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What are proteins?

Proteins are the most important biological molecules.

---> They are made up of the monomer, amino acids.

There are 20 amino acids in total.


Amino acids all have the same strucutre.

They have an amino group, a carboxyl group and a central carbon atom.

Each amino acid also has an R group. This group varies with each amino acid.

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Peptide bonds

Two amino acids can form a peptide bond.

How it forms:-

1) The carboxyl group of one amino acid and the amino group of the other  line up against each other.

2) This reacts and produces water - making this a condesation reaction.

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Structures of Proteins

There are four main structures of proteins:-

!) Primary Structure -  A long polypeptide change.

2) Secondary Structure -  Interactions between amino acid chains cause chains to form in 3D sections. (e.g. the alpha helix and beta-pleated sheets).

3) Tertiary Structure - The overall (often completed) protein shape. (There are ionic, hydrogen an disulfide bonds.)

4) Quarternary Structure - Some proteins have more then one chain and the arrangement of those is the quartenary structure. (The many chains can be called subunits.)

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Testing for Proteins

The Biuret Test

1) Place the sample to be tested in a test tube and add an equal volume of sodium hydroxide at room temperature.

2) Add a few drops of very dilute copper(ii) sulfate and mix gently.

3) A purple discolouration indicates the presence of peptide bonds, therefore a protein. No discolouration equals no protein.

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Types of proteins

There are two types of proteins, fibrous and globular.

Fibrous - These are proteins formed by parallel polypeptide chains held together by crosslinks.

              - Long, rope-like fibre.

              - High tensile strength.

              - Insoluble in water.

Examples include:- collagen (in skin'), keratin (nails, hair etc), silk.

Globular - Forms a spherical shape.

                - Caused by tightly folded polypeptide chains.

Examples include:- Transport proteins (haemoglobin etc), Enzymes (e.g. lipase) and hormones (oestrogen, insulin etc).

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