An Account of Proteins and Their Structure
It is difficult to describe in a simple sentence the role of proteins.
When there is something to do, it is a protein that does it.
Some examples of proteins
* Antibodies: they recognize molecules of invading organisms.
* Receptors: part of the cell membrane, they recognize other
proteins, or chemicals, and inform the cell.
* Enzymes: assemble or digest.
The role (or function) of a protein depends on its shape, and chemical
Proteins play a number of vital roles in all organisms. Unlike
carbohydrates and lipids they always contain nitrogen as well as
carbon, hydrogen and oxygen. Sulphuris often present.
The building blocks of the proteins are amino acids. Proteins are made
of a long chain of amino acids, sometimes modified by the addition of
sugars and phosphates. Amino acids unite to form proteins in much the
same manner the monosaccharides combine to form polysaccharides, and
fatty acids and glycerol combine to form fats and oils. This happens
when two amino acids reacts. The reaction occurs between the amino
group of one amino acid and the carboxyl group of another. To make
this happen a condensation reaction has to occur which involves the
removal of a molecule of water. Once this happens two amino acids
become joined by a peptide link to form a dipeptide. To form a
polypeptide a series of condensation reactions must happen which forms
a longer chain. The individuality of a particular protein is
determined by the sequence of amino acids comprising its polypeptide
chains, together with the pattern of folding and cross-linkages.
primary structure of a proteinThe primary structure is the sequence of
amino acids, which form a chain connected by peptide bonds. The amino
acid sequence of a protein determines the higher levels of structure
of the molecule. A single change in the primary structure (the amino
acid sequence) can have a profound biological change in the overall
structure and function.
The secondary structure is the way a small part, saptially near in the
linear sequence of a protein folds up into:
secondary structure Alpha - Helix: the first structure described by
Linus Pauling. It has a rod shape. The peptide is coiled around an
imaginary cylinder and stabilized by hydrogen bonds formed between
components of the peptide bonds.
Beta - pleated sheets: the amino acids adopt the conformation of a
sheet of paper and the structure is stabilized by hydrogen bonds
between amino acids in different polypeptide strands. Note that some
of the strands are parallel and some are antiparallel.
Other parts of the structure are not highly stable, and adopt a random
The tertiary structure refers to the way random coils, alpha helixes...