2.1.4 Enzymes

Question 1

enzyme definition

Answer 1

globular protein with specific tertiary structures

Question 2

enzyme features

Answer 2

globular (roughly spherical, soluble, unique shape)
biological catalyst (increased rate of reaction while staying chemically unchanged)
specific (has unique shape due to order of amino acids, allows active site to be complementary to shape of substrate)

Question 3

extracellular definition

Answer 3

found outside of cells

Question 4

intracellular definition

Answer 4

found inside of cells

Question 5

metabolite definition

Answer 5

substance formed in or necessary for metabolism

Question 6

anabolic definition

Answer 6

synthesis of larger molecules from smaller molecules

Question 7

catabolic definition

Answer 7

breaking down of larger molecules into smaller molecules

Question 8

turnover number in enzymes

Answer 8

number of substrate molecules converted per second by a single enzyme (when the enzyme is the rate-limiting factor)

Question 9

turnover number formula

Answer 9

turnover number = max rate of reaction/given enzyme concentration

kcat = Vmax/[ET]

Question 10

temperature coefficient (Q10)

Answer 10

measure of rate of change in rate of reaction when temperature increases by 10°C
Q10 = 2 means every 10°C, rate of reaction doubles

Question 11

factors affecting enzyme activity

Answer 11

temperature
pH
substrate conc.
enzyme inhibitors (competitive and non-competitive)

Question 12

how temperature affects enzyme activity

Answer 12

temperature increases
KE in substrates and enzymes increase
more successful collisions occur
more ESCs can form so faster rate of reaction

Question 13

temperature in denaturing of enzymes

Answer 13

temperature increases over optimum
too much KE
bonds vibrate too much and bonds break
disrupts tertiary structure of protein
active site is altered and no longer complementary to the substrate’s shape
protein denatured 
irreversible so reaction stops

Question 14

optimum temperature/pH definition

Answer 14

temperature/pH at which enzyme has highest rate of activity

Question 15

how enzymes adapt to extremely cold environments

Answer 15

more flexible structures (especially at active site)
less stable than enzymes working at higher temperatures
slight temperature changes will denature them

Question 16

how enzymes adapt to extremely hot environments

Answer 16

more stable than other enzymes
due to more bonds (specifically disulphide bridges and hydrogen bonds) in tertiary structure
so more resistant to change in temperature

Question 17

how pH affects enzyme activity

Answer 17

pH not at optimum
affects distribution of charge on enzyme molecule
disrupts hydrogen and ionic bonds
enzyme loses tertiary structure
changes shape of active site of enzyme
substrate no longer attracted to active site (due to altered charge)
substrate can’t bind to active site as no longer complementary
no ESCs formed = no reaction = no product
enzyme denatured at extreme pHs relative to optimum

Question 18

how substrate concentration affects enzyme activity

Answer 18

increased concentration
higher likelihood of successful collisions
more ESCs can form
faster rate of reaction

Question 19

how competitive inhibitors affect enzyme activity

Answer 19

similar shape to enzyme’s substrate
shape is complementary to active site so can bind and block active site, forming enzyme-inhibitor-complex
prevents ESCs forming, slows rate of reaction, less products formed
reversible as competitive inhibitors bind to active site temporarily
Vmax eventually reached at higher substrate concentration

Question 20

how non-competitive inhibitors affect enzyme activity

Answer 20

ligand binds to allosteric site of enzyme
alters tertiary structure of enzyme, changes shape of of active site
substrate no longer fits into active site, no ESCs can form so rate of reaction decreases
irreversible as non-competitor inhibitors binds permanently to enzyme
Vmax never reached

Question 21

effect of increasing enzyme conc. on enzyme activity for fixed substrate conc.

Answer 21

no enzyme = no ESCs formed = no reaction
more enzymes = more active sites = more ESCs = more product formed and higher rate of reaction
rate will continue to rise as long as substrate is in excess
all substrate molecules will be occupying all active sites and max rate will be reached
increasing enzyme conc has no effect on rate of reaction (substrate conc is limiting factor)
rate of reaction decreases since as substrate is used up

Question 22

end-product inhibition

Answer 22

term used for enzyme inhibitors that occurs when the product of a reaction acts as an inhibitor to the enzyme that produces it

Question 23

potassium cyanide

Answer 23

non-competitive inhibitor of enzyme cytochrome oxidase, needed for respiration
decreases use of oxygen so ATP can’t be made
organism has to respire anaerobically
lactic acid build up in blood
small amounts for adults = loss of consciousness in 10s, coma in 45 mins, death in 2 hours

Question 24

inhibitors as drugs examples

Answer 24

viral infections treated by protease inhibitors
antibiotics treat bacterial infections
ethanol for treatment when ingesting antifreeze

Question 25

how viral infections are treated

Answer 25

protease inhibitors inhibit protease enzymes required to build their viral coat
competitive inhibitors

Question 26

how bacterial infections are treated

Answer 26

antibiotic penicillin
inhibits enzyme that builds cell wall
prevents bacteria from reproducing
some bacteria are resistant as they have enzymes that break down penicillin

Question 27

how to treat ingestion of antifreeze

Answer 27

ethylene glycol (in antifreeze) broken down in liver by alcohol dehydrogenase into oxalic acid (highly toxic, leads to death)
treated by huge dose of ethanol
acts as inhibitor of alcohol dehydrogenase, slows production of oxalic acid so ethylene glycol can be removed

Question 28

cofactor definition

Answer 28

substances that must be present to ensure that enzyme-controlled reactions take place at the right rate

Question 29

cofactors

Answer 29

coenzymes
prosthetic groups
inorganic ion cofactors

Question 30

coenzymes definition and features

Answer 30

small, organic non-protein molecules that binds to the active site at the same time or just before the substrate does
take part in reaction
converted back to original state (usually by different enzyme)

Question 31

coenzymes examples

Answer 31

many B group vitamins are examples of coenzymes

pyruvate dehydrogenase from vitamin B3

Question 32

prosthetic group definition and features

Answer 32

permanent parts of some enzymes

vital to 3D shape, function and charges of enzyme

Question 33

prosthetic group example

Answer 33

carbonic anhydrase has Zn2+ prosthetic group, allows red blood cells to combine carbon dioxide with water to form carbonic acid so CO2 can be transported around the blood

Question 34

inorganic ion cofactor definition

Answer 34

increase rate of reaction, combine with enzymes or substrates which helps ESC to form more easily by altering charge or shape of the ESC

Question 35

inorganic ion cofactor example

Answer 35

amylase breaks down starch into maltose

only functions properly in the presence of Cl-

Question 36

induced fit hypothesis method

Answer 36

enzymes have active sites complementary to substrate molecule
substrate molecules form into the enzymes active site
active site changes shape slightly to mould itself around substrate
ESC formed, IM forces bind substrate molecule to active site
bonds in tertiary structure of substrate destabilise
substrate molecule converted to product molecules
still on active site, forms enzyme-product complex
product molecules slight different shape to substrate, detach from active site
enzyme free to catalyse another reaction with another substrate molecule of same type