Proteins and their functions

Proteins, they are vital to human life, approximately 18% of the body is composed of them (Fullick, 1994). They have many functions of which two and their structure will be discussed during this essay.
Proteins are made from amino acids which are considered the ‘building blocks’ of life. Below is an example (Figure one) of an amino acid, adapted from Boyle and Senior (Human biology, 2008, p.46).

Figure 1. Structure of amino acid

O R H

C C N

HO H H

As the example shows, the amino is made from oxygen (O), carbon (c), nitrogen (N). The element ‘R’ is known as the variable group. It differs between amino acids. When they come together the form what is called a peptide bond. They react to other amino acids and the reaction is known as condensation reaction, water is also formed during this process. They form dipeptide bonds then a polypeptide, this when more than three amino acids bond, which in turn forms a protein, like so;

Amino Acid- Peptide bond- Dipeptide bond- Polypeptide bond- Protein.

Primary Structure

The first structure of protein regards the number and the formation the amino acids are sequenced. These chains of amino acids are bound together by peptide bonds in what is called a polypeptide chain. (Boyle & Senior 2008, p.47) give an example of a simple protein polypeptide chain.

Alanine- Histidine- Phenylalanine- Glutamine- Cysteine

They do note however, that a small protein would normally consist of as little as 51 amino acids and not five, but for illustration purposes five are used.
Figure two shows the primary structure.
What the protein will be is determined by the sequence of the amino acids in the chain. Figure Two (www.studyblue.com)
Secondary Structure

The secondary structure is what happen when the amino acids begin to join together and fold. This is due to what is known as iconic bonding, a combination of metals and non-metals and hydrogen bonds. The resulting shapes can take two forms; α helix, which can be described analogously to a spiral staircase and β pleated sheet, similar to a sheet of cardboard with bumps across it. Figure three shows this.

Figure 3.

(Www.studyblue.com)

Tertiary Structure

The tertiary structure is where most proteins cease developing. This stage witnesses the forming of the proteins three dimensional shape. Both the helix and pleated sheet twist and turn, then when combined form a globular shape. As noted by Boyle and Senior (Boyle and Senior, 2008, p.48), the tertiary structure is vital for the protein to function. The structure of the protein reinforces it, thus giving it more strength. As noted this were proteins stop developing, as if a protein consists of just one polypeptide this will become its final stage. In figure four the two forms, helix and the pleated shape can be seen together.

Figure 4. α helix and ß pleated sheet

(www.chemguide.co.uk)
Quaternary structure

For proteins that advance to this stage, it is due to the protein consisting of more than one polypeptide chain. Boyle and Senior (2008, p.49) note that this stage occurs when several polypeptide chains combine with non-proteins to make it an extremely complex molecule. These non-protein groups can be also known as prosthetic. The polypeptides will contain the same amount of amino acids too. Figure five shows the final stage of structure.

Figure 5. Quaternary structure

(www.chemistry.umeche.maine.edu)

The first function of a protein that will discussed is its function as an enzyme.

The enzyme is vital to humans. Their primary