-1A: enzymes

Question 1

what are enzymes?

Answer 1

-tertiary structure proteins
-catalyse chemical reactions

Question 2

are they large/small compared to other biological molecules?

Answer 2

-large
-part that actually ‘catalyses’ reactions -> active site

Question 3

when substrate binds to active site, what does this form?

Answer 3

enzyme-substrate complex

Question 4

why does active site have unique + specific shape?

Answer 4

due to specific folding + bonding in tertiary structure of protein

Question 5

explain the tertiary structure of a protein + how its specific

Answer 5

-due to sequence of amino acids in primary structure
-determines position of hydrogen/ionic/disulphide bonds
-how polypeptide chain folds -> for unique 3D shape that has unique active site shape

Question 6

because of specific active site, what does this mean?

Answer 6

will only bind to complementary substrate

Question 7

define activation energy

Answer 7

minimum energy required for a chemical reaction to occur

Question 8

how do enzymes increase rate of reaction?

Answer 8

-active site binds to substrate -> enzyme-substrate complex
-> lowers activation energy needed for reaction to occur
-increasing rate of reaction

Question 9

what are the 2 models of enzyme theory?

Answer 9

-lock + key
-induced fit

Question 10

describe lock + key model:

Answer 10

-describes lock as enzyme, key as substrate as it will fit into lock due to its complementary shape
-active site -> fixed shape, due to random collisions between enzyme + substrate, cause enzyme to bind to active site -> enzyme-substrate complex
-charged groups in active site -> lower activation energy
-products released -> active site is empty + ready to be reused

Question 11

lock + key model (simple?)

Answer 11

active site + enzyme -> enzyme-substrate complex -> products released

Question 12

describe induced fit model:

Answer 12

-enzyme like a glove, substrate like a hand, when glove empty = not specific to shape of hand, but when hand enters glove, moulds around to become completely complementary
-active site is induced/slightly changes shape
-once enzyme-substrate complex is formed -> active site moulds around substrate -> puts strain + weakens bonds -> lowering activation energy
-products are released + active site returns to original shape
-current accepted model of how enzymes function

Question 13

induced fit model (simple?)

Answer 13

active site + substrate -> enzyme-substrate complex -> enzyme-product complex -> products released

Question 14

what is the key difference between the two models?

Answer 14

-in induced fit, when empty, active site is not completely complementary in shape to substrate + moulds whereas in lock + key, active site is fixed shape
-induced fit -> strain + weakening of bonds reduces activation energy, in lock + key, its charged groups in active site that lowers activation energy

Question 15

factors that affect enzymes?

Answer 15

-temperature
-pH
-substrate/enzyme concentration
-inhibitors

Question 16

how does temperature affect enzymes?

Answer 16

-too low -> not enough kinetic energy for collisions to occur between enzyme + substrate -> not enough enzyme-substrate complexes form
-too high -> denature -> too much kinetic energy, vibrations break bonds (hydrogen + ionic) holding tertiary structure in place -> changing shape of active site -> no longer complementary to substrate so no more enzyme-substrate complexes form -> decreasing rate of reaction

Question 17

what is optimum temp typically for enzymes?

Answer 17

body temp- 37C

Question 18

how does pH affect enzymes?

Answer 18

-too high/low -> denatures
-too high, too many H+ ions, too low, too many OH- ions
-charges on ions interfere with charges in amnio acids within active site -> breaks ionic + hydrogen bonds holding 3D tertiary structure in place -> changing shape of active site -> no longer complementary

Question 19

what is typical pH for enzymes, give an example where its different

Answer 19

-pH7
-pepsin -> stomach -> acidic conditions -> ph2

Question 20

enzyme concentration affecting enzymes?

Answer 20

-the more enzyme molecules there are in a solution the more likely substrate molecules are the collide to them forming enzyme-substrate complexes, so usually increasing enzyme conc increases rate of reaction
-however, if substrate concentration is limited, there comes a point where all of active sites in solution are occupied so adding more enzyme/increasing conc of enzyme has no further affect

Question 21

substrate concentration affecting enzymes?

Answer 21

-higher substrate concentration -> faster rate of reaction, as more substrate molecules so more likely to have collisions between enzyme molecules forming enzyme-substrate complexes
-only true up to saturation point, after, so many substrate molecules that active sites are full so adding more substrate creates no difference

Question 22

what else about substrate concentration, what does it decrease with and why?

Answer 22

-time, unless more is added to mixture
-so if no other variables are changed, rate if reaction will decrease over time also
-making initial rate of reaction, highest rate of reaction

Question 23

define inhibitor

Answer 23

a molecule that binds somewhere on an enzyme that prevents it from functioning

Question 24

2 types of inhibitors?

Answer 24

-competitive
-non-competitive

Question 25

competitive inhibitors?

Answer 25

-inhibitor same shape as substrate, binds to active site due to complementary shape
-enzyme-inhibitor complex prevents substrate from binding + reaction occuring
-however, if substrate concentration increased -> flood out/out compete inhibitor

Question 26

non-competitive inhibitor?

Answer 26

-binds away from active site, allosteric site -> slightly changing shape of tertiary structure -> changing shape of active site, no longer complementary to substrate -> no matter how much substrate is added, enzyme-substrate complexes can no longer form

Question 27

describe induced fit model:

Answer 27

-complementary substrate binds to active site of the enzyme
-form an enzyme-substrate complex
-as substrate binds + active site changes shape slightly, providing a better fit
-substrate is broken down to form products

Question 28

why would a change in the amino acid sequence change/affect enzyme action?

Answer 28

-change in amino acid sequence may alter tertiary structure
-changing shape of active site so substrate cant bind to it