Unit 1 - Proteins + Enzymes

Question 1

What elements do all proteins and amino acids contain?

Answer 1

Nitrogen, Carbon, Hydrogen and Oxygen. Some also contain Sulphur.

Question 2

General structure of an amino acid?

Question 3

Describe the structure of an amino acid?

Answer 3

Each amino acid contains a central carbon atom to which a nitrogen containing amine group and a carboxyl group are attached.

Question 4

How many amino acids are common in all organisms?

Answer 4

20

Question 5

How do amino acids differ?

Answer 5

Only in their R groups.

Question 6

How many amino acids are essential?

Answer 6

8 amino acids are essential and we have to have them in our diet. Others are nonessential and we can synthesis them from the essential 8.

Question 7

How are dipeptides formed?

Answer 7

The condensation of 2 amino acids.

Question 8

How and when is a peptide bond formed?

Answer 8

The hydroxyl group of one amino acid reacts with a hydrogen from the amine group in the second amino acid to form water. The water is removed in the formation of a peptide bond.

Question 9

When are polypeptides formed?

Answer 9

By the condensation of more than 2 amino acids.

Question 10

What are the 2 types of proteins?

Answer 10

Globular and fibrous.

Question 11

Globular proteins?

Answer 11

Have a tertiary structure so contain ionic, hydrogen and disulphate. Examples include enzymes, membrane proteins, receptors and haemoglobin.

Question 12

Fibrous proteins?

Answer 12

Only have a secondary structure so only contain hydrogen bonds. Examples include collagen, keratin and actin.

Question 13

Key points of a polypeptide chain?

Answer 13

1) It will always have an amine group at one end and a carboxyl group at the other end.
2) The number of peptide bonds will be one less than the number of amino acids originally joined together.

Question 14

What is the primary structure?

Answer 14

The number and sequence of amino acids in a polypeptide chain. Proteins differ from each other because their primary structures are different.

Question 15

What is the secondary structure?

Answer 15

This is the folding of the polypeptide into an alpha helix or beta-pleated sheet. This structure is maintained by hydrogen bonds between the amine group of one amino acid and the carboxyl group of another.

Question 16

What is the tertiary structure?

Answer 16

The further folding of the polypeptide chain into a specific 3D shape which forms the active site.

Question 17

How is the structure held together?

Answer 17

By bonds between R groups of different amino acids.
Hydrogen bonds-weak, but many together are strong.
Ionic bonds-weak and form between oppositely charged R groups.
Disulphide bridges-covalent bonds, which form between sulphur containing R groups.

Question 18

Why does the primary structure determine its shape?

Answer 18

The sequence of amino acids in the primary structure determines where the bonds form and therefore the shape of the protein. If you change the primary structure of the protein, the sequence of R groups changes. This would result in bonds in the tertiary structure forming in different places and the 3D structure of the protein changing.

Question 19

What is the quaternary structure?

Answer 19

More than one polypeptide chain joined together.

Question 20

Examples of proteins with a quaternary structure?

Answer 20

Haemoglobin, antibodies, collagen, actin and enzyme ATP synthase.

Question 21

What is the biological test for proteins?

Answer 21

The biuret test. Add biuret solution to a sample. A colour change from blue to purple/lilac of protein is present. The colour stays blue if protein isn’t present. It will only react if a peptide bond is present so no colour change for single amino acids.

Question 22

What are enzymes?

Answer 22

They’re biological catalysts that speed up the rate of reaction by lowering the activation energy needed for a chemical reaction.

Question 23

What type of protein are enzymes?

Answer 23

They’re globular proteins so they have a specific 3D tertiary structure shaped active site.

Question 24

How do enzymes act as catalysts?

Answer 24

They speed up the rate of reaction by helping to align the reactants through the formation of enzyme substrate complexes so bonds can break and form more efficiently, therefore less activation energy required.

Question 25

How would you determine the presence of an enzyme in a solution?

Answer 25

Enzymes are proteins so will show a positive result for the biuret test.

Question 26

The structure of an enzyme and its function?

Answer 26

An enzyme has a specific complementary active site to their substrate. This allows the substrate to bind to the active site forming an enzyme-substrate complex.

Question 27

What is the induced fit model of enzymes?

Answer 27

The substrate binds to the enzymes active site forming an enzyme-substrate complex. The binding of the substrate molecule indices the change in the shape of the active site so it becomes completely to the substrate. This puts pressure on the bonds in the substrate which causes them to break more easily. This reduces activation energy. When substrate leaves, the active site then returns to its previous shape allowing it to bind to other substrates.

Question 28

Why will an enzyme only catalyse one reaction?

Answer 28

Enzymes all have a specific complementary shape to only one specific substrate.

Question 29

What factors affect enzymes?

Answer 29

Temperature
pH
Inhibitors
Substrate concentration
Enzyme concentration

Question 30

The effect of temperature on enzymes?

Answer 30

Every enzyme has a temperature at which it works best (optimum).
As the temp increases up to its optimum the enzyme and substrate molecules have more kinetic energy and are more likely to collide and form enzyme substrate complexes. The rate of reaction increases. If the temp is increased beyond its optimum, then the hydrogen bonds holding the tertiary structure together start to break do the tertiary structure changes. This changes the shape of the active site so it is no longer specific and complementary to its substrate, meaning not more enzyme substrate complexes can form. The enzyme is denatured and can no longer catalyse any chemical reactions.

Question 31

Graph of effect of temperature?

Question 32

Effect of pH on enzymes?

Answer 32

pH is a measure of hydrogen ion concentration. A change in pH means a change in the concentration of hydrogen ions. If the pH alters from the optimum, then the charge on the R groups of the amino acids are altered and hydrogen and ionic bonds in the tertiary structure are broken so the tertiary structure changes. The active site changes shape and is no longer complementary to the substrate. No more enzyme substrate complexes can be formed and the rate of the reaction decreases either side of the optimum. The enzyme is denatured.

Question 33

Graph of effect of pH?

Question 34

Effect of substrate concentration on enzymes?

Answer 34

As the substrate concentration increases, the active sites are filled and the rate of reaction increases, due to more successful collisions between enzyme active sites and substrate so more enzyme substrate complexes form per second. The substrate is no longer a limiting factor. At high substrate concentrations, there is no further rise in rate of reaction since the enzymes cannot form any more enzyme substrate complexes as all active sites are filled. The concentration of enzymes is now the limiting factor.

Question 35

Effect of substrate concentration graph?

Question 36

Effect of enzyme concentration?

Answer 36

The more enzyme molecules there are in solution, the more likely they are to collide with a substrate with sufficient energy to form an enzyme substrate complex. As a result, increasing the enzyme concentration increases the rate of reaction. However, if the amount of substrate becomes limiting, increasing the enzyme concentration will have no affect on the rate of reaction.

Question 37

Effect of enzyme concentration graph?

Question 38

What are inhibitiors? What are the 2 types?

Answer 38

They are substances which decrease the rate of reaction. There are 2 types: competitive inhibitors and non-competitive inhibitors.

Question 39

How do competitive inhibitors affect rate of reaction?

Answer 39

They have a similar structure to substrates. They fit into the active site but do not react. They prevent the normal substrate from binding and hence slow the rate of reaction as FEWER enzyme substrates can be formed.

Question 40

Non-competitive inhibitors?

Answer 40

They bind to a site on the enzyme other than the active site. They alter the shape of the active site so that substrate cannot fit. NO more enzyme substrates can be formed and the rate of reaction is decreased.

Question 41

Effect of inhibitors graph?