GLYCOLYSIS AND ALTERNATIVES

BIOT 309Fall 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 formation

• Directly • Indirectly – G3P enters EMP < - -

*

*

*

< - - -

Entner Duodoroff Pathway

What do abbreviations

stand for?MAKE a list!!!

SIDE-BY-SIDE COMPARISON

From G6Pto

KDG/KDPA split into

G3P + pyruvate enzymes different

THIRD GLYCOLYSIS PATHWAY

Pentose Phosphate Pathway (PPP) = Hexose Monophosphate Pathway (HMP) =

Phosphogluconate Pathway

Sometimes called a shunt.

• Operates at same time as EMP

It’s a shunt

PPP is a shunt

• The pathway begins with the glycolytic 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 glycolytic pathway.

• It is for this reason that the PPP is often 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

aromatic amino acids• Other intermediates used in other pathways• Provides NADPH – major source of energy for anabolic

reactions, e.g., nucleic acids, lipids

• Used exclusively by Thiobacillus novellus and Brucella abortus

PATHWAY INTERMEDIATE USES

irreversible

irreversible

1st ReactionHigh [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

Regulation

• G-6-P is partitioned between EMP and PPP• Depends on

– NADP+ and NADPH concentrations• 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 EMP1 Glucose 2 pyruvate + 1 ATP + 1 NADH

+ 1 NADPHBacteria: 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 aromatic amino acids • reducing power = NADPH

Overall Oxidative Reaction: 1 Glucose 6 – P + 2 NADP+ + 1 H2O 1 Ribose 5-P + 1 CO2+ 2 NADPH + 2 H+

Non-Oxidative Reactions • change number of carbons in sugar molecules• make intermediates used in other biosynthetic pathways including feeding

back into PPP and EMP

Used exclusively by Thiobacillus novellus and Brucella abortus

Additional 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– Oxidation of pyruvate in TCA– Synthesis and oxidation of fatty acids

Acetyl Coenzyme A Structure

*

* What is this? Vitamin B5

END