Chapter 13 Responses

Glycolysis is an anaerobic process through which ATP is synthesized during

the conversion of the six-carbon sugar glucose to two molecules of the

three-carbon compound pyruvate. It has two phases: an energy investment

phase, where ATP is consumed, and an energy generation phase, where

ATP is produced.

A total of ten reactions are involved, each of which is

catalyzed by a different enzyme. Factors affecting the rate of glycolysis

do so by inhibiting or activating one or more of the enzymes

involved. Some of these factors include:

*the presence of iodoacetate or

heavy metals, which inhibit glyceraldehyde-3-phosphate dehydrogenase

(******is this why people get sick from mercury poisoning????****)

*the presence of carbohydrate, which stimulates the production of pyruvate

kinase in the liver, increasing rate of glycolysis

*the presence of oxygen, which inhibits substrate flow through

phosphofructokinase.

Inhibition of a certain enzyme can be detected by measuring the amounts of

reaction intermediates after addition of a particular

inhibitor/activator. For example, it was determined that oxygen inhibits

phosphofructokinase (which catalyzes the synthesis of fructose

1-6-bisphosphate) because levels of all intermediates past (&

including) fructose 1-6-bisphosphate decreased upon addition of O2.

Homeostasis must be maintained during glycolysis. This is acheived by

reoxidizing the 2 mol NADH (that are produced during glycolysis) back to

NAD+. In aerobic glycolysis, these electrons are used to reduce oxygen; in

anaerobic glycolysis, they drive the reduction of pyruvate to lactate.

Glycolysis is not completely efficient, releasing only a small amount of

the energy stored in the glucose molecule. Coupling glycolysis to the

citric acid cycle increases the amount of energy converted into ATP to

40%, through the synthesis of 38 additional mol ATP.

Glycolytic pathways exist for obtaining energy from sugars other than

glucose as well, including lactose, sucrose, and mannose. Energy is

obtained from polysaccharides such as glycogen and amylose through a

hormonally regulated metabolic cascade.

I found it interesting that glycolysis was an ancient metabolic pathway used

by the earliest known bacteria. I also did not know that lactic acid

fermentation was vital to the production of cheese. I did not before know the

definition of fermentation as an energy yielding metabolic pathway that does

not have a net oxidation state change. Do oxidation states change but cancle

eachother out? I'm not quite sure. I found the fairly in-depth sections on

the energy investment and energy generation phases of glycolysis to be

somewhat tedious. I will definitly have to re-read these sections to

understand them. The reason why pyruvate is converted into lactate in both

aerobic and anaerobic cells makes sense. I was surprised to read that red

blood cells derive most of their energy from anaerobic metabloism. I did not

know that skeletal muscle attains much of its energy when exerted from

glycolysis. I was also not aware that the products made in anaerobic

respiration such as lactate will then move through the body to parts of the

body which are heavily involved in aerobic respiration to be catabolized. I

was amazed that i had never before heard that glycolysis not only generates

ATP and pyruvate, but that it produces intermediates which are used to make

lipids and amino acids.

This chapter is mostly devoted to glycolysis and compounds associated with

glycolysis. Glycolysis was the first metabolic pathway understood, is

universal in most cells and the regulation of glycolysis is well

understood. This metabolic pathway consists of 10 steps, 5 energy

investment phases and 5 pay off phases. The book goes into great details

about the 10 steps including products, side products, enzymes andeven

strucutre. How detailed should our study of this process be? Also, the

analysis of key enzymes and products are also very detailed and seemingly

relevant, but some clue about the level of comprehension we need would be

nice.

Chapter 13 begins the detailed study on metabolici pathways with anaerobic

and aerobic glycolysis. The initial and a universal process, glycolysis

was widely studied in yeasts, whose genetic sequence was the subject of

our last lab. Glycolysis is divided into two phases: the energy

investment phases, which expences two ATP's, and the energy generation

phase which generates 4 ATP and 2 NADH anaerobically or 10 ATP

aerobically. Although glycolysis only releases a small fraction of energy

available from glucose, the energy is needed as fuel for aerobic

energy-generating pathways. The Pasteur effect is the inhibition of

glycolysis by oxygen. Other glycolytic controls are known and will be

further studied in later chapters.

Chapter 13 covered glycolysis. Glycolysis is a central part of the

metabolic processes of all cells. It is the first part of the pathway

to break down glucose and other sugars to produce ATP in aerobic

organisms, and the only source of ATP in anaerobic organisms. There are

ten steps in glycolysis, each of which is catalyzed by a different

enzyme. There are various control mechanisms, including a

feedback-controlled system, and oxygen inhibition. Glycolysis fits into

many different metabolic pathways, including digestion and conversion of

other sugars, monosaccharides and polysaccharides, into usable energy

for cells (ATP). The breakdown and use of glycogen, which we studied

earlier, in the chapter about carbohydrates, also involves glycolysis as

a central pathway.