Mod 2 Chap 4: Enzymes

Question 1

Describe enzymes in general.

Answer 1

• biological catalysts
• globular proteins that interact w/ substrate molecules, causing reactions at much faster rate, without need for harsh environmental conditions
• make many processes to life possible

Def: biological catalyst that speeds up biochemical processes, but remain unchanged at end of process

Question 2

Describe enzymes’ role in catalysing reactions.

Answer 2

• catalyse anabolic (building up) reactions + catabolic (breaking down) reactions
• catalyse digestion too
• changing temp, pressure, concentration, and pH can all have effect on rate of reaction by enzymes
• can only increase reactions up to a certain point (Vmax)

Question 3

Describe HOW enzymes carry out their role as biological catalysts.

Answer 3

• molecules in solution move + collide randomly, need to collide in correct position for reaction to occur
• when high temps / pressure applied, molecules increase in speed, so so will no. of successful collisions, so overall rate of reaction increases
• each enzyme catalyses one biochemical reaction, this is specificity of an enzyme
• energy required for most reactions to start (activation energy) can be so high it prevents reactions from occurring in normal conditions, so enzymes help molecules collide successfully, reducing activation energy required
  (Two hyptheses for how they do this)

Question 4

Describe the hypothesis: lock and key, for how enzymes help molecules collide more successfully in order to speed up rate of reactions.

Answer 4

• an area within tertiary structure of enzyme has complementary shape to shape of specific substrate molecule, this area = active site
• only a specific substrate will ‘fit’ into active site of an enzyme

Question 5

Describe the hypothesis: induced fit, for how enzymes help molecules collide more successfully in order to speed up rate of reactions.

Answer 5

• suggests active site actually changes as substrate enters (slightly)
• initial interaction between enzyme + substrate relatively weak, but weak interactions rapidly induce changes in enzymes tertiary structure, strengthening binding, putting strain on substrate molecule
• this weakens bond/s in substrate, lowering activation energy required for reaction

Question 6

What actually happens when a substrate molecule has bound to the active site of an enzyme?

Answer 6

• enzyme-substrate complex formed
• substrate/s then react + product/s released, leaving enzyme unchanged, able to take part in subsequent reactions
• substrate held in such a way by enzyme that right-atom groups are close enough to react
• R-groups within active site also interact w/ substrate, forming temporary bonds, putting strain on bonds within substrate, also helping reaction along

Question 7

Describe the role of enzymes in catalysing intracellular reactions.

Answer 7

• these are reactions within cells
• hydrogen peroxide = toxic product of many metabolic pathways
• so, enzyme: catalase ensures hydrogen peroxide is broken down to oxygen + water quickly, to prevent its accumulation
• found in both plant + animal tissue

Question 8

Describe the role of enzymes in catalysing extracellular reactions.

Answer 8

• caused as all reactions within cells require substrates (raw materials) to make products needed by organism, nutrients in diet supply these materials
• nutrients often in form of polymers e.g. Proteins / polysaccharides, + too large to enter cells directly through surface membrane
• SO extracellular enzymes released to break down large nutrient molecules in process of digestion
• (see digestion in single celled organisms)
• (see digestion in multicellular organisms)
• examples of extracellular enzymes: amylase, trypsin (for human digestion)

Question 9

Briefly describe digestion for single celled organisms.

Answer 9

• e.g. Bacteria + yeast release enzymes into immediate environment
• these break down larger molecules + produce smaller ones e.g. Amino acids + glucose
• smaller molecules now absorbed by cells

Question 10

Briefly describe digestion in multicellular organisms.

Answer 10

• eat food to gain nutrients, nutrients taken into digestive system, but large molecules still have to be digested so smaller molecules produced can be absorbed into bloodstream
• then transported around body to be used as substrates in cellular reactions

Question 11

Describe the digestion of starch.

Answer 11

• begins in mouth + continues in small intestine
• starch polymers partially broken down into maltose (a disaccharide) by enzyme amylase (produced by salivary gland + pancreas)
• maltose then broken down to glucose (a monosaccharide) by enzyme Maltase (present in small intestine)
• glucose small enough to be absorbed by cells lining digestive system, + so into bloodstream

Question 12

Describe the digestion of proteins.

Answer 12

• trypsin = a protease (type of enzyme that catalyses digestion of proteins into smaller peptides, can then be broken down into amino acids by other proteases)
• trypsin produced in pancreas + released in pancreatic juice into small intestine, where acts on proteins
• amino acids (produced by actions of proteases) absorbed by cells lining digestive system, + so into bloodstream

Question 13

Describe the effect of temperature on enzyme action.

