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Complete this table which is about the names given to the structural levels of protein!
Level Structural stage
Symbol
1st 1o
2nd Secondary
3rd
4th
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1.6 Proteins
• LO:• How are amino acids linked to form
polypeptides – the primary structure of proteins?
• How are polypeptides arranged to form the secondary structure and then tertiary structure of a protein?
• How is the quaternary structure of a protein formed?
• How are proteins identified?
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Proteins –uses in the body?
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Amino acid structure:
Draw the general structure of an amino acid and label the groups using a your ingenuity.
Basic amino acid structure - glycine
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Formation of a peptide bond:
Condensation
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Breaking of a peptide bond:
Hydrolysis
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Primary structure:
• Many amino acids (monomers) can be joined (polymerisation) by what reaction?
• Condensation.• The chain of many hundreds of
amino acids is called a polypeptide.• The sequence of amino acids forms
the primary structure.primary structure.
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Primary structure:
• The primary structure of a protein determines its shape and therefore its function.
• Change one amino acid in the polypeptide and you will change the shape of the protein.
• Simple proteins consist of a single polypeptide chain.
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Primary structure:
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Secondary Structure:
• -NH group are +ve. • The O of the –C=O
group is –ve. • -NH and –C=O
groups on either side form hydrogen bonds.
• The polypeptide is twisted into a 3-D shape called the α-helix.
• Sometimes you can get B-pleated configurations too
Alpha helix and polypeptide chain
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Tertiary Structure:
• The α helix can be twisted and folded even more to give a complex 3-D structure.
• This structure is maintained by 3 types of bond.
• Disulfide bonds Disulfide bonds (S)(S)
• Ionic bondsIonic bonds• Hydrogen bonds Hydrogen bonds
(more)(more)
The bonds responsible for maintaining tertiary structure
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Quaternary Structure:
• Large proteins may consist of more than 1 polypeptide chain.
• The quaternary structure arises from the combination of a number of different polypeptide chains and associated non-protein (prosthetic) groups.
• E.g. Haemoglobin – 4 polypeptide chains, each one with Fe at the centre
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Protein Structure:
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• Task – use the diagrams to explain how the structure of haemoglobin has been produced
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Complete this task on page 22
Primary structure of insulin
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Frederick Sanger & Insulin
1918 – 2013)
British biochemist who won the Nobel Prize for Chemistry twice,
(1 of only 2 people to
have done so in the
same category)
• Sanger's first triumph was to determine the complete amino acid sequence of the two polypeptide chains of bovine insulin in the 1950’s.
• Sanger proved that proteins have a defined chemical composition, which people hadn’t believed before then.
• By extension of it, it was concluded that every protein had a unique sequence.
• It was this achievement that earned him his first Nobel prize in Chemistry in 1958.
• This discovery was crucial for the later sequence hypothesis of Crick for developing ideas of how DNA codes for proteins.
Functions of Proteins
• Fibrous proteins – structural, e.g. collagen. • Globular proteins – metabolic functions, e.g.
haemoglobin.
• It is their structure that allows them to carry out their functions.
Collagen structure
1o structure – repeating units of proline, alanine and glycine
2o structure – tightly wound polypeptide
3o structure – tightly wound into another helix
4o structure – tightly wound - 3 polypeptide chains together like a rope
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Tasks:
• Make notes on the test for proteins (page 28)
• Answer summary questions on page 28
• Answer Application questions on page 29