proteins 1 Flashcards
what is an anabolic reaction
requires energy to build up large molecules from small
what is a catabolic reaction
releases energy when large molecules are broken down
describe the lock and key model
- complementary 3D structures
- no major atomic rearrangements
describe the induced fit model
- substrate induces a conformational change
- substrate fits well after reshape
what is activation energy
- extra energy required to reach a transitional state for a reaction to proceed
how is an enzyme used as a catalyst
- lower the activation energy of a reaction increasing the rate of reaction
- not consumed in the reaction
how does temperature affect enzymes
- actively accelerated by increased temperature
- if too high the enzyme will denature
how does pH affect enzymes
- affects side groups
- all have different optional pHs
what are the conditions which affect enzymes
- temperature
- pH
- ionic strength
- substrate concentration
what happens when an enzymes movement is restricted
- decreased activity
what is acid-base catalysis
- enzyme acts as partial proton donor or acceptor
what is covalent catalysis
- active site temporarily covalently modified
what is metal ion catalysis
- electrophilic catalyst - stabilising a negative charge
- generate a nucleophile - increasing the acidity of a nearby molecule
- metal ion may bind to substrate
what is approximation catalysis
- bringing two substrates together
what are cofactors
molecules that aid enzymatic function
what can be cofactors
- metal
- coenzymes - small organic cofactors
- prosthetic groups - tightly bound coenzymes
- cosubstrates - loosely associated coenzymes
what are the units for the rate of reaction and what can they be measured by
- Ms-1
- decrease In substrate over time
- increase in product over time
what is the rate constant
- relates chemical concentrations to rate
what are the units for a first and second oder constant
- first - s-1
- second - M-1S-1
what is maximal velocity (V max)
- reaction rate when enzyme is saturated and all active sites are filled
what is the Michaelis constant (Km)
- substrate concentration at half V max
what is the Michaelis menten equation
V0= V max x ( [S] / [S] + Km
what does the substrate concentration tell you about the order
- low - first order - V0 is proportionate to substrate concentration
- high - zero order - V0 is approximately Vmax
- substrate concentration = Km - V0 = Vmax/2
what occurs with the different shifts in the enzyme saturation curve
downwards - decrease Vmax
upwards - increase Vmax
right - increase Km - lower binding
left - decrease Km - higher binding
what are the catalytic factors making glucokinase work
- high Vmax
- high Km
- respond to large glucose concentration
what are the catalytic factors making hexokinase work
- lower Vmax
- lower Km
- not specific to glucose
what is Vmax dependent on
- enzyme concentration
- doubling enzyme concentration doubles the rate of reaction
what is the rate limiting step
- slower step in pathway
- high activation energy
- limited substrate concentration
what is the committed step
- first irreversible enzyme reaction in a pathway to a specific product
what are the types of enzyme regulation
- allosteric
- multiple forms of enzymes
- reversible covalent modification
- proteolytic activation
- expression control
- inhibition
what is competitive inhibition
- competitive inhibitor binds to the active site
what is an uncompetitive inhibitor
- binds to an allosteric site on the enzyme changing the active site shape
what is a noncompetitive inhibitor
binds to the enzyme substrate complex and slows the rate of reaction
what are irreversible/ suicide inhibitors
- inhibitor covalently binds enzymes
- reacts with active site
what is product inhibition
- product negative feedback
what occurs with competitive inhibition to Vmax and Km
- Vmax same
- Km increases
- slope is steeper
what occurs with uncompetitive inhibition to Vmax and Km
- Vmax lower
- Km lower
- no change in slope
what occurs with non-competitive inhibition to Vmax and Km
- Vmax lower
- Km same
- slope steeper
what is allosteric regulation
- activity at one functional site affects the activity at others
what do the allosteric proteins contain
- distinct regulatory sites
- multiple functional sites
why are zymogens/proenzymes
- enzymes that need activating by another enzyme to function
why is an enzyme saturation curve a sigmoidal curve
- velocity increases over a narrower range
- allows for on and off switch
