Proteins And Enzymes

Question 1

What are the monomers of proteins?

Answer 1

Amino acids

NH2CHRCOOH

Question 2

How are polypeptides formed?

Answer 2

Via condensation reactions between amino acids

Question 3

What is the primary structure of a protein?

Answer 3

The amino acid sequence and type of amino acids that are present

Question 4

What is the secondary structure of a protein?

Answer 4

The coiling or folding of the amino acid chain into an alpha helix or beta pleated sheet.
Held together via hydrogen bonds

Question 5

What is the tertiary structure of a protein?

Answer 5

The folding of the alpha helicies and beta pleated sheets into a 3D structure held together via hydrogen bonds ionic bonds or disulphide bridges between the r groups of amino acids.

Question 6

What is the quaternary structure of a protein?

Answer 6

More than 1 polypeptide chain bonded together forms a quaternary protein.

Examples are haemoglobin or antibodies

Question 7

What are fibrous proteins?

Answer 7

Proteins with an extended straighter structure which are insoluble in water, weak acids and bases.

Question 8

What are globular proteins?

Answer 8

Proteins that are spherical and therefore compact in shape and are soluble in water, acids and bases

Question 9

What is collagen?

Answer 9

A structural component found in the skin, arteries, bones, cartilage.

It provides mechanical strength.

It is a fibrous protein

Question 10

What is haemoglobin?

Answer 10

A quaternary protein that is found in the red blood cells.

Made from 4 polypeptide chains (2x alpha and 2x beta chains)

Has a haeme group which is an Fe^3 + ion

Transports oxygen from the lungs to the respiring tissues

Question 11

What are enzymes?

Answer 11

Biological catalysts that speed up metabolic reactions without being used up in the reactions.

Question 12

What are intracellular enzymes?

Answer 12

Enzymes that are used in metabolic pathways

Question 13

What are extracellular enzymes?

Answer 13

Enzymes that are secreted and often used for digestion of molecules before they are up-taken

Question 14

What is the structure of an enzyme?

Answer 14

Enzymes are tertiary proteins which have a specific tertiary structure relating to its function.
They have an active site which is complementary to their substrates.

Question 15

What are cofactors?

Answer 15

Substances that must be present to ensure that an enzyme catalysed reaction occurs at the correct rate.

Question 16

What are co-enzymes?

Answer 16

Small organic non protein molecules that temporarily bind to the active site and chemically changed

(They must be recycled)

Question 17

What is the lock and key hypothesis of enzyme action?

Answer 17

Enzymes have a specific shape and fit perfectly to their substrate

Question 18

What is the induced fit hypothesis of enzyme action?

Answer 18

There are subtle changes to the shape of the active site in the presence of substrates in order to get an exact fit when forming an enzyme substrate complex

Question 19

What are competitive inhibitors?

Answer 19

Have a complementary shape to the active site of an enzyme and can therefore bind in place of the substrate blocking the substrate from binding to the active site: this means that no enzyme substrate complexes can be formed.

Competitive inhibitors are not permanently bound to the active site.

Question 20

What are non competitive inhibitors?

Answer 20

Bind to an allosteric site which changed the tertiary structure of the enzyme and therefore the active site also change shape. This means that the active site is no longer complementary to the substrate and no enzyme substrate complexes can be formed.

This is a permanent change to the enzymes

Question 21

How does temperature affect enzymes?

Answer 21

Enzymes work at an optimum temperature where they have the highest kinetic energy and therefore have the most chances of successful collisions increasing the chances of forming ESC’s. This has the fastest rate of reaction

Below this temperature enzymes still function but at a slower rate of reaction.

Above he optimum temperature the enzymes start to denature as the hydrogen bonds between the r groups of the amino acids start to be disrupted. Therefore the tertiary structure of the enzyme changes and hence the active site changes shape and is no longer complementary to the substrate. This means no ESC’s form and the rate of reaction is reduced

Question 22

How does pH affect enzymes?

Answer 22

At optimum pH the enzymes can work efficiently and therefore the rate of reaction is greater due to more successful collisions between enzymes and substrates.

Away from the optimum pH at the extremes, the ionic bonds between the r groups of the amino acids are changed so the tertiary structure of the enzyme changes and therefore the active site is no longer complementary to the substrate.

Question 23

How does substrate concentration affect the rate of reaction with enzymes?

Answer 23

As the concentration of the substrate increase the rate of reaction increase until a certain point at which the limiting factor changes. This causes the rate of reaction to start to plateau.

Question 24

How does enzyme concentration affect the rate of reaction with enzymes?

Answer 24

As the enzyme concentration increases so does the rate of reaction until the number of enzymes exceeds the number of substrates present at which point the substrate number is now the limiting factor and the rate of reaction begins to plateau.