Metabolism (AQA GCSE Biology): Revision Notes
Metabolism
What is metabolism?
Metabolism refers to all the chemical reactions that take place inside cells and throughout your body. These reactions help your body break down nutrients for energy and build new substances that your body needs to function properly.
Think of metabolism as your body's chemical factory - it's constantly breaking things down and building things up to keep you alive and healthy.
Carbohydrates
Carbohydrates are one of the main types of molecules your body uses for energy. The simplest carbohydrate is glucose, which is a type of sugar.
Storage forms of carbohydrates
Your body can join sugar molecules together to create larger storage molecules:
- Glycogen - stored in your muscles and liver for quick energy
- Starch - how plants store energy in their cells
- Cellulose - gives plant cell walls their strength
How carbohydrates are processed
Your body has two main processes for dealing with carbohydrates:
- Digestion - breaking down complex carbohydrates (like starch) into simple sugars using an enzyme called amylase
- Synthesis - building up simple sugars into storage molecules like glycogen
Most animals, including humans, cannot digest cellulose. However, we can break down glycogen and starch to release glucose for energy.
Lipids
Lipids are fats and oils that your body uses mainly for energy storage and insulation. At room temperature, fats are solid whilst oils are liquid.
How lipids are formed
A lipid molecule is created when one glycerol molecule joins with three fatty acid molecules. This gives lipids their characteristic structure and properties.
Functions of lipids
Lipids serve important purposes in living organisms:
- Energy storage - they store more energy per gramme than carbohydrates
- Insulation - they help prevent heat loss in animals
Processing lipids
Like carbohydrates, lipids undergo two key processes:
- Digestion - breaking down lipids into glycerol and fatty acids using an enzyme called lipase
- Synthesis - building up glycerol and fatty acids into complete lipid molecules
Proteins
Proteins are complex molecules made from smaller building blocks called amino acids. They have many important jobs in your body.
What proteins do
Proteins include:
- Enzymes - special proteins that speed up chemical reactions
- Structural substances - like collagen in your skin and keratin in your hair
How proteins are made
Different amino acids can join together in many different combinations to form various proteins. This is why there are so many different types of proteins in your body.
Processing proteins
Proteins are processed through:
- Digestion - breaking down proteins into individual amino acids using an enzyme called protease
- Synthesis - joining amino acids together to build new proteins
The liver's important role
Your liver is like the body's main processing centre for metabolism. It has three key functions:
The liver's essential metabolic functions:
- Converting lactic acid to glucose - this happens when lactic acid builds up during exercise and needs to be recycled
- Converting excess glucose to glycogen - this stores extra sugar for when you need energy later
- Processing amino acids - converting excess amino acids into ammonia, then into urea which can be safely removed from your body
The liver helps keep the right balance of different substances in your blood and processes waste products safely.
Key enzymes in metabolism
Three important enzymes help break down the main food groups:
Essential Digestive Enzymes:
- Amylase - breaks down carbohydrates
- Lipase - breaks down lipids
- Protease - breaks down proteins
These enzymes are essential for digestion and help your body access the nutrients it needs.
Remember!
Key Points to Remember:
- Metabolism includes all chemical reactions in your body - both breaking down and building up molecules
- The three main molecule types are carbohydrates, lipids, and proteins
- Each type has specific enzymes that help digest them: amylase, lipase, and protease
- Your liver plays a crucial role by converting between different substances and processing waste
- Your body constantly switches between breaking down molecules for energy and building up molecules for storage and structure