Topic 3 - Enzymes

Question 1

What are enzymes?

Answer 1

Enzymes are globular proteins that act as biological catalysts because they speed up metabolic reactions in living organisms.

Question 2

Enzymes are catalysts because they speed up metabolic reactions but also because?

Answer 2

They remain unchanged at the end of the reaction (regenerated) so can be used again

Question 3

Because enzymes can be reused this means?

Answer 3

Small amount of enzymes can catalyse the conversion of a large amount of substrate molecules into product molecules.

Question 4

What is the turnover number?

Answer 4

This is the number of reactions an enzyme can catalyse per second.

Question 5

Where do enzymes work?

Answer 5

• Enzymes work within cells (intracellularly) e.g. aerobic respiration in mitochondria
• and outside of cells (extracellularly) e.g. digestion in mammals

Question 6

Are enzymes soluble in water?

Answer 6

Enzymes are soluble in water because the hydrophobic R groups of amino acids which make up its tertiary structure are hidden away, whilst the hydrophilic R groups of amino acids are in contact with the surrounding aqueous environment.

Question 7

Example of an intracellular enzyme?

Answer 7

Catalase

Question 8

What is catalse?

Answer 8

Catalase is an intracellular enzyme that works inside cells to catalyse the breakdown of hydrogen peroxide to harmless oxygen (O₂) and water (H₂O).

Question 9

Why is hydrogen peroxide broken down?

Answer 9

Hydrogen peroxide (H₂O₂) is the toxic by-product of several cellular reactions. If it builds up, it can kill cells.

Question 10

Structure of catalase?

Answer 10

Catalase consists of four polypeptide chains and each chain contains an iron-containing haem group.

Question 11

How fast does catalase act?

Answer 11

Catalase is the fastest-acting enzyme, having the highest turnover number known (about 6 million per second).

Question 12

In eukaryotic cells, what is catalse found in?

Answer 12

In eukaryotic cells, catalase is found inside small vesicles called peroxisomes.

Question 13

Application of catalase?

Answer 13

As catalase is toxic, white blood cells use it to help kill pathogens that they have ingested.

Question 14

What is the optimum PH for catalase in humans?

Answer 14

The optimum PH for catalase in humans is around PH7*

*This varies between species.

Question 15

What is the optimum temperature for catalase in humans?

Answer 15

The optimum temperature for catalse in humans is 45ᵒC*

*This varies between species.

Question 16

How do enzymes work intracellularly?

Answer 16

Each metabolic pathway is a series of consecutive reactions, in which each reaction is catalysed by a specific enzyme that produces a specific product.
The various reactants and intermediates act as substrates for specific enzymes until the the final product is made.
In these metabolic pathways, catabolic and anabolic enzymes are involved when making the final product.*

*State the function of these two types of enzymes in an exam.

Question 17

What are metabolites?

Answer 17

The reactants, intermediates, and products that take part in the reactions of a metabolic pathway are known as metabolites

Question 18

There are two types of enzymes?

Answer 18

Catabolic enzymes

Anabolic enymes

Question 19

What are catabolic enzymes?

Answer 19

Catabolic enzymes are enzymes that break down metabolites inro smaller molecules + release energy.

Question 20

What are anabolic enzymes?

Answer 20

Anabolic enzymes are enzymes that use energy to synthesize larger molecules from smaller ones.

Question 21

Examples of intracellular metabolic pathways?

Answer 21

Respiration

Photosynthesis

Question 22

Examples of extracellular enzymes?

Answer 22

Digestive enzymes such as amylase and trypsin.

Question 23

Where is amylase produced? What does amylase do?

Answer 23

• Amylase is produced in the mouth by salivary glands.

- Amylase catalyses the hydrolysis of the polysaccharide, starch, into the disaccharide, maltose, in the mouth.

Question 24

Where is trypsin produced? What does trypsin do?

Answer 24

• Trypsin is produced by the pancreas and secreted into the small intestine.
• Trypsin catalyses the hydrolysis of peptide bonds, converting polypeptides into smaller ones (which then get broken down into seperate amino acids by other enzymes).

Question 25

Structure of an enzyme?

Answer 25

A globular protein with a 3D tertiary structure. Has a specific active site that is complementary in shape to a certain substrate.

Question 26

What is an active site?

Answer 26

• An indented area on the surface of an enzyme that is highly specific and complementary in shape to a particular substrate - usually involved in catalysing one reaction only.
• The shape of the active site is determined by the enzyme’s 3D tertiary structure.

Question 27

How can the shape of an enzyme active site change?

Answer 27

• Changes in temperature and PH, affect the bonds that hold together the tertiary structure of enzymes.
• This causes the shape of the active site to change and thus its ability to catalyse a reaction.

Question 28

How are enzymes made?

Answer 28

Genes encode for a specific sequence of amino acids, that fold into a tertiary structure allowing it to become functional.

Question 29

What could happen if the gene coding for an enzyme mutates?

