What Are Proteins?

Proteins And The Body Part 1 by Jane Thurnell-Read

Although cells synthesise many different chemicals, a large part of the cellular machinery is devoted to producing proteins. Proteins determine the physical and chemical characteristics of cells and so are vitally important.

Proteins are used to produce enzymes, some hormones, organelles (cellular machinery), muscle (e.g. actin and myosin), structural components of skin and hair (e.g. collagen and keratin), plasma (blood) protein, antibodies, etc. The instructions for producing proteins are coded within the genes.

Proteins consist of amino acids that always contain carbon, hydrogen, oxygen and nitrogen. Proteins are giant molecules made by linking large numbers of amino acids, end to end, so they form a chain. In nature more than 100 amino acids are found, but only 20 are used in humans. The reason for this is that these 20 provide all the chemical and size groups needed to make a very large number of proteins. These 20 different amino acids join up in a variety of ways to make approximately 250,000 different human proteins. The same amino acid can occur many times along a chain making up a specific protein.

The amino acids are like letters and the proteins are like very big words. As with words the exact position of the letters is important: ‘male’ and ‘lame’ produce completely different images even though they are made up of exactly the same letters. The amino acids are made up of other letters - the DNA bases (nucleotides):

• A (adenine)
• T (thymine)
• G (guanine)
• C (cytosine)

There are only 4 DNA bases but there are 20 amino acids, so a sequence of three bases (a triplet) is used to code for each amino acid, e.g.

C-C-G = glycine
A-G-T = serine

If there is the sequence C-C-G-A-G-T this signals the amino glycine followed by the amino serine in the protein ‘recipe’. An insulin molecule consists of 51 amino acids; haemoglobin is 600 amino acids and collagen is 3000.

When all the amino acids are in place, they fold and coil and takes on the characteristic shape for that protein. The shape is determined by the function of the protein, e.g. keratin is in flat, flexible sheets suitable for inclusion in skin; some muscle proteins are long and thin; haemoglobin has spaces for haem to fit in so that it can be carried around the body.

Enjoyed this? Then have a look at Proteins & The Body part 2.