Question

In cellular respiration, the energy begins in glucose. Glucose is then converted to other molecules and its energy is stored in other molecules. For each of the 4 steps of cellular respiration, list which molecule contains most of glucose’s energy at the end of that step.

Answer 1

Energy come originally from glucose and see shuttle to the electron transport chain by electron carriers NAD+ and FAD which become NADH and FADH2 when they gain electrons

NAD+ + 2e- + 2H+ ---> NADH +H+

FAD + 2e- + 2H+ ---> FADH2

Four steps of cellular respiration :

1. Glycolysis : In glycolysis, glucose (6C sugar) undergoes a series of chemical transformations. In the end, it gets converted into two molecules of private, 3C organic molecule. In this reaction ATP is made and NAD+ is converted to NADH.

2. Pyruvate Oxidation : Each Pyruvate from glycolysis goes into the mitochondrial matrix the increment compartment of mitochondria. There it's converted into two carbon molecules bound to coenzyme A, known as acetyl CoA. CO2 is related and NADH is generated.

3. Citric acid cycle : The acetyl CoA made in last step combines with a 4C molecules and goes through a cycle of reactions, ultimately regenerating the 4C starting molecule ATP, NADH, FADH2 are produced and CO2 is released.

4. Oxidative Phosphorylation : The NADH and FADH2 made in others steps deposit their electrons in the electron transport chain, turning back into their "empty" forms (NAD+ and FAD). As electrons move down the chain, energy is released and used to pump protons out of the matrix, forming a gradient. Protons flow back into the matrix through an enzyme called ATP Synthase, making ATP. At the end of the electron transport chain, oxygen accepts electrons and takes up protons to form water.

Steps	ATP	NADH	FADH2	TOTAL ATP
Glycolysis	2	2	-	8
Pyruvate Oxidation	-	2	-	6
Citric acid cycle	2	6	2	24
TOTAL ATP	4	30 ATP	4 ATP	38

1 NADH = 3 ATP; 1FADH2 = 2 ATP.