enzymes Flashcards
what are enzymes
- enzymes are proteins that catalyse biological reactions
- speed up reactions without being permanently altered
how do enzymes work
- enzymes bind substrates in their active sites and convert them into products
- the substrates are bound to specific regions in the active site
what is energy called needed to form the product
- activation energy
how do enzymes lower the activation energy
- by stabilising the complex which then increases the rate of reaction
what are covalent inhibitors
- form covalent bonds with functional groups in active site and selectively inhibit enzymes
what is the binding of a substrate determined by
- electrostatic interactions
what factors can alter enzyme activity
- ph
- temperature
- substrate concentration
what does a change in ph do to enzyme activity
- alters the properties of functional groups within the active site and therefore change interactions
- different enzymes have different optimum ph values according to their function
how does a change in temp affect enzyme activity
- as temp increases the speed of reaction increases, increasing no of collisions and therefore the number of enzyme substrate complexes being formed
- but at too high of a temp change the bonds break within the enzyme changing shape of active site
how does a biological catalyst differ from chemical catalyst
- high reaction rates
- greater specificity
- can be regulated
- milder reaction conditions
substrate specificity
- the specificity of a reaction is a result of 3d arrangement of amino acids in the active site
- even if the shape is the same but the charge is different there will be no binding
what are co factors
- help enzyme substrate complexes form
- co factors are preserved
what are the two main types of co factors
- co enzymes
- metal ions
how are coenzymes synthesised and purpose
- usually synthesised from vitamins
- symptoms of vitamin deficiency due to loss of enzyme activity
- transfer of chemical groups
- can aid oxidation - reduction reactions
what do metal ions do
- helps bind substrate by coordinating negatively charged groups
- can accept and donate electrons in oxidation and reduction reactions
substrate conc
- rate of reaction increases with substrate concentration until saturation when maximum velocity is reached
how is the relationship between substrate concentration and reaction velocity described by
- Michaelis - menton equation
v = Vmax (s) / Km + S - km is a measure of the affinity an enzyme has for its substrate - low km = high affinity
- together with Vmax it can be used to determine the nature of a particular inhibitor
why is it important to know the affinity of an enzyme
- helps identify its physiological role
- helps design and study effect of a drug
eg. statins - which is used to reduce high cholesterol levels in the blood - competitively inhibit HMG co - reductase, enzyme required for cholesterol synthesis
4 regulations of enzyme activity
- allosteric interaction
- covalent modification
- protein - protein interaction
- proteolytic cleavage
allosteric interaction
- enzymes are allosteric - that they are inhibited or activated by molecules binding to them at a site other than the active site
- this binding alters the shape of the active site by changing the overall shape of the enzyme
what are the two types of allosteric inhibitors
- homotrophic
- heterotrophic
what is homotrophic
- the substrate itself binds to the enzyme somewhere other than its active site
- generally positive effectors
what is heterotrophic
- a molecule other than the substrate binds to the enzyme away from the active site
- can be positive or negative
- often occurs as feedback inhibition
why is allosteric important
- important in regulation of metabolic pathways which are often regulated by the rate of one key enzyme
what does protein kinase a and how is regulated
- activates a range of enzymes in different pathways
- regulated by hormones via allosteric regulator, cAMP
- cAMP binds to regulatory subunits of PKA, releasing active enzyme
what is covalent modification and why is it important
- involved addition and removal of phosphate group
- important for many cellular processes
- phosphorylation catalysed by another group of enzymes called kinases which use atp
- dephosphorylation carried out by phosphatases
- can positive or negatively influence enzyme activity
protein - protein interaction
- changes shape of active site resulting from interaction w another protein
- contains a hinge region which allows it to fold over target enzyme
- calcium ions can also bind many amino acids to cause conformational changes
- ca2+ a binding protein, calmodulin
regulation of expression
- level of enzyme present in a cell is tightly regulated
- can be controlled at level of synthesis or degradation
- transcription of rna encoding enzyme can be stimulated or repressed
- stability of transcript can be regulated
- rate of decay can be regulated
proteolytic cleavage
- some enzymes have a portion of their structure must be split to become functional
- example proteases
- synthesised as inactive ‘zymogen’ to prevent damage to cell
- only come by active when cut by another enzyme
enzymes in medicine
- enzymes target of many drugs eg aspirin
- most enzymes present in plasma
; changes in levels of activity of these enzymes are associated w various diseases
; plasma level of particular enzymes can be used as diagnostic tool
enzymes in heart disease
- creatine kinase occur in three forms (isoenzyme)
; mm
; mb
; bb - mb is exclusively expressed in heart muscle
- appearance of this isoenzyme in the blood is specific of myocardial infarction (heart attack)
