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A-Level EDUQUAS Biology > Core Concepts: Enzymes > Flashcards

Core Concepts: Enzymes Flashcards

1
Q

What is an ESC?

A

Enzyme-substrate complex

- intermediate structure formed where enzyme and substrate temporarily bind

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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
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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
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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
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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
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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
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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

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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
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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
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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
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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)

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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
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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)
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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)
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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
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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
Q

What are the general properties of enzymes?

A
  • 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
Q

Where does a substrate bind on the enzyme?

A

The active site -> a pocket or cleft area which is complementary to a specific substrate

27
Q

Why are enzymes used in large scale industrial production?

A
  • speed up rate of reaction
  • lower activation energies (lowers temperature and increases efficiency)
  • less waste products from fewer side reactions
28
Q

What are immobilised enzymes?

A

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

29
Q

What are the advantages of immobilised enzymes?

A
  • 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
Q

What are the disadvantages of using immobilised enzymes?

A
  • 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
Q

Uses of immobilised enzymes: lactose free milk

A
  • 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

A-Level EDUQUAS Biology (24 decks)

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