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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