Describe the condensation reaction involved in joining two amino acids together.
OH from the carboxylic acid group reacts with the H from the amine group in a condensation reaction. This removes a water molecule and forms a peptide bond between them. This is called a dipeptide (di=2)
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What is formed when many amino acids join together?
polypeptide chain.
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How do you calculate the number of peptide bonds in a polypeptide chain?
number of peptide bonds = number of amino acids - 1
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What are the 4 levels of protein structure?
Primary structure, secondary structure, tertiary structure and quaternary srtucture
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What is the primary structure of a protein?
The number and sequence of amino acids i the polypeptide chain. The primary structure is held by peptide bonds and it determines the tertiary structure of a protein such as an enzyme.
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What is the secondary structure of a protein?
The way the polypeptide chain folds or coils into alpha helixes and beta pleated sheets. Secondary structure is maintained by hydrogen bonds.
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What is the tertiary structure of a protein?
Further folding of the polypeptide chain into a specific three dimensional shape (for example an enzyme with its active site)
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What bonds form in the tertiary structure of a protein?
Hydrogen bonds (weak and break at high temperatures), ionic bonds form between oppositely charged R groups (weak and also break at high temperatures), disulphide bridges form between sulphur containing R groups (covalent and don't break at high temps
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What is the quaternary structure of a protein?
Two or more polypeptide chains chemically bonded, for example haemoglobin = 4 polypeptide chains chemically bonded
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How does a protein with quaternary structure become a conjugated protein?
If there are additional groups, such as iron in Haemoglobin, then the protein becomes a conjugated protein.
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What does the Biuret test test for?
The presence of peptide bonds
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Describe the Biuret test for proteins.
Place a small amount of the sample in a test tube and add Biuret solution. Colour change from blue to lilac/purple indicates the presence of protein, if it remains blue there is no protein present.
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What is chromatography?
Using a solvent to separate a mixture into its individual substances, these can then be identified. The substances in the mixture separate as they are soluble by different amounts.
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How do you calculate the RF value?
RF value = distance from origin to centre of amino acid spot / distance from origin to solvent front.
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How could you carry out two way chromatography?
Run the chromatogram in one direction then rotate 90' to further separate the substances or use a different solvent for the second run.
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Describe the tertiary structure of a protein.
Tertiary structure determined by the sequence & number of amino acids in the primary structure. Hydrogen, ionic and disulphide bonds form between the amino acid R groups, forcing the chain to fold into a specific 3D shape, essential for function.
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