Enzyme Activity Regulation Flashcards
enzyme regulation is important to what 3 reasons
- avoid problems of substrate cycles
- to link energy production and energy usage
- to respond to physiological changes
an effective way of regulating complex metabolic pathways is to regulate __ activity
enzyme
what are the 6 ways of regulating enzyme activity>
- substrate level
- allosteric/feedback control
- covalent modification (on/off switch)
- proteolytic cleavgae
- isoenzymes
- genetic control (transcription regulation)
what is the premise of substrate level control?
enzyme activity depends of surrounding concentrations or reactants or products
what is the premise of allosteric control /feedback control?
a product will bind reversibly to the first enzyme at its allosteric site (NOT BINDING SITE) and either in inhibit or stimulate production of more
an allosteric effect occurs when a ligand binds to an enzyme and changes what 2 things?
shape (conformational change) and therefore activity
allosteric enzymes do not conform to the M-M kinetics because they have a ____ shape caused by ___
sigmoidal; homoallostery
what is homoallostery?
cooperative substrate binding; binding of one favours the binding of more
allosteric enzymes can take what two forms?
tense and relaxed
which form of allosteric enzymes is capable of catalyzing reactions?
relaxed
homoallostery abides by what rule?
symmetry rule
what is the symmetry rule?
must have either all relaxed or all tense
in the absence of substrate or effector, which form or allosteric enzyme is more stable and more present?
T
T/F T can sometimes spontaneously turn into r
t
what can cause an increase in R-S binding?
a positive effector can bind to R to make it more stable and therefore present in higher amounts and more chance to bind to substrate
what can decrease R-S binding
a negative effector binding to T and stabilizing it
what may result from a loss of allosteric control?
pathologic conditions (disease)
give an example of a disease caused by lack of allosteric control
gout ( build up of urate)
what is the premise of covalent modification?
a molecule can covalently attach to an enzyme and act as an “on-off” switch
what are the two types of covalent modification?
- covalent activation
2. covalent inhibition
describe covalent activation
an enzyme in made in its active form and can be turn on
describe covalent inhibition
an enzyme is made in its inactive form and can be turned off
what is the most common type of covalent modification?
reversible phosphorylation
reversible phosphorylation is catalyses by 2 enzymes
- protein kinase
2. protein phosphatase
what are protein kinases and their role?
ATP-dependent enzymes that add a phosphoryl group to a OH group on some enzymes
what is the role of protein phosphatase?
hydrolyzes side-chain phosphate esters, releasing a phosphoryl group
what is the premise of proteolytic cleavage?
cutting out a part of an inactive enzyme to make it active
what is an inactive precursor enzyme called?
zymogen
what is the function of a zymogen?
inactive because being active in the wrong place/time could be harmful to the cell
what is proteolysis?
breaking proteins into smaller peptides or amino acids
what are isozymes?
enzymes that catalyses the same reactions, but have different amino acid sequence
what is the premise of isozymes as regulatory control?
can be activated by different things, at different stages, allowing for more precise “fine-tuning” of metabolism
what is the premise of genetic control in enzyme regulation?
induces the expression of an enzyme
