9. gycolysis and the PDC

Glycolysis is a _ pathway.

catabolic

Glycolysis is the conversion of 1 into 2 .

glucose; pyruvate

Glycolysis generates both and _.

ATP; NADH

__ is the opposing pathway of glycolysis.

gluconeogenesis

Glycolysis and glyconeogenesis are _ pathways, meaning?

non distinct; they share enzymes but oppose each other

What is glucose-6-phosphate?

important intermediate in glycolysis, gluconeogenesis, and accessing glycogen stores

CO2 produced from complete oxidation of ribose.

5

_ CO2 produced from complete oxidation of glucose.

6

Is C16:0 or C16:2 going to produce more energy?

C16:0 because C is bonded to more hydrogens

Glucose is a six carbon compound with one _ group and five _ groups.

aldehyde; hydroxyl

What is the most oxidized carbon in glucose? The most reduced?

C1, C6

When C-C is converted to C=C, who gets the electrons?

FAD

When a carbonyl is converted to a hydroxyl, who gets the electrons?

NADH

What is an aldohexose?

six carbon sugar with an aldehyde

How does glucose convert from linear form to cyclic form?

-lone pair on O bonded to C5 attacks C1
-H from OH is lost off C1
-carbonyl from C5 picks up H to become OH
-generates cyclical ether bond

Glycolysis occurs in the .

cytosol

Glycolysis serves as the first step in the __ of glucose to and _.

complete oxidation; CO2; H2O

Glycolysis produces a small amount of _.

ATP

Glycolysis can occur under or _ conditions, but usually is under ___ conditions.

aerobic; anaerobic; aerobic

Can only metabolize aerobically. Done in the _.

fat; matrix

What is the energy investment stage?

-glucose needs to be activated
-small amount of ATP is consumed
-involves hexose sugars

What is the energy payout phase?

-energy is harvested in the form of ATP
-NADH also generated
-involves triose sugars

What is the enzyme that does the only oxidation step in glycolysis?

glyceraldehyde-3-phosphate dehydrogenase

What is step 1?

glucose (C6) -> glyceraldehyde-3-phosphate (3C) (GAP) x2
-2 ATP consumed per glucose
-activation stage

What is step one catalyzed by?

hexokinase

What is the reaction of step 1?

glucose + ATP -> G-6-P + ADP + H+

hexokinase reaction

What are the energetics of step 1?

-irreversible
-exergonic (G << 0)
-regulated
-phosphate/phosphoryl transfer reaction
-coupled to ATP (lysis)

Hexokinase couples the breaking of a bond to the formation of a bond.

phosphodiester; phosphoester

Breaking a phosphoanhydride bond releases of energy.

-32 kJ/mol

Forming a phosphoester bond requires _ of energy.

+16 kJ/mol

Glucose and fructose are isomers.

structural

How is G3P converted to F6P?

-isomerization (aldehyde to ketone)
-reversible, G approximately zero

What is the reaction catalyzed by PFK-1?

F6P + ATP -> F-1,6-BP + ADP + H+
-essentially is just adding a phosphate to C1

What are the energetics of F6P to F-1,6-BP?

-irreversible
-exergonic
-tightly regulated
-coupled to ATP lysis
-phosphate/phosphoryl transfer reaction

What is the role of Mg2+ in these reactions?

to balance out the negative charges on ATP, helps with stability

The reaction catalyzed by PFK-1 is the ___ step in glycolysis.

committed

Why is the hexokinase reaction not tightly regulated?

it is not the committed step. G3P can be obtained from glycogen or the pentose phosphate pathway, bypassing hexokinase.

What is the main way of speeding/slowing glycolysis?

regulating PFK-1 reaction (reaction 3)

What is the fourth step of glycolysis?

aldolase splits fructose-1,6-phosphate into glyceraldyhyde-3-phosphate (important) and dihydroxyacetone phosphate

How are DHAP and GAP related?

isomers

What is step 5 of glycolysis?

Dihydroxyacetone phosphate ---> Glyceraldehyde 3-phosphate
Enzyme: Triose phosphate isomerase

One molecule of glucose produces molecules of GAP.

2

Why is GAP never converted to DHAP?

GAP is kept at a low concentration so the equilibrium is always shifted in the right direction

What is stage 2 of glycolysis?

GAP (x2) -> pyruvate (x2)
generating 4 ATP

What is a mixed anhydride bond?

phosphate attached to a carboxyl group. high energy! (COP)

Why is an acyl phosphate (mixed anhydride) high energy?

products of hydrolysis are resonance stabilized

What is step six of glycolysis?

G3P + NAD+ + Pi -> 1,3-BPG + NADH + H+
enzyme: GAPDH (gap dehydrogenate)
-oxidation reaction
-oxidation followed by phosphorylation
-energy capture step

What is an energy capture step?

step where high energy molecule is produced and released outside of pathway

What high energy molecules does step 6 generate?

NADH and 1,3-BPG

What is phosphate transfer potential?

free energies of hydrolysis for phosphate containing compounds

1.3-BPG has a large _ potential.

phosphoryl transfer

Is GAPDH reaction a phosphorylation transfer?

no, it is just a phosphorylation

A SLP reaction is a reaction, and ___ reaction, and specifically, a phosphate transfer reaction that produces a ______.

coupled; phosphate transfer; nucleoside triphosphate

Is O2 required for SLP?

no

Is formation of phosphocreatine from ATP SLP?

no, because no nucleoside phosphate is generated. it is a phosphate transfer

What is step 7 of glycolysis?

