GCSE Biology Unit 2 - Enzymes

Enzymes, Respiration, Digestive System, Digestion, Enzyme Uses

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Enzymes are biological cataysts. Catalysts are substances which change the reaction rate, but are not used up in the reaction.

Enzymes are made of protein. Every enzyme has a unique shape, with an active site, that is particular to one substance and one reaction. If the substance doesn't fit the active site, there is no reaction.

Enzymes need the temperature and pH level to be kept at a certain point.
The optimum temperature for human enzymes is 37ºC - the same as body temperature.
The optimum pH for human enzymes is normally pH7, or there abouts, but there are some, like pepsin, that work best in acid, or pH2.

 If the temperature is too high, or the pH is too low or high, the enzyme becomes denatured, and won't catalyse the reaction. When it is denatured the bonds holding the enzyme together break, the active site is damaged and changes shape.

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Breathing in and out is not respiration. Respiration is releasing energy from glucose. Their are two types of respiration, aerobic and anaerobic.

Aerobic respiration is respiration using oxygen;

Glucose + Oxygen --> Carbon Dioxide + Water + ENERGY

Aerobic respiration releases more energy than anaerobic respiration.

Aerobic respiration occurs inside mitochondria.

The energy from respiration has many uses;

- to make large molecules from smaller ones
- to allow muscles to contract
- to keep constant body temperature in animals and birds
- to build sugars, nitrates and other nutrients into amino acids, and then proteins (plants) 

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Digestive System

Organs involved and what they do:

- Salivary glands - produce the enzyme amylase
- Gullet - aka oesophagus
- Liver - bile production - bile neutralises stomach acid
- Gall bladder - bile is stored here
- Stomach - muscular walls break up food, pepsin production (a protease), HCl for killing bacteria, and the right pH
- Pancreas - protease, amylase and lipase production; then released into small intestine
- Small intestine - protease, amylase and lipase production, nutrients pass into blood stream
- Large intestine - excess water taken from food
- Rectum - where feaces is stored

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Big molecules can't pass through intestine walls into the blood stream. They have to be broken down into smaller molecules. There are enzymes that do this.

Amylase (or carbohydrase) - breaks starch into simple sugars; made in salivary glands, pancreas and small intestine

Protease - breaks proteins into amino acids; made in stomach (as pepsin), pancreas and small intestine

Lipase - breaks fats into glycerol and fatty acids; made in the pancreas and small intestine

There is also bile, which doesn't break molecules down, but neutralises the stomach acid in the small intestine and emulsifies fats. This breaks them up into little droplets, giving them a bigger surface area. Bile is made in the liver, stored in the gall bladder and then released into the small intestine.

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Uses of enzymes

Enzymes can be used outside of the body as well.

Biological detergents - contain proteases and lipases, which are ideal for removing stains from food, plant matter, or blood.

Baby foods - contain proteases, which 'pre-digest' the food, making it easier for the baby to digest.

Other foods - carbohydrases turn starch syrup into sugar syrup, and isomerase enzyme turns glucose syrup into fructose syrup - its sweeter, so less is needed.

In industry - speed up reactions.

Adv. - specific, lower temp = lower cost/less energy/less fossil fuels, work for a long time, biodegradable

Disadv. - allergies, easily denatured = need controlled conditions

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