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GLYCOLYSIS AND ALTERNATIVES
BIOT 309 Fall 2013
GLYCOLYSIS AND ALTERNATIVES
• Bacteria use 3 different pathways to convert glucose to PGA (3-‐phosphoglycerate) (see diagram)
1. Embden-‐Myerhoff (shown in next slide) 2. Entner-‐Dordoroff (ED) Pathway 3. Pentose Phosphate Pathway (shunt)/hexose
monophosphate shunt
Energy yields are different.
What are they?
QUICK REVIEW EMP
GLYCOLYSIS
ENTNER-‐DUODOROFF PATHWAY
• Uses EMP pathway for some steps • Unique enzymes and intermediates
ED PATHWAY*
* Be aware that this figure does not show ATP use or production since enzymes from EMP pathway perform these reactions.
ED PATHWAY
* * • Glucose begins pathway • E yield = 1 ATP + 1 NADH + 1 NADPH
• * From G6P to KDG split enzymes are different • Pyruvate forma^on
• Directly • Indirectly – G3P enters EMP < -‐ -‐
*
*
*
< - - -
Entner Duodoroff Pathway
What do abbreviations
stand for? MAKE a list!!!
SIDE-‐BY-‐SIDE COMPARISON
From G6P to
KDG/KDPA split into G3P +
pyruvate enzymes different
THIRD GLYCOLYSIS PATHWAY
Pentose Phosphate Pathway (PPP) =
Hexose Monophosphate Pathway (HMP) =
Phosphogluconate Pathway
Some^mes called a shunt.
• Operates at same ^me as EMP
It’s a shunt
PPP is a shunt
• The pathway begins with the glycolyTc intermediate glucose 6-‐P.
• It reconnects with glycolysis because two of the end products of the PPP are glyceraldehyde 3-‐P and fructose 6-‐P; two intermediates further down in the glycolyTc pathway.
• It is for this reason that the PPP is oXen referred to as a shunt.
PPP
• Provides ribose-‐5-‐phosphate = precursor to ribose and deoxyribose in nucleic acids
• Provides erythrose phosphate = precursor for synthesis of aroma^c amino acids
• Other intermediates used in other pathways • Provides NADPH – major source of energy for anabolic reac^ons, e.g., nucleic acids, lipids
• Used exclusively by Thiobacillus novellus and Brucella abortus
PATHWAY INTERMEDIATE USES
irreversible
irreversible
1st Reaction High [NADPH]
inhibits allosterically
High [NADP+] stimulates
allosterically
Transketolase 1 2 5C 1 7C + 1 3C
2 enzymes convert ribuloe-5-Pi to a ketose and an aldose both with 5 C
Transketolase 2 1 7C +1 3C 4C+6C
Transketolase 3 4C+5C 6C + 3C
MAKES SUGARS WITH DIFFERENT CARBON NUMBERS All reversible
Transketolase
• Requires thiamine diphosphate (TDP) and Mn2+ as co-‐factors
• TDP (TPP) is needed for redox
Regula^on
• G-‐6-‐P is par^^oned between EMP and PPP • Depends on
– NADP+ and NADPH concentra^ons • NADP+ high favors EMP • NADPH high favors PPP
ENTNER-‐DUDOROFF PATHWAY
• The Entner-‐Doudoroff pathway yields one ATP and two NADPH molecules from one glucose molecule.
• Uses 4 enzymes that are different from EMP 1 Glucose 2 pyruvate + 1 ATP + 1 NADH
+ 1 NADPH Bacteria: Pseudomonas, Rhizobium, Azotobacter, Agrobacterium, Enterococcus faecalis
PENTOSE PHOSPHATE SHUNT PATHWAY
• Precursors to the ribose and deoxyribose in nucleic acids • Provides erythrose phosphate which is a precursor for synthesis of aroma^c
amino acids • reducing power = NADPH
Overall Oxida<ve Reac<on: 1 Glucose 6 – P + 2 NADP+ + 1 H2O 1 Ribose 5-‐P + 1 CO2+ 2 NADPH + 2 H+
Non-‐Oxida^ve Reac^ons • change number of carbons in sugar molecules • make intermediates used in other biosynthe^c pathways including
feeding back into PPP and EMP
Used exclusively by Thiobacillus novellus and Brucella abortus
AddiTonal Topics
Coenzyme A
• CoASH • Free SH • role in TCA alpha KG -> succinyl CoA
Coenzyme A
• = acyl group carrier, donates acyl group to other molecules – Acetyl = acetyl CoA – Succinyl = succinyl CoA
• Roles in – Oxida^on of pyruvate in TCA – Synthesis and oxida^on of faey acids
Acetyl Coenzyme A Structure
*
* What is this? Vitamin B5
END