Hint: One of the two types of proteins is globular proteins, the other being Fibrous proteins. Globular proteins have a structure that is compact and relatively spherical. As opposed to fibrous proteins that tend to have a structural role, globular proteins are soluble in water and tend to be involved in metabolic functions.
Hemoglobin, a member of the globin protein family, is among the most known globular proteins. The alpha, beta and gamma (IgA, IgD, IgE, IgG and IgM) globulins are other globular proteins. As well as many signal transduction proteins, almost all enzymes with major metabolic functions are globular in shape.
Albumins are globular proteins as well, although they are completely soluble in water, unlike all of the other globular proteins. In oil, they are not soluble.
Globular proteins, unlike fibrous proteins that only play a structural function, can act as:
1.Enzymes, by catalysing organic reactions, which occur in mild conditions and with great specificity in the organism. Different esterases perform this function.
2.Messengers, through the transmission of messages to control biological processes. 3.Hormones, i.e. insulin etc., do this function.
4.Transporters, through membranes, of other molecules
5.Amino acid stocks.
6.Globular proteins rather than fibrous proteins also carry out regulatory roles.
7.Structural proteins are globular and soluble as monomers, such as actin and tubulin, but polymerize to form long, stiff fibres.
Given the hundreds of thousands of proteins and the more elegant and descriptive structural motif vocabulary, the term globular protein is quite old (dating probably from the 19th century) and is now somewhat archaic. Without the aid of modern techniques, the globular nature of these proteins can be determined, but only through the use of ultracentrifuges or dynamic light scattering techniques.
Hence, the correct answer is option (C)
Note: Globular proteins are soluble and compact and are an integral part of biological processes in living organisms. They function as proteins, hormones, enzymes, and so on.