Answer 29

If a mutation occurs in the gene this may alter sequence of amino acids, which in turn alters the tertiary structure of the enzyme. This may cause the shape of the active site so that it is no longer complementary to the specific substrate, preventing it from functioning.

Question 30

How can metabolic disorders occur?

Answer 30

Deficient and non-functioning enzymes:

• If an enzyme that catalyses a metabolic reaction is deficient, metabolic disorders can occur
• Mutation in gene coding for the enzyme, changes the shape of the active site preventing it from functioning

Question 31

What role do enzymes play that are involved with teh strucutral componenets of the body?

Answer 31

Enzymes catalyse the formation of structural components such as collagen in bone, cartilage, blood-vessel walls, joints and connective tissue.

Question 32

What happens when enzymes involved in structural components are affected?

Answer 32

Metabolic disorders e.g. malformations of connective tissue

Question 33

How come some enzymes catalyse two reactions?

Answer 33

This is because the enzyme is actually a really large enzyme complex and has more than one active site.

*This is why the same enzyme complex may be known by different names

Question 34

Most enzymes catalyse a reaction in either direction depending on the cell’s needs. Give an example of such an enzymes?

Answer 34

ATPase can catalyse the formation of ATP or the hydrolysis of ATP.

Question 35

What are cofactors?

Answer 35

This is a susbtance (a non-protein molecule) that has to be present to ensure that an enzyme-catalysed reactions takes place at the appropriate rate.

Question 36

Which type of enzyme catalysed reactions mainly require a cofactor?

Answer 36

Oxidation-reduction reactions

Question 37

What is a prosthetic group?

Answer 37

A prosthetic group is a cofactor that is permanently bound to an enzyme molecule by covalent bonds.

Question 38

Give an example of a prosthetic group?

Answer 38

The enzyme carbonic anhydrase contains a zinc ion Zn²⁺ prosthetic group, permanently bound to its active site.

Question 39

What is the role of carbonic anhydrase?

Answer 39

• Found in erythrocytes (RBCs) and catalyses the interconversion of carbon dioxide and water to carbonic acid, which then breaks down to protons and hydrogencarbonate ions.
• inteconversion means these reactions work in both ways, both the conversion of carbon dioxide and water to carbonic acid, but also the breakdown to proton and hydrogencarbonate ions.

Do we need to know the equation?

Question 40

Why is the reaction that carbonic anhydrase catalyses vital?

Answer 40

This is because it enables carbon dioxide to be carried in the blood from respiring tissues to the lungs.

Question 41

Some enzymes work in the presence of cofactors that are not permanently bound to them. These are:

Answer 41

Mineral ion cofactors and organic coenzymes, as opposed to prosthetic groups.

Question 42

In an enzyme-catalysed reaction, the enzyme and substrate bind together to form a?

Answer 42

enzyme-substrate complex

Question 43

How does the presence of certain mineral ion cofactors affect enzyme-catalysed reactions?

Answer 43

The presence of certain mineral ion cofactors may ease the formation of enzyme substrate complexes so increases the rate of the enzyme-catalysed reaction.

Question 44

How do mineral ion cofactors work?

Answer 44

• Act as co-substrates - they and the substrate together from the correct shape to bind to the active site of the enzyme.
• Change the charge distribution on the surface of the substrate molecule or on the surface of the enzyme’s active site, and make the temporary bonds in the enzyme-substrate complex easier to form.

Question 45

Example of a cofactor that is not permanently bound to enzymes?

Answer 45

The enzyme amylase digests starch to maltose, and will only function if chloride ions, Cl-, are present.

Question 46

What are coenzymes?

Answer 46

Small organic non-protein molecules that bind temporarily to the active site of enzyme molecules, either just before or at the same time the substrate binds.

Question 47

What happens to the coenzyme during reactions?

Answer 47

They are chemically changes during the reaction and so need to be recycled to their original state, sometimes by a different enzymes.

Question 48

What are many coenzymes derived from?

Answer 48

They are derived from water-soluble vitamins. If these vitamins are deficient in

Question 49

Which coenzyme is derived from the vitamin, B12, and what human deficiency disease occurs if this vitamin is deficient?

Answer 49

Cobalamin coenzymes are derived from the vitamin B12. Lack of B12 vitamin results in pernicious anaemia (progressive and fatal anaemia)

Question 50

Which coenzyme is derived from the vitamin, folic acid, and what human deficiency disease occurs if this vitamin is deficient?

Answer 50

Tetrahydrofolate is derived from the vitamin folic acid. Lack of folic acid results in megablatic anaemia (large, irregularly shaped erythrocytes)

Question 51

Which coenzyme is derived from the vitamin, nicotinamide/B3, and what human deficiency disease occurs if this vitamin is deficient?

Answer 51

NAD and NADP is the coenzymes derived from the vitamin, nicotinamide/B3. Lack of nicotinamide/B3 results in pellagra (diarrhoea, dermatitis and dementia)