Answer 13

• increasing temp increases KE of particles
• as temp increases, particles move faster + collide more frequently
• in an enzyme controlled reaction, higher temp = more frequent so more successful collisions between substrate + enzyme, so = increased rate of reaction
• this because increased temp causes changes in shape of active site, so enzymes more likely to come in contact w/ substrate
• temp coefficient (Q10) measures how much rate of reaction increases w/ a 10 degrees C temp rise, this usually 2, meaning ROR doubles w/ a 10 degrees C temp rise

Question 14

Describe denaturation.

Answer 14

• as temp increases, vibrations of bonds holding protein (enzyme) together increase too, until bonds strain + break
• results in change in tertiary (3D) structure of protein
• enzyme has changed shape, + so has denatured
• causes active site to change shape, making it no longer complementary to substrate shape
• so enzyme no longer functions as catalyst

Question 15

Describe optimum temperature.

Answer 15

• = temp at which an enzyme has highest rate of activity
• enzymes in human body = optimum temp of +/- 40 degrees C
• once enzyme denatures above optimum temp, decrease in ROR is rapid.

Question 16

Describe the effect of pH on enzyme activity.

Answer 16

• a change in pH = a change in H ion concentration
• are more H ions present in low pH (acidic) environment
• are fewer H ions present in a high pH (alkaline) environment
• H bonds + ionic bonds between amino acid R-groups hold proteins in their 3D shape
• these bonds result from interactions between polar + charged R-groups on amino acids forming primary structure

Question 17

Describe optimum pH.

Answer 17

• active site only correct shape at certain H ion concentration, this = optimum pH
• when pH changes from optimum, active site is altered
• yet, if pH returns to optimum, protein resumes normal shape + catalyses reaction again (this is renaturation)
• but, if pH changes significantly, enzyme = irreversibly altered + no longer substrate complementary, so now denatured, reducing ROR overall
• the more H ions present (low pH) = less able R-groups are to interact w/ eachother
• less H ions present (high pH) = more able R-groups are to interact w/ eachother
• so as pH changes, shape of enzyme changes, so will only function in a narrow pH range

Question 18

Give the functionable pH range for each of the enzymes below:
Amylase
Pepsin
Trypsin
Lipase
Maltase

Answer 18

Amylase: 7-8
Pepsin: 1-2
Trypsin: 8
Lipase: 8
Maltase: 8

Question 19

Describe the effect of substrate concentration on enzyme activity.

Answer 19

• increased substrate conc means no. of substrate molecules in a particular area / vol increases
• leads to increase in collision rate w/ active sites of enzymes + so formation of more enzyme - substrate complexes
• so overall ROR increases
• continues up to max rate (Vmax)

Question 20

Describe the effect of enzyme concentration on enzyme activity.

Answer 20

• when conc of enzyme increases, no. of available active sites in a particular area / vol increases, leading to formation of enzyme - substrate complexes at faster rate
• ROR then increases, up to its Vmax
• at Vmax, all active sites are bound w/ substrates, so no more enzyme-substrate complexes can form, until products are released from active sites
• ROR can only be increased after this by adding more enzyme / increasing temp
• reaction can rise to higher Vmax if enzyme conc is increased though

Question 21

Describe a practical investigation into the effects of temperature on enzyme activity.

Answer 21

Breakdown of starch into maltose w/ amylase as catalyst.
IV: temp of water baths for boiling tubes of enzymes + starch
DV: time taken for amylase to catalyse reaction to break down starch
Use:
- iodine to test for starch
- dropping tile
- record how fast amylase works to break down starch until it is no longer present
- repeat

Question 22

Describe a practical investigation into the effects of pH on enzyme activity.

Answer 22

Same as for temp (breakdown of starch into maltose w/ amylase enzyme) but add buffer solution w/ a diff pH to each test tube, instead of changing temp w/ water baths

Question 23

Describe a practical investigation into the effects of substrate concentration on enzyme activity.

Answer 23

Rate of hydrogen peroxide breakdown by catalase (DV), in diff substrate concentrations (IV)
Use:
- serial dilutions to make substrate solutions w/ diff concentrations
- put potato cylinder in flask of catalase +hydrogen peroxide + one substrate concentration (bunged)
- record time of 3 mins + record vol of gas given off (through delivery tube from flask into upside down test tube in water trough) every 30 secs
- repeat for diff substrate concentrations (created in dilution series)

Question 24

Describe a practical investigation into the effects of enzyme concentration on enzyme activity.

