glycolysis Flashcards
give 5 reasons why metabolic pathways are necessary.
-to produce energy in manageable packets
-to make complex transformations kinetically feasible using enzymes
-drive thermodynamically favourable reactions using coupling
-allows for high levels of control as there are lots of points you can check
-cytoplasm is packed so you don’t want your reactants meeting left to chance, or the possibility of unwanted side reactions
explain how carbons in an organic molecule have a redox number.
essentially you just count in how many of its bonds is carbon holding the electrons closer to itself i.e. carbon is more electronegative than what it is bonded to. in methane carbon is -4.
anabolic vs catabolic?
anabolic = positive delta G, thermodynamically unfeasible, endergonic
catabolic is just the opposite.
ATP isn’t special, so how does its hydrolysis provide energy?
its all in the equilibrium position.
at equilibrium the ratio of reactant to product is 1x10^6, delta G = 0, no energy can be provided.
but in the cell, the ratio is 0.0001, delta G = -57KJ/mol.
why is ATP synthesis endergonic?
in the matrix ATP/(ADP)(Pi) = +46KJ/mol
why is ATP less stable than ADP + Pi?
10 water interactions are stabilising, ADP + Pi has more possible interactions with water.
ADP + Pi has a higher entropy.
ATP has more -ve phosphates which repel one another.
glycolysis step 1 -
what is it?
what enzyme is used?
how does coupling help?
glucose to glucose phosphate using ATP.
hexokinase.
the phosphorylation is coupled with ATP hydrolysis, increasing our k value massively, so increases the concentration of products, because glucose + Pi has a +delta G
how does hexokinase work?
active site encloses ATP and glucose, creating a non-polar environment to exclude water so that the Pi is transferred directly to glucose.
the residu Asp 205 plays a key role by deprotonating the OH on carbon 6.
how is the phosphorylation of glucose beneficial for glucose uptake?
keeps cellular glucose concentration low, maintaining a concentration gradient.
gives glucose a negative charge so that it cannot eacape the cell.
glycolysis step 2 -
what is it?
what enzyme is used?
why is this step necessary?
glucose 6 phosphate isomerised to fructose 6 phosphate.
phosphoglucose isomerase.
aldose to ketose ensures 3-3 even split later.
glycolysis step 3 -
what is it?
what enzyme is used?
why is this step needed?
F6P to F-1,6-BP (fructose biphosphate) using ATP
phosphofructokinase
the additional Pi further destabilises the sugar promoting step 4 cleavage.
glycolysis step 4 -
what is it?
what enzyme is used?
how was this step facilitated by step 2?
F-1,6-BP cleaved to glyceraldehyde 3 phosphate (and DHAP)
Aldolase
isomerisation in step 2 ensures 3-3even split, so that only one further pathway is required, not two.
glycolysis step 5 -
what is it?
what enzyme is used?
why is this enzyme special?
DHAP is converted to GAP
triose phosphate isomerase
this enzyme is kinetically perfect and only limited by how hast the substrate can diffuse into the active site.
how is step 5 an example of the importance of compartmentalising reactions?
possibility for toxic side product, if not for the enzyme used, the enediol intermediate would decompose into the toxic compound methylglyoxal.
how can glycolysis be regulated?
1 - positive allosteric regulation of PFK by AMP - when there is a lack of ATP, 2ADP combine to produce ATP and AMP, so AMP is a sign that more ATP is needed.
2 - negative allosteric regulation of PFK by ATP - says we’ve got enough for now, slow down.
3 - negative allosteric regulation of PFK by citrate from the Krebs cycle, when concentrations of citrate are too high.
