4. Glycolysis Flashcards
Catabolism & two examples
(breakdown)
-all biochemical reactions
by which a cell OBTAINS ENERGY and simple chemical NUTRIENTS
-exergonic
ex. release energy in form of ATP!
1.aerobic cell resp
C6H12O6 + 6 O2 + 6 H2O → 12 H2O + 6 CO2
2.fermentation
Anabolism
(building up)
-all of the biochemical reactions by which a cell BUILDS UP COMPLEX biological MOLECULES, using energy and simple chemical nutrients
glycolysis developed before _______ when the world was still _____and ______
before photosynthesis
when the world was still anaerobic and reducing
how did early organisms extract free energy from glucose (2 steps)
1st - activate glucose by phosphorylation to increase glucose reactivity
2nd - collect energy from the high-energy (phosphorylated) metabolites
phosphorylation allows pathway intermediates to ________ the cell
remain inside the cell
primary energy storage in plants vs animals
plants - starch
animals - glycogen
hydrolysis of energy storage polysaccharides (2)
- from non-reducing ends (branched polymers have many n.r ends)
- allows for rapid mobilization of glucose
where does glucose mobilization take place?
- smooth ER
how many stages/steps are in glycolysis ?
what is the net produced from glycolysis ?
- 2 stages with 10 steps
-1. preparatory phase (energy investment)
-2. energy payoff phase
NET = 2 pyruvate, 2 ATP and 2 NADH
overview of what happens in stage 1
(activation of glucose by phosphorylation)
glucose + 2ATP → 2 ADP + glyceraldehyde-3-p (G3P) + dihydroxyacetone phosphate (DHAP)
results in 2 G3P
(steps 1-5)
Step #1
phosphorylation of glucose (via hexokinase)
-irreversible (-delta G)
-to activate glucose & increase reactivity & to trap glucose
-add phosphate to C6
—glucose— ATP + Mg2+ → ADP → —glucose
hexokinase 6-phosphate—
what enzyme would work in step #1 if it was a prokaryote?
- glucokinase
Step #2
isomerization of glucose-6-P to fructose-6-P
(via phosphohexose Isomerase)
-reaction is coupled to step #3
-creates another OH for next phosphate on C1 of fructose-6-P
-small “uphill” step
glucose-6-P(aldose) Mg2+ & p.i → fructose-6-
P(ketose)
Step #3
phosphorylation of fructose-6-P
(via phosphofructokinase-1)
-!!first irreversible step (-delta G) that is UNIQUE to glycolysis!!
-committed step !
-most regulated step / control point for glycolysis
-add phosphate to C1
fructose-6-P ATP + Mg2+ → ADP → fructose
PFK-1 1,6-biphosphate
which step is the control point for glycolysis ?
- step #3
which steps are irreversible ?
- steps #1,3, and 10
which step is a committed step and what does that mean?
- step #3
means that fructose 1,6-biphosphate is committed to become pyruvate and yield energy
what would happen if you could not couple step #3 to ATP hydrolysis?
- delta G would become positive
Step #4
cleavage of fructose 1,6-biphosphate
(via aldolase)
-reversible step
-the fate of glucose carbons
fructose 1,6-biphosphate into → dihydroxyacetone phosphate (DHAP) + glyceraldehyde-3-phosphate (G3P)
how to overcome such a high +delta in step #4
- convert all DHAP to G3P
Step #5
conversion of dihydroxyacetone phosphate (DHAP) into glyceraldehyde-3-phosphate (G3P)
(via triose phosphate isomerase)
DHAP (ketose) → G3P (aldose)
-ONLY G3P is the SUBSTRATE for the next enzyme
Glucose carbons G3P
C4 or C3 → C1
C5 or C2 → C2
C6 or C1 → C3
Overview of stage 2
the payoff phase (steps 6-10)
2 G3P + 4ADP + 2Pi + 2NAD+
→
2 pyruvate +4ATP +2NADH + 2H+
Step #6
oxidation of G3P to 1,3-biphoglycerate
(via glyceraldehyde-3-phosphate dehydrogenase)
-oxidation/phosphorylation
-phosphorylation uses inorganic phosphate & yields a high energy product
-oxidation of G3P (NAD+ accepts 2 e- & 1 proton to form NADH)
G3P + inorganic phosphate
NAD+ →NADH + H → 1,3 bi-
G3P dehydrogenase phosphoglycerate
what is the oxidizing agent in step #6
NAD+
how many molecules of G3P are formed per one glucose (C6)
2 molecules of G3P per one glucose
acyl-phosphate
high energy product that donates the phosphate group to ADP to make ATP in step #7
which pathways are NAD+ vs NADP+
NAD+ = catabolic pathway
NADP+ = anabolic pathway
explain how NAD+ turns into NADH
NAD+ + 2e- + H+ = NADH
→NAD+ being reduced
NADH being oxidized ←
Step #7
ATP made by substrate level phosphorylation
(via phosphoglycerate kinase)
-phosphorylation of ADP to form ATP
-1,3-biphosphoglycerate donates phosphate group to ADP to make ATP
-reaction is reversible even though -delta G
1,3-biphosphoglycerate + ADP
Mg2+ & phosphoglycerate kinase
→
3-phosphoglycerate +ATP
what is substrate level phosphorylation
-when a phosphate group is transferred from a substrate to ADP to form ATP, coupled with the release of free energy
Step #8
conversion of 3-phosphoglycerate to 2-phosphoglycerate
(via phosphoglycerate mutase)
-reversible isomerization reaction
-shifts phosphate group from C3 to C2
-driven through by -delta G in step 10
3-phosphoglycerate
Mg2+ & phosphoglycerate mutase
→2-phosphoglycerate
Step #9
dehydration of 2-phosphoglycerate to phosphoenolpyruvate (PEP)
(via enolase)
-want to create a better phosphoryl donor
-removal of H20
-low energy phosphate ester linkage into high energy ENOL phosphate linkage
- phosphate group attaches to OH group which binds to a C=C
2-phosphoglycerate H20 leaves
enolase
→phosphoenolpyruvate
Step #10
second level substrate phosphorylation
(via pyruvate kinase)
-irreversible (-delta G)
-phosphorylation of ADP = transfers Pi from PEP to ADP to form ATP
phosphoenolpyruvate + ADP
Mg2+, K+
pyruvate kinase
→ pyruvate + ATP
describe tautomerization in step #10
tautomers are isomers that differ only in position of protons/electrons
-lowers conc of immediate product
-drives reaction toward ATP formation
pyruvate with OH pyruvate with =O
(enol form) (keto form)
high energy metabolites
-have delta G more negative than -25kJ/mol
-made by reaction between carboxylic acid group & phosphate group
P + hydroxyl group then binds to C=C
what is the overall free energy change in glycolysis
-negative
?? which steps are coupled ??
- 1&3
- 6 & 7
- 8 - 10
