enzymes Flashcards
what is the role of enzymes?
they act as biological catalysts by affecting the structure and function in an organism
they affect metabolism at both cellular and whole organism level.
what are intracellular enzymes?
enzymes that work within cells
what are extracellular enzymes?
enzymes that work outside of cells
give an example of an intracellular enzyme and its function
catalase
works inside cells to catalyse the breakdown of hydrogen peroxide to oxygen and water
give 2 examples of extracellular enzymes and their fucntions
amylase
found in the saliva and secreted into the mouth by cells in the salivary glands . they catalyse the hydrolysis of starch to maltose
trypsin
catalyses the hydrolysis of peptide bonds produced by the pancreas and secreted into the small intestine
what is the structure of enzymes?
globular proteins
specific shape - active site where substrate binds
specific shape determined by tertiary structure
describe the lock and key model
the enzymes active site is exactly complementary to the substrate so they fit like a lock and key
when the substrate is bound to the active site an enzyme-substrate complex forms
the substrate is held in a way that the right atom groups are close enough together to react and r groups within the enzyme interact with the substrate and put strain on bonds within the substrate
the enzyme-product complex forms and products are released
enzyme is unchanged and can take part in subsiquent reactions
describe the induced fit model
recent evidence suggests that the enzyme actually changes shape slightly as the substrate enters
interactions between the enzyme and the substrate changes enzymes tertiary structure and strengthen the binding
this puts strain on the substrate molecule which can weaken a particular bond or bonds in a substrate so lowers activation energy for the reaction
what are the 4 factors that affect enzyme activity?
pH
temperature
enzyme concentration
substrate concentration
what is the effect of pH on enzyme activity?
all enzymes have optimum pH
at pH above or below this the H+ concentration and OH- concentration can mess up the ionic and hydrogen bonds within the enzyme which changes the enzymes tertiary structure and its active site, denaturing it
what is the effect of temperature on enzyme activity?
as temperatue increases, the rate initially increases as particles gain kinetic energy and therefore successful collisions become more frequent
as temperature increase further, the bonds within the enzyme begin to vibrate and can break.
the tertiary structure and active site change shape and the enzyme is denatured
what is the effect of enzyme concentration on enzyme activity?
increasing enzyme concentration increases the likelyhood that a substrate will collide so enzyme-substrate complexes form more frequently
but if the substrate concentration is limited there is a point where all substrate is in enzyme-substrate complexes so has no further effect
what si the effect of substrate concentration on enzyme activity?
increasing substrate concentration increases rate of reaction and collisions become more frequent
this is true untill all active sites are being used so has a Vmax where increasing substrate concentration has no further effect
how do cofactors work?
they transfer atoms or groups from one reaction to another in a multistep pathway or may form part of the active site of the enzyme
some enzymes need them to carry out their function
what are conenzymes?
organic cofactors
what are prosthetic groups?
prosthetic groups are tightly bound to form a permanent feature of the protein
give an example of a cofactor
Cl- is a cofactor of amylase
give an example of a prosthetic group
Zn2+ is a prosthetic group for carbonic anhydrase
what is a source of coenzymes?
vitamins
what are competitive inhibitors?
inhibitors of similar shape to the substrate that can bind to the active site of the enzyme and block it from the substrate
cannot carry out function so the enzyme is inhibited
what is the effect of competitive inhibitor on the rate?
decreases the rate as substrates and inhibitor compete for the active site, however if substrate concentration is increased it outcompetes the inhibitor therefore Vmax does not change
what is a non competitive inhibitor?
an inhibitor that binds to the enzyme away from the active site at the allosteric site. it changes the tertiary structure of the enzyme when it binds so changes the active site so it is no longer complementary to the substrate
increasing the substrate concentration will not overcome non-competitive inhibition
what bonds are ususally involved with irreversible and reversible inhibitors?
weak hydrogen and ionic bonds in reversible inhibitors
strong covalent bonds in irreversible inhibitors
give 2 examples of medicinal drugs that are competitive inhibitors
antiviral drugs such as reverse transcriptase inhibitor which inhibits the enzyme reverse transcriptase which catalyses the replication of viral DNA
anitbiotics such as penicillin inhibits transpeptidase which catalyses the formation of proteins of bacterial cell walls- weakens cell wall so it bursts
Give an example of a metabollic poison and what it does
cyanide
irreversible inhibitor of cytochrome c oxidase which is an enzyme that catalyses respiration reactions
what isproduct inhibition and why is it important?
a metabolic pathway is series of connected metabolic reactions . many enzymes in these pathways are inhibited by the product of the reaction they catalyse
it is important in controlling the amount of end product that gets made
always reversible so when level of product drops the level of inhibition starts to fall and enzyme fucntions again so more product is made
what are inactive precursor enzymes?
enzymes that are produced in the inactive form
normally if they would cause damage to the cell they’re produced in or to tissues they are released from
they need to undergo a change in tertiary structure
to change the shape of their active site to be activated.
this can be done by a cofactor, other enzymes or change in pH or temperature
why does pH need to be kept constant?
(so) charges in active site do not change ; ora
(so) hydrogen / ionic , bonds unaffected ; ora
(so) tertiary structure / 3D shape / active site ,
unaltered ; ora
(so) enzyme / tertiary structure , does not denature ;
ora
(so) substrate , fits / is complementary shape to , active
site ; ora
so the results are valid / as the rate (of reaction) will
vary if pH varies / so that only one
(independent) variable is changed
What is Cl- to amylase?
It is a cofactor
what is Zn2+ to carbonic anhydrase?
prosthetic group
