These notes will be very helpful for anyone who needs help with Biochemistry note making or studying. They are very precise, but contain all the points you should know about this topic. So, you can use these notes as your class notes, as well as your summaries. Hope you guys will love these !
Hydrolysis :- catalyzed by α-amylase , consume H2O.
[salivary α-amylase hydrolyzes the internal (α1→4) glycosidic linkages of starch, producing short polysaccharide
fragments or oligosaccharides ]
Phosphorolysis :- Catalyzed by phosphorylase and Involve Pi
Fates of Pyruvate under Anaerobic Conditions : Fermentation
Under aerobic conditions, the pyruvate formed in the final step of glycolysis is oxidized to acetate (acetyl-CoA) , which
enters the citric acid cycle and is oxidized to CO2 and H2O .
The NADH formed by dehydrogenation of glyceraldehyde 3-phosphate is ultimately re-oxidized to NAD+ by passage of its
electrons to O2 in mitochondrial respiration.
Under hypoxic ( low-oxygen ) conditions , however—as in very active skeletal muscle, in submerged plant tissues, solid
tumors, or in lactic acid bacteria—NADH generated by glycolysis cannot be re-oxidized by O2 .
Failure to regenerate NAD+ would leave the cell with no electron acceptor for the oxidation of
glyceraldehyde 3-phosphate and the energy-yielding reactions of glycolysis would stop.
NAD+ must therefore be regenerated in some other way.
Most modern organisms have retained the ability to continually regenerate NAD+ during anaerobic glycolysis by
transferring electrons from NADH to form a reduced end product such as lactate or ethanol .
Pyruvate Is the Terminal Electron Acceptor in Lactic Acid Fermentation
When animal tissues cannot be supplied with sufficient oxygen to support aerobic oxidation of the pyruvate and NADH
produced in glycolysis , NAD+ is generated from NADH by the reduction of pyruvate to lactate.
The reduction of pyruvate in this pathway is catalyzed by lactate dehydrogenase .
some tissues and cell types (such as erythrocytes, which have no mitochondria and thus can not oxidize pyruvate to CO2)
produce lactate from glucose even under aerobic condition
In glycolysis, dehydrogenation of the two molecules of glyceraldehyde 3-phosphate derived from each molecule of
glucose converts 2 molecules of NAD+ to 2 of NADH.
Because the reduction of two molecules of pyruvate to two of lactate regenerates two molecules of NAD+ , there is no
net change in NAD+ or NADH .
1
,The lactate formed by active skeletal muscles (or by erythrocytes) can be recycled .
It is carried in the blood to the liver, where it is converted to glucose during the recovery from strenuous muscular
activity.
When lactate is produced in large quantities during vigorous muscle contraction (during a sprint, for example), the
acidification that results from ionization of lactic acid in muscle and blood limits the period of vigorous activity.
The best-conditioned athletes can sprint at top speed for no more than a minute .
Although conversion of glucose to lactate includes two oxidation-reduction steps , there is no net change in the
oxidation state of carbon .
In glucose ( C6H12O6 ) and lactic acid ( C3H6O3 ) , the H:C ratio is the same.
Nevertheless , some of the energy of the glucose molecule has been extracted by its conversion to lactate — enough to
give a net yield of two molecules of ATP for every glucose molecule consumed.
Fermentation is the general term for such processes, which extract energy (as ATP) but do not consume oxygen or
change the concentrations of NAD+ or NADH .
Ethanol Is the Reduced Product in Ethanol Fermentation
Yeast and other microorganisms ferment glucose to ethanol and CO2 , rather than to lactate.
Glucose is converted to pyruvate by glycolysis , and the pyruvate is converted to ethanol and CO2 in a two-step process
In the first step, pyruvate is decarboxylated in an irreversible reaction catalyzed by pyruvate decarboxylase.
This reaction is a simple decarboxylation and does not involve the net oxidation of pyruvate.
Pyruvate decarboxylase requires Mg2+ and has a tightly bound coenzyme , thiamine pyrophosphate ( TPP ) .
In the second step, acetaldehyde is reduced to ethanol through the action of alcohol dehydrogenase , with the reducing
power furnished by NADH derived from the dehydrogenation of glyceraldehyde 3-phosphate.
This reaction is a well-studied case of hydride transfer from NADH .
Ethanol and CO2 are thus the end products of ethanol fermentation, and the overall equation is ;
As in lactic acid fermentation , there is no net change in the ratio of hydrogen to carbon atoms when glucose ( H:C ratio
= 12/6 = 2) is fermented to two ethanol and two CO2 (combined H:C ratio = 12/6 = 2).
In all fermentations, the H:C ratio of the reactants and products remains the same.
NO O2 is involved !
2
, Ethanol fermentation
Pyruvate decarboxylase is present in brewer’s and baker’s yeast (Saccharomyces cerevisiae) and in all other organisms
that ferment glucose to ethanol, including some plants.
The CO2 produced by pyruvate decarboxylation in brewer’s yeast is responsible for the characteristic carbonation of
champagne .
In baking , CO2 released by pyruvate decarboxylase when yeast is mixed with a fermentable sugar causes dough to rise.
The enzyme is absent in vertebrate tissues and in other organisms that carry out lactic acid fermentation.
The production of ethanol as a renewable fuel
Ethanol can be produced from relatively inexpensive and renewable resources rich in sucrose, starch, or cellulose—
starch from corn or wheat, sucrose from beets or cane, and cellulose from straw, forest industry waste, or municipal
solid waste.
Alcohol dehydrogenase is present in many organisms that metabolize ethanol , including humans.
In the liver it catalyzes the oxidation of ethanol , either ingested or produced by intestinal microorganisms, with the
concomitant reduction of NAD+ to NADH.
In this case , the reaction proceeds in the direction opposite to that involved in the production of ethanol by
fermentation .
Alcohol dehydrogenase and acetaldehyde dehydrogenase determine how much you can drink!
3
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller mandarachalangi. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $7.99. You're not tied to anything after your purchase.
