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By the end of this section, you will be able to:
  • Explain how a circular pathway, such as the citric acid cycle, fundamentally differs from a linear pathway, such as glycolysis
  • Describe how pyruvate, the product of glycolysis, is prepared for entry into the citric acid cycle

Introduction to pyruvate oxidation and the tca cycle

A note from the instructor

As with the module on glycolysis, there is a lot of material in this module. I do not expect you to memorize specific names of compounds or enzymes. However, I will give you those names for completeness. For exams I will always provide you with the pathways we discuss in class and in the BioStax Biology text modules. What you need to be able to do is understand what is going on in each reaction. We will go over in lecture, problems that will be similar to those I will ask of you on exams. Do not be overwhelmed with specific enzyme names and specific structures. What you should know are the general types of enzymes used and the types of structures found. For example you do not need to memorize the structures of malate or succinate. You will need to know that both are carboxylic acids if the structure is given to you and should be able to identify the important functional groups. In addition, you will not need to know which reactions specifically generate GTP or NADH, but if given the reactions you should be able to tell if a red/ox reaction is occurring. Finally, you will not be expected to memorize enzyme names, but like in glycolysis you will be expected to know the various types of reactions a type of enzyme can catalyze, for example, a dehydrogenase catalyzes a red/ox reaction. That is the level of understanding I expect. If you have any questions please ask.

Pyruvate oxidation and the tca cycle

The end-product of glycolysis are 2 pyruvate molecules, 2 ATPs and 2 NADH molecules. The question becomes, what does the cell do with them. ATP can be used for a variety of cellular functions including biosynthesis, transport, replication etc. NADH, is a problem, it needs to be recycled to NAD + . This occurs either through fermentation, in the absence of an electron transport chain, or can be used to generate a proton motive force (PMF) or "energized membrane", which can then lead to either ATP formation or other forms of work (transport of nutrients, cellular locomotion, etc. and will be discussed in later modules). That leaves the cell to deal with pyruvate.

    The fate of cellular pyruvate

  • Pyruvate can be used as a terminal electron acceptor in fermentation reactions, as was discussed in Module 7.2.
  • Pyruvate could be secreted from the cell as a waste product.
  • Pyruvate could be further oxidized to extract even more usable cellular energy, which is what will be discussed below.

The further oxidation of pyruvate

The pruvate formed in glycolysis has a variety of fates depending upon the cell type, physiology and environment the cell is in. In many instances, cells can further oxidize pyruvate, generating additional energy in the form of GTP and reducing power, the formation of NADH (and FADH2) along with the production of a variety of additional precursors, which can be used for biosynthesis as required by the cell. In aerobically respiring eukaryotic cells, the pyruvate molecules produced at the end of glycolysis are transported into mitochondria, which are the sites of cellular respiration and house the oxygen consuming electron transport chain. In respiring bacteria and archaea, the pyruvate is further oxidized in the cytoplasm. All three use similar mechanisms to further oxidize the pyruvate to CO 2 . Regardless of the organism, if pyruvate is to be further oxidized, the reactions are basically universal: first pyruvate will be transformed into an acetyl group that will be picked up and activated by a carrier compound called coenzyme A (CoA) and the resulting acetyl-CoA feeds directly into the Tricarboxylic Acid Cycle also referred to as the TCA cycle    or the Krebs Cycle . This process is detailed below.

Questions & Answers

How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
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
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
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.
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
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
How can I make nanorobot?
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
how can I make nanorobot?
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
in a comparison of the stages of meiosis to the stage of mitosis, which stages are unique to meiosis and which stages have the same event in botg meiosis and mitosis
Leah Reply
what does post-translational control refer to?
Teresa Reply
Bioremediation includes
Rachel Reply

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Source:  OpenStax, Ucd bis2a intro to biology v1.2. OpenStax CNX. Sep 22, 2015 Download for free at https://legacy.cnx.org/content/col11890/1.1
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