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

Amino acids are the building blocks of proteins. Amino Acids

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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,

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

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

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

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

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

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

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

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

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