Glycolysis Pt 2 (last little bit) and Fermentation

Committed step:

a step in a pathway commits the metabolite to that pathway.

Is 1 the committed step?

NO! Usually the first irreversible is the committed step in a pathway, but Glucose-6-phosphate is used in other pathways.

what is the committed step in glycolysis?

The conversion from Fructose-6-phosphate to Fructose 1,6 bisphosphate

• This is highly regulated.

• phosphofructokinase-1 is the enzyme that is used to do this!

You do not regulate things at

equilibrium, you regulate things that are out of equlibirum so you can start or stop something! If you are regulating stuff at equilibrium, nothing will happen since already balanced!

To generate energy out of pyrvuvate you need what?

oxygen!

What is the overall reaction of glycolysis?

Glucose + 2NAD+ + 2ADP + 2 Pi → 2 Pyruvate + 2NADH + 2ATP

What happens to pyruvate after glycolysis for aerobic organisms?

• This is what happens in humans

• Break down pyruvate to H2O and Co2 (TCA cycle)

• Use electrons in NADH to make more ATP (oxidative phosphorylation) which requires O2 to extract energy from NADH

What happens to pyruvate after glycolysis for anaerobic organisms?

don’t do the TCA cycle: Can’t get energy from the NADH generated

• They don’t break down pyruvate

• Need to regenerate NAD+ for the next round of glycolysis pathway!

• They lack O2 to be a terminal electron acceptor!

• They do glycolysis over and over!

T/F: pyruvate can be involved in starting gluconeogenesis?

TRUE!

• When you are fasting, you need a way to make glucose to supply to the brain and other cells!

Pyruvate can be made into what amino acid?

Alanine

If you have oxygen, you can convert it to

acetyl coA and feed this into the TCA cycle!

If you are anaerobic, how do you rengenerate NAD+ ?

You do fermentation and produce ethanol or lactate!

T/F: pyruvate has a lot of energy in it?

TRUE!

T/F: the anerobic organisms are wasting energy?

Yes, because they cannot use NADH to make ATP, they must turn it back to NAD+. You need to reduce pyruvate to lactate for example to get NAD+!

Pyruvate vs lactate what is oxidized and what is reduced?

• Pyruvate has 2 electrons and lactate has 4 electrons. Lactate is the more reduced molecule!

• Those two extra electrons came from the NADH to transform it back to NAD+!

What is the process of ethanol production?

• You start with the decarboxylation of pyruvate into acetaldehyde and then this gets reduced to form ethanol! NAD+ is oxidized now and ethanol recieved those electrons!

Why is ethanol fermentation necessary:

Because of the step in glycolysis where you go from D-Glyceraldehyde-3 phosphate to 1,3 bisphosphoglycerate via oxidation and added a phosphate and you create NADH (reduced) from this reaction!

• In the alcohol form, you decarboxylate pyruvate, and then use the NADH to reduce aldehyde to ethanol!

What is the main gist of lactate fermentation:

Use the pyruvate directly and reduce it to lactate! We do this when we use muscles in anaerobic situations! We do not have the oxygen!

• Turtles when they hybernate, they can convert pyruvate to lactate and do glycolysis this way! Build up lactate in the shell!

Cori cycle:

• When the muscles are using a lot of energy in an anaerobic setting, you build up lactate!

• The lactate can get transported through the blood to the liver and the liver can regnerate the NADH and use a lot of energy to make glucose —> gluconeogenesis, and this can be fed to the muscles so they can use the glucose again!

T/F: preferentially we use glucose has a sugar source.

true! However, we can use lactose, maltose, sucrose, mannose, and fructose as glucose sources.

T/F: fructose can get fed in directly?

true!!! It just needs to be phosphorylated to become part of the glycolysis pathway!