Molecular Microbiology Course

Outcomes: In this article I will be discussing aboutstructure of a protein it is not completely possible to
proteins and its structure.predict the entire structure of a protein accurately
WHAT ARE PROTEINS?just from the sequence
Proteins are a kind of macromolecules which mostlyTwo types of folding motifs can be seen in a
executes the genetically instructed programs andsecondary structure they are 1. Alpha helix: It is
tasks which takes places both inside and outside ofmainly characterised by hydrogen bonds along the
the cells, tissues and even organisms.chains. Hydrogen bonds between the chains help to
Proteins are determined in the form of primary,form the helix in the protein chain. The presence of
secondary and tertiary and quaternary structures.some amino acids like alanine, aspartic acid glutamic
Primary Structure:acid and leucine favours the alpha helix formation.
Proteins are the type of polymers which are formedThe presence of amino acids like proline and glycine
from alpha-amino carboxylic acids which is also knowndisrupt the alpha helix formation. Because of this
as amino acids.disruption of alpha helix it leads to the folding of
All the amino acids have amino group (+H3N) and aprotein molecules.
carboxyl group (Coo)-. These both amino and theBETA SHEETS:
carboxyl group are attached to the central atom (H)These are the parallel/antiparellel sheets. Parallel beta
Mostly amino acids differ from each other dependingsheet: In this the peptide chains which are adjacent
upon the side group attached to central carbon atomto each other proceeds in the same direction i.e., (in
Secondary Structure:the direction of N-terminal to C-terminal ends in the
In the secondary structure bond lengths and bondsame direction.) Anti -parallel sheets: In this type of
angles don't vary much.sheets the adjacent peptide chains proceeds in the
In proteins with similar function may typically haveopposite direction to the parallel sheets.
the same type of structure.TERTIARY STRUCTURE:
The proteins which have similar structure tend to beIt is the 3-dimensional structure of a polypeptide
more conserved than the exact sequence of thechain of a protein molecule. The secondary structures
amino acids.fold themselves which leads to the formation of
Even though the sequence helps to determine thethese tertiary structures.