1. Our body is close to 20% protein and many of the foods we eat also contain protein.

2. Amino acids are the building blocks of proteins. Amino Acids

3. Amino acids link together to form polypeptide chains. Polypeptide Chains Link Together Amino Acids

4. Proteins are made up of one or more Polypeptide Chains And proteins are typically very large molecules made up of one or more polypeptide chains. Polypeptide Chains Link Together Amino Acids

5. Here, we’ll look at how amino acids link together to form polypeptide chains, Polypeptide Chains Link Together Amino Acids

6. And how polypeptide chains break apart into their building blocks, amino acids. Amino Acids Break Apart Polypeptide Chains

7. The general formula for an amino acid can be depicted as a molecule like this. R CCN O OH H H H The General Formula for an Amino Acid

8. All amino acids have an Amino group, which is the NH2. R CCN O OH H H H The General Formula for an Amino Acid Amino Group

9. And a carboxyl group, which is COOH. This can also be called a carboxylic acid group. It is the amino group and the carboxylic acid group that gives these compounds the name amino acids. R CCN O OH H H H The General Formula for an Amino Acid Amino Group Carboxyl Group

10. The R group in this general formula represents various side chains that can be attached to the central carbon atom. There are 21 amino acids used in our body, which means there are 21 different side chains that can be represented by R. R CCN O OH H H H The General Formula for an Amino Acid Side Chain

11. If we replace the symbol R by (click) a single hydrogen atom, we get the simplest amino acid, which is called (click) glycine R CCN O OH H H H H Glycine

12. If we replace the symbol R by (click) a methyl group, CH3, we get the amino acid, which is called (click) alanine R CCN O OH H H H CH 3 Alanine

13. Replacing R with this group (click), gives us the amino acid called (click) valine. R CCN O OH H H H Valine CH CH 3 H3CH3C

14. Some contain the element sulphur like (click) this one, giving us the amino acid (click) methionine R CCN O OH H H H Methionine S CH 2 CH 3 CH 2

15. Some contain a benzene ring, or phenyl group like (click) this one, giving us the amino acid (click) phenylalanine. Using a biology text book or searching on the internet, you can find tables that show you the structures for all 21 amino acids. R CCN O OH H H H Phenylalanine CH 2

16. Here we have two amino acids beside each other. We have used the letter “R” to represent any of the 21 possible side chains.

17. One of the H atoms on the amino group of one amino acid,

18. And the OH from the carboxyl group on a neighbouring amino acid, can be removed in a dehyration synthesis…

19. This releases a water molecule and the two amino acids bond together. water Dehydration Synthesis

20. To form a larger molecule made up of two amino acids. This is called a (click) dipeptide A Dipeptide water

21. The new bond that forms between the carbon with the oxygen on one amino acid and the nitrogen atom on the other amino acid, is called (click) a peptide bond. A Dipeptide water A Peptide bond

22. In a new dehydration synthesis, another amino acid bonds to the dipeptide to form a larger peptide chain… Dehydration Synthesis

23. Dehydration synthesis can continue and the peptide chain continues to grow, while water molecules are released.. Dehydration Synthesis

24. A large number of amino acids bonded together, form a polypeptide chain. Polypeptide chains can get very large, and can contain hundreds or even thousands of amino acids. A Polypeptide Chain

25. Proteins are made up of one of more Polypeptide Chains A Polypeptide Chain Proteins are made up of one of more Polypeptide Chains

26. Proteins are synthesized in the ribosomes found in our cells and in the cells of other animals and also plants. Ribosomes Free Ribosomes

27. 12 of the 21 amino acids humans require can normally be made by our cells (with some exceptions).

28. These are called non-essential amino acids because we don’t need to get them from the foods we eat.

29. 9 of the amino acids required cannot be synthesized in our body.

30. They are called the essential amino acids because we must get these from the foods we eat.

31. To get essential amino acids into our bloodstream, we first need to digest proteins in foods that we eat. In our digestive system, when appropriate enzymes are present,

32. polypeptide chains in these proteins (click) break apart into smaller peptide molecules, and eventually into (click) amino acids. Amino Acids Break Apart Polypeptide Chains

33. Here is a small polypeptide chain. If we add a (click) water molecule to this in the presence of the correct enzyme, a (click) hydrolysis reaction will take place (click). Hydrolysis

34. And an amino acid will be removed from the chain like this. Hydrolysis Amino Acid

35. Another water molecule can be added in the process of hydrolysis, releasing another free amino acid. Hydrolysis Amino Acid

36. As more water molecules are added to this peptide chain, hydrolysis eventually breaks it down into single amino acids. Hydrolysis

37. To review, we’ve seen how amino acids link together to form polypeptide chains using the process of dehydration synthesis. Polypeptide Chains Link Together Amino Acids

38. Proteins are made up of one or more Polypeptide Chains And that proteins are very large molecules made up of one or more polypeptide chains. Polypeptide Chains Link Together Amino Acids

39. Proteins in the foods we consume are made up of polypeptide chains. Polypeptide Chains Proteins are made up of one or more Polypeptide Chains

40. polypeptide chains in these proteins (click) break apart into smaller peptide molecules, and eventually into (click) amino acids using the process of (click) hydrolysis Amino Acids Break Apart Polypeptide Chains Hydrolysis