Cell biology pt 2
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metabolism
all the chemical reactions that occur within the human body
what do metabolic pathways involve?
the building up and breaking down of molecules
what do anabolic pathways require?
energy
what are anabolic pathways?
biosynthetic (building up) processes
catabolic pathways release…?
energy
what do catabolic pathways involve?
the breakdowns of molecules e.g the breakdown of glucose in glycolysis
are the steps of metabolic pathways reversible?
metabolic pathways have both reversible and in-reversible steps
what is activation energy?
the energy needed to break chemical bonds in the reactant chemicals is called activation energy
how does activation energy work?
the bonds break when the molecules of the reactant have been absorbed enough energy to make them unstable (this is called the transition state) and the reaction can occur
what is the rate of chemical reaction indicated by?
the quantity of chemical change that occurs per unit time
what is an enzyme?
an enzyme is a biological catalyst which lowers the activation energy required by the reactants to form the transition state and speeds up the rate of reaction. it also is made of proteins
what factors affect enzyme activation?
temperature pH substrate concentration enzyme concentration
what affect do inhibitors have on the rate of enzyme controlled reactions?
they may slow them down or bring them to a halt
what is an active site?
an enzyme contains an active site which is a specific shape (due to the structure and bonding of the amino acids in the polypeptide chain) it is also where a substrate molecule binds and undergoes a chemical reaction
why do enzyme’s only act on one substrate?
an enzyme only acts on one substrate because the enzyme is specific to its substrate and the molecules of the substrate are complementary to the enzymes active site for which they show on affinity (chemical attraction)
what happens to the products after enzyme reaction?
the products have low affinity for the active site and are released leaving the enzymes free to repeat this process with new molecules of the substrates
is the active site of an enzyme a rigid structure?
the active site of an enzyme is not a rigid structure it is instead flexible and dynamic
what happens when a molecule of a substrate enters the active site of an enzyme?
the shape of the enzyme molecule and the active site change slightly making the active site fit very closely round the substrate molecule, this is called induced fit
what happens if there is more than one substrate involved in a reaction?
the shape of the site determines the orientation if the reactions. this ensures that they are held together in such a way that the reaction can take place
what are metabolic pathways controlled by?
the presence and absence of an enzyme
what is a competitive inhibitor?
it is a substance which has a similar molecular structure to the substrate and competes with the substrate for the active site on the enzyme, it blocks the active site preventing the substrate from binding so the rate of reaction decreases
how are competitive inhibitors reversed?
by increasing the substrate concentration
qualities of a non-competitive inhibitor?
• does not have similar molecular structure • does not combine directly with the active site • attaches to a non-active (allosteric) site and changes the shape of the enzyme molecule • • indirectly altering the shape of the active site so the substrate cannot bind and rate of reaction decreases
when does feedback inhibition happen?
it occurs when the end product in the metabolic pathway reaches a critical concentration