1. National 5
Proteins & Enzymes
Mr G Davidson

2. Variety of Proteins
Proteins are complex molecules composed of a large number of sub-units called amino acids.
They contain the elements carbon (C), hydrogen (H), oxygen (O) and nitrogen (N).
Wednesday, 19 September 2018Wednesday, 19 September 2018
Mr G Davidson

3. Variety of Proteins There are about 20 different amino acids.
As seen in the last unit, the sequence of amino acids is determined by the genetic code on DNA.
Depending on the sequence of the amino acids, proteins can take the form of different shapes.
Wednesday, 19 September 2018Wednesday, 19 September 2018
Mr G Davidson

4. Variety of Proteins
The shape of the protein can determine the function of the protein, e.g.
Structural proteins such as those present in the cell membrane. These proteins kepp the membrane together as well as allowing the transport of materials across it.
Carrier proteins such as those found in the cell membrane. These are responsible for the transport of certain materials across the cell membrane.
Enzymes are spherical shaped protein molecules and they are important in the metabolism of the cell. They are also important outside the cell in organisms, e.g. digestive enzymes in the human gut, enzymes to convert glucose to starch in plants, etc...
Wednesday, 19 September 2018Wednesday, 19 September 2018
Mr G Davidson

5. Variety of Proteins
Hormones are also proteins. These are chemical messengers transported in the blood to target organs or tissues where they are responsible for causing a change. Examples include regulating growth in an organism, controlling blood glucose level in human blood (insulin), osmoregulation in animals, etc....
Antibodies are also composed of protein molecules. They are made by white blood cells and their function is to fight off bacteria which cause diseases.
Wednesday, 19 September 2018Wednesday, 19 September 2018
Mr G Davidson

6. Enzymes Chemical reactions all occur at different rates.
Some are very quick and some are extremely slow.
We can speed up some chemical reactions by:
Increasing the temperature
Adding a catalyst
Wednesday, 19 September 2018Wednesday, 19 September 2018
Mr G Davidson

7. Enzymes
Since it is not always appropriate to increase the temperature of a living organism, biological catalysts called ENZYMES are used to increase the rate of reactions.
Enzymes are made by all living cells.
Although they speed up reactions, enzymes remain unaltered by the reaction and can therefore be used again and again.
Wednesday, 19 September 2018Wednesday, 19 September 2018
Mr G Davidson

8. Enzymes
Catalase is an enzyme, made by living cells, which can break down hydrogen peroxide.
If we add a piece of living tissue to hydrogen peroxide, we can see bubbles of oxygen being released.
The more bubbles released, the more catalase there is in the tissue.
Wednesday, 19 September 2018Wednesday, 19 September 2018
Mr G Davidson

9. Specificity
Catalase can only speed up the breakdown of hydrogen peroxide, not any other reaction.
It is said to be specific.
Each enzyme catalyses only one reaction.
The substance the enzyme catalyses is called the substrate.
Wednesday, 19 September 2018Wednesday, 19 September 2018
Mr G Davidson

10. Specificity
Enzymes have an area on their surface which is a specific shape, and it is here that the substrate attaches.
This area is called the active site.
The enzyme’s shape and the substrate’s shape are said to be complementary.
The substrate locks onto the enzyme at the active site and the reaction occurs.
Wednesday, 19 September 2018Wednesday, 19 September 2018
Mr G Davidson

11. Specificity This is called the Lock and Key Theory. Substrate
Active site
Enzyme
Product
Product
Wednesday, 19 September 2018Wednesday, 19 September 2018
Mr G Davidson

12. Enzyme Action
In order to function at its best, enzymes require the best possible conditions.
We call these conditions the optimum conditions.
Two important factors in ensuring enzymes work at their optimum are temperature and pH.
Wednesday, 19 September 2018Wednesday, 19 September 2018
Mr G Davidson