Answer 24

Serial dilutions of trypsin concentrations to catalyse break down of milk protein
IV: concentration of trypsin
DV: rate of milk protein breakdown
Use:
- serial dilutions of trypsin concentrations
- 5 diff test tubes of milk powder
- add trypsin to milk powders one at a time, record time taken for solution to become transparent to read observation sheet behind
- repeat for all diff concentrations of trypsin

Question 25

Describe the need for cofactors, coenzymes and prosthetic groups in some enzyme controlled reactions.

Answer 25

• some enzymes need non-protein ‘helper’ component to carry out their functions as biological catalysts
  COFACTORS:
• may transfer atoms / groups from one reaction to another in multistep pathway / may form part of active site of an enzyme
• obtained as minerals e.g. iron, calcium, chloride + zinc ions via diet
  COENZYMES:
• are when cofactor is an organic molecule
• derived from vitamins, a class of organic molecule found in diet

Question 26

Describe prosthetic groups.

Answer 26

• are cofactors required by certain enzymes to carry out their catalytic function
• but, are only cofactors that are tightly bound + form a permanent feature of the enzyme protein.

Question 27

Describe precursor activation.

Answer 27

• enzymes produced in an inactive form = inactive precursor enzymes
• often need to undergo change in shape (tertiary structure), particularly active site, to be activated
• this can happen by addition of a cofactor
• before cofactor added, precursor protein = an apoenzyme, after added + enzyme is added, precursor protein = a holoenzyme

Question 28

Describe the effect of inhibitors on the rate of enzyme controlled reactions.

Answer 28

• important that reactions don’t happen too fast + are controlled, otherwise leads to build up of excess products, wasting resources
• inhibitors inactivate enzymes as biological catalysts
• are molecules that prevent enzymes from carrying out catalytic function / slow this down
• two types of inhibition: competitive + non-competitive

Question 29

Describe competitive inhibition.

Answer 29

• a molecule, or part of one, w/ similar shape to substrate of an enzyme fits into active site of enzyme
• this blocks substrate from entering active site, preventing enzyme from catalysing reaction, so enzyme is inhibited of its role
• substrates + inhibitors continue to compete to bind w/ active sites of enzymes catalysing reactions
• this reduces no. of substrate molecules successfully binding w/ active sites, so slows ROR
• so these inhibitors are called competitive inhibitors
• degree of inhibition depends on relative concs of substrate, inhibitor + enzymes
• effect of comp inhibitors = reversible as only bind temporarily to active site, apart from exceptions e.g. Aspirin
• examples of comp inhibitors: succinct Dehydrogenase, statins, aspirin

Question 30

Describe non-competitive inhibition.

Answer 30

• inhibitors bind to enzyme somewhere other than active site, this = allosteric site
• binding of inhibitor changes enzyme’s tertiary structure, meaning active site changes shape too
• results in active site no longer having complementary shape to substrate, so unable to bind w/ it
• enzymes then inhibited + cannot carry out function
• inhibitor does not compete w/ substrate so known as non-competitive-inhibitor
• examples of non-comp inhibitors: organophosphates, proton pump inhibitors, copper sulphate

Question 31

Describe End Product Inhibition.

Answer 31

Term used for enzyme inhibition that occurs when product of a reaction acts as inhibitor to enzyme that produces it.

Question 32

Define a catalyst.

Answer 32

A substance that speeds up a chemical reaction without being used up itself, by providing an alternative route for reaction w/ a lower activation energy.

Question 33

Define the active site.

Answer 33

A cleft or indentation found on surface of an enzyme, made from only a few amino acids within the enzyme structure.

Question 34

Define a substrate.

Answer 34

A substance used, or acted on, by another process or substance. For e.g. A reactant in an enzyme catalysed reaction.

Question 35

Define metabolism.

Answer 35

All the chemical activities that keep organisms alive.

Question 36

Define a metabolic pathway.

Answer 36

• Consist of chains / cycles of reactions catalysed by enzymes
• Usually consists of series of steps, each controlled by an enzyme.
• Usually carried out in designated compartments of cell, where necessary enzymes are clustered + isolated.

Question 37

Define extracellular.

Answer 37

Enzymes that work outside of the cell.

Question 38

Define intracellular.

Answer 38

Enzymes that work inside of the cell.

Question 39

Define anabolic.

Answer 39

A type of metabolic action that build ups complex molecules + is biosynthetic, e.g. Photosynthesis.

Question 40

Define catabolic.

Answer 40

A type of metabolic action that breaks down complex molecules so is degradative, e.g. cellular respiration.