Exercise & Metabolism - Metabolism (GCSE Biology)
Metabolism
Making Large Molecules
Large molecules in cells are made up of lots of smaller molecules, called monomers. Together these monomers join together to form polymers.
Starch
A starch molecule is made up of lots of glucose molecules joined together.
When we eat bread, starch in the bread is broken down by the digestive system to give glucose molecules, which can be absorbed into the blood.
Lipids
A lipid (fat) molecule has one glycerol molecule bonded to three fatty acids.
Again, when we eat ice cream, lipids are broken down by the digestive system into glycerol and fatty acids.
Proteins
A protein molecule is made up of many amino acids joined together in a chain. Amino acids are themselves made up of glucose and nitrate ions.
Each protein has a different chain or order of amino acids. For example, an enzyme (a protein) has a specific chain of amino acids which ensures that it’s the correct shape to catalyse a reaction.
Breaking Down Large Molecules
In the body, these large molecules often need to be broken down:
- Respiration – in respiration, glucose is broken down to produce energy for cell processes.
- Digestion – as we discussed above, digestion involves breaking down large insoluble molecules in food (e.g. starch), into small soluble molecules (e.g. glucose) that can be absorbed into the bloodstream.
- Protein breakdown – additional excess proteins in the body are broken down into urea, which is removed from the body in urine.
Metabolism
The metabolism of a cell or body is the combination of all the reactions occurring in them.
Metabolism includes:
- The formation of polymers from monomers (as described in the examples above)
- The process of respiration
- The breakdown of excess proteins to form urea for excretion
The energy for these metabolic processes come from respiration.
The metabolic reactions which occur in cells to synthesise new molecules or break them down are often controlled by specialised proteins called enzymes.
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