MPSC Notes - Protein Structure Parts -I

Protein Structure Review

Protein Structure
Review of Peptide Bond
Conformations and More

1. What are proteins? How can the protein diversity of living beings be explained?

Proteins are molecules made of sequences of amino acids bound by a peptide bond.

The genetic code codifies twenty different amino acids that can compose proteins. So there are numerous combinations of amino acid which can form polypeptide chains and for this reason protein molecules can be immensely diverse.

2. What is the importance of proteins for living beings?

Proteins play a fundamental role in nearly all biological processes. Due to their diversity they can assume many different configurations and they can play varied roles in cells and tissues.

Some protein functions are noteworthy: the structural function (cell membrane proteins, cytoskeleton proteins, proteins of the connective tissue), the enzymatic function (enzymes are proteins), the energy storage function (proteins can be degraded into acetyl-CoA and “cycle” the Krebs cycle), the osmotic regulation function (albumin), the transportation function (membrane channels, respiratory pigments), the immune protection function (antibodies), the movement function (contractile proteins), the endocrine integration function (hormones) and the informative function (membrane receptors, intracellular signalers). There are also many proteins whose biological functions are not yet known.

3. What is the constitutional unit of proteins?

The constitutional units of proteins are the amino acids.4. What is an oligopeptide? How is it different from a polypeptide?

Peptide is the molecule formed by the union of amino acids through the peptide bond. Oligopeptide is a peptide made of few amino acids (oligo = few). Polypeptides are peptides with many amino acids (poli = many), in general more than 50.

5. How many are the known amino acids that form proteins in living beings?

There are twenty different known amino acids that form proteins related to the genetic code of the living beings.

There are still many other amino acids as yet not known.

6. Does every amino acid have a central carbon? To which organic group is that central carbon bound?

A carboxyl group –COOH, an amine group – NH2, an atom of hydrogen –H and a variable radical -R necessarily are bound to the central carbon of an amino acid.

7. How can amine groups be classified?

Amines can be classified into primary amines, those to which one –R (variable radical) is attached to a –NH2, secondary amines, those where one hydrogen of NH2 is substituted by another –R, thus having two –R, and tertiary amines, those with no hydrogen bound to the nitrogen and with three –R.

8. What is the structural representation of a carboxyl group?

Carboxyl groups have a carbon attached to one hydroxyl group by a simple bond and to one oxygen by a double bond. The other site of binding in the carbon is available to other chemical entities.

9. What is the structural flat representation of an amino acid molecule?

An amino acid has a central carbon to which a carboxyl group binds on a side and to which a –R (variable radical) binds on the opposite side. In the perpendicular direction of those ligands an amine group binds the central carbon on one side and a hydrogen binds on the opposite side.

The bind of the carboxyl group to a carbon where a hydrogen is laterally attached is responsible for the name “acid” in amino acids. The bound of an amine group in the central carbon provides the name “amino”.

10. What is the importance of the –R group (variable radical) in an amino acid molecule?

The –R group, also called a lateral chain, is the variable part of the amino acid molecule. The –R group can be a complex carbonic chain, a substituting methyl group (forming then the amino acid alanine) or even only a hydrogen (forming glycine, the simplest amino acid). So the –R group is important because it is the differentiation factor of amino acids.

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