Lecture 6: Glycolysis: Enzymatic Reactions Flashcards
glycolysis pathway
ANAEROBIC
doesnt need oxygen
what does gycolysis do?
cleaves glucose into 2 pyruvates
net yeild of 2ATP
what are the two stages of glycolysis
ATP investment stage
ATP earning stage
glucose chemical equation
C6H12O6
pyruvate chemical equation
C3H3O3
What do they 3 enzymes do (boradly)
catalyze very exergonic reactions (irreversible)
these drive metabolic flux
Substrate level phosphorylation
use phosphoryl transfer rxns independent of mitochondrial ATP synthase complex
directly phosphorylaye ADP to make ATP
2 happen in glycolysis
Facts about glycolysis and its importance in nature
1) ancient, it evolved very early on
2) primary way to make ATP under anaerobic conditions (also in cells lacking mitochondria)
3) Metabolites of glycolysis are precursors for interependent patways (like mitochondrial ATP synth)
ex) pyruvate!!!!!
What does glycolysis accomplish for the cell?
generates 2ATP/glucose (small amount) (crit for anaerobic condtions)
generates pyruvate (used to make acetyl-CoA also lactate and sometimes ethanol
Overall net reaction of glycolysis?
Glucose+ 2NAD + 2ADP +2Pi–> 2 pyruvate + 2NADH +2H+ + 2 ATP +2H2O
deltaG^0’=-35.5kJ/mol
WHat are the key regulated enzymes in glycolysis?
Hexokinase
Phosphofructokinase-1
Pyruvate Kinase
What are examples of glycolysis in real life?
anaerobic conditions
intense exercise
where does glycolysis take place?
in the cytosol!
where is bulk of ATP generated
in mitochondria
by oxidative phosphorylation
chem equation for complete glucose oxidation
Glucose+ 6O2–> 6CO2 + 6H2O
deltaG^0’=+30.5kJ/mol
Theoretical Max yield of glucose oxidation vs. actual yield
90 ATP/Glucose
actual is 32 ATP/glucose
why so different?
because some energy is lost as heat!!!!!
what does glycolysis MEAN?``
splitting of glucose
glucose used to be called glycos
net loss in glycolysis??
NO net loss of carbon or oxygen atoms
First stage of glycolysis overview
ATP investment (in steps 1 and 3)
generate GAP
GAP oxidized to produce NADH and 1,3-bisphophoglycerate
TWO ATP USED
listen to slide 9
listen to slide 9
what we end up with
from 1 6-carbon molec to 2 3-carbon molecs (made identical in step 5?)
Second Stage of Glycolysis overview
we get energy back
Remember, each reaction happens TWICE, once on each of the 3-carbon molecules
from each glucose molecule, we get TWO pyruvate molecules
ATP tields from stage 2
4 TOTAL ATP
2 NET ATP
look at slide 11 a lot
look at slide 11 a lot
what does NADH do?
NADH is the source of reducing power for the cell
we need a molec of NAD+ to reduce every time we oxidize GAP
NAD+ is regenerated from the metabolism of pyruvate
Large negative delta G and delta G^0’ values
irreversible under actual conditions
favorable under actual conditions
delta G^0’ and delta values that are close to 0 (pos or neg, -2.5 or +1.7 for ex)
actual conditions in cell can influence directionality of reaction
Reaction 1
phosphorylation of glucose by hexokinase or glucokinase
use of ATP to phosphorylate glucose
GLUCOSE CANNOT LEAVE CELL AFTER ITS BEEN PHOSPHORYLATED
helps keep it in the cell so it can be used for the rest of the reaction
hexokinase is in all cells, glucokinase pretty much just liver and pancreas
Reaction 2
Isomerization of glucose-6-P to fructose-6-P
catalyzed by phosphoglucose isomerase
directionality depends on metabolite concs (very small delta G change)
Reaction 3
phosphorylation of fructose-6-P to fuctose1,6-BP
use phosphofucktokinase 1
irreversible
***one of key regulated steps!!!!
control how much you commit to glycolysis pathway
b/c ATP being used, we don’t want to use ATP if we don’t have to. don’t want to be wasteful
Reaction 4
cleavage of fructose-1,6-BP by aldolase to make glyceraldehyde-3-+ and dihydroxyacetone-P
this is where we make the 6-carbon molecule two 3-carbon molecules
directionality of rxn depends on metabolite concs!
Reaction 5
Isomerization of dihydroxyacetone-P to GAP
use triose phosphate isomerase
step that makes DHAP into GAP so that we have 2 identical GAP molecules! (now we can procede with identical reaction in the rest of the pathway)
directionality depends on metabolite concs!
Reaction 6
oxidation and phosphorylation of glyceraldehyde-3-P to make 1,3 bisphosphoglycerate
use glyceraldehyde-3-P dehydrogenase
Need CONSTANT supply of (oxidized) NAD+
NAD+- reduced to NADH
NAD+ regeneration for reaction 6
AEROBIC: NADH formed in glycolysis transfers electrons to O2 through ETC (acetyl coA from pyruvate goes on to the ETC).
ANAEROBIC: NAD+ regenerated by reduction of pyruvate to lactate or ethanol(fermentation)
Reaction 7
Generation of ATP from 1,3-biphosphoglycerate to 3-phosphoglycerate
done by phosphoglycerate kinase
Substrate level phosphorylation
in this case, the phosphase donor 1,3-BGP is a substrae with high phosphoryl-transfer potential
this compound has HIGHER phosphoryl transfer potential than ATP, so it can be used to directly phosphorylate ADP to make ATP
WE HAVE used 2 ATP (in phase one) and we just made 2 ATP (remember, one per each 3-carbon molec)
substrate level phosphorylation means….
using molecules to make ATP
generate ATP INDEPENDENT of ATP synthase
need a substrate that has a higher phosphoryl transfer potential than ATP?
Reaction 8
phosphoryl shift by phosphoglycerate mutase
convert 3-phospoglycerate to 2-phosphoglycerate
move the phosphate group
directionality depends on metabolite concs
Reaction 9
dehydration of 2-hposphoglycerate by enolase forms phospoenolpyruvate (PEP)
make an enol containing compound
phosphate ester of alcohol has LOW phosphoryl transfer potential, won’t work to phosphorylate ADP
instead, use enol phosphate, which has HIGH phosphoryl-transfer potential
direction depends on metabolite concs
Reaction 10
GENERATION OF ATP
by pyruvate kinase
when phosphoenolpyruvate is converted to pyruvate
substrate level phosphorylation generates ATP (independednt of ATP synthase)
ATP and Pyruvate are final products)
