Flashcards in Mod 2 Chap 4: Enzymes Deck (40)
Describe enzymes in general.
- 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
Describe enzymes' role in catalysing reactions.
- 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)
Describe HOW enzymes carry out their role as biological catalysts.
- 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)
Describe the hypothesis: lock and key, for how enzymes help molecules collide more successfully in order to speed up rate of reactions.
- 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
Describe the hypothesis: induced fit, for how enzymes help molecules collide more successfully in order to speed up rate of reactions.
- 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
What actually happens when a substrate molecule has bound to the active site of an enzyme?
- 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
Describe the role of enzymes in catalysing intracellular reactions.
- 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
Describe the role of enzymes in catalysing extracellular reactions.
- 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)
Briefly describe digestion for single celled organisms.
- 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
Briefly describe digestion in multicellular organisms.
- 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
Describe the digestion of starch.
- 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
Describe the digestion of proteins.
- 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
Describe the effect of temperature on enzyme action.
- 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
- 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
Describe optimum temperature.
- = 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.
Describe the effect of pH on enzyme activity.
- 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
Describe optimum pH.
- 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
Give the functionable pH range for each of the enzymes below:
Describe the effect of substrate concentration on enzyme activity.
- 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)
Describe the effect of enzyme concentration on enzyme activity.
- 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
Describe a practical investigation into the effects of temperature on enzyme activity.
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
- iodine to test for starch
- dropping tile
- record how fast amylase works to break down starch until it is no longer present
Describe a practical investigation into the effects of pH on enzyme activity.
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
Describe a practical investigation into the effects of substrate concentration on enzyme activity.
Rate of hydrogen peroxide breakdown by catalase (DV), in diff substrate concentrations (IV)
- 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)
Describe a practical investigation into the effects of enzyme concentration on enzyme activity.
Serial dilutions of trypsin concentrations to catalyse break down of milk protein
IV: concentration of trypsin
DV: rate of milk protein breakdown
- 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
Describe the need for cofactors, coenzymes and prosthetic groups in some enzyme controlled reactions.
- some enzymes need non-protein 'helper' component to carry out their functions as biological catalysts
- 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
- are when cofactor is an organic molecule
- derived from vitamins, a class of organic molecule found in diet
Describe prosthetic groups.
- 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.
Describe precursor activation.
- 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
Describe the effect of inhibitors on the rate of enzyme controlled reactions.
- 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
Describe competitive inhibition.
- 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