-1A: enzymes Flashcards
what are enzymes?
-tertiary structure proteins
-catalyse chemical reactions
are they large/small compared to other biological molecules?
-large
-part that actually ‘catalyses’ reactions -> active site
when substrate binds to active site, what does this form?
enzyme-substrate complex
why does active site have unique + specific shape?
due to specific folding + bonding in tertiary structure of protein
explain the tertiary structure of a protein + how its specific
-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
because of specific active site, what does this mean?
will only bind to complementary substrate
define activation energy
minimum energy required for a chemical reaction to occur
how do enzymes increase rate of reaction?
-active site binds to substrate -> enzyme-substrate complex
-> lowers activation energy needed for reaction to occur
-increasing rate of reaction
what are the 2 models of enzyme theory?
-lock + key
-induced fit
describe lock + key model:
-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
lock + key model (simple?)
active site + enzyme -> enzyme-substrate complex -> products released
describe induced fit model:
-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
induced fit model (simple?)
active site + substrate -> enzyme-substrate complex -> enzyme-product complex -> products released
what is the key difference between the two models?
-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
factors that affect enzymes?
-temperature
-pH
-substrate/enzyme concentration
-inhibitors
how does temperature affect enzymes?
-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
what is optimum temp typically for enzymes?
body temp- 37C
how does pH affect enzymes?
-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
what is typical pH for enzymes, give an example where its different
-pH7
-pepsin -> stomach -> acidic conditions -> ph2
enzyme concentration affecting enzymes?
-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
substrate concentration affecting enzymes?
-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
what else about substrate concentration, what does it decrease with and why?
-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
define inhibitor
a molecule that binds somewhere on an enzyme that prevents it from functioning
2 types of inhibitors?
-competitive
-non-competitive
competitive inhibitors?
-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
non-competitive inhibitor?
-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
describe induced fit model:
-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
why would a change in the amino acid sequence change/affect enzyme action?
-change in amino acid sequence may alter tertiary structure
-changing shape of active site so substrate cant bind to it
