Analse the process of celluar respiration with diagram
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Answer:
Cellular respiration is one of the most elegant, majestic, and fascinating metabolic pathways on earth. At the same time, it’s also one of the most complicated. When I learned about it for the first time, I felt like I had tripped and fallen into a can of organic-chemistry-flavored alphabet soup!
During cellular respiration, a glucose molecule is gradually broken down into carbon dioxide and water. Along the way, some ATP is produced directly in the reactions that transform glucose. Much more ATP, however, is produced later in a process called oxidative phosphorylation. Oxidative phosphorylation is powered by the movement of electrons through the electron transport chain, a series of proteins embedded in the inner membrane of the mitochondrion.
These electrons come originally from glucose and are shuttled to the electron transport chain by electron carriers \text{NAD}^+NAD
+
start text, N, A, D, end text, start superscript, plus, end superscript and \text{FAD}FADstart text, F, A, D, end text, which become \text{NADH}NADHstart text, N, A, D, H, end text and \text{FADH}_2FADH
2
start text, F, A, D, H, end text, start subscript, 2, end subscript when they gain electrons. To be clear, this is what's happening in the diagram above when it says ++plus \text {NADH}NADHstart text, N, A, D, H, end text or ++plus \text{FADH}_2FADH
2
start text, F, A, D, H, end text, start subscript, 2, end subscript. The molecule isn't appearing from scratch, it's just being converted to its electron-carrying form:
\text {NAD}^+NAD
+
start text, N, A, D, end text, start superscript, plus, end superscript ++plus 2 e^-2e
−
2, e, start superscript, minus, end superscript ++plus 2 \text H^+2H
+
2, start text, H, end text, start superscript, plus, end superscript \rightarrow→right arrow \text {NADH}NADHstart text, N, A, D, H, end text ++plus \text H^+H
+
start text, H, end text, start superscript, plus, end superscript
\text {FAD}FADstart text, F, A, D, end text ++plus 2e^-2e
−
2, e, start superscript, minus, end superscript ++plus 2 \text H^+2H
+
2, start text, H, end text, start superscript, plus, end superscript \rightarrow→right arrow \text {FADH}_2FADH
2
start text, F, A, D, H, end text, start subscript, 2, end subscript
To see how a glucose molecule is converted into carbon dioxide and how its energy is harvested as ATP and \text{NADH}NADHstart text, N, A, D, H, end text//slash\text{FADH}_2FADH
2
start text, F, A, D, H, end text, start subscript, 2, end subscript in one of your body's cells, let’s walk step by step through the four stages of cellular respiration.
Glycolysis. In glycolysis, glucose—a six-carbon sugar—undergoes a series of chemical transformations. In the end, it gets converted into two molecules of pyruvate, a three-carbon organic molecule. In these reactions, ATP is made, and \text{NAD}^+NAD
+
start text, N, A, D, end text, start superscript, plus, end superscript is converted to \text{NADH}NADHstart text, N, A, D, H, end text.
Pyruvate oxidation. Each pyruvate from glycolysis goes into the mitochondrial matrix—the innermost compartment of mitochondria. There, it’s converted into a two-carbon molecule bound to Coenzyme A, known as acetyl CoA. Carbon dioxide is released and \text{NADH}NADHstart text, N, A, D, H, end text is generated.
Citric acid cycle. The acetyl CoA made in the last step combines with a four-carbon molecule and goes through a cycle of reactions, ultimately regenerating the four-carbon starting molecule. ATP, \text{NADH}NADHstart text, N, A, D, H, end text, and \text{FADH}_2FADH
2
start text, F, A, D, H, end text, start subscript, 2, end subscript are produced, and carbon dioxide is released.
Oxidative phosphorylation. The \text{NADH}NADHstart text, N, A, D, H, end text and \text{FADH}_2FADH
2
start text, F, A, D, H, end text, start subscript, 2, end subscript made in other steps deposit their electrons in the electron transport chain, turning back into their "empty" forms (\text{NAD}^+NAD
+
start text, N, A, D, end text, start superscript, plus, end superscript and \text{FAD}FADstart text, F, A, D, end text). 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.
Glycolysis can take place without oxygen in a process called fermentation. The other three stages of cellular respiration—pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation—require oxygen in order to occur. Only oxidative phosphorylation uses oxygen directly, but the other two stages can't run without oxidative phosphorylation.
