They are also used for transporting food reserves around in plants usually from the leaves as this is where starch (a polysaccharide) is produced and it is also the raw material used to produce ethanol which is an alcohol widely used in beverages.
Polysaccharides are comprised of many monosaccharides joined by glycosidic bonds. These are complex carbohydrates and are what starch, cellulose, glycogen and chitin are made of. Starch is the main food storage in plants and is the usual derivative of glucose in digestion used in aerobic respiration in plants and animals. Starch is made up of a mixture of two polysaccharides amylose and amylopectin with amylopectin only differing form amylose by having a branched structure.
Starch which is composed of amylose and amylopectin
Cellulose is made up of straight chain beta glucose joined by 1,4 glycosidic linkages and expresses optical isomerism. These straight chain structures encourage the formation of fibres joined by weak hydrogen bonds. Cellulose is what makes up the cell wall and is partially permeable allowing small nutrients to pass through and prevents the plant cell from bursting when turgid.
Cellulose
Glycogen is made of alpha glucose in a chain similar to amylopectin but more branched. It is stored in animals instead of starch and provides reserves of energy. The main glycogen storage is in the liver and in muscle tissue so aerobic respiration can happen when there is a lack of glucose.
Glycogen
Chitin is what exoskeletons are made up of. Like cellulose this is a polymer made up of beta 1,4 linked molecules but there are complex amine groups instead of a OH group the result of which is a tough and resilient exoskeleton found on most insects and arthropods.
Chitin
Proteins:
All proteins are polymers made up of amino acids. They contain the functional group for a carboxylic acid hence the term “acid” in amino acid and the elements present are that of oxygen, carbon, hydrogen and as the name “amino” suggests nitrogen. Proteins therefore have these elements present in them.
In order to form long chains which in turn form proteins they undergo condensation reactions to form peptide bonds (which is also reversible in the process of hydrolysis).
Individual molecules containing this atomic arrangement are called amino acids, which when joined to another by a peptide bond produces a dipeptide. This can go on to produce long complex chains called polypeptides producing proteins. With amino acids being the constituents of protein the protein contains composites of the amino acids. There are only 20 amino acids but they go on to make up thousands of different proteins.
The primary structure of a protein refers to the number of sequencing of amino acids in a polypeptide chain joined by peptide bonds. This determines the 3D shape of the protein.
The secondary structure refers to the folding of a polypeptide chain either in an alpha helix or a beta pleated sheet. Which is the type of structure found in fibrous protein such as keratin present in nails, hair and wool or collagen (the main protein present in connective tissue). The beta pleated sheet is a different form of a secondary structure where the polypeptide chains are folded and attached by weak hydrogen bonds this type of structure is present in the protein fibroin which is the main composite of silk.
The tertiary structure of a protein is the way in which its structure folds into a 3d globular shape which is held in place by weak hydrogen bonds, ionic bonds and disulphide bonds.
The Quarternary structure refers to the way that one or more polypeptide chains associate together to form a protein. This is what the structure of haemoglobin is composed of. Haemoglobin has four polypeptide chains and in it is a prosthetic group (iron or Fe) which bonds to the globular protein globing to form a conjugated protein.
Globular proteins are less physical in that they act as hormones, antibodies and other bodily secretions but they are indeed just as important as fibrous protein.
Proteins are very important as their order of sequencing (determined by genetics) allow for the shapes of cells to form and enable the ability to repair damaged tissues synthesized by the ribosomes of each individual cell which in turn is instructed by the genetic information stored in the nucleus which even then is partially determined by amino acids.
Lipids:
Lipids contain the elements Carbon, Hydrogen and Oxygen but there is a smaller portion of oxygen than there is in carbohydrates. Lipids occur in different forms such as oils, fats and waxes, the difference being that fats are solid at room temperature and oils are liquids at room temperature.
Lipids contain an OH group and a fatty acid chain characterised by the presence OH group and a carbonyl group at the end of their chains which is the functional group for a carboxylic acid.
Both fats and oils are made up from fatty acids and glycerol and occur as saturated fats or unsaturated fats. Saturated fats have repeating CH2 units linked by single bonds where the compound is full of hydrogen whereas unsaturated fats have double bonds between their carbon atoms and are not full of hydrogen.
The formation of mono, di or triglycerides happens in a condensation reaction when the OH groups on the end of glycerol (an alcohol) forms a single bond with an oxygen which then to for fill its valence, bonds with the other carbon atom, the result of which is a triglyceride and three molecules of water.
These oxygen linkages are called ester bonds.
A triglyceride
Fats are stored in adipose tissue and work to provide energy when needed which provide approximately 30Kj of energy per gram whilst carbohydrates provide 17Kj per gram.
Fats also provide insulation, which in amphibious mammals is specialised as blubber.
They also provide protection for delicate organs like the kidneys.
Another attributable function is that they provide the materials for cell membranes composed of phospholipids glycerol and 2 fatty acids.
This diagram shows the phospholipids arranged as they would be in the cell membrane. The hydrophilic heads point outwards and forms hydrogen bonds with water molecule whereas the hydrophobic tails point outwards.
Cholesterol is used to make certain types of lipids called sterols used to make steroid sex hormones like oestrogen and testosterone.
Waxes are fats which have an alcohol other than glycerol, these provide weather protection of some animals.
