Unit 1 - Key Area 4 - Proteins

Question 1

Describe the structure of proteins.

Answer 1

Proteins are composed of chains of amino acids.
Different proteins are made of different combinations of amino acids.
The sequence of amino acids in the chain determines how the chain will fold up to make the proteins, so different proteins have different 3-dimensional shapes.
The 3-dimensional shape of protein determines its function.

Question 2

Name the different functions of proteins.

Answer 2

Proteins have many functions such as:
•	Structural
•	Hormones
•	Antibodies
•	Receptors 
•	Enzymes

Question 3

Describe the properties of enzymes.

Answer 3

Enzymes are made by all living cells.
Enzymes are made of protein.
Enzymes are biological catalysts.
Enzymes speed up cellular reactions.
Enzymes are unchanged by the reaction.

Question 4

Describe the action of enzymes.

Answer 4

A substrate is a chemical that the enzyme acts on.
Product(s) are the end chemical produced.

Enzymes can synthesise smaller substrates into larger products. (Synthesis)

Enzymes can breakdown larger products into smaller substrates. (Degradation)

Question 5

Write word equations for the two types of enzyme reactions.

Answer 5

Synthesis - Building up
Hydrogen Peroxide —–Catalyse—-> Oxygen +Water

Degradation – Breaking down

Glucose-1-Phosphate —–Phosphorylase—-> Starch

Question 6

Describe the structure of enzymes.

Answer 6

The active site of an enzyme is where the chemical reaction occurs.
The shape of the active site is said to be “complementary” to its specific substrate(s) meaning the enzyme and the substrate shape match each other exactly.
An enzyme-substrate complex forms facilitating the reaction.
Enzymes are specific as only one enzyme acts on only 1 substrate due to their complementary shape.

Question 7

Give 3 examples of enzymes.

Answer 7

Fats – Lipase –> Fatty acids and glycerol

Proteins – Protease –> Amino Acids

Starch – Amylase –> Maltose

Question 8

Describe the effect of changing temperature on enzyme activity.

Answer 8

As temperature increases the enzyme activity increases.
The temperature where the enzymes are most active is called it’s optimum temperature.
Above the optimum temperature, enzymes activity decreases.
At very high temperatures, the enzymes active site changes shape, the enzyme is said to be denatured.
When enzymes are denatured the substrate can no longer fit the enzyme active site and the rate of reaction will be affected.

Question 9

Describe the effect of changing pH on enzymes.

Answer 9

Enzymes have an optimum pH, this is the pH where the enzyme is most active.
Enzymes are most active within a range of pH’s depending on the type of enzyme.
If the pH is too acidic or alkaline for that particular enzyme the enzymes active site changes shape, the enzyme becomes denatured and the rate of reaction will be affected.

Question 10

What does the term denatured mean?

Answer 10

Active site has changed so the substrate no longer fits specifically. The rate of enzyme reaction is affected.

Question 11

Describe the stages of enzymes.

Answer 11

Stage 1:
Enzyme and substrate join/bind

Stage 2:
Reaction occurs at the active site of the enzyme.

Stage 3:
Smaller substrates are formed/produced
OR
Larger products are formed/produced