1. The preparatory phase yields 2 molecules of glyceraldehyde 3 phosphate

2. Step 6 of glycolysis involves oxidation-reduction
The aldehyde group of G3P is dehydrogenated, not to a free carboxyl group but to a carboxylic acid anhydride with phosphoric acid

3. Glyceraldehyde 3 Phosphate dehydrogenase reaction mechanism
This reaction is a source of NADH and protons for the cell

4. Iodoacetate is a potent (suicide) inhibitor of G3P dehydrogenase

5. Reaction 7, getting some ATP from glycolysis

6. Another example of energy coupling in metabolic pathways
Note the standard free energy change in reaction 6 was positive.
DG = DG’o + RT ln [products]/[reactants]
By reducing the [1,3 bisphosphoglycerate] through reaction 7, reaction 6 becomes favorable

7. Substrate-level phosphorylation
Formation of ATP by phosphoryl group transfer from a substrate is referred to as substrate-level phosphorylation
This term distinguishes this process from respiration-linked phosphorylation (ATP synthase-mediated)

8. Step 8 is about phosphate group movement
Mutases are a subclass of isomerases that transfer a group from one position to another on the same molecule

9. Phosphoglycerate mutase works through a phosphorylated intermediate

10. Step 9: Formation of PEP
Condensation catalyzed by enolase

11. Step 10: Getting more ATP from glycolysis

12. Pyruvate switches from enol to keto form

13. Glycolysis accounting
Glucose + 2NAD+ + 2ADP + 2 Pi  2 pyruvate + 2 NADH + 2 ATP + 2 H2O
Chemical transformations that occur during glycolysis include 1) degradation of glucose to pyruvate; 2) phosphorylation of ADP to ATP and 3) transfer of hydride ion with its electrons to NAD to form NADH

14. Fate of pyruvate
In animal cells, pyruvate can go to mitochondria and be metabolized by the TCA, citric acid, or Kreb’s cycle (same cycle)
However, when oxygen is limiting, cells ferment pyruvate to lactic acid or ethanol
Fermentation allows the oxidation of NADH to NAD+ (Protons are conserved among metabolites during fermentation)
Pyruvate acts or supplies a terminal electron acceptor for fermentative processes
In addition to ethanol and lactate, some microbes make useful solvents or products through fermentation.

15. Lactic acid production
The resulting
NAD+ can then
be used for
glycolysis
Also used in
yogurt production

16. Other cells (i.e. yeast) ferment pyruvate to ethanol
Note, in all fermentations
The C:H ratio of reactants
And products remain the same.
Glucose H:C = 12/6 = 2
2 ethanol and 2 CO2
H:C = 12/6 = 2

17. Pyruvate decarboxylase has a vitamin-like cofactor, TPP
Thiamine pyrophosphate (TPP) is a derivative of vitamin B1
TPP plays an important role in the cleavage of bonds adjacent to a carbonyl gorup

20. Cells tightly regulate levels of ATP
This regulation is achieved by the regulation of key enzymes in catabolism.
For glycolysis, these include
Glycogen phosphorylase
Hexokinase
Phosphofructokinase
Pyruvate kinase

21. Regulating glycogen?
Glycogen, and other saccharides feed glycolysis

22. Other monosaccharides enter glycolysis through phosphorylation
Fructose can be phosphorylated either at C1 or C6 depending on tissue (Fructose-1-phosphate is cleaved by an aldolase enzyme to produce DHAP and glyceraldehyde,both of which are converted to glyceraldehyde-3-phosphate
Mannose is phosphorylated at C6 carbon by hexokinase, then phosphomannose isomerase makes fructose-6-phosphate from mannose-6-phosphate

23. Galactose entry into glycolysis is seemingly more complex
Galactose is first phosphorylated at the C1 position by galactokinase
Galactose-1-phosphate is then converted to it’s epimer glucose-1-phosphate through a set of reactions utilizing uridine diphosphate, which acts as a coenzyme

25. Back to: Glycogen and Starch are degraded by phosphorolysis
Glycogen phosphorylase attacks the non-reducing end of glycogen, breaking the a1-4 glycosidic bond using inorganic phosphate to generate a glucose-1-phosphate.
You have seen before that glycogen phosphorylase is regulated by post-translational modification – phosphorylation, but more complex

26. Glycogen breakdown

27. Connecting glycogen to glycolysis
In addition to glycogen phosphorylase, a debranching enzyme is necessary for glycogen breakdown (cleaves a1-6 bonds)
Glucose-1-phosphate enters glycolysis through a phosphoglucomutase-mediated reaction which isomerizes this molecule to Glucose-6-phosphate.

28. More regulation of glycogen phosphorylase
In addition to covalent modification, there are two allosteric control mechanisms that regulate this enzyme.
Calcium binds and activates transformation of the inactive form of this enzyme (phosphorylase b) to active (phosphorylase a)
AMP (adenosine mononucleotide) activates phosphorylase (High ATP levels outcompete AMP for this binding site; competitive inhibition)

29. Hormonal regulation
The hormone glucagon also regulates glycogen phosphorylase activity
When blood glucose level is too low, glucagon activates phosphorylase b kinase which converts inactive phosphorylase b to its active a form
When blood glucose levels get high enough, glucose binds to phosphorylase a, leading to dephosphorylation via a phosphatase