Unit 1.4 - Enzymes and Biological Reactions

Question 1

Metabolism

Answer 1

All the organism’s chemical processes, comprising anabolic and catabolic pathways.

Question 2

Metabolic pathway

Answer 2

Sequence of enzyme controlled reactions in which a product of one reaction is a reactant in the next.

Question 3

1) State an example of a anabolic reaction.

2) State an example of a catabolic reaction.

Answer 3

1) Building up molecules - protein synthesis

2) Breaking down molecules - digestion.

Question 4

Enzyme

Answer 4

Biological catalyst; globular protein made by cells that speeds up rate of a chemical reaction without being used up.

Question 5

Catalyst

Answer 5

Atom or molecules that alters rate of chemical reaction without taking part or being changed by the reaction

Question 6

State 4 properties of enzymes.

Answer 6

Speed up reactions, not used up, not changed, high turn-over number.

Question 7

1) What structure do enzymes have?
2) What makes enzymes soluble?
3) What does the R-group determine?

Answer 7

1) Tertiary structure
2) Chain folds into globular shape with hydrophilic R-groups on the outside of the molecule.
3) Determines bonds the amino acids make with each other.

Question 8

Which bonds help to maintain an enzymes structure?

Answer 8

Hydrogen bonds, disulphide bridges and ionic bonds.

Question 9

Active site

Answer 9

Specific 3 dimensional site on an enzyme molecule to which the substrate binds by weak chemical bonds.

Question 10

1) What happens to enzymes on extracellular sites?

2) State an example.

Answer 10

1) Enzymes are secreted from cells by exocytosis.

2) Amylase moves down the salivary ducts to the mouth.

Question 11

1) What happens to enzymes on intracellular sites in a solution?
2) State an example.

Answer 11

1) Act in solution inside cells.

2) Enzymes catalyse glucose breakdown in glycolysis (respiration).

Question 12

1) What happens to enzymes on intracellular sites where it is membrane bound?
2) State an example.

Answer 12

1) Attached to membranes.

2) Cristae of mitochondria.

Question 13

Enzyme-substrate complex

Answer 13

Intermediate structure formed during an enzyme-catalysed reaction in which the substrate and enzyme bind temporarily.

Question 14

What is the lock and key model?

Answer 14

Active site and substrate are complementary to each other.

Question 15

Induced fit

Answer 15

Change in shape of the active site of an enzyme, induced by the entry of a substrate, so that the enzyme and substrate bind closely.

Question 16

1) What is the induced fit model?

2) State an enzyme that undergoes this formation.

Answer 16

1) Enzyme shape alters slightly to accommodate the substrate (flexible).
2) Lysozyme - anti-bacterial enzyme found in saliva.

Question 17

Activation energy

Answer 17

Minimum energy that must be put into a chemical system for a reaction to occur.

Question 18

1) At what temperature do most enzymes begin to denature?

2) How will lowering the activation energy effect the temperature?

Answer 18

1) Above 40°C.

2) Allow enzymes to take place at lower temperatures found in cells.

Question 19

State 4 factors that affect enzyme action.

Answer 19

Temperature, pH, substrate concentration and enzyme concentration.

Question 20

Denaturation

Answer 20

Permanent damage to the structure and shape of a protein molecule.

Question 21

Inactivation

Answer 21

Reversible reduction of enzyme activity at low temperature as molecules have insufficient kinetic energy to form enzyme-substrate complexes.

Question 22

State the relationship between the rate of reaction and temperature rise.

Answer 22

Rate of reaction doubles for each 10°C rise in temperature.

Question 23

Describe how an enzyme becomes denatured above 40°C.

Answer 23

Increase kinetic energy, increase vibrations break hydrogen bonds, changes shape of active site, enzyme and substrate are no longer complementary to each other and so no products are formed.

Question 24

1) What happens at low and high pH?

2) Which bonds are disrupted?

Answer 24

1) Low pH - excess H+ ions attracted to negative charges and neutralise them.
High pH - excess OH- ions neutralise positive charges.
2) Ionic and hydrogen bonds.

Question 25

Limiting factor

Answer 25

Factor that, when in short supply, limits the rate of a reaction.

Question 26

1) What happens to the rate of reaction when the enzyme concentration is constant?
2) When is an enzyme saturated?

