Biological Molecules

AS BIOLOGY NOTES

UNIT 1: BIOLOGICAL MOLECULES

Biological Molecules

All cells in living organisms contain only a few groups of carbon based compounds that interact in similar ways.  Despite, the variation of life on Earth the biochemical basis for life is pretty similar.

Hydrogen: 1 bond

Oxygen: 2 bonds

Nitrogen: 3 bonds

Carbon: 4 bonds

The atoms of carbon, hydrogen, oxygen and nitrogen combine in different ways to form biological molecules.

Monomers are single subunits of molecules.  E.g. amino acids, nucleotides

Polymers are made of lots of monomers linked together.

A condensation reaction links two monomers together to form a di-mer.

Many monomers join together through a series of condensation reactions to form a polymer.

Every time a new bond is made through a condensation reaction a molecule of water is released.

Hydrolysis reactions are the opposite of condensation reactions.

This is where a water is added to polymers to break bonds and release monomers.

Carbohydrates

Monosaccharides

Monosaccharides are the single subunits, which make larger carbohydrates.  Glucose, fructose and galactose are the most common monosaccharides.  They all have the formula: C6H12O6, it is the arrangement of the atoms that makes them differ.

There are two structural isomers of glucose, called Alpha and Beta.  The difference between alpha and beta glucose is that on the first carbon the hydroxide group is below the ring in alpha but above in beta.

Monosaccharides link together by a condensation reaction, which removes water and forms a glycosidic bond through the remaining oxygen.

Disaccharides

There are three common disaccharides, which are: maltose, sucrose and lactose.  These are all formed through condensation reactions.

Polysaccharides

Polysaccharides are formed by the condensation reaction of many glucose subunits, which is a process known as polymerisation.  There are three common polysaccharides; starch, glycogen, cellulose

Starch

Starch is a plant storage carbohydrate.  It is made from alpha glucose.  Within starch, alpha glucose forms different structures.  These are called amylose (long chain, coils) and amylopectin (branches).

Glycogen

Glycogen is an animal storage polysaccharide.  It is formed from maltose forming condensation reactions with each other.  It is stored in muscle and liver cells as a result of excess glucose in the blood.  Like starch, it is insoluble, which is important in terms of osmotic properties of the cell.  It is also branched and compact.

Cellulose

Cellulose is also a polymer of glucose, but it is beta.  This produces long, straight polysaccharide chains.  To form the long, straight chains, the beta glucose subunits alternate the way they arrange themselves.  The straight unbranched chains lie parallel to each other and hydrogen bonds form between them.  Because there are many hydrogen bonds it gives strength and structure to cellulose, which makes its purpose in cell walls.

 Test For a Reducing Sugar

          Add Benedict's Reagent to the solution.

          Heat in a water bath.

…