1-4 Proteins

Question 1

What are proteins?

Answer 1

• Amino acids are the monomers from which proteins are made.
• Amino acids contain, an amino group (NH2), carboxylic acid group (COOH) and a variable R group which is a carbon containing chain.
• Joined by peptide bonds formed in condensation reaction.
• Dipeptide contains two amino acids.
• Polypeptide contains three or more amino acids.

Question 2

Describe the structure of proteins?

Answer 2

• Determined by the order and number of amino acids, bonding present and the shape of the protein.
• Primary structure, order and number of amino acids in a protein.
• Secondary structure, shape that the chain of amino acid chains form, either alpha helices or beta pleated sheets. These are held together by hydrogen bonds.
• Tertiary structure, 3D shapes of the protein and is formed from further twisting and folding. These are held together with disulphide bridges, ionic bonds and hydrogen bonds.
• Proteins can be globular, enzymes and compact, or fibrous such as keratin and long so can be used to form fibres.

Question 3

What is the biuret test?

Answer 3

• The biuret test can be used to test for the presence of peptide bonds in a protein.
• 1. Place the sample in a test tube and add sodium hydroxide.
• 2. Add a few drops of copper sulphate solution and mix.
• 3. A purple colouration indicates the presence of a peptide bond and hence a protein. Negative result, solution would remain blue.

Question 4

What are enzymes?

Answer 4

• Enzymes increase rate of reaction by lowering the activation energy of the reaction.
• They are 3D tertiary structured globular proteins.
• Active site, area of enzyme made up of only a few amino acids and forms a small depression in the overall enzyme.
• The molecule that the enzyme acts upon is called the substrate.
• Enzymes are specific to substrates.
• When an enzyme and substrate bind it is called an enzyme substrate complex and the structure of the enzyme is altered so that the active site of the enzyme fits around the substrate. This is called the induced fit model.

Question 5

What are the factors that affect the rate of enzyme-controlled reactions?

Answer 5

• Temperature
• pH
• Enzyme concentration
• Substrate concentration