Download Ms Gentry`s Proteins powerpoint File

Biological Molecules:
Proteins
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Links to GCSE
Bonding
Balanced diet & food tests
Hormones & immunity
Haemoglobin
• Give the functions of some proteins.
• Describe the structure of an amino acid.
• Explain what is meant by ‘essential’ and
‘non essential’ amino acids.
Key definition:
Amino acids
 Amino acids are the monomers of all
proteins. All amino acids have the same
basic structure. The 20 different amino
acids involved in protein synthesis differ
only in the R-group bonded to the central
carbon
Amino acid structure showing R-group (side chain)
Week 14
Basic amino acid structure - glycine
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Amino acids
 There are about 20 standard amino acids.
 Around 8 of these are known as ‘essential amino acids’ because they
are required in the diet.
 The rest can be synthesised by the body.
 Most are found in meat.
 Soya is a good source for vegetarians.
 The amino group makes an amino acid toxic when too much is
present so we do not store excess amino acids.
 The removal of the amino group by the liver is called DEAMINATION.
 It produces UREA, removed by urination.
• Describe the formation and breakage of peptide
bonds in the synthesis and hydrolysis of
dipeptides and polypeptides.
• Explain the term primary structure.
• Explain the term secondary structure with
reference to hydrogen bonding.
• Explain the term tertiary structure with reference
to hydrophobic and hydrophilic interactions,
disulfide bonds and ionic interactions.
Week 14
Condensation and hydrolysis
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Key definition
 The primary structure of a protein is
given by the specific sequence of amino
acids that make up the protein.
Week 14
Primary structure of insulin
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Week 14
Four-amino-acid structure
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Forming different proteins
 In a polypeptide that is 4 amino acid residues
long,
 any of the 20 amino acids may be present at
any position in the chain.
 Therefore there are 20x20x20x20 possible
combinations.
 This equals 160,000 different sequences with a
mere 4 amino acids.
 A small protein may be 100 amino acids long.
 Therefore, in theory, the number of different
possible proteins is immense!
Enzymes
 Covalent bonds are VERY strong and do not
simply form nor fall apart.
-Protease enzymes break peptide bonds not
just in the digestive system e.g. hormones
must be broken down when their effect is no
longer required
 Skin loses elasticity because it is difficult to
rebuild collagen in older skin when it is broken
down.
 Other (complex!) reactions involve anabolic
enzymes e.g polymerase to build molecules
up.
Key definition: secondary
structure
 Refers to the coiling and pleating of parts of the
polypeptide molecule.
 The specific order of the amino acids is
determined by the DNA.
 Hydrogen bonds stabilise the long molecules
as they are produced and so is dependent on
the primary structure.
 This may be an alpha helix or beta pleated
sheet
Week 14
Alpha helix and polypeptide chain
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Key defintion: tertiary
structure
 Refers to the overall 3D structure of the
final polypeptide or protein molecule.
 This is vital to its function.
Week 14
The bonds responsible for maintaining tertiary structure
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Individual student
presentations
 Title: Denaturation
 5-8 slides to explain the science behind
the term.
 Use images.
 No more than 15 words per slide.
 Work alone or in pairs.
 BEWARE only 1 of pair will be randomly
selected to present!
Week 14
• Explain the term quaternary structure with
reference to the structure of haemoglobin.
• Describe the structure of a collagen molecule.
• Compare the structure and function of
haemoglobin and collagen.
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This document may have been altered from the original
Key definition:
Quarternary structure
 Refers to the fact that some proteins are
made up of more than one polypeptide
subunit joined together, or a polypetide
and an inorganic component.
 These polypeptide units may be identical
or not.
Globular vs fibrous proteins
 There are 2 categories of 3d shapes
 Globular proteins roll up into a compact globe
-Hydrophobic r groups tend to turn inwards towards the
centre
-Hydrophilic r groups tend to be on the outside
-This makes the protein water soluble
 Fibrous proteins from fibres.
-Most have regular repetitive sequences of amino
acids and are usually insoluble
-Collagen fibres consist of 3 alpha helix coils, coiled
around each other to form a superhelix!
Haemoglobin
 Present in red blood cells
 2 α and 2 β chains
 Haem group with an
Iron ion to carry O2
 Coloured bright red in
combination with O2
Collagen: structural molecule
Week 14
Collagen structure
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This document may have been altered from the original
•Give the functions of some proteins.
•Describe the structure of an amino acid.
•Explain what is meant by ‘essential’ and ‘non essential’ amino acids.
•Describe the formation and breakage of peptide bonds in the synthesis and hydrolysis
of dipeptides and polypeptides.
•Explain the term primary structure.
•Explain the term secondary structure with reference to hydrogen bonding.
•Explain the term tertiary structure with reference to hydrophobic and hydrophilic
interactions, disulfide bonds and ionic interactions.
•Explain the term quaternary structure with reference to the structure of haemoglobin.
•Describe the structure of a collagen molecule.
•Compare the structure and function of haemoglobin and collagen.