Answer 26

1) Rate of reaction increases as the substrate concentration increases.
2) All the active sites are full.

Question 27

1) Why can a low enzyme concentration be used to catalyse a large number of reactions?
2) What is the relationship between enzyme concentration and the rate of a reaction?

Answer 27

1) Enzyme molecule can be reused.

2) Enzyme concentration increases, more active sites available therefor the rate of reaction increases.

Question 28

Inhibitor

Answer 28

Molecule or ion that binds to an enzyme and reduces the rate of the reaction the enzyme catalyses.

Question 29

Competitive inhibition

Answer 29

Reduction of rate of an enzyme-controlled reaction by a molecule or ion that has a complementary shape to the active site, similar to substrate, and binds to the active site blocking the substrate from binding.

Question 30

State an example of competitive inhibition.

Answer 30

Malonic acid has a similar shape to succinct acid and so compete for the active site of succinc dehydrogenase.

Question 31

Competitive inhibition

1) How will increasing the concentration of the substrate affect the inhibitor?
2) What happens when the inhibitor concentration increases?

Answer 31

1) Reduces effect of inhibitor because more substrate molecules present, the greater their chance of binding to active sites, leaving fewer available for inhibitor.
2) Binds and blocks to more active sites and so rate of reaction is slower.

Question 32

Non-competitive inhibitor

Answer 32

Atom, molecule or ion that reduces rate of enzyme controlled reaction by binding to enzyme at a position other than active site, altering shape and preventing substrate from successfully binding to it.

Question 33

1) State 2 examples of non-competitive inhibitors.

2) What do they do?

Answer 33

1) Cyaninde and heavy metal ions (lead) bind to allosteric site.
2) Alter shape, substrate can’t bind to active site and no enzyme-substrate complexes form.

Question 34

Non-competitive inhibition

1) What happens when the inhibitor concentration increases?
2) What happens when you increase the substrate concentration?

Answer 34

1) Rate of reaction and final mass of product decrease.

2) No effect.

Question 35

Immobilised enzyme

Answer 35

Enzyme molecules bound to an inert material, over which the substrate molecules move.

Question 36

When are enzymes immobilised?

Answer 36

Bound to an inert matrix such as sodium alginate beads or cellulose microfibrils.

Question 37

Describe how an enzyme is immobilised in a column.

Answer 37

Substrate added to top of column, molecules bind to enzyme molecules’ active site both on beads surface and inside beads as molecules diffuse in.
Smaller beads, higher rate of reaction.

Question 38

State 5 advantages of immobilised enzymes.

Answer 38

1) Increased stability over wider range of temperatures and pH than enzymes free in a solution.
2) Products aren’t contaminated with the enzyme.
3) Easily recovered for reuse.
4) Sequence of columns can be used so several enzymes with differing pH/optimum temp can be used in one process.
5) Easily added or removed, giving greater control over reaction.

Question 39

1) Why does immobilising enzymes with a polymer matrix make them more stable?
2) What effect does trapping an enzyme molecule have?

Answer 39

1) Creates microenvironment allowing reactions to occur at higher temperatures or more extreme pH than normal.
2) Prevents the shape change that would denture its active site, so enzyme can be used in wider range of physical conditions than if it were in free solution.

Question 40

State 3 differences between immobilised and free enzymes.

Answer 40

Rate of reaction is greater at every temperature with immobilised enzymes, denatures at a higher temperature and has a greater range of optimum temperatures.

Question 41

State how lactose-free milk is made.

Answer 41

Milk passed down column containing immobilised lactase. Lactose binds to active site on lactase and is hydrolysed into glucose and galactose.

Question 42

1) What signal do biosensors use?

2) What are they used for?

Answer 42

1) Turn chemical signals into electrical signals.

2) Accurately detect, identify and measure low concentrations of important molecules.

Question 43

Describe how biosensors are used to detect blood glucose.

Answer 43

Glucose oxidase immobilised on a selectively permeable membrane placed in a blood sample, glucose binds to glucose oxidase. Produces a small electric current detected by electrode and read on the screen.

Question 44

Describe how high-fructose corn syrup is manufactured from starch.

Answer 44

Starch (a amalyse, 90°C) > Oligosaccharides (glucoamylase, 60°C) > glucose (glucose isomerase) > fructose.