Core Concepts: Enzymes Flashcards

1
Q

What is an ESC?

A

Enzyme-substrate complex

- intermediate structure formed where enzyme and substrate temporarily bind

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the effect of pH on the rate of enzyme action?

A

Small changes to the pH (around the optimum)
- causes small reversible changes to enzyme structure and reduced its activity

Extreme changes to pH

  • Charges on amino acid side-chains of active site affected by H+ and OH- ions
  • at a very LOW pH excess H+ ions are attracted to negative charges on active site
  • at a very HIGH pH excess OH- ions neutralise positive charges
  • both disrupt ionic and hydrogen bonds holding the tertiary shape, changing the enzyme shape, no ESC, denatures enzyme and enzyme activity is lost
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Describe the effect of a low substrate concentration?

A
  • fewer substrate molecules
  • fewer enzyme-substrate complexes being formed
  • results in fewer products being produced
  • the time taken for the reaction is longer
  • substrate concentration is the limiting factor
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Describe the effect of high substrate concentration?

A
  • a point is reached where all the enzymes are saturated (all active sites are full)
  • rate of reaction is at a maximum so a further increase in substrate concentration will not change the rate of reaction, stays constant
  • enzyme concentration is the limiting factor
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Describe the effect of low enzyme concentrations?

A
  • fewer enzyme molecules, fewer active sites
  • fewer ESCs formed
  • fewer products are produced
  • time taken for the reaction is longer
  • the enzyme concentration is the limiting factor
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Describe the effect of very high enzyme concentration?

A
  • a point will reach when there are more active sites available than substrate molecules
  • therefore increasing the enzyme concentration will decrease time taken, remains constant
  • substrate concentration is the limiting factor
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is an inhibitor?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is a competitive inhibitor?

A
  • has a complementary shape to the active site, similar to the substrate
  • binds to the active site and forms an enzyme-inhibitor complex blocking the active site from the substrate
  • this causes less ESCs to form and the rate of the reaction is lowered
  • however increasing the concentration of substrate, reduces the effects of the inhibitor as there is a greater chance of the substrate binding instead of the inhibitor
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is an example of a competitive inhibitor?

A
  • ethanol is a inhibitor/antidote for ethylene glycol poisoning (antifreeze)
  • ethylene glycol metabolises into oxalic acid if ingested, crystallises major organs (e.g. brain) which can be fatal
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is a non-competitive inhibitor?

A
  • binds to an allosteric site on the enzyme (doesn’t compete with the substrate)
  • this binding distorts the tertiary structure, which changes the shape of the active site
  • enzyme is no longer complementary to its specific substrate, no ESC
  • rate of reaction is decreased
  • increase in substrate concentration has no effect
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is an example of a non-competitive inhibitor?

A

Cyanide-respiratory inhibitor

- inhibits the enzyme cytochrome C oxidase which releases ATP in respiration (fatal)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How are enzymes made?

A
  • Culturing microbe in fermentation vessels as microbes produce enzymes as their normal metabolic activity
  • microbes are the killed and enzymes are extracted and purified for use
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Uses of immobilised enzymes: Biosensors

A
  • Detects particular molecules (even at very low temperatures) turning a chemical signal into an electrical signal to accurately detect, identify and measure a substance
  • immobilised enzymes have the substrate bind to them (the particular substance) which produces the chemical signal
  • used for medical or environmental monitoring
  • also used on test strips (e.g. detecting glucose in urine)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the effect of temperature on the rate of enzyme action?

