Name: Pentose phosphate pathway - Cyclic structures and anomers | Biomolecules | MCAT | Khan Academy
Uploaded: 2020-03-22T16:10:12.000Z
Duration: 12 min 52 s
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Participle clauses with adverbial meaning

- [Voiceover] When talking about carbohydrate metabolism

we can't forget to mention the pentose phosphate pathways.

Relative clauses (Restrictive vs. nonrestrictive)

So, where does the pentose phosphate pathway fit into

So, let's go ahead and review the breakdown of glucose

as we normally kind of usually conceive of it as.

So, we go ahead and start out with glucose,

which I'm drawing here to symbolize it with

And we usually imagine that glucose begins to be broken down

a series of reactions that we call glycolysis.

And then, of course, it goes through the Krebs cycle

in the mitochondria, also known as the TCA cycle.

And then, finally, it goes to the electron transport chain

So, that's kind of usually the end product we think of

when we think about breaking down glucose.

is kind of a unique pathway, because it turns out

that in this pathway no ATP is consumed or produced.

So, where does it fit in to this overall pathway?

It turns out that the linear way I've written

cellular respiration is actually only partly true.

but there are many branches or kind of side reactions

that are taking place almost simultaneously

and the pentose phosphate pathway is one of these.

to go through glycolysis, some of it is shunted away

to produce different products than it would

if it continued through going through glycolysis,

and Krebs, and then to the electron transport chain.

So, as you can see, I've written pentose phosphate pathway

kind of suggestively by highlighting pentose and phosphate

that there are two primary products in this pathway.

So, pentose is just another word for five-carbon sugar,

And this sugar, so it's a five-carbon sugar,

I'll go ahead and draw that to remind us of that,

is an important substrate in producing DNA and RNA.

So, if you remember, DNA and RNA contain nucleotides,

and the nucleotides contain a nitrogenous base,

a phosphate group, and a five-carbon sugar.

So, in the case of DNA, it's deoxyribose,

But, in either case, this ribose-five-phosphate

is an important precursor to creating DNA and RNA,

Now, the second primary product of this reaction,

is a phosphorylated molecule that is usually abbreviated

as N-A-D-P, P standing of course for the phosphate

So, this is not to be confused with the NADH, which,

if you recall, I'll go ahead and actually draw that in here,

in cellular respiration during the breakdown of glucose.

So, this produces NADH, which, of course, contributes

electrons to the electron transport chain.

So, of course, the question you might have in your mind

is how is NADH different from the easily confused NADPH,

because they sound like similar molecules,

So, they actually both exist in pairs inside the cell,

so, NAD-plus we know is inter-converted with NADH,

and NADP-plus is inter-converted with NADPH.

So, of course, the H forms of these molecules

and the plus, or oxidized form of these molecules,

But, what's different about these two pairs of molecules

is the relative amount of the reduced form

the ratio of NAD-plus to NADH is about 1000.

In other words, if you took the amount of NAD-plus

and divided it by the amount of NADH in the body,

you would have about 1000 times more NAD-plus.

On the other hand, if you took the amount of NADP-plus

divided by the amount of NADPH, you would get 0.1.

So, essentially what this is telling us is that

and a lot of NADPH in the body, but not much

And, knowing this actually helps me remember

So, first, I reason out to myself that if there's

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Pentose phosphate pathway - Cyclic structures and anomers | Biomolecules | MCAT | Khan Academy

essentially

process

metabolism

consume