enzymes (bio) Flashcards
what are enzymes
- biological catalysts
- speed up rate of chemical reactions without themselves being chemically changed at the end
- hence can be reused and are effective in small concentrations
define catabolic reactions
break up complex molecules into simpler molecules
define anabolic reactions
build up simpler molecules into complex molecules
explain the structure of enzymes
most enzymes are proteins with unique 3D structure
explain what a substrate, active site and specificity of an enzyme is
substrate: molecule which enzyme acts on
active site: where substrate binds, can only allow specific substrate(s) to fit in
Specificity: attributed to complementary shape between substrate and active site
deifine activation energy
energy that must be supplied to the reactant molecules for them to react
how does activation energy help molecules react
- often supplied in the form of heat
- absorption of thermal energy increases the speed of the reactant molecules –> collide more frequently and forcefully in the correct orientation
- thermal agitation of atoms within the molecules oso make bonds more likely to break
Heating speeds up chemical reaction, but is inappropriate for a biological system. Why?
High temp dentaure proteins and kill cells. Heating oso speed up all chemical reactions, not just intended ones
explain enzymatic reaction
- effective collision between specific substrate(s) and enzyme at the correct orientation causes substrate molecules to enter active site of enzyme
- substrate molecules bind to the activie site of the enzyme –> enzyme-substrate complex
- formation lowers activation energy
- chemical reaction –> products formed
- products dissociate from enzyme and the chemically unchanged enzyme is ready for another cycle of chemical reaction
explain the lock-and-key hypothesis [5]
- substrate is “key” and enzyme is “lock”
- substrate has a shape complementary ro the shape of active site (x same shape)
- with active site of enzyme having a specific shape into which the substrate fits exactly
- substrate binds to the active site of enzyme, forming ES-complex
once products formed, no longer fit into active site if the enzyme and released into surrounding medium
explain the induced fit model [5]
- active site of enzymes is complementary in shape but not a perfect fit to substrate it catalyses
- when substrate binds to active site of enzyme, induces a change in shape of active site
- allows substrate to fit more tightly into active site
- binding of substrate to active site of enzymes occurs and ES-complex forms
- chemical reaction occurs –> forming products –> released into the surrounding medium as they no longer fit into active site of enzyme
characteristics of enzymes [5]
- speed up chemical reactions by lowering activation energy (extremely effiecient –> speed up by 10^3 to 10^8 times faster than uncatalysed reactions) and remain chemically unchanged
- (since can be reused, required in small concentrations)
- specific in action (due to 3D shape, with active site complementary in a shape to a specific substance)
- affected by temp and pH
- lowers activation energy
factors affecting rate of enzyme-catalysed reaction
temp
pH
enzyme concentration
substrate concentration
what is an optimum temp
temperature at which the rate of enzyme activity is at its maximum
explain what happens to enzyme reactions as temp rises
- as temp rises, kinetic energy of substrate and enzyme molecules increase
- enzyme becomes more active
- substrate and enzyme molecules collide more often –> increases no. of effective collisions and formation of enzyme-substrate complexes –> rate of reaction increases
- reaction rate doubles for every 10 degrees rise in temp until optimal temp is reached
explain what happens to enzyme reactions beyond optimum temp
- rate starts to decrease
- enzyme loses 3D shpe (as high temp breaks weak hydrogen bonds between amino acids) and active site no longer able to bind to substrate. enzyme said to be denatured (irreversible)
- as temp continues to increase, more enzyme molecules become denatured –> rate of reaction decreases further
explain what happens to enzyme reactions beyond optimum pH
- rate starts to decrease
- enzyme loses 3D shpe and active site no longer able to bind to substrate. enzyme said to be denatured (irreversible)
- as pH continues to increase, more enzyme molecules become denatured –> rate of reaction decreases further
define limiting factor
factor that directly affects rate of a chemical reaction if its quantity is changed
explain the effects of varying enzyme concentration
- lower enzyme concentrations –> adding more enzyme increases the rate of chemical reaction – enzyme concentration said to be limiting
- enzyme concentration increase –> more effective collisions occur, resulting in formation of more ES-complexes
- rate of reaction increases until a point where further increase in enzyme concentration will no longer the rate of reaction – rate of reaction becomes constant and reaches a plateau
- enzyme concentration no longer limiting factor
- not enough substrates to occupy active sites of enzymes – substrate concentration becomes limiting factor
explain the effects of varying substrate concentration
- low substrate concentrations –> few substrate molecules present –> many available enzyme actives sites for effective collisions to occur
- adding more substrate increases rate of chemical reaction – substrate concentration is limiting
- substrate concentration increases –> more effective collisions occur –> formation of more ES complexes
- rate of reaction increase until a point where further increase in substrate concentration will no longer increase rate of reaction – rate if reaction becomes constant and reaches a plateu
- all active sites of enzyme molecules saturated with substrate molecules, concentration of product formed per unit time remains the same – enzyme concentration is now limiting factor
how to determine rate of reaction
measure:
- amt of product formed per unit time
- amt of substrate used per unit time
what do control-boiled reactants do
denature enzymes, all other factors kept constant
what do factors that affect enzyme activity do
alter rate of enzyme-catalysed reaction
