biochem ch. 14 glycolysis

glucose → synthesis of structural polymers →

ECM, cell wall polysaccharides

glucose → storage →

glycogen, starch, sucrose

glucose → oxidation via glycolysis →

pyruvate

glucose → oxidation via penrose phosphate pathway →

ribose 5-phosphate

what is the basic definition of glycolysis

***universal glucose catabolism***

glucose degraded by enzyme catalyzed reactions to yield 2 (3C) pyruvate

some free energy conserved as ATP and NADH

what are the two phases of glycolysis

preparatory phase

payoff phase

characteristics of the preparatory phase

ATP consumed

∆G of intermediates increases

hexose carbon chains converted to glyceraldehyde 3-phosphate

characteristics of the payoff phase

energy conserved as 2 ATP and 2 NADH

2 pyruvate produced

by what type of process is ATP produced in glycolysis

substrate-level phosphorylation

which steps are the irreversible steps

1, 3, 10

1: phosphorylation of glucose - hexokinase activates glucose by phosphorylating at C6 to yield glucose 6-phosphate

3: phosphorylation of fructose 6-phosphate to fructose 1,6-bisphosphate (catalyzed by PFK-1)

10: transfer of phosphoryl group from phosphoenolpyruvate to ADP by pyruvate kinase, yielding pyruvate

what are the 3 noteworthy chemical transformations of glycolysis

degradation of carbon skeleton of glucose to yield pyruvate

phosphorylation of ADP to ATP by compounds with high phosphoryl group transfer potential

transfer of hydride ion to NAD+ forming NADH

ATP and NADH formation is ________ to glycolysis

coupled

what’s the overall reaction for glycolysis

glucose + 2NAD+ + 2ADP + 2Pi → 2 pyruvate + 2NADH + 2H+ + 2ATP + 2H2O

the conversion of glucose to pyruvate is ________

EXERGONIC

glucose + 2NAD+ → 2 pyruvate + 2 NADH + 2H+

∆G’º1 = -146 kJ/mol

the formation of ATP from ADP and Pi is _________

ENDERGONIC

2 ADP + 2 Pi → 2 ATP + 2 H2O

∆G’º2 = 61.0 kJ/mol

what is the overall standard free energy change for glycolysis

∆G’ºsum = -85 kJ/mol

coupled reaction is overall exergonic

under standard cellular conditions, glycolysis is essentially _______

IRREVERSIBLE

what is stored in pyruvate

energyyyyy

energy stored in pyruvate can be extracted by…

aerobic processes: oxidative reactions in CAC, oxidative phosphorylation

anaerobic processes: reduction to lactate, reduction to ethanol

can provide carbon skeleton for alanine/fatty acid synthesis

all 9 intermediates in glycolysis are _______

phosphorylated

what is the function of the phosphoryl groups of glycolysis intermediates

1. prevent glycolysic intermediates from leaving the cell

2. serve as essential components in enzymatic conservation of metabolic energy

3. lower activation energy & increase specificity of enzymatic reactions

what is needed (energy wise) for the preparatory phase of glycolysis

2 molecules of ATP are invested - activate glucose to fructose 1,6-bisphosphate

step 1

phosphorylation of glucose: hexokinase activates glucose by phosphorylating at C6, yielding glucose 6-phosphate

ATP is phosphoryl donor

hexokinase requires Mg2+

irreversible

step 2

convert glucose 6-phosphate to fructose 6-phosphate

phosphohexose isomerase catalyze reversible isomerization

mechanism has enediol intermediate

readily proceeds in either direction

need Mg2+

step 3

phosphorylation of fructose 6-phosphate to fructose 1,6-bisphosphate by PFK-1

transfer phosphoryl group from another ATP

irreversible

first “committed” step in glycolytic pathway (rate limiting?)

describe the allosteric regulation of PFK-1

activity increase when ATP is depleted or when ADP and AMP accumulate

fructose 2,6-bisphosphate is potent allosteric activator

ribulose 5-phosphate indirectly activates

step 4

fructose 1,6-bisphosphate is cleaved by reverse aldol condensation, catalyzed by aldolase, yields glyceraldehyde 3-phosphate and dihydroxyacetone phosphate

reversible

*class 1 aldolase reaction (has schiff base intermediate)

class II aldolase reaction

found in fungi and bacteria

do not form schiff base intermediate

step 5

triose phosphate isomerase catalyzes conversion of dihydroxyacetone to glyceraldehyde 3-phosphate

reversible

final step in preparatory phase

step 6

oxidation of glyceraldehyde 3-phosphate into 1,3-bisphosphoglycerate catalyzed by glyceraldehyde 3-phosphate dehydrogenase

energy-conserving reaction — formation of acyl phosphate group conserves free energy of oxidation (have high standard freee energy of hydrolysis)

NAD+ → NADH + H+

step 7

phosphoglycerate kinase transfers high energy phosphoryl group from 1,3-bisphosphoglycerate to ADP, forming ATP and 3-phosphoglycerate

substrate level phosphorylation

step 6 and 7 constitute an ___________ process

energy-coupling

combined ∆G’º is negative

step 8

conversion of 3-phosphoglycerate to 2-phosphoglycerate catalyzed by phosphoglycerate mutase

reversible shift

requires Mg2+

step 9

dehydration of 2-phosphoglycerate to form phosphoenolpyruvate (PEP), catalyzed by enolase

reversible removal of water

energy conserving reaction

mechanism has Mg2+ stabilized enolic intermediate

step 10

transfer of phosphoryl group form phosphoenolpyruvate to ADP by pyruvate kinase

irreversible step

requires K+ and either Mg2+ or Mn2+

tautomerization of pyruvate

spontaneously tautomerize from enol form to keto form

what are the net products of glycolysis

2 pyruvate

2 ATP (-2, +44)

2 NADH