Unit 1



  • Water is a polar molecule: There is an uneven distribution of charge across the atoms. The       electron density is higher around oxygen
  • Oxygen is more electronegative than hydrogen
  • Water molecules react non- covalently: hydrogen bonding- partially negative oxygen forms an electrostatic bond with the partially positive hydrogen atom of another water molecule.


  1. Polarity of water enables it to act as a transport medium, and solvent form many essential chemical species which are polar and/ or charged
  2. High latent heat of vaporisation enabling cells to provide a thermostable environment
  3. Water molecules are cohesive(held together) as a result of the hydrogen bonds: - Key for support in tissue systems and acts as a lubricant e.g. mucus  
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  • Main respiratory substrate
  • When broken down, it releases energy --> Energy released is captured by cells --> Energy enables cells to drive a whole range of processe


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Monosaccharide: monomeric carbohydrate unit

Disaccharde: a sugar formed by the condensation of two monosaccharide units

Ogliosaccharide: a carbohydrate made up of a chain of few monosaccharide units

Polysaccharide: A carbohydrate consisting of a number of glucose molecules bonded together

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  • When two monosaccharides join together, they form a disaccharide. This happens in a condensation reaction in which a water molecule is released and a glycosidic bond is formed between the carbon 1 and carbon 4 atoms
  • "Maltose" is made from two alpha glucose units


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  • An alpha- glucose polymer made up of alpha(1-->4) glycosidic linkages as well as alpha(1-->6) linkages.
  • The alpha(1-->6) linkages make the polymer heavily branched
  • Glycogen synthesis involves glucose condensation
  • To mobilise the glucose, a phosphorolysis reaction takes place by which phosphate is added which attacks the alpha(1-->6) glycosidic linkages at the terminals. This reaction is catalysed by the enzyme glycogen phosphorolase
  • Stored in the liver and muscle cells
  • Glycogen is a useful biopolymer as it is: Insoluble- doesn't affect the water content of the cell and Highly Branched- Lots of glucose molecules can be stored in a more compact space
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Fats (Lipids)

Primary roles in biological systems:

  • Energy Storage (limitless)
  • Cell Membranes
  • Heat Insulation
  • Internal Organ Shielding

Fats are stored in adipose tissues- Adipose cells consist of a nucleus and a large globule of fat

Fat molecules are non-polar making them hydophobic- They cannot interact with water

Excess carbohydrase can be converted into fat

Fats are also known as triglycerides (TG):

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Structure of a triglyceride:


Glycerol is an alcohol and so has hydroxyl groups and fatty acids are carboxylic acids

The hydroxyl groups of the glycerol react with the carboxyls of three fatty acids in a condensation reaction (+elimination of water) to form ester linkages. As there are three links, this forms a triester.


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Fatty Acids

Saturated Fatty Acids:

All the carbon-carbon bonds are single and there is the maximum number of hydrogen atoms in the chain. They tend to have higher boiling points- Mainly solid at room temp.

Unsaturated Fatty Acids:

Some of the carbon atoms have double bonds between them and therefore there is less room for hydrogen atoms in the chain. Mainly liquid at room temp.

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