Proteins
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Proteins are compounds that contain
Nitrogen in addition to C, H, and O.
Consist of one or more chains of amino
acids.
Amino Acids
Structural unit of protein
Contains:
1. A carboxyl group (COOH)
2. An amino acid group (NH2) – amine
3. A single H atom
4. A side chain which is different in each
amino acid - R
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20 different amino acids are found as part
of proteins (8 amino acids are essential
because they cannot be made by people)
The 20 amino acids can be linked together
in any sequence whatsoever, and in chains
of varying lengths. This explains why there
are so many proteins.
A chain of amino acids is called a
polypeptide.
All proteins are made up of one or more
polypeptide chains.
Seven Classes of Proteins based
on Function
1. Enzymes - (biological catalysts) which enable
complex chemicals; reactions to take place with
precision and speed
2. Structural Proteins – form parts of the body
of an organism such as hair, nails, and the
tough materials of cartilage and connective
tissue.
3. Signal Proteins – Hormones are the chemical
messengers that regulate body functions in
plants and animals.
4. Contractile Proteins – are involved in
movement. Actin and myosin are
proteins that enable muscles to contract.
5. Storage Proteins – e.g. albumin /
ovalbumin - the protein store that forms
the white of eggs.
6. Defensive Proteins – Antibodies, which
protect animals bodies against foreign
substances and disease organisms.
7. Transport Proteins – E.g. hemoglobin,
the carrier of oxygen in the blood
Shapes of Proteins
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Protein shapes are broadly categorized into
two categories: fibrous or globular.
Fibrous proteins have elongated shapes,
tend to be insoluble in water and physically
tough, e.g. keratin, collagen
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Globular proteins tend to be compact and
rounded and they are water soluble.
Enzymes and antibodies are globular
proteins.
Peptide Bond
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The bond formed between two amino
acids by dehydration synthesis, (the amino
group of one amino acid and the carboxyl
group of the adjacent amino acid).
4 levels of structure in a protein
1.
2.
Primary structure - sequence of amino
acids that are organized in a linear
arrangement.
Secondary structure - Hydrogen
bonds between amino acids causes the
protein to arrange in helical coils or in
pleated sheets.
3. Tertiary Structure - 3D shape is formed
when the R groups interact, folding the
polypeptide in 3 dimensions and forming a
unique shape. The bonds holding the
tertiary structure together can only form if
the amino acids are in the correct order.
4. Quaternary structure. More than one
polypeptide chain chemically bonds to
each other. E.g. hemoglobin has 4
polypeptide chains.
Denaturation is a change in 3D shape of a
protein caused by changes in
temperature, pH, ionic concentration or
etc.
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Readings: P. 35 - 49