Glycolysis

Is glycolysis an anabolic or a catabolic pathway?

Catabolic pathway (it breaks down 1 molecule of glucose into 2 molecules of pyruvate to harvest energy).

Does ATP have a role in energy storage? Answer yes or no.

NO (ATP is used for immediate energy transfer; long-term energy is stored as glycogen or fats).

Why is it necessary to maintain a steady-state concentration of the majority of substrates in the glycolytic pathway, even when the pathway is turned off?

To allow quick flux through the pathway when energy is needed and to allow shared intermediates to be rapidly utilized in alternative pathways like gluconeogenesis.

Name all enzymes present in the glycolysis pathway that are classified as isomerases.

Glucose-6-phosphate isomerase (Phosphoglucose Isomerase), Triose phosphate isomerase, Phosphoglycerate mutase.

Name all enzymes that catalyze regulated steps of glycolysis.

Hexokinase (Step 1), Phosphofructokinase-1 / PFK-1 (Step 3), Pyruvate kinase (Step 10).

What is the purpose of phosphorylating glucose in the first step of glycolysis?

It adds a negative charge to glucose so it cannot pass back out of the cell through GLUT transporters (trapping it inside the cytosol).

Name all substrates and co-substrates that bind at the active site of Phosphoglycerate Kinase (Step 7).

1,3-Bisphosphoglycerate, ADP, and Mg2+ (or MgADP).

Name all substrates and co-substrates that bind at the active site of Hexokinase (Step 1).

Glucose, ATP, and Mg2+ (or MgATP).

Name all substrates and co-substrates that bind at the active site of Glyceraldehyde 3-Phosphate Dehydrogenase (Step 6).

Glyceraldehyde 3-phosphate (G3P), NAD+, and Inorganic Phosphate (Pi).

What is the purpose of converting pyruvate to L-lactate under anaerobic conditions?

To regenerate NAD+ from NADH so that glycolysis can continue producing ATP in the absence of oxygen.

If a high concentration of fructose 2,6-bisphosphate is added to a reaction mixture containing PFK-1 and all its substrates, will the reaction rate increase or decrease?

Increase (Fructose 2,6-bisphosphate is a potent allosteric activator of PFK-1).

If physiological concentrations of ATP are high (e.g., 5 mM) with no AMP present, will PFK-1 activity increase or decrease?

Decrease (High ATP acts as an allosteric inhibitor by binding to PFK-1's regulatory/inhibition site).

How does AMP override ATP inhibition on Phosphofructokinase-1 (PFK-1)?

AMP binds to the allosteric activation site, stabilizing PFK-1 in the active R-state and preventing ATP from binding to the low-affinity inhibition site (T-state).

Name all allosteric effectors (activators and inhibitors) of Phosphofructokinase-1 (PFK-1).

Activators: AMP, Fructose 2,6-bisphosphate. Inhibitors: ATP, Citrate.

What enzyme catalyzes the feedforward activation of Pyruvate Kinase (Step 10)?

Fructose 1,6-bisphosphate (product of Step 3) activates Pyruvate Kinase.

Which step of glycolysis is considered the primary COMMITTED STEP, and why?

Step 3 (catalyzed by PFK-1), because once Fructose 1,6-bisphosphate is formed, it has no other metabolic fate and must proceed through glycolysis.

What is the net gain of ATP and NADH produced per 1 molecule of glucose during glycolysis?

Net gain of 2 ATP and 2 NADH per glucose (2 ATP invested in Venture phase, 4 ATP generated in Pay-off phase).

Under aerobic conditions, what are the four possible metabolic fates of pyruvate?

1. Conversion to Acetyl-CoA (for TCA cycle) 2. Conversion to Oxaloacetate (for gluconeogenesis) 3. Conversion to Lactate (anaerobic) 4. Conversion to Ethanol (yeast fermentation).

How does fructose enter glycolysis in skeletal muscle versus in the liver?

In muscle: Hexokinase phosphorylates fructose to Fructose 6-phosphate. In liver: Fructokinase phosphorylates it to Fructose 1-phosphate, bypassing PFK-1 regulation.

Why can high dietary intake of fructose lead to increased liver fat production compared to glucose intake?

Fructose metabolism in the liver bypasses the two major regulatory steps (Hexokinase and PFK-1), leading to unregulated pyruvate production and conversion into fats.

How does galactose enter the glycolytic pathway?

Galactose undergoes 5 reactions (via Galactokinase, UDP-glucose, etc.) to be converted into Glucose 6-phosphate before entering Step 2 of glycolysis.

What enzyme present in red blood cells converts 1,3-BPG into 2,3-BPG, and what is the function of 2,3-BPG?

Bisphosphoglycerate mutase (BPGM); 2,3-BPG binds hemoglobin, converting it from the R-state to the T-state to promote oxygen release to tissues.

Which coenzyme acts as the primary electron carrier/oxidizing agent in Step 6 of glycolysis, and at which specific carbon does it accept a hydride ion?

NAD+ (Nicotinamide adenine dinucleotide); accepts a hydride ion (H-) at position C4 of the nicotinamide ring.

What specific amino acid residues act as a nucleophile and a base in the active site mechanism of Glyceraldehyde 3-Phosphate Dehydrogenase (GAPDH)?

Cys149 acts as the nucleophile (forming a thiohemiacetal intermediate) and Glu acts as a base.

Which step of glycolysis generates a high-energy enol ester with a hydrolysis free energy change (ΔG°') of approximately -62 kJ/mol?

Step 9: Dehydration of 2-Phosphoglycerate to Phosphoenolpyruvate (PEP), catalyzed by Enolase.