NUTR 3210 Lecture Notes - Lecture 4: Oxaloacetic Acid, Fatty Acid Metabolism, Coenzyme A
27 Jun 2018
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Unit 04
Review of Intermediary Metabolism
Video
Review of Intermediary Metabolism Part 2
Transcript
Slide 1
The HMPS is also called the pentose phosphate pathway, because it produces
five carbon or pentose sugars that are phosphorylated. It occurs in the cytosol of
various cells types, and the purpose of the pathway is to make the reducing
equivalent NADPH as well as five carbon sugars. One unique characteristic of
the HMPS is that it can follow two different routes depending on the body’s
needs. The oxidative route will produce both pentose sugars and NADPH, while
the non-oxidative route will only produce the pentose sugars. So, the difference
between them is that the oxidative pathway makes NADPH while the non-
oxidative pathway does not. The signal for taking the oxidative route is an
increase in oxidative stress, since NADPH is used in oxidant defence, as we will
see in unit 10. This signal is mediated by changes in the ratio of NADP+, which is
oxidized, to NADPH, which is reduced. This ratio is called a “redox couple”, and it
is an important indicator of metabolic health. In a healthy cell, there will be more
NADPH, which can be used in oxidant defence, in contrast to NADP+, which
signals that the cell is under oxidative stress. Both the oxidative and non-
oxidative pathways produce five carbon pentose sugars that can be used to
produce DNA and RNA that are used in cell growth and division. The HMPS is
active when someone is well fed, and blood glucose levels are high. It is
considered anabolic metabolism as it is building products required for cell growth
and division.
Slide 2
Let’s shift now from looking at pathways that use glucose to the further
metabolism of pyruvate produced in glycolysis. Under aerobic conditions, much
of the pyruvate will be metabolized to acetyl CoA in a reaction catalyzed by the
pyruvate dehydrogenase complex. This complex is actually comprised of three
enzymes, each of which catalyzes a different reaction, and which uses several
different nutrient cofactors, including thiamine, niacin, riboflavin, and pantothenic
acid, which are all B vitamins. We will look at the way this enzyme complex
works in more detail in unit 11, but for now, we will consider it simply as the
reaction that metabolizes pyruvate to acetyl CoA. The pyruvate dehydrogenase
reaction occurs in the mitochondrial matrix, so it is limited to cells that have
mitochondria, which excludes red blood cells. The pyruvate dehydrogenase
reaction can be thought of as having three substrates, which include pyruvate,
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Document Summary
The hmps is also called the pentose phosphate pathway, because it produces five carbon or pentose sugars that are phosphorylated. It occurs in the cytosol of various cells types, and the purpose of the pathway is to make the reducing equivalent nadph as well as five carbon sugars. One unique characteristic of the hmps is that it can follow two different routes depending on the body"s needs. The oxidative route will produce both pentose sugars and nadph, while the non-oxidative route will only produce the pentose sugars. So, the difference between them is that the oxidative pathway makes nadph while the non- oxidative pathway does not. The signal for taking the oxidative route is an increase in oxidative stress, since nadph is used in oxidant defence, as we will see in unit 10. This signal is mediated by changes in the ratio of nadp+, which is oxidized, to nadph, which is reduced.
