino group (-NH2) and a carboxyl group (-COOH).
  • Example – Hemoglobin, Chlorophyll


  • Structure of protein is determined by the number of amino acids and their kind and order in which they arranged in the polypeptide chain.
  • Proteins are globular or fibrous in shape.
  • Globular proteins play a functional role and fibrous protein plays a structural role.

Biological importance of protein:

  • Protein is the main constituent of enzymes which are responsible for biochemical reactions in cells.
  • Proteins helps in formation of many hormones which regulates many metabolic activities of cell
  • Antibodies made up of proteins and provides resistance against invading pathogenic bacteria
  • It helps in respiration process by transport of oxygen.

Nucleic acids:

Structure of nucleic acids:

  • Nucleic acids are polynucleotide made up of by joining two or more nucleotide unit together.
  • Example- DNA and RNA
  • Each nucleotide is made up of three sub units – sugar, nitrogenous base and phosphoric acid.
  • Sugar is pentose type where DNA contains Deoxyribose sugar and RNA contains rebose sugar.
  • Nitrogenous base are cyclic compound and are of two types
1.  Purine – Adenine and Guanine
2.  Pyrimidine – Cytosine, Thymine and Uracil

  • DNA does not contains uracil and RNA does not contain thymine
  • Phosphoric acid is associated with phosphate.

Formation of nucleic acid:

  • A nitrogenous base attached with sugar by covalent bond and forms nucleoside
  • Nucleoside is then attached with phosphoric acid by ester bond and forms nucleotide.
  • Nucleotide joins together by phspho-di-ester bond and forms a chain of nucleotide called as polynucleotide.
  • RNA contains one polynucleotide chain whereas DNA contains two polynucleotide chains.

Biological importance of nucleic acid:

  • It acts as a currency of energy in cell in form of ATP.
  • It is associated with co-enzymes and vitamins
  • They are responsible for inheritance inc all organism.

Self study:

Example-1: Which of the following is not present in DNA?
a)  Adenine
b)  Guanine
c)  Cytosine

d)  Uracil

Answer: DNA does not contain Uracil.

Example-2:  Nucleic acids are responsible for …………..in all organisms
a) 
Inheritance
b)  Respiration
c)  Reproduction
d)  None

Answer: Nucleic acids are responsible for inheritance in all organisms


Example-3: Which of the following is the building block of proteins?
a)  Carboxylic acid
b)  Alcohol
c) 
Nucleic acid
d)  Water

Answer: Nucleic acids are the building blocks of proteins.



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