1.4 - Enzymes and Biological Reactions

Question 1

What is a metabolic pathway?

Answer 1

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

Question 2

What is an anabolic reaction?

Answer 2

Building up molecules (eg protein synthesis)

Question 3

What is a catabolic reaction?

Answer 3

Breaking down molecules (eg digestion)

Question 4

What are enzymes?

Answer 4

Enzymes are globular proteins that are biological catalysts and are made of living cells

Question 5

Why are enzymes good catalysts? (4 points)

Answer 5

• speeds up reactions
• they are not used up
• they are not changed
• they have a high turn over number

Question 6

Sites of enzyme action in extracellulars?

Answer 6

Secreted from cells by exocytosis and catalyse extracellular reactions

Question 7

Sites of enzyme action in intracellular solutions?

Answer 7

Acts in solution inside cells

Question 8

Sites of enzyme action in intracellular membrane bound?

Answer 8

Intracellular enzymes may be attached to membranes like on the cristae of mitochondria

Question 9

What is an active site?

Answer 9

A 3d site on an enzyme molecule to which the substrate binds by weak chemical bonds

Question 10

What is an enzyme substrate complex?

Answer 10

In an enzyme catalysed reaction in which the substrate and the enzyme bind temporarily

Question 11

What is the lock and key model?

Answer 11

• active site is perfect for substrate
• enzyme substrate complex formed
• products created leaves active site

Question 12

What is the induced fit model?

Answer 12

• active site isnt perfect for substrate
• shape of active site changes to create enzyme substrate complex
• products created leaves active site, returning to its original shape

Question 13

What is activation energy?

Answer 13

The minimum energy that must be put into a chemical system for a reaction to occur

Question 14

How can kinetic energy be used to make chemicals react?

Answer 14

• increasing the kinetic energy to make collisions between molecules more likely
• heat speeds up reactions however above 40* in living organisms can cause denaturing, this enzymes are used instead

Question 15

What can enzymes do to activation energy?

Answer 15

Enzymes work by lowering the activation energy.

Question 16

Describe the effect of temperature on the rate of enzyme reaction

Answer 16

• at low temps, the enzyme is inactivate as the molecules have very low KE, the shape remains unchanged so the enzyme will work again if the temperature is raised
• above 40*, molecules have higher kinetic energy but the reaction rate goes down because their increasing vibration breaks hydrogen bonds changing the tertiary structure. This changes the active site so the substrate will not fit, enzymes then become denatured.

Question 17

Describe the effect on pH on the rate of enzyme action

Answer 17

-the charge on amino acid side chains of the enzymes active site are effected by hydrogen
-at a low pH, excess H+ ions are attracted to negative charges to neutralise them
- at high pH, excess oh- ions neutralise the positive ions
- this disrupts the ionic and hydrogen bonds maintaining the shape of the active site (the shape changes so the enzyme denatures)

Question 18

Describe the effect of substrate conc on enzyme ROR

Answer 18

• as it increases, substrate conc is a limiting factor, only a limited number of substrate molecules to fill the active sites
• plateus at the top as substrate conc is not a limiting factor, excess substrate molecules unable to find any free active sites (maximum ROR)

Question 19

Describe the effect of enzyme conc on ROR

Answer 19

• once product leaves active site, the enzyme can be reused, so only a low enzyme concentration is needed to catalyse a larger number of reactions
• as the enzyme conc increases, there are more active sites available therefore the ROR increases

Question 20

What is the ‘turn over number’?

Answer 20

The number of substrate molecules that one enzyme molecule can turn into products in a given time

Question 21

What is an enzyme inhibiter?

Answer 21

A molecule or ion that binds to an enzyme and reduces the rate of the reaction it catalyses

Question 22

What is competitive inhibition?

Answer 22

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

Question 23

What is non-competitive inhibition?

Answer 23

An atom, molecule or ion that reduces the rate of an enzyme by binding at a position other than the active site, altering the shape of the active site and preventing the substrate from successfully binding to it

Question 24

What are immobilised enzymes?

Answer 24

Enzyme molecules bound to an intert material, over which the substrate can move

Question 25

What are the 5 advantages of immobilised enzymes?

Answer 25

• increased stability over a wider range of temperatures and pH than in free solution
• products are not contaminated with the enzyme
• enzymes are easily recovered for reuse
• a sequence of collumns can be used so several enzymes can be used in one process
• enzymes can easily be added or removed, giving greater control over the reactions

Question 26

What are 3 uses of immobilised enzymes?

Answer 26

• lactose free milk (lactose binds to active site and is hydrolised into its components, glucose and galactose)
• biosensors (turns a chemical signal into an electrical signal)
• high fructose corn syrup manufacture (HFCS)