The Chemical Basis of Life-5
Lecture 23
ORGANIC MOLECULES:
2. Proteins
Life Chap. 3
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Figure 3.3 Substances Found in Living Tissues
Water
(70%)
The relative proportions of
these macromolecules is
similar in all living things!
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Proteins



large, complex molecules
made up of many smaller units called
amino acids, which are attached to
one another in long chains.
required for the structure, function, and
regulation of the body’s tissues and
organs.
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Proteins
They are the most structurally & functionally diverse group
of biomolecules
Function: involved in almost everything
 enzymes (control molecules)
 structure (keratin, collagen)
 carriers & transport (membrane channels)
 receptors & binding (defense)
 contraction (actin & myosin)
 signalling (hormones)
 storage (bean seed proteins)

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Protein Structure:
Proteins are made up of one or more
polypeptide molecules.
 Polypeptides are chains of amino
acids


Have a complex 3-D shape
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What Are the Chemical Structures of Proteins?
The primary structure of a protein is
its amino acid sequence.


amino acid sequence is determined by
DNA
the sequence determines the secondary
and tertiary structure i.e. how the
protein is folded.
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Primary
Assembly
PROCESS
STRUCTURE
Protein Structure…
Secondary
Folding
Tertiary
Packing
Quaternary
Interaction
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Amino acids Structure
central carbon
 amino group
 carboxyl group (acid)
 R group (side chain)

 variable group from 1 atom
to 20.
 confers unique
chemical properties
of the amino acid
O
H
H
||
|
—C—C—OH
—N—
|
H
R
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Generalised and specific amino acids
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Building proteins

Peptide bonds: dehydration
synthesis
 linking NH2 of 1 amino acid
to COOH of another
 C–N bond
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Building proteins

Polypeptide chains
 N-terminal = NH2 end
 C-terminal = COOH end
 repeated sequence (N-C-C) is
the polypeptide backbone

grow in one direction
Example: glycine & Phenylalanine
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



2 amino acids linked to form a Dipeptide
3 amino acids linked to form a Tripeptide
4-10 amino acids linked by a peptide bond
to form an Oligopeptide
more than 10 amino acids linked to form a
Polypeptide
Proteins in the body and diet are long
polypeptides (100s of amino acids)
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