Proteins

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Proteins
Largest and most diverse group, many functions:
Structure Enzymes Transport Pumps Motors Hormones Receptors Antibodies
Storage Blood Clotting Lubrication Toxins Antifreeze and more!
Proteins are made of amino acids, made up of Carbon, Oxygen, Hydrogen, Nitrogen and Sulphur.
The general structure is shown below:
H2N: Amino group (base)
H: a Carbon
COOH: Carboxylic acid group (acidic)
R: Variable group
Opposite chains, acid and base, have opposite charges. The charge changes with PH change, this
explain the effect PH has on enzymes as they are proteins.
There are twenty different R groups and so twenty different amino acids each with different
properties.
Polypeptides
Amino acids are joined together with peptide bonds, this is a condensation reaction, so water is
formed from it. The new molecule formed from two is known as a dipeptide, three it is a tripeptide
and then polypeptide for more than three. In a polypeptide there is always a free amino group and a
free carboxyl group.
Structure of Proteins
Primary
Sequence of amino acids in the polypeptide chain .
Secondary
Basic protein folding
The secondary structure is held together by hydrogen bonds between the carboxyl groups
and the amino groups in the polypeptide backbone. The two most common secondary
structure motifs are the -helix and the -sheet.

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A helix: Polypeptide chain wound to form helix, held together by hydrogen bonds running
parallel with a helical axis, the sheer number of hydrogen bonds mean this is a very stable
and strong structure
B helix: Polypeptide chain zigzags back and forward forming a sheet of anti-parallel
strands, held by hydrogen bonds.
Tertiary Structure
Compact globular structure formed by folding of entire polypeptide chain, tertiary structure of
every protein unique, responsible for properties and function.…read more

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