as 2 1 1 protein structure

8/10/2019 As 2 1 1 Protein Structure

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Proteins from Amino Acids

Two amino acids joined together make a

dipeptide, as more and more join together by

peptide bonds, a polypeptide is formed

The amino acids in a polypeptide chain are

sometimes referred to as residues because

part of the molecule is lost in the

condensation reaction that produces the

peptide bond


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Protein Synthesis

Polypeptides are made (synthesised)

inside cells on the ribosomes.

Messenger RNA (mRNA) puts the amino

acids in the right order to make a specific

polypeptide chain


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Protein Synthesis

As the mRNA passesthrough the ribosome,the amino acids arejoined one at a time by a

condensation reactionforming a peptide bond

Eventually a longer andlonger chain of aminoacids is formed

The mRNA determinesthe sequence of aminoacids and therefore thetype of protein


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Forming Different Proteins

We will look at a peptide chain that is 3amino acids long.

The R group of an amino acid may be any

one of the 20 available.

To calculate the total number of different

possibilities, we need to multiply the totalnumber of possibilities at each point.

In this case: 20 x 20 x 20 = 8000

This means that 8000 different sequences

of four amino acids are possible- 8000

different proteins can be made.

Given that most proteins are 100 amino

acids long, in theory the number of different

possible proteins is extremely large


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Protein Structure Task

We can look at proteinsin various levels ofdetail. The first is theirprimary structure, this isfollowed by the

secondary, tertiary andquaternary structures

Task: Using CambridgeBiology p110- 113, anda two page spread in

your book, summarisethe 4 levels of proteinstructure (including thebonding involved)


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Primary Structure

The sequence of amino acids that formsthe protein


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Secondary Structure

The chain of amino

acids coils or folds to

form an alpha helix or

a beta pleated sheet Hydrogen bonds hold

the coils in place

weakly, but as so

many are formedthey give stability to

the protein molecule


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Tertiary Structure

When the coils and pleats themselves coil or fold

Held together by:

Disulphide bonds: a covalent bond between 2 sulphuratoms

Ionic bonds: the R groups are sometimes charged (+veor ve) so they attract each other

Hydrogen bonds: +ve hydrogen atoms and ve oxygenatoms attract

Hydrophobic and hydrophilic interactions: hydrophobicamino acids will be drawn into the centre of themolecule, and hydrophilic amino acids will be found onthe outside.


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Heating Proteins

Heating a protein increases the kinetic

energy in the molecule

This causes the molecule to vibrate,

breaking the bonds

as 2 1 1 protein structure

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