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Summary Topic 4: Biological molecules
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Topic 4: Biological molecules: IGCSE Biology course notes which will help you study for your papers. By studying these notes I achieved a 9 - A* on my Igcse
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TOPIC 4: BIOLOGICAL MOLECULES4.1 CARBOHYDRATES, FATS & PROTEINS
-Most of the molecules in living organisms fall into three categories: →Carbohydrates, Proteins and Lipids.
Most of our body is made of water:
-Metabolic reactions can only take place if the
chemicals which are reacting are dissolved in water.
-Water is an important solvent.
-Water is also needed in blood plasma so substances
can dissolve in it (i.e. glucose).
Carbohydrates
→Long chains of simple sugars
→Glucose is a simple sugar/monosaccharide: can dissolve in water.
→When 2 simple sugars (i.e. glucose) join together a disaccharide is formed (i.e. maltose): can dissolve in water.
→When lots of simple sugars join together a polysaccharide can form (i.e. starch, glycogen or cellulose)
-FUNCTIONS:
-Needed for energy (1g of carbohydrate – 17kJ of
energy) which is then released by respiration.
-The carbohydrate used in respiration is glucose.
-Plant cells transport glucose in the form of sucrose
(change it when use it) and store it as starch
-Animals store carbohydrates in the form of
polysaccharide glycogen.
Fats
→Most fats (lipids) in the body are made up of triglycerides
→Their fat molecule is formed by 1 glycerol molecule chemically bonded to 3 fatty acid chains
→The fatty acids vary in size and structure
→Lipids are divided into fats (solids at room temperature) and oils (liquids at room temperature): both insoluble in
water.
-FUNCTIONS:
-Fats and oils can be used to release energy (1g of fat – 39kJ of
energy)
-Used as energy when carbohydrates have been used.
-Very good stores of energy
-Adipose tissue (layer of cells) helps keep body warmth.
Proteins
→Long chains of amino acids (smaller molecules)
→They all contain the same basic structure but the ‘R’ group is different for each one
→When amino acids are joined together a protein is formed
→The amino acids can be arranged in any order, resulting in hundreds of thousands of different proteins, but the
order of each amino acid is precise.
→Even a small difference in the order of the amino acids results in a different protein being formed.
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