Post on 28-Apr-2015
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GLIKOLISISGLIKOLISIS
Major Pathways of Glucose Utilization
These three pathways are the most significant in terms of the amount of glucose that flows through them in most cells.
The Two Phases of Glycolysis
What is the net yield (in energy equivalents) per molecule glucose?
Glucose + 2NAD+ + 2ADP + 2Pi →2 pyruvate + 2NADH + 2H+ + 2ATP + 2H2O
Formation of 2 Pyruvates:
Glucose + 2NAD+ → 2 pyruvate + 2NADH + 2H+ ΔG’1O= -146 kJ/mol
Formation of 2 ATP:
2ADP + 2Pi → 2ATP + 2H2O ΔG’2O= 61.0 kJ/mol
Hexokinase: First ATP Utilization
Reaction 1 : Transfer of a phosphoryl group from ATP to glucose
to form glucose 6-phosphate (G6P)
ΔG’° = -16.7 kJ/mol
Phosphohexose Isomerase
Recation 2: Phosphohexose isomerase catalyzes the conversion of G6P to F6P, essentially the isomerization of an aldose to a ketose.
ΔG’° = 1.7 kJ/mol
PFK-1: Second ATP Utilization
Reaction 3: Phosophofructokinase-1 (PFK-1) phosphorulates fructose-6-phosphate (F6P)
PFK-1 plays a central role in control of glycolysisbecause it catalyzes on of the pathway’s rate determening reactions.
ΔG’° = -14.2 kJ/mol
Aldolase
Reaction 4: Aldolase catalyzes cleavage of fructose-1,6-bisphosphate (FBP)
ΔG’° = 23.8 kJ/mol
Triose Phosphate Isomerase
Reaction 5: Interconversion of the triose phosphates Only GAP continues along the glycolytic pathway Dihydroxyacetonphosphate is rapidly and reversible
ΔG’° = 7.5 kJ/mol
Glyceraldehyde-3-Phosphate Dehydrogenase
Reaction 6: Glyceraldehyde-3-phosphate dehydrogenase forms the first “high-energy” intermediate.
ΔG’° = 6.3 kJ/mol
Phosphoglycerat Kinase: First ATP Generation
ΔG’° = -18.5 kJ/mol
Phosphoglycerate Mutase
Reaction 8: Catalyzes of a reversible shift of the phosphoryl group between C-2 and C-3 of glycerate; Mg2+ is essential.
ΔG’° = 4.4 kJ/mol
Pyruvate Kinase : Second ATP Generation
ΔG’° = -31.4 kJ/mol
Lactate Fermentation
Enzyme = Lactate Dehydrogenase
Pyruvate + NADH + H+ L-Lactate + NAD+
Regenerates NAD+ from NADH (reducing equivalents) produced in glycolysis
Lactate fermentation is important in red blood cells, parts of the retina and in skeletal muscle cells during extreme high activity.Also important in plants and microbes growing in absence of O2.
ΔG’° = -25.1 kJ/mol
Alcoholic Fermentation
Two enzymes involved: Pyruvate decarboxylase irreversibleAlcohol dehydrogenase reversible
Pathway is active in yeast
Regenerates NAD+ from NADH (reducing equivalents) produced in glycolysis.
Second step is reversible → ethanol oxidation eventiually yields acetate
→ enters fat synthesis
The Pentose-Phosphate Pathway (PPP)
orThe Hexose-monophosphate Shunt
The Pentose Phosphate Pathway: Functions
1. Production of NADPH
2. Biosynthesis/degradation of other sugars(C3 ,C4, C5, C6, C7)
3. Biosynthesis and degradation of ribose
Determined by cell-specific needs for NADPH, ATP, sugars
Roles for NADPH
1. Reductant in biosynthetic reactions(e.g., fatty acid synthesis, steroid synthesis)
2. Production of reactive oxygen species (ROS)(e.g., innate immune response)
3. Regulation of redox homeostasis(e.g., erythrocytes, detoxification reactions)
4. Separation of catabolic and anabolic steps(e.g., in cytosol: low NADH, but high NADPH)
The Pentose Phosphate Pathway: Reactions
(Cytosol)
1. Oxidation Phase (C6 C5 + CO2)
2. Isomerization Phase (C5 C5)
3. Rearrangement Phase (xC5 yC6)
Phase 1: Oxidative Reactions