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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 environment affect demand and supply of commodity ?
Amos Reply
Wht at the criteria for market ?
what is difference between monitory policy and fiscal policy?
Malik Reply
monetary policy is a policy thrust by National Govt(CBN) to influence government spending, purchase &taxes
necessity of economics
Pamela Reply
I will say want,choice,opportunity cost,scarcity,scale of preference
what is monopoly market.How price output are determined under monopoly market
b) Monopoly market is an impecfect market where s single firm having the innovation to produce a particular commodity.Prices are determined through output since there are no other competitive.
Monopoly market:firm has market power & does not respond to market price
Explain the process of price determination under perfect competition market with suitable diagram
bisham Reply
Price determination under perfect competition via this process :firms have no market power to influence price rather firms respond to market price.
price is different from demand- demand is amount of commodity
Effah Reply
demand is amount /quantity of commodity a potential buyer is willing to buy at a given price at market
demand is a desire of customer on commodity with the ability to pay it and willing to buy it at given price of commodity
demand is price of what
Faith Reply
show that shortrun average cost
Baby Reply
what is economics
Mbah Reply
what is money
what is money
Difine macro economics
money is a medium of exchange between goods and services,maybe inform of currency.
Economics is study of how human beings strive to satisfy numerous wants using limited available resources.
how do you find the maximum number of workers the firms should employ order to produce where there are increasing returns
what are implications of computing national income?.
what is the formulae for calculating national income
it calculated by value added method
classify the production units like agriculture, banking, transport etc
money is anything that is generally acceptetable for human
Estimate the net value added(NVA) at fixed cost by each industrial structure
definition of unemployment
Adam Reply
what are the causes of unemployment?
Mbubi Reply
The main causes of unemployment are listed below. 1. Frictional unemployment 2. Cyclical unemployment 3. Structural unemployment
We can also categorize the causes on a broader sense as: 1. Political and 2. Social cause As unemployeement root causes are embaded in this two.
would opportunity cost exist if there was no scarcity?
yes just because the opportunity cost arose when there is Alternative to choose among the alternatives.
I am thinking that, if our resources were unlimited, then there wouldn't be any need to forgo some wants. Hence the inexistence if opportunity cost
politics has done what?
consider time assani
I'm Emmanuel,...I taught the main cause is the change in gov't.
...Lack of capital to set up a firm respectively
I would like to bring in Educational levels can also be the cause the cause of the problem respectively
lack of skills among the new generation is the serious issue.
Where I come from , I don't see why education or personal aspects seem to do with unimployment, technically the motivation and eigerness in all works of live is there , dispite the cultural influence and physical bearriors;the thing we lacking is Government Support and open market ethics.
sorry about that-(repation). We have a over powering ethical political system that's displacing the marketing asspects of economy and causing large scale unemployment right across the board...
can someone Explain Expansionary Monetary Policy and Contractionary Monetary Policy Using one of the instrument of Monetary Policy? Please am kinda lost here?. ta
Emmanuel Reply
using a graph show the case of substitute and compliment goods
Ade Reply
can anyone give me a simple explanation to Five Sector Macroeconomics?
Can someone please define what economics is
jason Reply
economics simply is a social science subject that study human behavior.
economics is a social science which studies human behaviour as a relationship between ends and scarce means that has alternative uses
Can someone please tell me how to calculate GDP
emmanual kapal to calculate GDP (Gross Domestic Product) has three method in calculating it (1)income approach (2) expenditure approach (3) value added method
thanks Alae
u are welcome
in basic terms economics is revered to as battery system, it date back to when Men sees the need to exchange sapless goods and produce to gain , either wealth , basic necessities or to establish trading ties for personal benefit or social asspects in terms of coexistence and continuity, future .
what is the law of demand
Berlinda Reply
keep other thing constant, when the price increases demand decrease when the price decreases demand increases of the commodity.
all things being equal,quantity demanded decrease as price increase and increase as price decrease
there's practial joke to it ..." the higher the demand ; scarcity, increase in production and drop in quality"... quite the controversy - for example China vs Europe, United States and we are all boxed up in between somewhere...
Other thing remain constant the low price of commodity the high quantity of commodity and vice versa is true
Explain Effective demand
Anita Reply
What is effective demand
like Modi is in demand...best example of effective demand
Don't get you
Anita you mean you don't get me or who?
level of demand that represents a real intention to purchase by people with the means to pay
Difference between extinct and extici spicies
Amanpreet Reply
While the American heart association suggests that meditation might be used in conjunction with more traditional treatments as a way to manage hypertension
Beverly Reply
Researchers demonstrated that the hippocampus functions in memory processing by creating lesions in the hippocampi of rats, which resulted in ________.
Mapo Reply
The formulation of new memories is sometimes called ________, and the process of bringing up old memories is called ________.
Mapo 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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