The document discusses several key aspects of carbohydrate metabolism that must be considered when studying carbohydrates: 1. Central pathways like glycolysis, the Entner-Doudoroff pathway, and the pentose phosphate cycle. 2. Mechanisms of ATP production like substrate-level phosphorylation and oxidative phosphorylation. 3. Metabolic steps involving reduction or oxidation. 4. The role of oxygen in aerobic vs. anaerobic metabolism. 5. Metabolic intermediates used for biosynthesis.

1. Vías centrales del metabolismo
de los carbohidratos

2. El estudio de los carbohidratos debe
considerar
1. Central pathways of carbohydrate metabolism
2. Conversion of compounds to intermediates usable in central pathways
3. Mechanisms of energy (ATP) production
a) Substrate-level phosphorylation
b) Oxidative phosphorylation
c) Other mechanisms of energy transfer

3. El estudio de los carbohidratos debe
considerar
4. Metabolic steps involved in the generation and use of reducing activity
a) Reduction of pyruvate or other substrates to fermentation end products
b) Biosynthetic reactions requiring reducing action

4. El estudio de los carbohidratos debe
considerar
5. Oxygen involvement in energy-generating reactions
a) Aerobic metabolism
b) Anaerobic metabolism
c) Facultative metabolism
6. Metabolic intermediates serving as biosynthetic precursors

5. El estudio de los carbohidratos debe
considerar
8. Reactions that replenish biosynthetic intermediates (anapleurotic
reactions)
9. Metabolic and genetic regulatory system

6. Los carbohidratos no son los únicos compuestos
utilizados como fuente de energía por los
microorganismos
 Fatty acids, lipids, amino acids, purines, pyrimidines, and a wide variety of
other compounds can also serve as carbon and energy sources.

7. Los carbohidratos no son los únicos compuestos
utilizados como fuente de energía por los
microorganismos
 Generally, utilization of an alternate substrate involves its conversion to an
intermediate intrinsic to one of the central pathways of carbohydrate
metabolism.

8. Vias principales del metabolismo de
carbohidratos
 Glucolisis o via de Embden-Meyerhof-Parnas, o via de la Fructosa bisfosfato –
aldolasa
 Entner-Doudoroff o Cetogluconato
 Ciclo oxidativo de la Pentosa fosfato
 Gluconeogénesis y síntesis de glicógeno.

9. FRUCTOSE BISPHOSPHATE - ALDOLASE OR
EMBDEN-MEYERHOF-PARNAS
(EMP)PATHWAY OF GLYCOLYSIS.

10. Fructose Bisphosphate Aldolase Pathway

11. Reacciones más importantes de de la ruta
de EMP
1. Phosphorylation of glucose and fructose-6-phosphate by ATP
2. Cleavage of fructose-1,6-bisphosphate to trioses by a specific aldolase
3. Structural rearrangements
4. Oxidation–reduction and Pi (inorganic phosphate) assimilation

12. Fructose Bisphosphate Aldolase Pathway

13. Fructose Bisphosphate Aldolase Pathway

14.  The enzyme fructose bisphosphate (FPB) aldolase is one of the most critical
steps in the pathway. In the absence of this enzyme, glucose or other hexose
sugars must be metabolized via one of several alternative pathways,

15. Regulación metabólica de las enzimas de la
glucólisis y del ciclo de los ácidos tricarboxílicos

16. Alternate Pathways of Glucose Utilization
Warburg and Christian
• described the oxidation of glucose-6-phosphate to
6phosphogluconate (6-P-G) via G-6-P dehydrogenase).
They also described the decarboxylation of 6-P-G to form
a pentose sugar.
Entner-Doudoroff or Ketogluconate Pathway
• differs from the EMP pathway primarily in the form of
the 6-carbon intermediate that undergoes C3-C3 cleavage
(aldol cleavage) to form three-carbon intermediates.

18. Inicio de la vía del 6 fosfo gluconato

21. Phosphoketolase
Pathway

22. Oxidative Pentose
Phosphate Cycle

23. After one turn of the cycle, the net reaction is
Encircled P, phosphate group; G-6-P, glucose-6-phosphate; 6-PG, 6-
phosphogluconate; F-6-P, fructose-6-phosphate; F-1,6-BP, fructose-1,6-
bisphosphate; DOHAP, dihydroxyacetone phosphate; GA-P, glyceraldehyde-3-
phosphate.

24. Tarea
¿Cuál es el destino de los carbonos 3 y 4 marcados con
radiactividad de una glucosa que entra a la vía
1. EMP
2. Entner-Doudoroff
3. Pentosa fosfato
4. Fosfogluconato
5. Ciclo oxidativo de pentosa fosfato ?

25. Diferencias entre la glucólisis y la via de la
pentosa fosfato
 Glycolysis generates NADH, which can be reoxidized by linkage to the
electron transport system, or under anaerobic conditions it can be used to
reduce an oxidized substrate, such as pyruvate, to lactate.

26. Diferencias entre la glucólisis y la via de la
pentosa fosfato
 The pentose phosphate pathway generates NADPH, which is used primarily
for reducing power in biosynthetic reaction (e.g., the conversion of α-
ketoglutarate to glutamate or the incorporation of acetate into fatty acids)
and is not linked to the terminal respiratory system.

27. Operation of the TCA
cycle under
anaerobic
conditions.

28. GLUCONEOGENESIS
 Growth of microorganisms on poor carbon sources,
 (L-malate, succinate, acetate, or glycerol),
 requires the ability to synthesize hexoses for the production of other
compounds
 (cell wall mucopeptides, storage glycogen, and other compounds derived from
hexose, such as pentoses, for nucleic acid biosynthesis).

29. Pyruvate kinase is not reversible
12. Pyruvate kinase (pykA; pykF). Generates ATP from ADP
14. Pyruvate carboxylase. Converts pyruvate to oxaloacetic acid (OAA) via carbon
dioxide (CO2) fixation using ATP.
15. PEP carboxykinase. Forms phosphoenolpyruvate from OAA using GTP..

30. A second irreversible enzyme is
phosphofructokinase
5. Phosphofructokinase (pfkA).
Phosphorylation of F-6-P to FBP using ATP.
16. Fructose-1,6-bisphosphatase. Removes
Pi from F-1,6-bisP to form F-6-P.

31. The third bypass reaction required for gluconeogenesis
involves dephosphorylation
of G-6-P
the formation of glucose from pyruvate
requires a considerable
expenditure of energy

32. Gluconeogenesis Regulation
 A major regulatory step is PEP carboxykinase, encoded by pckA in E. coli.
 By catabolite repression, a process in which gluconeogenesis is inhibited when
glucose or other carbohydrate carbon sources are available.

33. Gluconeogenesis Regulation
 Maximum levels of PEP carboxykinase are induced at
 the onset of the stationary phase of growth,
 to ensure the synthesis of adequate carbohydrate storage reserves or
 to provide metabolites from the upper part of the EMP pathway as the organism
converts proteins to gluconeogenic amino acids.

34. Gluconeogenesis Regulation
 The stationary phase induction of PEP carboxykinase requires
 Cyclic AMP and
 a regulatory signal, (not been fully elucidated)

35. Glycogen Synthesis