1,3-bisphosphoglycerate + ADP --> 3-phosphoglycerate + ATP
enzyme: phosphoglycerate kinase
-ATP synthesis coupled to breaking acyl phosphate
-energy capture step

Consumption of 1,3-BPG in reaction pulls reaction forward.

7; 6

What is step 8 of glycolysis?

3-phosphoglycerate ---> 2-phosphoglycerate
Enzyme: Phosphoglycerate mutase
-third isomerization
-reversible

What is step 9 of glycolysis?

2-phosphoglycerate (2PG) --> Phosphoenolpyruvate (PEP) + H2O
enzyme: enolase
-dehydration reaction
-NOT energy capture

What is step 10 of glycolysis?

phosphoenolpyruvate + ADP --> pyruvate + ATP
-generates unstable pyruvate in enol form, then undergoes tautomerization to convert to keto form
-energy capture step (2 ATP made)
-SLP

Breaking a phosphoester bond releases ___ kJ/mol of energy

-16

Tautomerization of enolpyruvate to pyruvate releases _ kJ/mol of energy

-46

Forming a phosphoanhydride bond requires kJ/mol of energy

+31

What are the energy capture steps?

6, 7, and 10

1,3-BPG is used to produce what molecule in erythrocytes? What does this mean for glycolysis?

2,3-BPG. often do not complete glycolysis

What is the net equation for glycolysis?

glucose + 2NAD+ + 2Pi + 2ADP -> 2 pyruvate + 2NADH + 2H+ + 2ATP + 2H2O

What are the high energy intermediates?

1,3-BPG and PEP

What are the high energy products?

ATP and NADH

Is F-1,6-BP a high energy molecule?

no

Regulation of glycolysis is important for:

-cells energy needs met
-fuel is not wasted
-there are appropriate levels of intermediates required for other purposes

What is the rate of flux through metabolic pathways regulated by?

-substrate availability
-alteration of enzyme activity (short term activity, allostery and covalent modification)
-alteration of amount of enzyme (longer term regulation)
-subcellular localization/compartmentalization

Most enzymes in a pathway function equilibrium and their net rates vary with the ___.

near; concentration of their substrates

Enzymes that function far from equilibrium catalyze _ reactions. These enzymes are often sites of _ and their activities are increased or decreased in response to .

irreversible; regulation; signalling molecules

Which three enzymes cannot be reversed in glycolysis?

pyruvate kinase, PFK-1, hexokinase

What two things impact regulation in glycolysis?

-substrate availability
-enzymes regulation (HK, PFK-1, PK)

How does substrate availability regulate glycolysis?

glucose import (transporters). cells with need for glucose have high affinity transporters (neurons, RBCs)

Why do RBCs have high affinity glucose transporters?

they lack mitochondria, so glucose is their only energy source

How is hexokinase regulated?

glucose-6-phosphate is an inhibitor

What type of inhibition in G3P on HK?

product inhibition

How is PFK-1 regulated?

-allosterically regulated by ADP/AMP and PEP
-ADP/AMP allosterically activates
-PEP does feedback inhibition

Why does ADP/AMP activate PFK-1?

an increase in ADP means the cell needs to make more ATP, so PFK-1 is turned on to activate glycolysis

Why does PEP inhibit PFK-1?

elevated PEP levels signal that the products of glycolysis are not being consumed

What is the regulation of PFK-1 and PK together called?

synchronous regulation

How is PK regulated?

-allosterically
-inhibited by ATP
-activated by F-1,6-BP (feedforward activation)

Pyruvate kinase and PFK-1 are part of regulation (glycolysis and glyconeogenesis).

reciprocal

F-1,6-BP is a ___ activator of PK.

heteroallosteric

ATP is an allosteric of pyruvate kinase.

inhibitor

PFK-1 and PK are both _ by ATP. This is an example of:

inhibited. synchronous regulation

ATP is both a _ and an __ of PFK-1. How is this possible?

substrate; inhibitor. PFK-1 has two binding sites for ATP. the substrate binding site is high affinity and the allosteric inhibitor site is low affinity

What is the net energy gain when 1 mol of glucose is converted to pyruvate?

2 mols of NADH and 2 mols of ATP

What is the net energy gain when 1 mol of G6P is converted to pyruvate?

2 mols of NADH and 3 mols of ATP

What is the gross energy gain when 1 mol of G6P is converted to pyruvate?

2 mols of NADH and 4 mols of ATP

What is the net energy gain when 1 mol of dihydroxyacetone phosphate is converted to pyruvate?

1 mol of NADH and 2 mols of ATP

What two reactions does glycogen metabolism begin with?

glycogen(n) + Pi -> glycogen(n-1) + glucose-1-phosphate (phosphorolysis)
glucose-1-phosphate

What are the fates of pyruvate in mammalian cells?

lactate, acetyl CoA, alanine, oxaloacetate

How is pyruvate converted to lactate?

-reduction (C=O -> C-OH)
-anaerobic
-in rapidly contracting muscle, erythrocytes

How is pyruvate converted to acetyl CoA?

-decarboxylation
-aerobic
-CAC + oxidative phosphorylation
-thioester (high energy)

How is pyruvate converted to oxaloacetate?

-carboxylation
-CAC intermediate

Why is an anaerobic fate for pyruvate required?

to regenerate NAD+ for the oxidation reaction in glycolysis under anaerobic conditions