1. OPTION B: Human Biochemistry B2: Proteins

2. Objectives Jan 3, 2010 B.2.1 Draw the general formula of 2-amino acids B.2.2 Describe the characteristic properties of 2- amino acids. B.2.3 Describe the condensation reaction of 2-amino acids to form polypeptides B.2.4 Describe and explain the primary, secondary, tertiary structure of proteins. B.2.5 Explain how proteins can be analysed by chromatography and electrophoresis. B.2.6 List the major functions of proteins in the body.

3.  Natural polymers made by amino acids.  Proteins important to humans are made of 20 α-amino acids (in data booklet) Essential amino acids: amino acids our body cannot synthesize (10) Complete protein: a protein made of essential amino acids, e.g. casein (milk, eggs, soybeans) Jan 3, 2010Human Biochemistry3

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8. Jan 3, 2010Human Biochemistry8 H + + H 2 N-CHR-COO - ← H 3 N + -CHR-COO - → H 3 N + -CHR-COOH + OH - >At low pH >Extra H + reacts with OH - >[OH - ] drops >Equilibrium shifts to the right >H 3 N + -CHR-COOH form >positive charge >At high pH >Extra OH - reacts with H + >[H + ] drops >Equilibrium shifts to the left >H 2 N-CHR-COO - form >negative charge >At isoelectric point >identical ionizations >only zwitterion > H 3 N + -CHR-COO - form > no net charge

9. Jan 3, 2010Human Biochemistry9 H 3 N + -CHR-COO - + H + → H 3 N + -CHR-COOH + H 2 O >when H + is added >equilibrium shifts to right >[H + ] drops >pH remains the same >buffer action >when OH - is added >equilibrium shifts to left >[OH - ] drops >pH remains the same >buffer action H 2 O + H 2 N-CHR-COO - ← OH - + H 3 N + -CHR-COO -

10. Jan 3, 2010Human Biochemistry10

11. Jan 3, 2010Human Biochemistry11 Amino Left Acid Right

12. Jan 3, 2010Human Biochemistry12 Primary structure >sequence of amino acids >characteristic of protein function Secondary structure >folding of polypeptide chain >by Hydrogen bonds α-helix: between atoms of the same chain, e.g. hair, wool pleated sheet: between parallel chains, e.g. silk random coil: no repeating pattern Tertiary structure >3D shape of secondary structure > several types of interaction Quaternary structure >3D shape of tertiary structures of different polypeptide chains

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14. Jan 3, 2010Human Biochemistry14 Tertiary structure Myoglobin

15. Jan 3, 2010Human Biochemistry15 Quaternary structure Haemoglobin

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18. Structural (collagen, keratin) Catalysts (enzymes) Hormones (insulin) Antibodies (interferons) Transport (haemoglobin) Energy (from muscles) Jan 3, 2010Human Biochemistry18

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20. Jan 3, 2010Human Biochemistry20 distance traveled by compound distance traveled by solvent R f = R f is specific for each amino acid

21. Jan 3, 2010Human Biochemistry21 H + + H 2 N-CHR-COO - ← H 3 N + -CHR-COO - → H 3 N + -CHR-COOH + OH - >At isoelectric point (pH of buffer) >identical ionizations >only zwitterion > H 3 N + -CHR-COO - form > no net charge >not affected by electric field Different amino acids have different isoelectric points

22. Jan 3, 2010Human Biochemistry22 Electrophoresis (constant pH)

23. Jan 3, 2010Human Biochemistry23