Enzymes Flashcards
what are catalysts
catalysts speed up chemical reactions without themselves being changed as a result of it
what are enzymes
catalysts in living cells, that accelerate specific reactions in biological systems millions of times faster
how do enzymes relate to the equlibrium of reactions
they do not alter the actual equilibrium, but rather they accelerate the time to reach the equilibrium
why are enzymes important
they are vital for life, they catalyse chemical reactions such as our metabolism in cells that keep us alive
what are the roles of the enzymes in living organisms
aiding:
- respiration
- digestion
- muscle and nerve function
what are examples of enzymes found in the oral environment
- alkaline phosphatase
- amylase
- maltase
- lysozyme
what are examples of enzymes found elsewhere in the body from the mouth
- pepsin
- trypsin
- acetylcholinesterase
- dna polymerase
what is alkaline phosphatase
enzyme found throughout the body that is involved in mineralisation of tissue and bone
what is amylase
enzyme found in saliva that converts starch into sugars
what is maltase
enzyme found in saliva, breaks the sugar maltose into glucose
what is lysozyme
antimicrobial enzyme that is an innate part of the immune system that breaks down the peptidoglycan layer in cell walls of bacteria, and is found in many secretions including saliva, tears, human milk, mucous
what is pepsin
digestive enzyme of the stomach that breaks down the proteins into smaller peptides
what is trypsin
enzyme found in the small intestine that breaks down proteins into amino acids. produced by the pancreas.
what is acetylcholinesterase
enzyme that breaks down the neurotransmitter acetylcholine in nerves and muscles
what is dna polymerase
synthesises DNA from deoxyribonucleotides
what are the different models that enzymes can work by
lock and key model, induced fit model
what is the lock and key model of enzymes
the enzyme active site is complementary in shape to that of the substrate. the active site precisely shaped to hold specific substrates
what is the induced fit of enzymes
the active site and substrate do not fit together exactly. instead, the enzyme changes shape when the substrate binds, and the active site has a shape complementary to the substrate only after the substrate has bound
are all enzymes proteins
no only most are
what are the exceptions to enzymes that are not proteins
ribozymes (the catalytic rna molecules)
what is the enzymic activity of proteins dependent on
the maintenance of their three dimensional structure
what is enzyme activity affected by
temperature and pH
what can occur to enzymes at extremes of pH and temperature
the enzyme may lose its 3D structure (denature) and become totally inactive
what is the standard free energy change
the difference between energies of the reactants and the products
what does reaction rate depend on
the activation energy
what is activation energy
the energy input required to initiate reaction
is activation energy for a catalysed reaction higher or lower than an uncatalysed reaction
lower
can enzymes alter the free energy change
no
what factors affect the rate of an enzyme reaction
temperature
pH
enzyme concentration
substrate concentration
inhibitors and activators
covalent modification
what is thermodynamic activation
increase in free energy
what is thermodynamic inactivation
the protein is denatured
what is the relationship between enzyme concentration and reaction rate
an increase in enzyme concentration will increase the reaction rate
what happens to the concentrations of product and substrates once equilibrium is reached
they will no longer change
what is [E]
enzyme concentration
what is [S]
substrate concentration
what is [V]
reaction rate
when is reaction rate linearly proportional to substrate concentration
when substrate concentration is small
describe the effect of substrate concentration on reaction rate when the concentration of substrate is low
- an increased substrate concentration gives a steep increase in reaction rate
- not all the enzyme active sites are occupied, as they are waiting for the substrate to bind for much of the time
- the rate of the product formation is limited by the amount of available substrate
explain the effect of substrate concentration on reaction rate when the substrate concentration is high
- the enzyme is working at maximum rate due to being saturated with substrate
- all the active sites are occupied
- the rate of product formation now depends on the activity of the enzyme itself, adding more substrate will not significantly affect the reaction rate and maximum reaction rate will be achieved
what is Vmax
the maximum rate of reaction
when does Vmax occur
when the enzyme is saturated with substrate
what is Km
the substrate concentration at which V = 0.5 Vmax and is a measure of the affinity of the enzyme for its subsrate: the lower the Km, the higher the affinity
what does the relationship between the reaction rate and substrate concentration depend on
the affinity of an enzyme for its substrate
what does the Km of an enzyme relative to the concentration of its substrate determine
if the rate of product formation will be affected by substrate availability
if there is a low Km, is the enzyme more or less saturated with substrate
the enzyme will normally be saturated with the substrate at a low Km - it will also be fairly constant rate regardless of the variations in substrate concentration
if there is a high Km, is the affinity of the enzyme for the substrate higher or lower, and how does this affect its activity
the enzyme will not normally be saturated with the substrate, and its activity will vary as substrate concentration varies.
