Protein Molecules example essay topic

How the Molecular Structure of Carbohydrates, Proteins and Lipids affect their function in living things. Living cells contain many small molecules such as water and inorganic ions like nitrogen. They also contain a vast number of larger molecules, called macromolecules that are built from smaller, simple molecules. They are also known as organic molecules because they contain carbon. All living things on earth are carbon based life-forms because the element can bond with itself repeatedly to form an infinite variety of molecules. Carbohydrates are organic molecules, including all sugars and starch, and contain three elements: carbon, hydrogen and oxygen.

Carbohydrates are the first molecules produced in photosynthesis, as lipids, proteins and nucleic acids are synthesised from them. There are three basic types of carbohydrate molecule; monosacharides, disaccharides and polysaccharides. Monosacharides are monomers or single sugars, the type varying on the number of carbon atoms in the chain. A disaccharide is a double sugar made from two monosacharides, and like monosacharides they are classed as sugars.

Polysaccharides are multiple sugars, or polymers of many monosacharides. Monosacharides are the chemical building blocks of other important carbohydrates. They are sweet-tasting, soluble in water and capable of reducing other chemicals by donating electrons to other substances. Glucose is a monosaccharide and is widespread within living things.

It is the main source of energy for a large number of organisms and most of the common polysaccharides are glucose polymers. Glucose is a hexose and has 6 carbon atoms in its chain and has the formula C 6 H 12 O 6. All other hexose sugars have the same formula, such a B-Glucose, Fructose and Galactose. They have the same formula, but have slightly different structure and so are known as Isomers of each other.

The differences are very small but do greatly affect properties such as sweetness, digestibility and the nature of the polymers formed when the monomers join together. When monosacharides link they join together in a condensation reaction and a glycosidic link is formed. Disaccharides are formed from the condensation of two units of glucose by a glycosidic bond. They are again, sweet tasting and soluble in water, however they may not be reducing as in some types of Disaccharide there are no free electrons. Polysaccharides come in two main divisions. Structural Polysaccharides, in which the sugar unit residues present in long chain molecules of the polymer are straight and cross linkages between chains occur giving the material strength.

The other division, Storage Polysaccharides, are used for storing sugar molecules so they are not used up immediately by the cells. The general properties are a contrast to both monosacharides and disaccharides as polysaccharides are non-sweet tasting and not truly soluble in water. Starch is the most abundant storage chemical within plants and consequently is the single largest provider of energy for most of the world's population. Starch has the three properties that are necessary for a storage compound.

It is compact, insoluble and readily accessible when needed. It is a mixture of two compounds, amylase and amylopectin. Glycogen is the human equivalent to starch as a storage carbohydrate. The structure is similar to amylopectin but is even more frequently branched. During frequent exercise when the immediate supply of glucose is used up the body restores its supplies by breaking down glycogen. Cellulose is an example of a structural polysaccharide, and it gives strength and rigidity to plant cell walls.

Cellulose molecules are long unbranched chains of containing glycosidic linkages of B-glucose. The molecules are straight and lay side by side forming hydrogen bonds along their length. The result of which are strong bundles of chains called micro fibrils that form a strong lattice arrangement. Lipids are a group of compounds that include fats and oils. Lipids contain the elements carbon, hydrogen, oxygen and sometimes phosphorus and nitrogen. The triglycerides, which act mainly as energy stores within plants and animals are a large and important group of lipids.

They consist of one glycerol molecule bonded with 3 fatty acids through a condensation reaction. The glycerol molecule is consistent in all triglycerides and so the different properties are dependant upon the nature of the fatty acids. Fatty acids vary in the length of the chain and the degree of saturation. A saturated fatty acid already has the maximum amount of hydrogen and therefore has no double bonds. Unsaturated fatty acids possess one or more C = C bond. Triglycerides generally form "hard" fats such as lard and suet that are solid at room temperature.

This is due to the length of the carbon chain and the degree of saturation of the fatty acids. Many animals store energy in the form of triglycerides as they yield more than twice as much energy as proteins or carbohydrates. They are highly reduced compounds as they contain many C-H bonds which yield energy during respiration. Phospholipids have a similar structure to Triglycerides but one of the fatty acids is replaced by a polar phosphoric acid. The result of which is the molecule receives a polar head and a non polar tail.

When placed in water one end is hydrophilic and the other, hydrophobic which results in bilayers. Phospholipid bilayers form the basis of all biological membranes. Proteins have a central part in the structure and metabolism of all living things. Protein molecules have a huge variety of shapes and sizes and it is this versatility that gives proteins such a key role in the cells. Proteins make up different enzymes which are each designed to catalyze a specific cellular metabolic reaction. Proteins make up the carrier molecules that each substance requires to pass a cell membrane.

Proteins make up every different antibody which are needed to combat the chemicals produced by the many (and constantly changing) disease causing organelles. Structurally proteins are large and complex molecules. In addition to the elements carbon, hydrogen and oxygen, proteins always contain nitrogen and sometimes sulphur. The basic chemical building blocks are called amino acids. All amino acids contain an amino group and a carboxylic acid group.

Both these groups are attached to a central carbon atom, known as the alpha carbon which is the backbone of the amino acid. The R group varies between different amino acids and is what allows the great variation between them. Amino acids are readily soluble in water. When in solution they can resist a change in pH by mopping up or releasing both hydrogen ions and hydroxyl ions, accepting as buffers, that is, regulators of pH. Maintaining a constant pH is an important aspect of homeostasis.

Amino acids join together in long chains to form proteins by means of peptide bonds via a condensation reaction.