Docsity
Docsity
Prepare for your exams
Prepare for your exams

Study with the several resources on Docsity

Earn points to download
Earn points to download

Earn points by helping other students or get them with a premium plan

Guidelines and tips
Guidelines and tips
Sell on Docsity
Sell on Docsity
Docsity AI
Docsity AI
Log inSign up

Prepare for your exams

Study with the several resources on Docsity

Find documents

Prepare for your exams with the study notes shared by other students like you on Docsity

Search for your university

Find the specific documents for your university's exams

Docsity AINEW

Summarize your documents, ask them questions, convert them into quizzes and concept maps

Explore questions

Clear up your doubts by reading the answers to questions asked by your fellow students

Earn points to download

Earn points by helping other students or get them with a premium plan

Share documents
download point icon20 Points

For each uploaded document

Answer questions
download point icon5 Points

For each given answer (max 1 per day)

All the ways to get free points
Get points immediately

Choose a premium plan with all the points you need

Study Opportunities

Choose your next study program

Get in touch with the best universities in the world. Search through thousands of universities and official partners

Community

Ask the community

Ask the community for help and clear up your study doubts

Free resources

Our save-the-student-ebooks!

Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors

Pentose Phosphate Pathway Study Guide, Study Guides, Projects, Research of Chemistry

United States International UniversityChemistry

Pentose Phosphate Pathway Study Guide

Typology: Study Guides, Projects, Research

2025/2026

Available from 02/20/2026

bestlearner
bestlearner 🇰🇪

1.4K documents

1 / 15

Toggle sidebar

This page cannot be seen from the preview

Don't miss anything!

bg1
Pentose Phosphate Pathway Study Guide
AKA: Hexose Monophosphate Shunt; (HMS) Hexose Monophosphate Pathway (HMP)
Understand the functions, active tissues, control of the pentose phosphate pathway
At this point in the course we have encountered two different forms of reducing power;
NADH and FADH2. However, both of these are rapidly oxidized by oxidative
phosphorylation or in the case of NADH, by the enzyme lactate dehydrogenase (or other
fermentative enzymes) to regenerate NAD+. Consequently, these molecules are NOT
available as reducing agents for macromolecule synthesis.
Reducing power for biosynthesis (anabolism) is provided by the molecule NADPH.
For synthesis to be able to occur and for generation of protection against reactive
oxygen species, we need a method to produce NADPH.
There are two basic parts of the PPP. One part is called the Oxidative Pathway, while
the other is called the NON-Oxidative Pathway.
•NET RESULT of oxidative pathway:
ooxidatively decarboxylated glucose-6-P (a hexose) to ribose-5-P (a
pentose) and transferred hydride ions to 2NADP+ to form 2
NADPH.
oRibose-5-P used for nucleotide synthesis.
oNADPH used for reductive biosynthetic reactions.
pf3
pf4
pf5
pf8
pf9
pfa
pfd
pfe
pff

Partial preview of the text

Download Pentose Phosphate Pathway Study Guide and more Study Guides, Projects, Research Chemistry in PDF only on Docsity!

Pentose Phosphate Pathway Study Guide

AKA: Hexose Monophosphate Shunt; (HMS) Hexose Monophosphate Pathway (HMP) Understand the functions, active tissues, control of the pentose phosphate pathway At this point in the course we have encountered two different forms of reducing power; NADH and FADH 2. However, both of these are rapidly oxidized by oxidative phosphorylation or in the case of NADH, by the enzyme lactate dehydrogenase (or other fermentative enzymes) to regenerate NAD+. Consequently, these molecules are NOT available as reducing agents for macromolecule synthesis. Reducing power for biosynthesis (anabolism) is provided by the molecule NADPH. For synthesis to be able to occur and for generation of protection against reactive oxygen species, we need a method to produce NADPH. There are two basic parts of the PPP. One part is called the Oxidative Pathway , while the other is called the NON-Oxidative Pathway.

