Transcript Glycolysis and Gluconeogenesis

Glycolysis and
Gluconeogenesis
Glycolysis
 What is glycolysis?
 sequence
of reactions that converts one
molecule of glucose to two molecules of
pyruvate with the formation of two ATP
molecules
 anaerobic
Glycolysis
 Why is glucose such a commonly used
fuel?
 tends
to exist in ring form, very stable,
doesn’t generally glycosylate proteins
 formed from formaldehyde under prebiotic
conditions
Glycolysis
 What are the possible fates of glucose?
Glycolysis
 What’s the difference between a
facultative anaerobe and an obligate
anaerobe?
 Can you give an example of habitatdependent anaerobiosis?
 What about activity-dependent
anaerobiosis?
Glycolysis
 All the intermediates in glycolysis have either
3 or 6 carbon atoms
 All of the reactions fall into one of 5
categories
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phosphoryl transfer
phosphoryl shift
isomerization
dehydration
aldol cleavage
Glycolysis
 Entire reaction sequence may be
divided into three stages
 glucose
is trapped and destabilized
 six carbon molecule is split into two three
carbon molecules
 ATP is generated
Glycolysis – Stage 1
 glucose converted to glucose-6-PO4
 ATP is needed
 catalyzed by hexokinase or glucokinase
 induced fit
 G01= -4.0 kcal/mole
Glycolysis – Stage 1
 phosphoglucoisomerase
 aldose is converted to ketose
 G01=+0.4 kcal/mole
Glycolysis – Stage 1
 rate limiting enzyme – allosteric
 inhibited by high ATP, citric acid, long-chain fatty acids
 stimulated by ADP or AMP
 G01= - 3.4 kcal/mole
Glycolysis
Glycolysis – Stage 2
 six carbon molecule split into 2- 3 carbon molecules
 aldose and ketose
 G01=+ 5.73 kcal/mole
Glycolysis – Stage 3
 At equilibrium most mixture exists as
dihydroxyacetone phosphate
 G01=+ 1.83 kcal/mole
Triose Phosphate Isomerase
Glycolysis – Stage 3
 redox reaction
 energy from redox used to form acyl
phosphate
 G01= +1.5 kcal/mole
Glycolysis – Stage 3
 Consists of two coupled processes
Glycolysis – Stage 3
 formation of ATP – substrate level
phosphorylation
Glycolysis – Stage 3
 phosphoryl shift – uses 2,3
bisphosphoglycerate G01= +1.1 kcal/mole
 dehydration G01 = +.44 kcal/mole
 phosphoryl transfer G01 = -7.5 kcal/mole
Glycolysis
Fate of Pyruvate
Alcoholic Fermentation
 Which organisms carry out this process?
 yeast
 other microorganisms
 PDC requires thiamine pyrophosphate as coenzyme
 NAD+ is regenerated
Lactic Acid Fermentation
 Occurs in muscle cells, microorganisms
 Regenerates NAD+
NAD+ and Dehydrogenases
 Various dehydrogenases have a similar binding
domain for NAD+ showing their common origin

Rossman fold
Glycolysis
 How can fructose be
used for energy?
Glycolysis
 To use galactose it must be converted to
glucose-6-PO4
Glycolysis
Glycolysis
 What causes lactose intolerance?
Glycolysis
 What is galactosemia?
 inability
to metabolize galactose
 missing galactose 1-phosphate uridyl
transferase
liver disease
 development of cataracts
 CNS malfunction
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Control of Glycolysis
 Of what value is glycolysis for cells?
 provides energy in form of ATP
 provides building blocks for synthetic reactions
 Where are most control points found?
 enzymes that catalyze irreversible reactions
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hexokinase
phosphofructokinase
pyruvate kinase
Phosphofructokinase
 Most important control point in
mammalian glycolytic pathway
 allosteric
enzyme
activated by AMP and fructose 2,6
bisphosphate
 inhibited by high levels of ATP, citrate, fatty
acids
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Phosphofructokinase
Hexokinase
 Hexokinase is inhibited by its product
glucose-6-PO4
 glucose
remains in blood
 Glucokinase, an isozyme of hexokinase
is not inhibited by glucose-6-PO4
 found
in liver
 has lower affinity for glucose
Pyruvate Kinase
 Pyruvate kinase exists as isozymes
 L form – predominates in liver
 M form – mostly in muscle and brain
 PK is an allosteric enzyme
 activated by fructose 1,6 bisphosphate
 inhibited by ATP, alanine
 L form of PK influenced by covalent
modification
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inhibited by phosphorylation
Pyruvate Kinase
Glucose Transport
 What is the role of glucose transporters
in animal cells?
