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Learning objectives:
· How are amino acids linked to form polypeptides ­ the primary
structure of proteins?
· How are polypeptides arranged to form the secondary structure
and then the tertiary structure of a protein?
· How is the quaternary structure of a protein formed?
· How are proteins identified?
Specification reference: 3.1.2…read more

Slide 2

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protein is a Greek word meaning of `first
· Proteins are very large molecules.
· The types of carbohydrates and lipids in all organisms are
relatively few and they are very similar.
· each organism has numerous proteins that differ from
species to species. The shape of any one type of protein
molecule differs from that of all other types of proteins.
Proteins are the most important molecules to life.
· One group of proteins, enzymes, is involved in almost every
living process.
· There is a vast range of different enzymes that between
them perform a very diverse number of functions.…read more

Slide 3

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Structure of an amino acid
· Amino acids are the basic monomer units which combine to make up a polymer called a
polypeptide. Polypeptides can be combined to form proteins. About 100 amino acids have been
identified, of which 20 occur naturally in proteins.
· Every amino acid has a central carbon atom to which are attached four different chemical groups:
· amino group (--NH2) - a basic group from which the amino part of the name amino acid is derived
· carboxyl group (--COOH) - an acidic group which gives the amino acid the acid part of its name
· hydrogen atom (--H)
· R group - a variety of different chemical groups. Each amino acid has a different R group.
· The general structure of an amino acid is shown on the next slide.…read more

Slide 4

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Slide 5

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The formation of a peptide bond
· amino acid monomers can combine to form a dipeptide.
· The process involves the removal of a water molecule in a
condensation reaction.
· The water is made by combining an --OH from the carboxyl group
of one amino acid with an --H from the amino group of another
amino acid.
· The two amino acids then become linked by a new peptide bond
between the carbon atom of one amino acid and the nitrogen atom
of the other.
· The formation of a peptide bond is illustrated in the next slide. In
the same way as a glycosidic bond of a disaccharide can be broken
by the addition of water (hydrolysis), so the peptide bond of a
dipeptide can also be broken by hydrolysis to give its two
constituent amino acids.…read more

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