A
  • Increasing the temperature higher than the optimum increases the KE of molecules, molecules vibrate more
  • This weakens and breaks H-bonds in enzymes changing the tertiary structure
  • This alters the shape of the active site, substrate will never fit and rate of reaction drops as no ESCs form
  • Enzyme is therefore denatured, permanent change in structure (irreversible)
  • At low temperatures the enzyme is inactivated as enzymes have little kinetic energy (shape is unchanged and is reversible)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Explain the shape of the graph (mass of product v time - steep gradient which then plateaus)

A
  • When the enzyme and substrate are first mixed together there are many substrate molecules so more active sites are filled by many successful collisions
  • If conditions are optimal and there’s excess substrate, the enzyme concentration is the LF as there aren’t enough free active sites
  • As the reaction continues there is less substrate (enzyme concentration is constant) substrate concentration is the limiting factor
  • Eventually the line plateaus as all the substrate is used up
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are the 3 ways enzyme reactions can be measured?

A
  1. concentration of products produced (moldm^3)
  2. time taken for reaction to occur
  3. rate of reaction
17
Q

How do enzymes change the activation energy?

A
  • Enzymes lower the activation energy as the molecule shape changes when it enters the active site (less energy needed to break down the substrate)
  • Reactions can occur at lower temperatures (heating would speed up the reaction but cause enzymes to be denatured)
18
Q

What is an example enzyme for induced fit theory?

A

Lysozyme

- an anti-bacterial enzyme in human saliva, mucus and tears

19
Q

Describe the ‘Induced Fit’ Model?

A
  • substrate collides with a non-complementary active site
  • active site fits more closely around substrate molecule, held in position by oppositely charged groups
  • an enzyme-substrate complex is formed
  • the change in enzyme shape places a strain on substrate which weakens bonds, breaks easily (lowers activation energy)
  • products don’t fit into the active site anymore so products are released
20
Q

Describe the ‘Lock and Key’ model?

A

Enzymes have a uniquely shaped active site which is complementary to the shape of one substrate type
- bind together to form an ESC and the the products leave the active site

21
Q

Where are the 3 sites where enzymes act?

A
  1. Extracellular - outside the cell (e.g. digestive enzymes like amylase which is secreted from the salivary glands to mouth)
  2. Intracellular in solution - inside cells in a solution
  3. Intracellular membrane bound - attached to membranes
22
Q

Uses of immobilised enzymes: High-fructose corn syrup (HFCS) manufacture

A
  • multi-step process from starch

- many several immobilised enzymes used which requires different physical conditions

23
Q

What is meant by ‘metabolism’?

A

All the reactions in the body, in a sequence called metabolic pathways, including anabolic and catabolic reactions which are catalysed by enzymes

  • Anabolic = larger molecules synthesised
  • Catabolic = larger molecules broken down into smaller molecules
24
Q

What is a metabolic pathway?

A

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

25
What are the general properties of enzymes?
- globular proteins that are specific to one substrate and are biological catalysts - R-groups determine bonds amino acids make with each other - speed up reactions - not used up or changed in the reaction - high turn-over number - require specific conditions - lower activation energies
26
Where does a substrate bind on the enzyme?
The active site -> a pocket or cleft area which is complementary to a specific substrate
27
Why are enzymes used in large scale industrial production?
- speed up rate of reaction - lower activation energies (lowers temperature and increases efficiency) - less waste products from fewer side reactions
28
What are immobilised enzymes?
Enzyme molecules bound to an inert material, over which substrate molecules move
29
What are the advantages of immobilised enzymes?
- polymer matrix creates a microenvironment for enzymes, increases stability and function over wider ranges of temperature and pH - products are not contaminated - enzymes are easily recovered for reuse - a sequence of columns can be used for continuous process of enzymes with different optimum conditions - enzymes can be easily or removed, greater control of reaction
30
What are the disadvantages of using immobilised enzymes?
- if enzymes are held inside beads it would take time for the substrate to diffuse into it - in absorption the enzyme may become detached - alginate gel may alter the active site, reducing activity - chemically bonding the enzymes is a complex and expensive process - any contamination is costly because the whole system has to be shut down and the vessel re-sterilised
31
Uses of immobilised enzymes: lactose free milk
- this is an important industrial use of immobilised enzymes - milk is passed down a column containing immobilised lactase - lactose is hydrolysed into glucose and galactose