2.4 enzymes

Question 1

what is an enzyme

Answer 1

• biological catalysts
• globular proteins with complex tertiary structures
• sometimes may be quaternary structures
• control metabolic pathways

Question 2

role of enzymes

Answer 2

• anabolic reactions - build up molecules together
• catabolic reactions - breaking molecules down
• speed up reactions (catalysts, reduce the activation energy)

Question 3

mechanism of enzymes

Answer 3

• have an active site that is complementary to a specific substrate
• an enzyme is a protein - usually tertiary structure sometimes a protein with a quaternary structure
• enzyme specificity - complementary naturebetween theshapeof theactive siteon the enzyme and itssubstrate
• enzymes can be extracellular or intracellular

Question 4

extrecellular enzymes

Answer 4

• have an active site that is complementary to a specific substrate
• an enzyme is a protein - usually tertiary structure sometimes a protein with a quaternary structure
• enzyme specificity - complementary naturebetween theshapeof theactive siteon the enzyme and itssubstrate
• enzymes can be extracellular or intracellular

Question 5

intercellular enzymes

Answer 5

enzymes that act within cells eg catalase (breaks down hydrogen peroxide), DNA polymerase

Question 6

lock and key hypothesis

Answer 6

• active site is an area within the tertiary structure of the enzyme which is complementary to the shape of a specific substrate molecule
• substarte held in such a way by enzyme that the right atom-groups are close enough to react, R-group within the actiev site of the enzyme also interact with the substrate forming temporary bonds putting strain on bonds within substrate also helping the reaction along

Question 7

induced fit hypothesis

Answer 7

• enzyme changes shape slightly - conformational changes
• initial interactions between the enzymes and substrate is relatively weak but these weak interaction rapidly induces changes in the substrate molecules - weakens particular bonds in substrate therefore lowering activation energy for reaction

Question 8

factors affecting enzymes

Answer 8

• temperature
• pH

Question 9

how does temperature affect eznymes

Answer 9

• increase in temp means substrates and enzymes get more kinetic energy so more collisions between enzymes and substrate therefore higher frequency of successful collisions so increase in reaction
• As temp increases vibrations increase until bonds strain and break result in a change in the precise tertiary structure of the protein - denaturing
• denaturing - changed active shape so substrate no long can fit and enzyme can no longer function
• optimum temperature is the temp when enzymes have the highest rate of reactivity
• once enzymes denatured above optimum temperature decrease in rate of reaction is rapid
• when temp below optimum enzymes don’t denature, they are just less active

Question 10

what is the temperature coefficient

Answer 10

Temperature coefficient = (rate of reaction at (x+ 10) °C) ÷ (rate of reaction atx°C)
Temperature coefficient Q10 is a measure of how much the rate of a reaction increase with a 10C rise in temperature, usually take as 2 so rate of reaction doubles with a 10C temp increase

Question 11

how have organisms adapted for extreme tmperatures

Answer 11

living organisms have evolved to cope with extreme temperatures eg in cold temperatures enzymes have more flexible structure making them less stable as smaller temperature changes will denature them, hot temperatures have increased number of bonds - H bonds and sulfur bridges in tertiary structure - more resistant to temperature rises

Question 12

how does pH affect enzymes

Answer 12

• Hydrogen bonds and ionic bonds between amino acid R-groups hold proteins in their precise three-dimensional shape
• change in pH refers to change in H+ ion concentration
• more H+ ions present in low pH(acid), less H+ ions in high pH(alkaline, more3 OH-)
• active site only in right shape at certain H+ concentration - optimum pH
• when pH changes form optimum structure of enzyme and therefore active site is altered
• HOWEVER if pH returns back to normal the enzymes will resume its normal shape and catalyse again - renaturation
• when pH change is more significant shape is irreversible and active site no longer complementary - denatured
• more H+ ions present the less R-groups are able to interact with each other - leads to breaking bonds and shape of enzyme changing, reverse true when less H+ ions
• enzymes only work within a narrow pH ranges

Question 13

how does substrate concentration affect rate of reaction

Answer 13

• increased number of substrate particles leads to a higher collision rate with active sites of enzymes and so formation of more enzymes-substrate complexes so rate of reaction increases
• If the enzyme concentration remainsfixedbut the amount of substrate is increased past a certain point, however, all available active sites eventually becomesaturatedand any further increase in substrate concentration willnot increasethe reaction rate
• When the active sites of the enzymes are all full, any substrate molecules that are added havenowhere to bindin order to form anenzyme-substrate complex

Question 13

how does enzyme concentration affect rate of reaction

Answer 13

• when concnetration of enzymes increases it increases the number of available active sites in a particular area or volumes leading to formation of enzyme-substarte complexes at a faster rate
• As long as there issufficient substrate available, the initial rate of reactionincreases linearlywith enzyme concentration
• If the amount of substrate is limited, at a certain point any further increase in enzyme concentration willnot increasethe reaction rate as the amount of substrate becomes alimiting factor

