An overview of the topic: Enzymes

I used the GCSE AQA Biology Revision Guide to produce these cards.

Hope this helps and good luck with the exam.

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  • Created by: jenny100
  • Created on: 13-05-12 13:01


  • Biological Catalysts = substance which increases the speed of reaction without being changed or used up 
  • Enzymes are all proteins
  • All proteins are made up of chains of amino acids
  • Every enzyme has a unique shape that fits into the substance involved in the reaction
  • Enzymes usually only catalyse one reaction
  • Enzymes work best at a high temp and optimum pH
  • Enzymes become denatured if too hot or wrong pH <-- bonds holding enzyme together break and destroys the enzymes special shape
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Enzymes and Respiration

  • Enzymes are used to synthesize molecules like amino acids
  • Enzymes catalyse protein synthesis by joining amino acids
  • Respiration involves lots of reactions, which are all catalysed by enzymes
  • Respiration is the process of releasing energy from the breakdown of glucose in every cell of the body
  • Aerobic Respiration = the most efficient way of releasing energy from glucose (occurs in mitochondria)
  • Glucose + Oxygen ----> CO2 + water + energy

Respiration Releases Energy:

  • To build up larger molecules (e.g. amino acids --> proteins)              
  • Allow muscles to contract                                                                         
  • In mammals and birds to keep their body temp steady                            
  • In plants to build sugars, nitrates and other nutrients into amino acids --> proteins  

Cyanide stops respiration by affecting enzymes involved in the process, affects brain, heart and liver first cause of the high energy demands

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Enzymes and Digestion

Digestive Enzymes break down BIG molecules into smaller molecules.

  • Amylase converts STARCH into SIMPLE SUGARS: made in Salivary Glands, Pancreas & Small Intestine
  • Protease converts PROTEINS into AMINO ACIDS: made in Stomach, Pancreas & Small Intestine
  • Lipase converts FATS into GLYCEROL & FATTY ACIDS: made in Pancreas & Small Intestine 

BILE is produced in the LIVER and stored in the GALL BLADDER then released into the small intestine to make the acidic conditions (hydrochloric acid) there more alkaline so the enzymes can work at there best.

Bile also emulsifies fat (breaks it down into tiny droplets) this gives a larger surface area for the enzyme lipase to work making digestion faster.

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The Digestive System

Enzymes used in the digestive system are produced by specialised cells in GLANDS in the GUT LINING

Different enzymes catalyse the breakdown of different food molecules.

  • Salivary Glands: produce amylase enzyme in the saliva
  • Gullet (Oesophagus)
  • Stomach: pummels food with its muscular walls, produces the protease enzyme (pepsin), produces hydrochloric acid to: kill bacteria and give the right pH for protease to work (pH2-acidic)
  • Liver: bile is produced which neutralises stomach acid and emulsifies fat
  • Gall Bladder: where bile is stored
  • Pancreas: produces amylase, protease and lipase enzymes, then releases then into the small intestine
  • Small Intestine: enzymes from pancreas complete digestion and food is absorbed out of the digestive system into the body
  • Large Intestine: excess water is absorbed from the food
  • Rectum: faeces is stored here, made up from indigestible food
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Uses of Enzymes

  • Biological Detergents: mainly protein and fat digesting enzymes (proteases & lipases). These enzymes attack plant and animal matter so are ideal for removing stains like food or blood
  • Change Foods: proteins in some baby foods are pre-digested using proteases so the baby can digest them more easily. Carbohydrases can turn starch syrup into sugar syrup. Glucose syrup can be turned into fructose syrup using an isomerase enzyme. Fructose is sweeter so less needs to be used therefore its good for slimming foods & drinks)
  • Industry to Control Reactions: speed up reactions without the need for high temp, they can be trapped in an alginate bead or a latticework of silica gel


  • Specific: only cataylse one reaction. Lower cost & saves energy: use lower temps and pressures. Enzymes work for a long time: long-term savings. Biodegradable: cause less environmental pollution


  • Allergies can be developed. Conditions enzymes work in must be tightly controlled: denatured by slightest change in temp or pH. Contamination between enzyme and other substance can affect reaction 
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