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It is the destiny of wine to be drunk, and it is the destiny of glucose to be oxidized. But it was not oxidized immediately: its drinker kept it in his liver for more than a week, well curled up and tranquil, as a reserve aliment for a sudden effort; an effort that he was forced to make the following Sunday, pursuing a bolting horse.
Primo Levi, The Periodic Table , 1975

If oxygen is available, aerobic cellular respiration will go forward. In eukaryotic cells, the pyruvate molecules produced at the end of glycolysis are transported into mitochondria, which are the sites of aerobic cellular respiration. There, pyruvate (three carbons) will be transformed into an acetyl group (two carbons) that will be attached to a carrier compound called coenzyme A (CoA). The resulting compound is called acetyl-CoA . CoA is made from vitamin B5, pantothenic acid. Acetyl-CoA can be used in a variety of ways by the cell, but its major function is to deliver the two-carbon energy source derived from pyruvate to the next stage of the aerobic cellular respiration pathway.

Oxidation of pyruvate

In order for pyruvate, the product of glycolysis, to enter the next pathway, it must undergo several changes. The conversion is a three-step process ( [link] ).

This illustration shows the three-step conversion of pyruvate into acetyl CoA. In step one, a carboxyl group is removed from pyruvate, releasing carbon dioxide. In step two, a redox reaction forms acetate and NADH. In step three, the acetate is transferred coenzyme A, forming acetyl CoA.
Upon entering the mitochondrial matrix, a multi-enzyme complex converts pyruvate into acetyl-CoA. In the process, carbon dioxide is released and one molecule of NADH is formed.

Step 1. A carboxyl group is removed from pyruvate, releasing a molecule of carbon dioxide into the surrounding medium. The result of this step is a two-carbon hydroxyethyl group bound to the enzyme (pyruvate dehydrogenase). This is the first of the six carbons from the original glucose molecule to be removed. This step proceeds twice for each glucose molecule (remember: there are two pyruvate molecules produced at the end of glycolsis). Thus, two of the six carbons will have been removed at the end of this step in aerobic cellular respiration.

Step 2. The hydroxyethyl group is oxidized to an acetyl group, and the electrons are picked up by NAD + , forming NADH. The high-energy electrons from NADH will be used later to generate ATP.

Step 3. The enzyme-bound acetyl group is transferred to CoA, producing a molecule of acetyl-CoA.

During the oxidation of pyruvate, the incoming pyruvate is converted to acetyl-CoA, NAD + is reduced to NADH and a carbon dioxide is released for each pyruvate entering the stage ( [link] ).

Overview of oxidation of pyruvate
This image is an overview of the oxidation of pyruvate. During this stage, carbon dioxide is release, NAD + is reduced to NADH and acetyl-CoA is formed. (Image by Eva Horne and Robert Bear)

Krebs cycle

In the presence of oxygen, the two carbons in acetyl-CoA are added to to a four-carbon molecule, oxaloacetate, to form citrate (aka citric acid), a six-carbon molecule. This is the starting point of the Krebs Cycle, which will harvest the remainder of the extractable energy from what began as a glucose molecule. This single pathway has several different names: the citric acid cycle (for citric acid, the first compound in the cycle), the tricarboxylic acid (TCA) cycle (since citric acid has 3 carboxyl groups, and is thus a tricarboxylic acids), and the Krebs cycle , after Hans Krebs, who first identified the steps in the pathway in the 1930s in pigeon flight muscles. This work earned Krebs a share (with Fritz Lippman) of the 1953 Nobel Prize in Physiology and Medicine.

Questions & Answers

what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
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Source:  OpenStax, Principles of biology. OpenStax CNX. Aug 09, 2016 Download for free at http://legacy.cnx.org/content/col11569/1.25
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