Glycolysis/Gluconeogensis

Which steps of glycolysis are irreversible?

Steps 1, 3, and 10

Which steps of glycolysis are substrate level phosphorylation?

Step 7 (1,3-bisphosphoglycerate ⇌ phosphoglycerate kinase - enzyme ⇌ 3-phosphoglycerate), and step 10 (Phosphoenolpyruvate ⇌ pyruvate kinase - enzyme ⇌ pyruvate)

What is glycogen?

The storage form of glucose in a glycogen polymer

Which steps comprise the energy investment phase in glycolysis?

Steps 1-5

Which steps comprise the energy payoff phase in glycolysis?

Steps 6-10

What is the net result of glycolysis?

2 pyruvate, 2 NADH (can be used in ETC to generate more ATP), and 2 ATP (2 input and 4 output)

What step is the committed step of glycolysis?

Step 3 (fructose 6-phosphate ⇌ phosphofructokinase-1 ⇌ fructose 1,6-bisphosphate)

What step of glycolysis is considered disfavorable or endergonic?

Step 5 (DHAP + GAP ⇌ Triose Phosphate Isomerase ⇌ GAP), the reaction proceeds forward because GAP is quickly consumed in the next step

What is the only redox reaction in glycolysis?

Step 6 (GAP + NAD⁺ + P_i ⇌ GAP Dehydrogenase ⇌ 1,3-BPG + NADH + H⁺) NAD⁺ gets reduced to NADH (will be used in ETC to generate more ATP later on), also a phosphorylation step

How is the process of glycolysis generally made to be favorable?

By taking place in the body (a fixed space), the cellular concentrations of metabolites can be controlled in a way to ensure that all reactions are spontaneous under physiological conditions (wouldn’t normally be favorable), high concentrations of substrates will push reaction forward towards products even if reaction is normally is disfavorable (Le Chatelier)

What two molecules can the gluconeogensis pathway use to reform glucose?

Pyruvate (initially generated from glycolysis) or oxaloacetate (initially generated from the TCA cycle)

Where can gluconeogensis be performed?

It can only be performed in the liver and somewhat in the kidney’s, other cells lack the necessary enzymes to perform the pathway

How many ATP does gluconeogensis consume?

6 ATP

Where in the cell does gluconeogensis occur?

It occurs in the cytosol

What happens if glycolysis and gluconeogensis are turned on at the same time in the same cell?

Glycolysis generates 2 ATP but gluconeogensis uses 6 ATP, so there would be a net LOSS of 4 ATP, explains why it is important that a cell only be performing one of the pathways at a time (redundant)

At what step is glucogenogensis regulated and what is it regulated by?

It is regulated at the fructose bisphosphatase step (F1,6-BP ⇌ FBPase ⇌ F6-P), fructose 2,6-bisphosphate is responsible for regulating both glycolysis and gluconeogenesis and serves as a switch to ensure that both pathways are not occuring at the same time. When F2,6-BP is high, PFK-1 is turned on/activated and FBPase is turned off/inhibited (↑ F2,6-BP = ↑ PFK-1 = ↓ FBPase)

How is glucose 1-phosphate made?

Glucose 6-phosphate is converted to glucose 1-phosphate by phosphoglucomutase (G6-P ⇌ Phosphoglucomutase ⇌ G1-P)

How is UDP-glucose made?

G1-P reacts with UTP to yield UDP-glucose, the reaction is driven by the hydrolysis of pyrophosphate (a by-product of the G1-P + UTP reaction, breaks two inorganic phosphates bound together into two free inorganic phosphates, very exergonic)

How is glycogen made?

UDP-glucose is combined with the extending glycogen molecule, resulting in the extension of the glycogen chain and release of the UDP molecule

How is glycogen broken down (glycogenolysis)?

It occurs via different reactions, linear chains are broken down via phosphorolysis and branched chains are broken down by hydrolysis

How is the UTP consumed when generating glycogen compensated for when breaking glycogen down?

Through the breakdown of glycogen, G6-P is generated and able to feed into the glycolysis pathway at step 2, resulting in one less ATP being consumed and there by compensating for the UTP consumed when the glycogen was generated