Ptroteins

(1) The word protein was coined by Berzelius in 1838 and was used by G. J. Mulder first time 1840.  

(2) 15% of protoplasm is made up of protein. Average proteins contain 16% nitrogen, 50–55% carbon, oxygen 20–24%, hydrogen 7% and sulphur 0.3 – 0.5%. Iron, phosphorous, copper, calcium, and iodine are also present in small quantity.

(3) Structure of proteins: It is due to different rearrangement of amino acids. When carboxyl group of one amino acid binded with amino group (– NH2) of another amino acid the bond is called peptide bond. A peptide may be dipeptide, tripeptide and polypeptide. The simplest protein is Insulin. According to Sanger (1953) insulin consists of 51 amino acids. A protein can have up to four level of conformation.

(i) Primary structure: The primary structure is the covalent connections of a protein. It refers to linear sequence, number and nature of amino acids bonded together with peptide bonds only. e.g. ribonuclease, insulin, haemoglobin, etc.

(ii) Secondary structure: The folding of a linear polypeptide chain into specific coiled structure (α - helix) is called secondary structure and if it is with intermolecular hydrogen bonds the structure is known as ß - pleated sheet. α - helical structure is found in protein of fur, keratin of hair claws, and feathers. ß - pleated structure is found in silk fibres.

(iii) Tertiary structure: The arrangement and interconnection of proteins into specific loops and bends is called tertiary structure of proteins. It is stabilized by hydrogen bond, ionic bond, hydrophobic bond and disulphide bonds. It is found in myoglobin (globular proteins).

(iv) Quaternary structure: It is shown by protein containing more than one peptide chain. The protein consists of identical units. It is known as homologous quaternary structure e.g. lactic dehydrogenase. If the units are dissimilar, it is called as heterogeneous quaternary structure e.g. hemoglobin which consists of two α - chains and two ß - chains.

Nucleic Acid

 (1) Definition: Nucleic acids are the polymers of nucleotide made up of carbon, hydrogen, oxygen, nitrogen and phosphorus and which controls the basic functions of the cell.

(2) These were first reported by Friedrich Miescher (1871) from the nucleus of pus cell.

(3) Altmann called it first time as nucleic acid.

(4) They are found in nucleus. They help in transfer of genetic information.

(5) Types of nucleic acids : On the basis of nucleotides i.e. sugars, phosphates and nitrogenous bases, nucleic acids are of two types which are further subdivided. These are DNA (Deoxyribonucleic acid) and RNA (Ribonucleic acid).

(A) DNA (Deoxyribonucleic acids) 

(i) Types of DNA: It may be linear or circular in eukaryotes and prokaryotes respectively.

(a) Palindromic DNA: The DNA helical bears nucleotide in a serial arrangement but opposite in two strands.

                              -T-T-A-A-C-G-T-T-A-A….

                              -A-A-T-T-G-C-A-A-T-T….

(b) Repetitive DNA: This type of arrangement is found near centromere of chromosome and is inert in RNA synthesis. The sequence of nitrogenous bases is repeated several times.

(c) Satellite DNA: It may have base pairs up to 11 – 60bp and are repetitive in nature. They are used in DNA matching or finger printing (Jefferey). In eukaryotes, DNA is deutrorotatory and sugars have pyranose configuration.

(B) RNA or Ribonucleic acid: RNA is second type of nucleic acid which is found in nucleus as well as in cytoplasm i.e. mitochondria, plastids, ribosomes etc. They carry the genetic information in some viruses. They are widely distributed in the cell.