13. Enzyme Action
At very low temperatures, enzymes work very slowly or not at all.
As the temperature rises, the substrate molecules and the enzyme molecules bump into each other more often and, therefore the reaction speeds up.
Wednesday, 19 September 2018Wednesday, 19 September 2018
Mr G Davidson

14. Enzyme Action
There will be a temperature (usually around 35oC) when the enzyme cannot work any faster.
This will be that particular enzyme’s optimum temperature.
Once the temperature is too high the enzyme (being a protein) is damaged and we say it has been denatured.
Wednesday, 19 September 2018Wednesday, 19 September 2018
Mr G Davidson

15. Temperature v Enzyme Activity
Temperature (oC) 10 20 30 40 50
Increasing rate of Reaction
Optimum
temperature
Increasing
enzyme
activity
Enzyme
being
denatured
Wednesday, September 19, 2018Wednesday, September 19, 2018
Mr G Davidson

16. Effect of pH on Enzymes
pH is a measure of how acid or alkali something is.
The pH scale goes from 0 to 14, with 0 being very acidic, 14 being very alkaline and 7 being neutral.
The shape of an enzyme can be affected by changes in pH and this will affect how well the enzymes work.
Wednesday, September 19, 2018Wednesday, September 19, 2018
Mr G Davidson

17. Effect of pH on Enzymes
Like temperature, enzymes have an optimum pH, i.e. a pH when they are most efficient.
The optimum pH varies from enzyme to enzyme.
Our digestive system has a range of pH’s as the food passes through it, and this creates ideal conditions for specific enzymes.
Wednesday, September 19, 2018Wednesday, September 19, 2018
Mr G Davidson

18. Effect of pH on Enzymes Enzyme Activity (%) pH20 40 60 80
100 1 2 3 4 5 6 7 8 9 10 11 12 pH
Enzyme Activity (%)
Pepsin
Catalase
Lipase
Wednesday, September 19, 2018
Mr G Davidson

19. Breakdown of Hydrogen Peroxide
Hydrogen peroxide (H2O2) is a harmful by-product of reactions inside cells.
H2O2 can be broken down into water H2O and oxygen O2.
Hydrogen peroxide Water + Oxygen
(H2O2) (H2O) (O2)
Wednesday, September 19, 2018Wednesday, September 19, 2018
Mr G Davidson

20. Breakdown of Hydrogen Peroxide
Hydrogen peroxide can be broken down to water and oxygen by increasing the temperature.
If it is placed in water baths of increasing temperatures, the number of bubbles of oxygen released increases with temperature.
Wednesday, September 19, 2018Wednesday, September 19, 2018
Mr G Davidson

21. Breakdown of Hydrogen Peroxide
Catalase is the enzyme, made by living cells, which can break down hydrogen peroxide.
If we add a piece of living tissue to hydrogen peroxide, we can see bubbles of oxygen being released.
The more bubbles released, the more catalase there is in the tissue.
Wednesday, September 19, 2018Wednesday, September 19, 2018
Mr G Davidson

22. Starch & Amylase Starch is a carbohydrate.
It contains energy and is found in many foods.
Starch molecules are very large and cannot pass through cell membranes.
Therefore, they need to be broken down to smaller molecules.
Wednesday, September 19, 2018Wednesday, September 19, 2018
Mr G Davidson

23. Starch & Amylase This is done by an enzyme called AMYLASE.
Amylase is found in our saliva.
The starch is broken down to molecules of a sugar called maltose.
AMYLASE
STARCH
MALTOSE
(Enzyme)
(Substrate)
(Product)
Wednesday, September 19, 2018Wednesday, September 19, 2018
Mr G Davidson

24. Starch & Amylase Starch molecule Amylase Maltose molecules
Wednesday, September 19, 2018Wednesday, September 19, 2018
Mr G Davidson

25. Uses of Enzymes Enzymes have many uses and some examples are below.
Used in our digestive system to break down food.
Used in biological washing powders to digest stains.
Used to make bread.
Used to make cheese.
Used to make yoghurt.
Wednesday, 19 September 2018Wednesday, 19 September 2018
Mr G Davidson