what does the rate of product formation depend on when the Km is high
substrate availability
how does the concentration of an unbound enzyme change with time
decreases in the pre steady state when the bound ES is forming, after this it slowly increases again
how does the concentration of the bound enzyme and substrate change over time
increases initially, then levels off, then starts to gradually decrease
how does the concentration of unbound substrate change with time
gradually decreases
how does the total concentration of enzyme change with time
remains constant
how does the concentration of product change with time
slowly increases
what is the michaelis menten equation
V = Vmax[S]/(Km+[S])
what is one of the main components of dental plaque
the polysaccharide dextran - a polymer of glucose. the enzyme that makes it is dextran sucrase, and the substrate is sucrose.
what does plaque formation depend on
how long you have sweet things in your mouth
what is the lineweavr burk plot
a more accurate estimate of Vmax and Km - is obtained by plotting 1/V against 1/[S]. gives a straight line for most enzymes
give a brief explanation of irreversible inhibitors
these inhibitors damage enzymes beyond repair, and generally cause covalent modification of the enzyme
give a brief explanation of reversible inhibitors
most natural enzyme inhibitors fall into this category, and the enzyme will regain full activity once the inhibitor has been removed
what does control of metabolic pathways usually occur by
feedback inhibition
give a summary of feedback inhibition
- when the product of a metabolic pathway builds up in the cell, inhibition of the pathway often occurs.
- this is often done by the product of the pathway acting as an inhibitor of an earlier step in the pathway
- an example of this is the pathway that forms isoleucine from threonine
what is an example of feedback inhibition
the feedback inhibition of threonine deaminase by the end product isoleucine. if isoleucine is not metabolised by the cell it accumulates and switches off further synthesis
give a brief summary on competitive inhibitors
- substrate and inhibitor compete for the same active binding site. they are structural analogues that prevent the substrate from binding
- inhibition can be overcome with large quantities of substrate - the substrate will ultimately occupy all binding sites, and the enzyme will be fully operative
give a brief summary of non competitive inhibition
- binds to an allosteric site on the enzyme, is structurally unrelated to the substrate, but it cannot be reversed by adding large quantities of substrate
how does competitive inhibition affect Vmax
it is unaltered - a large quantity of sustrate can compete out the inhibitor
how does competitive inhibition affect Km
it is increase - as the inhibitor competes with the substrate for binding to the active site, the affinity of the substrate will appear to decrease. the Km is an inverse measure of affinity
how does non competitive inhibition affect Vmax
the Vmax will be decreased, as a proportion of enzyme molecules will be inactive at any time due to binding by the inhibitor
how does non competitive inhibition affect Km
it is unchanged, as the binding of the substrate can still occur
give a brief summary of allosteric enzymes
- they possess multiple subunits
- in addition to active sites they possess allosteric sites where non substrate modulators bind, which creators a conformational change in the subunits
- many important regulator enzymes are allosteric
how do the subunits on the allosteric enzymes interact
such that the binding site of a substrate, inhibitor, or activator to one subunit alters the conformation of all the subunits
what are positive modulators
these increase the affinity for substrates at an active site
what are negative modulators
these decrease the affinity for substrates at active sites
do allosteric enzymes conform to the michaelis menten kinetics
no
give a brief summary of the control of enzyme activity by covalent modification of enzyme molecules
- many enzymes can be covalently modified
- common modification is the addition of a phosphate group to serine, threonine or tyrosine hydroxyl
- glycogen phosphorylase, which breaks down glycogen to provide glucose, is activated by phosphorylation
- phosphorylase kinase is the enzyme which brings this about, and is in turn activated indirectly by adrenaline and glucagon
- reversed by phosphorylase phosphatase
