Understanding Glycolysis - AP Biology

Glycolysis happens in the cytosol (the fluid containing the organelles) of the cell. The next step in cellular respiration, the citric acid cycle, occurs in the mitochondria.

NAD+ is required as an oxidizing agent (accepting electrons from other molecules) during glycolysis. As it accepts electrons, it becomes NADH, a byproduct of glycolysis. NADH can be reverted back to NAD+ to continue glycolysis through the process of fermentation, but is usually used to donate the added electron to the electron transport chain later in the cell metabolism process. The electron is used to power the protein pumps that create the proton gradient that powers ATP synthase.

Glycolysis is the first step of cellular respiration and, in the process of splitting glucose into two pyruvate molecules, does not require oxygen.

Pyruvate decarboxylation, the citric acid cycle, and oxidative phosphorylation are all steps in aerobic respiration, and thus require the presence of oxygen.

Fermentation oxidizes molecules of NADH to NAD+ so the cell can have oxidizing agents for any subsequent glycolysis reactions. It does not, however, produce any usable energy in the process.

Fermentation leads to the production of ethanol in yeast cells and lactic acid in muscle cells.

Glycolysis occurs in the cytosol of cells. Once finished, the two pyruvate products are transported into the mitochondria to go through the citric acid cycle, at a cost of 1 ATP per pyruvate. Neither the nucleus, nor the endoplasmic reticulum have any function in glycolysis or the citric acid cycle.

The conversion of glucose to two pyruvate molecules in glycolysis produces a net total of two direct ATP. When fructose-1,6-bisphosphate enters glycolysis, it bypasses the two steps involved that normally cost one ATP each, therefore, there is no required input and the net total is four produced ATP.

We have to remember that each step beyond the conversion of fructose-1,6-bisphosphate to glyceraldehyde-3-phosphate and dihydroxyacetone phosphate happens twice, or we would come up with two ATP created.

Glycolysis is the first step in cellular respiration, and is seen in both aerobic and anaerobic respiration. The products of glycolysis are pyruvate, NADH, ATP, and water. Oxygen is only a product of the light reactions of photosynthesis; it is consumed as a reactant in the electron transport chain.

This question requires you to determine where aerobic and anaerobic respiration diverge in terms of a biochemical pathway. Both start with glucose, which undergoes glycolysis in both pathways. The completion of glycolysis results in two molecules of pyruvate, regardless of the availability of oxygen. Once pyruvate is created, it can do one of two things:

1. It can be converted to acetyl-CoA and enter the citric acid cycle (aerobic respiration).

2. It can be reduced to ethanol or lactic acid (anaerobic).

As a result, pyruvate's ultimate path is what determines whether the cell will be using aerobic or anaerobic respiration.

Glycolysis, which occurs in the cytoplasm, is the first step of cellular respiration. Though it does not produce a large amount of ATP by itself, it incorporates several important steps that must take place to yield a much more significant amount of ATP later. Notable events that occur during this multi-step process include the breakdown of each glucose molecule into two 3-carbon pyruvate molecules, the production of two molecules of , and the net production of two ATP molecules.

Unlike the next two steps (the citric acid cycle and oxidative phosphorylation), glycolysis can occur in the absence of oxygen. The only step given that is not part of glycolysis is the transfer of electrons from carrier molecules to oxygen via a series of steps. This happens during oxidative phosphorylation and, unlike glycolysis, is an aerobic process.

Fermentation is the metabolic process that takes place in anaerobic environments to regenerate for glycolysis, which takes place in both aerobic and anaerobic environments. Since glycolysis is unaffected by the presence of oxygen, pyruvate concentrations will be the same in either environment. During fermentation the cell changes the pyruvate into acetaldehyde. Ethanol is also a product of fermentation. We would not expect to see more acetaldehyde or ethanol in aerobic metabolism.

Adenosine triphosphate (ATP) is the main product of cellular respiration, and the molecular energy of the cell. Aerobic metabolism results in a much higher yield of these energy carrying molecules due to the fact that it can use oxygen as a final electron acceptor in the electron transport chain.

