Section 2 c) Summary

Proteins are long chains of amino acids. Made up of carbon, hydrogen, oxygen and nitrogen: CHON

Carbohydrates are long chains of simple sugars. Made up of carbon, hydrogen and oxygen: CHO

Lipids are made of glycerol and three fatty acids. Made up of carbon, hydrogen and oxygen: CHO

Enzymes are biological catalysts, they're specialized proteins that speed up biological reactions, such as digestion, without becoming chemically involved. They are adapted to work in ideal conditions depending on where they should be, for example human enzymes work at an optimum temperature of around 37 ℃, because this is average body temperature.
Protease in the stomach, and enzyme that breaks down proteins into amino acids, works at an optimum pH of 2, which is the acidity of the hydrochloric acid found in the stomach, however salivary amylase, found in the mouth, is denatured in these conditions as the mouth is much less acidic.
An enzyme will become denatured in extremes of pH, as well as high temperatures. Low temperatures will not denature the enzyme, but will slow it so it isn't able to work efficiently.

These two graphs depict enzyme activity based on temperature and pH:

Optimum temperature of enzymes can be found by completing the following experiment:

1. Mixing amylase (protein that breaks down carbohydrates into glucose) with starch in test tubes, and placing them in water baths of varying temperatures (should be regular intervals).
2. Testing samples for starch with iodine every 30 seconds
3. Record how long it takes for the iodine to test negative for starch, this is when the amylase has broken down all or most of the starch.

Graph the results to determine the optimum temperature.

Iodine is an orange-brown colour, but turns black-blue when exposed to starch. This is how we test for starch.

Benedict's solution is blue in colour, but when heated with a simple sugar such as glucose, it turns red. This is how we test for glucose.

Section 2 c) Key Words

Active site: The part of the enzyme that catalyses the reaction, the 'key' part of the lock and key model.

Amino acid: The monomer of a protein. A molecule made up of carbon, hydrogen, oxygen and nitrogen that bonds with other amino acids to form proteins.

Carbohydrates: Long chain molecules (polymers) made up of monosaccharides, e.g. starch or glycogen

Denatured: When the active site of an enzyme is changed

Disaccharide: Made up of two monosaccharides. e.g. sucrose

Enzyme: A biological catalyst. It is a type of protein that has an 'active site' that it uses to break down substrates into products, or bind them together. e.g. amylase, protease

Fatty acid: Three of these bind with a molecule of glycerol to form a lipid. Made of carbon, hydrogen and oxygen.

Glucose: A monosaccharide that makes up carbohydrates such as starch or glycogen.

Glycerol: One of the building blocks of a lipid. Attaches to three fatty acids.

Glycogen: A carbohydrate that animals make to store glucose. A polymer.

Lipid: Oil or fats, made up of glycerol and three fatty acids (Each made of carbon, hydrogen and oxygen: CHO)

Monomer: A single unit, simple molecule. Many of these bind together to form a long-chain polymer.

Monosaccharide: A simple, single sugar, e.g. glucose

Polymer: A long-chain molecule made up of lots of monomers bound together

Polysaccharide: A complex sugar made up of lots of monosaccharides.

Protein: Polymer of amino acids. Organic chain of molecules.

Starch: Storage of carbohydrates in plants, long-chain molecule of glucose.

Substrate: The 'reactants' in an enzyme-aided reaction.

Section 2 c) Specfication

2.5 identify the chemical elements present in carbohydrates, proteins and lipids (fats and oils)

In carbohydrates and lipids, there are CHO: Carbon, Hydrogen and Oxygen.
In proteins, there are CHON: Carbon, Hydrogen, Oxygen and Nitrogen.

2.6 describe the structure of carbohydrates, proteins and lipids as large molecules made up from smaller basic units: starch and glycogen from simple sugar; protein from amino acids; lipid from fatty acids and glycerol

Starch and glycogen are carbohydrates that are polymers, their monomers being simple sugars (monosaccharides) such as glucose: C6H12O6

Proteins are made of amino acids, which join together to form unique shapes and combinations, important for each protein to have its own properties.

Lipids are made up of fatty acids and glycerol, in this structure:

2.7 describe the tests for glucose and starch

Starch: Test using iodine solution. If it changes from brown-orange to blue-black, there is starch present.

Glucose: heat with Benedict's solution. It will turn red if positive.

2.8 understand the role of enzymes as biological catalysts in metabolic reactions

Enzymes work with the lock and key model. They are a certain shape that allows substrates to fit in, then bond together or break apart in the active site. It speeds up the reaction. They are useful in digestion, enzymes such as protease break up proteins, amylase breaks up starch into glucose,

2.9 understand how the functioning of enzymes can be affected by changes in temperature, including changes due to change in active site

The active site of the enzyme is the most important part of it. It allows the enzyme to take part in metabolic reactions, however if it is put in conditions that are too far from the optimum it can be damaged. In high temperatures, the shape of the active site can be changed, rendering the enzyme useless. The enzyme is denatured.

This curve depicts the way temperature affects enzymes:

Beyond the optimum temperature, the enzyme is denatured. Leading up to the optimum temperature, the enzyme activity increases due to increasing kinetic energy of the particles which increases the rate of collisions.

2.10 understand how the functioning of enzymes can be affected by changes in active site caused by changes in pH

Extreme change in pH can also cause the enzyme to be denatured. This varies depending on the optimum pH of the enzyme, but a very extreme pH will denature any enzyme. 

2.11 describe experiments to investigate how enzyme activity can be affected by changes in temperature.

1. Place test tubes containing the same mixture of amylase and starch in water baths of different temperatures with regular temperature intervals (e.g. 20℃, 30℃, 40℃, 50℃, 60℃, 70℃)
2. Take a sample from each at regular time intervals (every 30 seconds) and test for starch with iodine
3. Record which sample was the first to not test positive for starch.
From this, you can see how long it took for the enzyme to break down the starch. It can be graphed to determine the optimum temperature.