Question 14

what are co-enzymes

Answer 14

• ORGANIC non-protein molecules
• Bind to active site of enzyme - some are oermanantly bound often in or near the actiive site some are temporarily
• involved incarrying electrons or chemical groupsbetween enzymes, aiding in catalysis
• May be involved in multiple reactions - link different enzyme-catalysed reactions into a sequence duringmetabolic processes,
• source of coenzymes are vitamIns
• Can carry substances between enzymes
• example of coenzymes - During many of the reactions inrespiration, the coenzymesNADandFADare alternatelyreducedandoxidised,transferring energyin the form ofhydrogen ions

Question 15

what are cofactors

Answer 15

• NORGANIC non-protein ions
• Affect charge distribution —> enzyme shape changed
• Speed up formation of enzyme-substrate complexes
• Prosthetic groups
• Iron - catalase function
• Amylase contains a chloride ion that is necessary for the formaiton of a corectly shaped actiev site

Question 16

what are prosthetic groups

Answer 16

• co-factors
• required by certain enzymes ot carry out their catalytic funtion
• tightly bound and forma permanant feature of the protien
• eg. Zn2+ in carbonic anhydrase, an nnezyme necessary for the metabolism of CO2

Question 17

what is a precuror enzyme

Answer 17

• many enzymes produced in an inactive form - inactive precursor enzymes
• these ate enzymes that can cause damage within the cells producing them or to tissues where they are released or enzymes who actions needs to be controled and only activated under certain condition
• often need to undergo a change in the actiev shape to be activated
• can be achieved by adding a cofactor - before cofactor added the proteins called and apoenzyme, then when added called a holoenzyme
• soemtimes change in tertiary structure brougth about by change in pH or temp - zymogens or prenzymes
• sometime change in structure brought about by action of an other enzyme eg protease whihc cleaves serain bonds in molecule
• when an inactive pepsinogen released into the stomach too digest proteins the acid pH brings about the transformation into the active enzyme pepsin - protects body’s tissue against digestive action of pepsin

Question 18

what is a competitive inhibitor

Answer 18

• Fit into active site of enzymes ue to similair shaoe to substartee of an enzyme
• blocks substate form entering the actibe site preventing enzyme from catalysing reaction
• enzyme can’t carry out its function so is inhibited
• Called active-site directed inhibitors - block substrate from binding
• Effects are reversible - only bind temporarily
• Degree to which they inhibit enzyme action depends on relative concentration of substarte and inhibitor
• reduces rate of reaction for a given concnetration of substrate
• aspirin IRRIVERSIBLY competitive inhibitor
• statins compeittive inhibotrs of an enzyme used in the synthesis of cholesterol

Question 18

what is a non-competitive inhibtor

Answer 18

• Non-actiev site directed inhibitors, do not bind to active site - allosteric site
• Alters shape of actiev site
• Substrate may still be able to bind but active site doesn’t catalyse reaction or at a slower rate
• Can be reversible or permanant
• Degree to which the inhibit enzyme reaction is not dependant on substrate concnentration
• increasing cincnentration of enzyme or substrate will bot ovrcome the effect of non-competitive inhibros, increasing conco of inhibitor decreases rate of reaction frtehr as morea ctiev sites becone unavailable

Question 19

what is end product inhibition

Answer 19

• term used for enyme inhibiton that occurs when the rpprodcut fo a reaction acts as an ihibotlr to the enzyme tht procues it
• Reversible inhibitors can act asregulatorsinmetabolic pathways
• Metabolic reactions can becontrolledby using theend-productof a particular sequence of metabolic reactions as anon-competitive, reversible inhibitor

Question 20

describe/outline process of end product inhibition

Answer 20

• s the enzyme converts the substrate into product, the process is itselfslowed downas theend-productof the reaction chain binds to an alternative site on the original enzyme, changing the shape of the active site and preventing the formation of further enzyme-substrate complexes
• The end-product can thendetachfrom the enzyme and be used elsewhere, allowing the active site toreformand the enzyme to return to anactive state
• This means that as product levels fall, the enzyme begins catalysing the reaction once again, in a continuousfeedback loop

Question 21

what is ethylene glycol

Answer 21

• Substance broken down into oxalic acid by alcohol dehydrogenase - enzyme produced by liver
• Oxalic acid poising causes rapid chronic kidney failure and death
• Treated by massive dose of ethanol which acts as competitive inhibitor of alcohol dehydrogenase
• Rate of oxalic acid production reduced and ethylene glycol can be extracted

Question 22

what is penicilin

Answer 22

• Inhibits enzyme that forms cross-links in bacteria cell walls - COMPETYIVE INHIBTOR
• Growing bacteria have incomplete cell walls and con no longer reproduce
• Bacteria population doesn’t continue to grow

Question 23

what happens if you increase the concnetration of an inhibtor

Answer 23

- reduces the rate of reaction - if inhibitor concentration continues to be increased, the reaction will stop completely

Question 23

what effect will an increase of susbtrate cocnnetration have on the rate of reatction with competitive inhibitors

Answer 23

- can increase the rate of reaction once more - more substrate molecules mean they are more likely to collide with enzymes and form enzyme-substrate complexes

Question 24

what effect will an increase of susbtrate cocnnetration have on the rate of reatction with non-competitive inhibitors

Answer 24

- cannot increase the rate of reaction once more - shape of the active site of the enzyme remains changed and enzyme-substrate complexes are still unable to form