Download Topic 2.2: Proteins

Topic 2.2a:
Proteins
Introduction
 CF
is caused by a faulty channel protein
in the cell surface membrane
 Water and salt transport is affected and
mucus is too sticky.
Protein Structure
 What
monomer are proteins made up of?
 Amino acids
 How many different types of amino acids
are there?
 20
 General stucture of amino acid:
Identify the amino groups, carboxylic acid groups and R
groups for each amino acid
The amino acids
Primary structure
2
amino acids can join together to form
dipeptides.
 Condensation reaction: water lost.
 Many amino acids join to form a
polypeptide.
Condensation reaction
forming a dipeptide:
Primary Structure
 The
sequence of
amino acids in the
polypeptide chain.

The primary structure
determines the
tertiary structure and
therefore the
function.
Secondary structure
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The C=O of the
carboxyl group and the
N-H of the amine group
can be attracted to
each other.
Hydrogen bonds form
between the H and the
O.
Alpha helix: H bonds
form between every 4th
amino acid
Beta pleated sheets
can also form: parallel
chains joined by H
bonds.
Secondary structure

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The C=O of the
carboxyl group and the
N-H of the amine group
can be attracted to
each other.
Hydrogen bonds form
between the H and the
O.
Alpha helix: H bonds
form between every
4th amino acid
Beta pleated sheets
can also form: parallel
chains joined by H
bonds.
Tertiary structure
 Proteins
have precise 3D shapes due to
bending and folding of peptide chains.
 Caused by interactions between R
groups.
 Covalent bonds (disulphide bridges)
 Ionic bonds
 Hydrogen bonds
 Also hydrophilic and hydrophobic
interactions
Tertiary structure


Unique 3D folding of
polypeptide due to
interactions between
the R groups.
Types of interactions
between R groups
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Covalent bonds
(disulphide bridges)
Ionic bonds
Hydrogen bonds
Hydrophillic and
hydrophobic
interactionshydrophobic R groups
face inwards and the
hydrophillic ones face
outwards
Tertiary structure

The primary structure ensures that R
groups are always in the same position,
therefore the bonding between Rgroups will always be the same, and
the hydrophobic and hydrophillic
interactions will always be the same
and therefore the tertialy structure of a
specific protein is always identical.
Image from Modis et al, Nature, 2004
Quaternary structure
 Proteins
composed of
more than one
polypeptide
chain have a
quaternary
structure
 Can be linked by
H-bonds, ionic, or
covalent bonds
Example of quaternary
structure:
The influenza virus envelope protein
Conjugated proteins
 Some
proteins have
another chemical
group added to
them.
 Examples:



Glycoproteins
Haemoglobin
Lipoproteins
Haemoglobin (right) is made up of 4
subunits, each carrying an ironcontaining heme molecule.
Fibrous and Globular
Proteins
 Use
your textbook (p. 64) to complete the
table comparing fibrous and globular
proteins.
Fibrous and Globular Proteins
Use your textbook (p. 64) to complete the table comparing
fibrous and globular proteins.
Globular - haemoglobin
Fibrous - Collagen
Globular Proteins
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Irregular amino acid sequence
Sequence highly specific and never varies between 2
examples of the same protein.
Polypeptide chains folded into spherical shape.
Length always identical in 2 examples of the the same
protein.
Relatively unstable structure.
Soluble
Metabolic functions
Examples: all enzymes, some hormones (insulin), and
haemoglobin
Fibrous Proteins

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Repetitive regular sequences of amino acids- may
vary slightly.
Polypeptide chains form long parallel strands.
Length of chain may vary in 2 examples of the
same protein.
Stable structure
Insoluble
Support and structural functions
Examples: collagen and keratin
Interactive Tutorial
 Activity
2.6