Collagen is a fibrous protein that is found in skin, tendons, cartilage, bones and the walls of blood vessels. It is an important structural protein for not only just us humans but almost all animals. Like all proteins collagen is made up of the basic components of amino acids.
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(b)
In the above diagram there is a visual representation of a collagen molecule. The molecule consists of three polypeptide chains (it is not an Alpha-helix as it isn’t as tightly wound). The three helical polypeptides wind round each other to make a three stranded ‘rope’ shape. Inside each polypeptide chain there are amino acids and almost every third amino acid is glycine. This allows the three strands to lie close together because of its small size. The three strands that wind up are held together by hydrogen bonds. Each complete collagen molecule (three stranded) interacts with other collagen molecules which run parallel to it. Bonds form between the R groups of lysine in molecules lying next to each other. These cross-links made hold many collagen molecules together which are side by side, this forms fibres. The ends of these parallel molecules are staggered; if they weren’t there would be a weak spot running right across the collagen fibre. Collagen has tremendous tensile strength; it needs to be like this as it needs to withstand large pulling forces.
Protein has a countless amount of jobs and another one is transport. The most obvious transport protein in the human body is haemoglobin. Haemoglobin, the oxygen carrying pigment which is found in red blood cells, is a globular protein. It is made up of four polypeptide chains. Two of the four chains make an identical pair and they’re called ‘Alpha chains’. The other two make another identical pair but are different from the first two pair and are called ‘Beta chains’. The haemoglobin molecule is a near spherical shape.
The haemoglobin molecule contains
two α-globin chains (pattern A) and
two ß-globin chains (pattern B).
Two of the four haem molecules
are visible (pattern C).
The four polypeptide chains are packed closely together with their hydrophobic R groups pointing the centre and their hydrophilic ones pointing away from the centre. Each of the two Beta chains has a tertiary structure. The interactions between the hydrophobic R groups in the molecule are important in maintaining its correct 3-dimensional shape. The outward hydrophilic R groups play a part in keeping the solubility of the haemoglobin. It is important in having a polar amino acid on the outside of the molecule in the R group such as glutamine, by having a non-polar amino acid you make the haemoglobin less soluble and this causes unpleasant and hazardous symptoms in anyone whose haemoglobin is full of this ‘faulty’ type.
Each polypeptide chain contains a haem group which is an important and permanent part of protein molecules but it isn’t made up of amino acids. This is called a prosthetic group. Each of these heam groups contains an ion iron, Fe ². One oxygen molecule can bind with each iron ion. Because of this a complete haemoglobin molecule can carry four oxygen molecules on the four heam groups. It is the heam group which is responsible for the colour of haemoglobin. The colour changes depending on whether or not the ion irons are combined with the oxygen molecule.
Most Enzymes are proteins and can be described as catalysts. Most if not every metabolic reaction which takes place within a living organism is catalysed by enzymes.
Enzymes are globular proteins. Like all globular proteins, enzyme molecules are coiled into a specific three-dimensional shape with side chain hydrophilic R groups on the outside of the molecule. This ensures that the enzyme is soluble. Enzymes have a special feature and this is that they posses an active site. This is a region on the enzyme to which another molecule or molecules can bind onto it. This is the substrate of the enzyme. The shape of the specific shape allows the substrate to fit in just right. Also it is held by temporary bonds. This is called the enzyme-substrate complex as a simplified diagram below shows.
Each type of enzyme acts on a specific type of enzyme that the enzyme is fit to do as the shape of its active site has a specific shape that only allows that one type of substrate to fit in. The enzyme may catalyse a reaction causing the substrate molecule to split (2 or more) as shown in the diagram. Alternatively catalysing may cause a joining of two molecules. After this process the molecules leave the unchanged enzyme leaving it for another substrate molecule to go and bond onto it.
Hormones such as insulin are proteins. It is a small protein which brings blood sugar levels down from high levels. Disulphide bonds are found in hormones such as insulin. The hormone insulin in made by the pancreas and is released to bring sugar levels down. It turns glucose into glycogen which is a storage sugar in animals. Diabetic people use insulin injections to keep their sugar levels low.
Protection against viruses is important and antibodies help in getting rid of viruses. Antibodies are also proteins. Antibodies come from white blood cells and are in the blood stream. Any foreign molecule that is detected is an antigen and what antibodies do is detect these foreign molecules and isolates them. By engulfing them and dissolving the dangerous molecule. The virus or dangerous molecules are memorized by the antibodies so if the same virus or dangerous molecules appear, they can be gotten rid of quickly and efficiently.
Proteins are used in so many ways for many different things and there are so many ways of creating a chain of amino acids in numerous orders. This enables protein to do much more than just one thing and can take different 3-dimensional shapes to do the job that it needs to do whether it be a transport protein or an enzyme.
Bibliography: These are the sources that I used to do my essay:-
Cambridge: Advanced Sciences Biology 1 (OCR) Book