Glycolysis takes place in the cell cytosol, and can take place under anaerobic conditions. After the completion of glycolysis, the product pyruvate is transported to the mitochondria for the citric acid cycle and electron transport chain.

The nucleus houses the cell's DNA, and the endoplasmic reticulum is involved with protein modification.

Glycolysis is the process that converts glucose to pyruvate. It produces a total of four ATP, but consumes two ATP, for a net yield of two ATP. Glycolysis is not dependent on the presence of oxygen and can occur in either aerobic or anaerobic environments.

The citric acid cycle, or Krebs cycle, is used to generate NADH from pyruvate. The NADH is then used in the electron transport chain to generate a proton gradient, which fuels oxidative phosphorylation. Since oxidative phosphorylation requires an oxygen molecule, the citric acid cycle and electron transport chain cannot continue in anaerobic environments.

Glycolysis produces four molecules of ATP, but two molecules are used to complete reactions during the initial steps of the process. With four molecules produced and two molecules consumed in the process, there is a net yield of two ATP from each glucose molecule in glycolysis

During ATP synthesis in the electron transport chain, approximately 32 additional ATP are generated.

Fructose-2,6-bisphosphatase is an enzyme that is responsible for regulating glycolysis and gluconeogenesis. When serine-32 is phosphorylated on fructose-2,6-bisphosphatase, glycolysis is stimulated and gluconeogenesis is inhibited.

Glycolysis produces two molecules of pyruvate and two molecules of NADH. The cell technically produces four molecules of ATP during glycolysis; however, it uses two molecules to initiate the process. The net production of ATP is only two. FADH2 is produced in the Krebs cycle.

Remember that glycolysis produces a net product of two ATP, two NADH, and two pyruvate molecules. NADH is produced by reducing NAD+, and ATP is produced by substrate level phosphorylation of ADP. Pyruvate is a three-carbon molecule that is derived from the six-carbon glucose. The six-carbon glucose is broken down to create two pyruvate molecules (3 carbons each).

During the Krebs cycle pyruvate is further broken down, and some carbons are used to form carbon dioxide.

Aerobic processes require oxygen, while anaerobic processes can continue in the absence of oxygen. Glycolysis can function under aerobic or anaerobic conditions to produce small amounts of ATP. The Krebs cycle and electron transport chain, however, require oxygen as the final electron acceptor in the electron transport chain. These processes cannot continue in anaerobic environments.

Fermentation is used to generate NAD+ from NADH. In glycolysis, NAD+ is a reactant and NADH is a product. During anaerobic respiration NAD+ becomes the limiting reagent of glycolysis. Fermentation regenerates this reactant to allow glycolysis to continue producing small amounts of ATP in the absence of oxygen.

Pyruvate is an end product of fermentation; however, unlike the pyruvate from glycolysis the pyruvate from fermentation does not go into the Krebs cycle. The pyruvate is either converted into lactic acid or ethanol. Yeast undergoes fermentation, but they produce ethanol from pyruvate, not lactic acid. Finally, fermentation and glycolysis occur in the cytosol of cells, not in the cell membrane.

The only answer choice you are left with is that fermentation converts NADH back into NAD+. During anaerobic respiration, glycolysis is used to produce small amounts of ATP. NAD+ is used as a reactant in this process, and NADH is a product. Over time, NAD+ becomes the limiting reagent if it is not regenerated by the electron transport chain. The primary function of fermentation is to restore this reactant and allow glycolysis to proceed.

Glycolysis produces a total of four ATP molecules. The initial steps of glycolysis, however, include an energy investment phase in which two ATP are utilized. Since two ATP are used and four are produced, the net ATP yield for glycolysis is two ATP.

In order for glycolysis to occur, two molecules of ATP are required to initiate the process. The reaction as a whole produces four ATP, making the net production of glycolysis two ATP. Though glycolysis is somewhat self-sustaining, since it generates ATP, it still requires an initial energy input.

Though ATP is required for glycolysis, oxygen is not. Glycolysis, unlike the electron transport chain and Krebs cycle, can proceed under anaerobic conditions.