 facilitate
movement of glucose across cell
membrane
 What kind of molecule is a transporter
and where is it located?
 small
protein embedded in plasma
membrane
Glucose Transport
 mammalian glucose transporter
Glucose Transport
Glycolysis and Cancer
 Why are rapidly growing tumor cells
dependent upon glycolysis?
 insufficient
oxygen supply
 What is the function of HIF-1?
 hypoxia-inducible transcription factor
stimulates synthesis of many glycolytic
enzymes and GLUT-1 and 3
 also stimulates vascular endothelial growth
factor
Gluconeogenesis
 What is gluconeogenesis?
 synthesis of glucose from non-carbohydrate
precursors
 Why is this an important pathway?
 What are some of the major precursors?
 lactate, amino acids, glycerol
 Where does this process occur?
 liver, kidney
Gluconeogenesis
 If gluconeogenesis involves the conversion of
pyruvate to glucose why is it not simply the
reverse of glycolysis?
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glycolysis contains several irreversible reactions
 Which reactions in glycolysis are irreversible?
 phosphoenolpyruvate to pyruvate
 fructose 6-phosphate to fructose 1,6bisphosphate
 glucose to glucose 6-phosphate
Gluconeogenesis
 What is the first reaction?
O
CH3 CCO2 Pyruvate
biotin
+ CO 2 + A TP
pyruvate
carboxylase
O
CH2 CCO2 - +
CO 2 Oxaloacetate
A DP + P i
Gluconeogenesis
 Why is pyruvate carboxylase of special
interest?
 structural
properties
contains ATP-grasp domain at N-terminal end
 contains biotin-binding domain at C-terminal
end
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Gluconeogenesis
 What is the role of biotin in this reaction?
 prosthetic group lined to -amino group of lysine
residue
 carrier of activated carbon dioxide
Gluconeogenesis
 Pyruvate
carboxylase is an
allosteric enzyme
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activated by acetyl
CoA
needed to form
carboxybiotin
Gluconeogenesis
 Carboxylation of
pyruvate occurs in
the mitocondria but
next step in reaction
sequence occurs in
cytosol
Gluconeogenesis
Decarboxylation of oxaloacetate is coupled with
phosphorylation by GTP
enzyme is phosphoenolpyruvate carboxykinase
O
CH2 CCO2 CO 2 Oxaloacetate
+ GTP
OPO 3 2 CH2 = CCO2 - + CO 2
Phosphoenol pyruvate
+ GD P
Gluconeogenesis
 Which other steps in glycolysis are
irreversible?
 conversion
of fructose 1,6-bisphosphate to
fructose 6-phosphate
 conversion of glucose 6-phosphate to
glucose
Gluconeogenesis
HO
CH2 OP O3 2 -
CH2 OH
C O
C O
H
H
OH
H
OH
CH2 OP O3 2 -
fructose-1,6-bisphosphatase
H2 O
Fructose-1,6-bisphosphate
Pi
HO
H
H
OH
H
OH
CH2 OP O3 2 -
Fructose-6-phosphate
 G° = -16.7 kJ mol-1
 fructose-1,6-bisphosphatase is an allosteric
enzyme, inhibited by AMP and activated by ATP
Gluconeogenesis
 Enzyme that catalyzes last reaction not found
in all tissues
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liver and kidney cortex
Gluconeogenesis
 Is gluconeogenesis an energetically
favorable reaction in the cell?
 What drives this reaction?
 Are glycolysis and gluconeogenesis
active at the same time?
Regulation of Glycolysis and
Gluconeogenesis
 What are some of the factors that
ensure the reciprocal regulation of these
processes?
 allosteric
regulators of key enzymes
 energy charge
 fructose 2,6-bisphosphate
 hormones
Regulation of Glycolysis and
Gluconeogenesis
Regulation of Glycolysis and
Gluconeogenesis
 fructose 2,6-bisphosphate stimulates
PFK and inhibits fructose 1,6bisphosphase
 controlled
by insulin and glucagon and
reflects the nutritional status of the cell
Regulation of Glycolysis and
Gluconeogenesis
 How do hormones influence the
enzymes associated with these
processes?
 influence
gene expression
change transcription rate
 influence degradation of m-RNA
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– insulin PFK, PK
– glucagon PEPCK, fructose 1,6-bisphosphatase
Regulation of Glycolysis and
Gluconeogenesis
 What are substrate
cycles and why are
they important?
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can amplify
metabolic signals
can generate heat
Regulation of Glycolysis and
Gluconeogenesis
 What is the Cori cycle and why is it
important?
Regulation of Glycolysis and
Gluconeogenesis