A- Human body is majorly composed of proteins, which is important for our existence. Proteins are the main constituents of skin, muscles, organs, bones and nails.

The shape, size, structure and biological functions of proteins are determined by the number, type and arrangement of amino acids.

One of the important mechanisms of cell communication is through reversible phosphorylation and dephosphorylation of proteins. These reactions are catalysed by kinases and occur through a cascade mechanism.

Collagen is the most abundant protein in the animal world which accounts for 30% of total protein content in the human body. Collagen is a key constituent of all the connective tissues. It is found in joints, bones, skin, hair, etc. This protein helps the skin to move, stretch and rebound into shape. It is present throughout the body and keeps the cells together. Without collagen the body would fall apart into pieces. 

The Bt toxin is encoded by a gene named cry. The protein encode by cry IAb control corn borers.The protein encoded by the genes cry I Ac and cry II Ab control the cotton boll worms.

The numerous permeases that belong to ABC superfamily of proteins is present in number of bacterial cell. The ATP is hydrolysed by these proteins  to transport specific amino acids, sugars, vitamins, or even peptides into the cells. One such permease is galactose permease, which is responsible for transportation of galactose.

Proteins are the most important and versatile biomolecules in living systems. They are involved in general body-building, catalytic role as enzymes, and body defence in immunological reactions. Energy currency of living systems are usually nucleotides like ATP. They are hydrolysed to provide energy as and when required.

Proteomics is the cataloging and analyzing every protein in the human body most proteins differ in their folding manner .

Keratin is a simple fibrous protein, which is made up of only amino acids. It forms external protective structures of animals like hair, feathers, nails, horny layer of skin. Thus, the correct answer is B.

Proteins are large molecules of high molecular weight containing C, H, O and nitrogen (N) . The presence of N distinguishes them from carbohydrate and fat. Iron, copper, iodine, sulphur and phosphorus may also be present in a very low proportion. Proteins are found in fish, meat, egg, wheat, bean, ground-nut and pulses.

A) Keratin is the protein that is the structural material making up hair, horns, claws, hooves and the outer layer of human skin.

• Histones are a family of basic proteins that associate with DNA in the nucleus and help condense it into chromatin, they are alkaline (basic pH) proteins, and their positive charges allow them to associate with DNA.
  
• Five types of histones have been identified: H1 (or H5), H2A, H2B, H3 and H4.
• The core histones are H2A, H2B, H3, and H4, and the linker histones are H1 and H5. These types of histones are smaller, each consisting of 100-150 residues.
  
• H1 and its homologous protein H5 are involved in higher-order structures of chromatin consisting about 220 residues.
  
• The ratio of H1 and H3 proteins in chromatin is 1:2