1.6- metabolic pathways Flashcards
what is metabolism?
all the reactions that take place in a living cell
what are metabolic pathways?
integrated and controlled pathways at enzyme-controlled reactions within a cell
2 types of cell reactions
catabolic
anabolic
what happens in catabolic pathways?
substrate is usually a large molecule
products are small molecules
energy is released
what happens in anabolic pathways?
substrate is usually a small molecule
products are large molecules
energy is required
what are metabolic pathways made up of and how do they work?
chains of enzyme catalysed reactions
the product of one reaction is the substrate for the next
what happens in alternative routes of metabolic pathways?
allows steps in the pathway to be bypassed
2 things that control metabolic pathways
presence or absence of particular enzymes
regulation of the rate of reaction of key enzymes
what do enzymes do in a metabolic pathway and how?
speed up rate of reaction
by lowering the activation energy needed by the reactants to form the transition state
what is the lock and key hypothesis?
that enzymes are large, complex proteins folded into specific shapes so they can fit a particular substrate
what is induced fit?
enzymes only act on one specific substrate complementary to and fits into the active site
when a substrate enters the active site, the active site can change shape slightly to better fit the substrate after the substrate binds
2 things induced fit ensures
enzymes active site comes into very close contact with the molecules of the substrate
increases the chances of a reaction taking place
affinity between substrate and active site
substrate molecules have a high affinity for the active site
affinity between product and active site
subsequent products have a low affinity allowing them to leave the active site
how is the orientation of reactants determined?
by the shape of the active site when the reaction involves 2 or more substrates
what is activation energy?
the energy needed to break chemical bonds in the reactant chemicals
when do the chemical bonds break in the reactant chemicals?
when the molecules of the reactant have absorbed enough energy to make them unstable
what happens once the chemical bonds break?
they are now in the transition state and the reaction can occur
how does an enzymes presence effect activation energy and what’s the outcome?
lowers activation energy
makes it easier to start a reaction
what happens as the substrate concentration increases in a reaction?
more and more of the enzymes active sites become used until there are none available
what happens at a low concentration of substrate in a reaction?
reaction rate is low since there are too few substrate molecules present
how do you increase the reaction rate?
by increasing the substrate concentration
what happens when increasing substrate concentration no longer increases the reaction rate?
enzyme concentration now becomes the limiting factor and the graph levels off
how do you reverse a metabolic pathway?
abundance of one metabolite and the scarcity of the one prior
enzyme between metabolites can go into reverse and convert some back until balanced state is restored
3 types of inhibition
competitive
non-competitive
feedback
what are competitive inhibitors?
have the same shape or partial shape as the natural substrate for the enzyme
where do competitive inhibitors bind and what is this effect?
at the active site
prevents the substrate from binding
what can reverse competitive inhibition and how?
by increasing the substrate concentration
increases the likelihood of the substrate molecule combining with the active site and not the inhibitor
where do non-competitive inhibitors bind and what is this effect?
bind away from the active site
change the shape of the active site preventing the substrate from binding
what can reverse non-competitive inhibition?
non-competitive inhibition is a permanent change
cannot be reversed by increasing the substrate concentration
when does feedback inhibition take place?
when the end product in the metabolic pathway reaches a critical concentration
how does feedback inhibition work and what is the effect?
end product then inhibits an earlier enzyme blocking the pathway
prevents further synthesis of the end product
