Flashcards in Enzymes Deck (57):
what are enzymes?
globular proteins that act as catalysts for biological reactions
how do enzymes differ from chemical catalysts? (4)
- they can catalyse very high reaction rates
- are highly specific
- work well at mild pH/temperatures
- can be regulated
what are ribozymes?
catalytic RNA compounds with no protein component
what are co-factors?
a non-protein component of an enzyme that is crucial to its activity (tend to me metal ions)
what are coenzymes?
complex organic molecules that are usaully produced form vitamins and help to enhance an enzymes activity
what are prosthetic groups?
cofactors covalently bonded to the enzyme or very tightly associated with the enzyme
what is an apoenzyme?
the protein component of an enzyme that contains a prosthetic group
what is a holoenzyme?
the "whole" enzyme, i.e apoenzyme plus the cofactor/s
what ending is usually used when naming enzymes?
*name usually refers to function
what are the 6 classes of enzymes?
what do oxidoreductases do?
what do transferases do?
what do hydrolases do?
what do lysases do?
form or add groups to double bonds
what do isomerases do?
transfer groups within a molecule
what do ligases do?
formation of C-C, C-S, C-O and C-N bonds
what do enzymes do? (3)
- increase rate of spontaneous reactions
- lower the activation energy of biochemical reactions
- accelerate movement towards reaction equilibrium
how does an enzymes structure allow it function?
they have active sites complimentary to the transition state of the substrate/s
what is binding energy?
the energy released when enzymes form non-covalent bonds with the substrate/s
what do reactants need to break in order to react?
the energy barrier
how do enzymes work
- reduce entropy (bring reactants closer together)
- desolvation (substrate-enzyme bond overcome H-bonds)
- induced fit
what is Vmax?
the maximum rate of reaction that occurs when all the active sites have been filled
what equation can be used to analyse reaction kinetics?
the michaelis-menten equation
what does the michaelis-menten reaction deuce about reaction speeds?
the breakdown of ES to E + P is slower than the formation of ES form E + S
what is another technique (graphical) used to analyse reaction kinetics?
what does the x-interecpt and y-intercept show on a lineweaver-burk plot?
x-intercept = 1/Km
y-interecpt = 1/Vmax
what is the definition of Km?
the ratio of rate constant of breakdown of ES to E+S cmpared to the rate constant of the formation of ES from E+S
what does a high Km show?
a less stable ES complex i.e low affinity between enzyme and substrate
what are isozymes?
enzymes that catalyse the same reaction
what are the properties and location of glucokinase?
- high Km (for glucose)
- high Vmax
- found in liver
what properties and location does hexokinase show?
- low Km
- Low Vmax
- found in all body cells
what happens to glucokinase activity when blood glucose drops and why is this useful?
glucokinase activity drops allowing glucose released by glucokenesis to leave the liver (as it isn't converted to glucose-6-phosphate)
what reaction do glucokinase and hexokinase catalyse?
glucose + ATP ----> glucose-6-phosphate + ADP
what do increased levels of intracellular enzymes in plasma indicate?
tissue damage resulting from trama, necrosis etc
what technique can be used to separate different forms of enzymes?
how many forms of creatine phosphate are there?
3 forms (CK1, CK2 and CK3)
what is a ternary complex?
a complex which holds all of the reacting substrates and enzyme together
what are the diffrent types of reaction mechansims for enzyme catalysed reactions with more than one substrate?
- random ordered with a ternary structure
- ordered with a ternary structure
- no ternary structure formed (sequential)
what type of mechansim does lactose dehydrogenase use?
an ordered sequential mechanism with a ternary structure
- NADH + pyruvate ----> lactate and NAD+
describe the mechansim of creatine kinase
random sequential mechansim with a ternary structure
- 2x ATP + 2x Creatine -----> 2x Phosphocreatine + 2x ADP
describe the mechansim between amino acids and ketoacids
double displacement (ping-pong) mechanism in which the substrates bounce on the enzyme and then off again once they've reacted, meaning no ternary structure forms
what are allosteric enzymes?
enzymes made up of many sub-units, all of which contain active sites
what factors affect enzyme activity?
what are the different types of inhibitors and how do they work?
COMPETITIVE: resemble substrate and bind non-covalently to active site (lowering Km)
NON-COMPETITIVE: bind to part of enzyme that's not the active site non-covalently (lowers Vmax)
UNCOMPETITIVE: inhibitor binds above active site after the substrate has bound, preventing the product molecules form being released
give an example of a competitive inhibitor and explain how it functions?
- inhibits reverse transcriptase as it is an analogue to a DNA precursor TTP
what are irreversible inhibitors?
inhibitors that bind to enzymes covalently
- e.g cyanide which binds to cytochrome c oxidase disrupting terminal respiration, starving cells of ATP
what are the two types of regulatory enzymes?
allosteric enzymes and covalently modified enzymes
give an example of feedback inhibition
threonine dehydrogenase which is inhibted by the final product in a pathway; l-isoleucine
- l-isoleucine binds to enzyme causing a confromational change that blocks the enzymes activity
what is feedback inhibition?
a build of the end product in a pathway that slows the entire pathway by altering the enzymes activity
what are allosteric effectors?
cell metabolites that bind non-covalently to part of an enzyme (non-competitive) chnaging the enzymes activity
- can be activators or inhibitors
explain the concerted model
allosteric enzymes have two confromations that they randomly switch between, one conformation binds the substrate well, the other doesnt
- the binding of substrate locks the enzyme in an "open" conformation allowing other substrates to bind
what shape of curve do allosteric enzyme kinetics show?
a sigmoid shape
explain the sequential model
there is no flipping between confromations, instead the binding of a substrate causes a conformational change that "opens" the next sub-unit allowing a second substrate molecule to bind and so on
what is covalent modification?
modification of enzyme activity through covalent bonding (often involves transfer of groups) e.g phosphorylation
what do protein kinases do?
add phosphoryl groups
what do protein phosphatases do?
remove phosphoryl groups