Proteins (Biology)

  • Proteins are polypeptide structures which are made up of amino acids, connected by a peptide bond.
  • Amino acids have a general formula @@IMAGE___, where 'R' is the side chair
  • Glycine is the simplest amino acid, as its 'R' group is hydrogen.
  • Only L-form (Laevorotatory) of amino acids are used by human body cells; D-form is usually taken by bacterial cell walls.
  • Antibiotics, ornithine, Citrulline, GABA, Diaminopimelic acid are certain non protein amino acids.
  • Sulfur-containing amino acids are methionine, cysteine.
  • Serine and threonine are alcoholic amino acids.
  • Phenylalanine, Tyrosine, Tryptophan are considered as aromatic amino acids.
  • Lysine and Arginine are positively charged amino acids.
  • Amino acids exist as Zwitterion / Dipolar ionic form, where the same compound exhibit both (+) and (−)ve charge, at a certain pH point, called as isoelectric point (PI).
  • Nerve cells produce peptides called enkephalins for the response of pressure and pain.
  • The four configurations of protein structure are
    Primary structure
    Secondary structure
    Tertiary structure and
    Quaternary structure
  • The linear chain of amino acids connected by peptide bonds starting with amino terminal and ending with carboxy terminal, is 1° structure of a protein and the length between 2 amino acids are 0.35nm.
  • Secondary structure is of 2 types. (i) α-helices (ii) β-sheets.
  • α-helices are formed due to intermolecular ‘H’ bonding. Eg: keratin, fibrin, myosin.
  • β-sheets are developed due to intermolecular ‘H’ bonding, which is of 2 types. Parallel β-sheet (eg. β-keratin) and Antiparallel sheet (eg. Fibroin of silk).
  • Tertiary structure is a 3-D structural globelar format, which is soluble in aqueous solution. All the enzymes exist definitely in the tertiary state which is formed by many other bonds.
  • More than one 3° are connected to form quarternary.
  • Amino acids are of 2 types.
    (i) Non-essential (The amino acids produced by the body cells itself).
    (ii) Essential (which has to been taken through diet).
  • All the essential amino acids are present in a first class protein source. Eg. Milk, egg, soya, meat etc. If one (or) 2 essential amino acids are missed in a protein, then it is named as incomplete amino acids. Eg. Plant proteins except for soya.

View this video for the topic proteins from 3:33 to 40:35

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