ENZYMES

Question 1

what are enzymes

Answer 1

enzymes are globular proteins that act as catalysts
most enzymes are very large molecules but only a small part of them is involved in catalysis
this is the active site

Question 2

what is a catalyst

Answer 2

alter the rate of a chemical reaction without undergoing permanent changes to themselves

Question 3

intracellular enzymes

Answer 3

cells require hundreds of biochemical reactions to survive and function
nearly all of these intracellular reactions are catalysed by large globular proteins- enzymes

Question 4

enzyme structure

Answer 4

the amino acid sequence determines the shape of an enzymes active site
substrates that fit the enzymes active site are held there by temporary bonds forming (es complex)

Question 5

what is the lock and key theory

Answer 5

an early model
active site small cleft
complementary rigid shape maintained by 3D structure
substrate fits like key in lock
held by various bonds forming enzyme substrate complex

Question 6

positive of lock and key theory

Answer 6

explains the specificity of enzymes

Question 7

negative of lock and key theory

Answer 7

doesn’t explain lowered activation energy or inhibition

Question 8

describe the induced fit model

Answer 8

before reaction active site not complementary to substrate
shape of active site changes as substrate binds and becomes complementary
say specific instead of complementary
both enzyme and substrate undergo dynamic conformational changes (changing shape) upon binding
the enzyme contorts the substrate into its transition state thereby increasing the rate of the reaction
when the substrate is within the active site the active site molds itself around the substrate

Question 9

how does induced fit model explain lowered activation energy

Answer 9

the formation of bonds in the enzyme substrate complex and the change of shape
causes pressure placed onto the bonds within the substrate
reduces activation energy for reaction

Question 10

how to measure rate of enzyme activity

Answer 10

either:
decrease in substrate
increase in product
change in concentration / time

Question 11

what four factors affect rate of enzyme activity

Answer 11

temperature
pH
enzyme concentration
substrate concentration

Question 12

what is needed for enzymes to work

Answer 12

must come into physical contact with the substrate
have an active site that can be induced to fit around the substrate

Question 13

what is the effect of enzyme concentration

Answer 13

at first when slowly rising, too few enzymes, not all substrates have an active site, half the maximum possible rate for the reaction
in the middle, more substrates can occupy an active site and form products, rate of reaction has increased as all active sites are filled
plateau, addition of further enzymes has no effect on rate
more enzymes than substrate and al, substrates have already occupied an active site

Question 14

effect of substrate concentration

Answer 14

at first, some active sites free at low substrate concentrations, when plateau all active sites become filled and addition of further substrate has no effect on rate`

Question 15

temp

Answer 15

increasing temperature increases the rate of reaction forming more product
more kinetic energy means more frequent collisions
some thermophilic bacteria have optimum temps of 85

Question 16

effect of increasing temp

Answer 16

increasing temp increases the kinetic energy that the substrate molecules possess, this means there are more random collisions between molecules per unit time
since enzymes catalyze reactions by randomly colliding with substrate molecules, increasing temperature increases rate of the reaction.

Question 17

other effect of increasing temp

Answer 17

increasing temperature also increases the vibrational energy that molecules have, specifically in this case enzyme molecules, which puts a strain on bonds that hold them together
as temp increases, more bonds especially the weaker hydrogen and ionic bonds, will break as result of the strain. this will cause the active site to change shape
means active site is less complementary to the shape of the substrate so is less likely to catalyse the reaction

Question 18

what does pH affect simply

Answer 18

formation of hydrogen bonds and sulfur bridges in proteins altering shape

Question 19

affect of pH

Answer 19

more enzymes will have active sites whose shapes are not or are less complementary to the shape of their substrate.
small changes in pH above or below optimum don’t cause a permanent change since bonds can be reformed

Question 20

2 ways in which active sites become less complementary

Answer 20

1. altered charges of amino acids that make up its active site
2. bonds of the tertiary structure being broken by ions within the acid/alkali

Question 21

what is a competitive inhibitor

Answer 21

inhibitor preferentially binds to the active site, preventing the formation of enzyme substrate complexes

Question 22

what is a non competitive inhibitor

Answer 22

inhibitor binds to another site (allosteric site), altering the active sites shape, preventing the formation of enzyme substrate complexes

Question 23

penicillin example

Answer 23

inhibitor = penicillin
enzyme = transpeptidase (catalyzes the last step in bacterial cell-wall biosynthesis)
effect=interference with the synthesis of cell wall of reproducing bacteria, defective walls cause bacterial cells to burst