Roles of Enzymes | 9-1 GCSE Science Biology | OCR, AQA, Edexcel

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They key points covered in this video include:
1. Why do we need food?
2. Why are enzymes important?
3. Breaking down carbohydrates
4. Synthesis of carbohydrates
5. Breaking down proteins
6. Breaking down lipids
7. The digestive System
8. Digestive enzymes and bile
9. Digestive enzyme summary
10. Calorimetry

Why are Enzymes Important?

We need enzymes to get energy and nutrients from the food we eat. Chemical reactions in cells transfer energy from the chemical stores in food. The speed this happens is called the metabolic rate. Food is too large to be absorbed straight away - it needs to be broken down. To do this, enzymes break down carbohydrates, proteins and lipids into smaller parts - these are then absorbed into the bloodstream. Carbohydrates, proteins and lipids are biological molecules that are found in all organisms. An example of a carbohydrate is starch - this is found in bread. Proteins are large molecules made out of chains of amino acids. Lipids are fats and oils. Different enzymes break down carbohydrates, lipids and proteins. They also have to make carbohydrates, lipids and proteins from smaller molecules. This is called synthesis.

Breaking down Carbohydrates

Polymers are molecules made up of smaller molecules. Carbohydrates are an example of polymers. Carbohydrates are made from smaller carbohydrate molecules called simple sugars. Sucrose is a simple sugar used to make cake, lactose is found in milk. Carbohydrates are broken down into simple sugars by carbohydrase enzymes. Amylase is an example of carbohydrase enzyme that acts in your mouth. It is made in the salivary glands, pancreas and small intestine. Amylase breaks down starch into maltose and other sugars. These sugars can go through the gut wall and into the blood to provide energy.

Synthesis of carbohydrates

We can build carbohydrates up from smaller parts using enzymes. One example is glycogen synthase, an enzyme which makes glycogen from glucose molecules. Glycogen is an energy store.

Breaking down Proteins

Proteins are polymers made up of amino acids. The order the amino acids are joined determine the protein synthesised. Proteins are broken down by protease enzymes. This happens in the stomach and small intestine. The stomach has powerful acid that helps break down proteins. Protease enzymes break down proteins into amino acids. Pepsin is an example of a protease enzyme that works in the stomach. Enzymes can also make proteins from amino acids.

Breaking down Lipids

Lipids are broken down by lipase enzymes. Lipase enzymes break down the lipid polymer into a glycerol molecule and three fatty acids molecules. Bile produced by the liver emulsifies fats - this means it helps break down fats into small droplets. This gives a bigger surface area for lipase to work on - this makes digestion easier. Lipids are made from fatty acids and glycerol using enzymes.

The Digestive System

The digestive system is an organ system that breaks down food. These are the organs in the digestive system: Digestion works in two ways: Mechanical digestion, Chemical digestion.

Digestive Enzymes and Bile

Digestive enzymes are secreted into the gut from glands and the gut lining. In the gut they mix with carbohydrates, proteins and lipids and help break them down. Bile is stored in the gall bladder and released into the small intestine. The acid from the stomach makes the small intestine acidic. Bile neutralises the acid making it more alkaline - enzymes work best in these conditions.

Calorimetry

You can measure the amount of energy contained in food - this is calorimetry. To do this, we burn food and measure the temperature increase of water held over the burning food. To calculate the energy in food we use this formula: To work out the energy in food per gram we use this formula: For example, a student burned 2 g of bread under 30 cm3 of water. The temperature change of the water was 5.5˚C. Work out the energy per gram of bread. Step 1: Write down the formula for the total amount of energy in food. Step 2: Put the numbers in. Step 3: Work out the energy in food per gram. This is only an estimation of the amount of energy in food as much of the energy is transferred to the environment instead of heating up the water.


Summary
1. Enzymes break down carbohydrates, lipids and proteins
2. Enzymes also make these in synthesis reactions
3. Carbohydrase enzymes break down carbohydrates into simple sugars
4. Protease enzymes break down proteins into amino acids
5. Lipase enzymes break down lipids into fatty acid and glycerol
6. The digestive system is an organ system that breaks down food - either mechanically or chemically
7. Calorimetry can be used to estimate the energy content of food by burning it and using the energy to heat water