  • NET RESULT of oxidative pathway : o oxidatively decarboxylated glucose-6-P (a hexose) to ribose-5-P (a pentose) and transferred hydride ions to 2NADP+ to form 2 NADPH. o Ribose-5-P used for nucleotide synthesis. o NADPH used for reductive biosynthetic reactions.
  • Non-oxidative pathway: o 3 ribose-5-P =====> 2 fructose-6-P + glyceraldehyde-3-P o Excess ribose-5-P not needed for nucleotide synthesis is converted into glycolysis intermediates, ▪ Keeps the pentose phosphate pathway operating for the purpose of generating NADPH. Purpose:
  • PPP is going to be most active in those cells that have high demand for NADPH o The largest demand for NADPH is in fatty acid synthesis fatty acids are almost entirely hydrocarbons (very reduced form of carbon). o Thus the pathway is very active in tissues actively synthesizing fatty acids and steroids, such as the mammary gland, liver, and adipose tissue and, for example, not very active in skeletal muscle.
  • ...and in those cells that have a high demand for pentoses. o Seen in growing and regenerating tissues, and in tumors (all of which have a need for nucleic acid synthesis for new cells). Regulation:
  • glucose 6-phosphate dehydrogenase is allosterically regulated by the levels of NADPH/NADP+. o When there is an elevated level of NADPH the enzyme is inhibited. o When there is a deficiency of NADPH (an elevated level of NADP+) the enzyme is activated. o This is the only regulation of the entire PPP.
  • Transaldolase o Transfers a dihydroxyacetone unit from a ketose to an aldose. o No prosthetic groups. o The enzyme is indiscriminant in its choice of substrates in that it will accept almost any sized ketose as the source of the three carbon fragment and any aldose phosphate as the acceptor of the three carbon fragment.
  1. xylulose-5-P + erythrose-4-P =====> glyceraldehyde-3-P + fructose-6-P o also catalyzed by transketolase. o products are two glycolysis intermediates. o xylulose-5-P comes from epimerizing ribulose-5-P, same as before.
  • The NON-oxidative pathway then can catalyze the alternative transfers for 2- carbon or 3-carbon ketose fragments to aldose-phosphate acceptors.
  • The reactions catalyzed by transketolase and transaldolase are readily reversible. Direction of reaction depends only on concentration of reactants. Know the intermediates that are common to glycolysis and the pentose phosphate pathway.
  • Glucose-6-P (in oxidative pathway) - also the starting molecule of glycolysis, made by hexokinase
  • glyceraldehyde-3-P (Step 5)
  • fructose-6-P (Step 6)
  • glyceraldehyde-3-P + fructose-6-P (transaldolase reaction, Step 7) I. Where we are Catabolism produces energy-depleted end products (CO 2 , H 2 O) and energy (in the form of ATP, NADH, and FADH 2 ). Anabolism, or synthesis of macromolecules, uses precursor molecules and consumes ATP, and uses reducing power in the form of NADPH. A major concept in biochemistry to understand is that we do NOT store energy as ATP. Actually we have only limited amounts of ATP + ADP + AMP in our cells. Similarly, we have only limited amounts of NAD+^ + NADH in our cells. When we are experience times of fuel excess we store molecules that can produce energy (glycogen, fatty acids). And, when we experience times of limited fuel molecules (starvation) we generate energy from the storage molecules via catabolic reactions.

L E O says G E R o l x a l e s e i i e d s c d n c u t a t c r t r t o i o i n o n o s n s n Reducing reactions consume energy Oxidizing reactions release energy In the broadest view reducing power is needed to convert CO 2 (most oxidized form of carbon) to glucose (a more reduced form of carbon)--this is the domain of photosynthesis, one of the most important of the biochemistry stories but unfortunately not one we will address in this course. In addition to biosynthesis other needs for readily available reducing power include

  1. the generation of reactive oxygen molecules for protection against microbes and
  2. for protection against the same reactive oxygen molecules as well as free radicals that are generated during metabolism. At this point in the course we have encountered two different forms of reducing power; NADH and FADH 2. However, both of these are rapidly oxidized by oxidative

phosphorylation or in the case of NADH, by the enzyme lactate dehydrogenase (or other fermentative enzymes) to regenerate NAD+. Consequently, these molecules are NOT available as reducing agents for macromolecule synthesis. Reducing power for biosynthesis (anabolism) is provided by the molecule NADPH. For synthesis to be able to occur and for generation of protection against reactive oxygen species, we need a method to produce NADPH. NADP+ differs from NAD+ in having a 2' phosphoryl group. III. Pentose Phosphate Pathway Oxidative pathway

  1. glucose-6-P + NADP+ ======> 6-phosphogluconolactone + NADPH (Glucose-6-P - also the starting molecule of glycolysis, made by hexokinase.) Reaction catalyzed by glucose-6-P dehydrogenase. Mg++ needed An oxidation coupled to reduction of NADP+. Enzyme specific for NADP+.
  2. 6-phosphogluconolactone + HOH ======> 6-phosphogluconate + H+ The pyranose ring hydrolyzed to chain form, catalyzed by lactonase.

C5 + C4 =======> C3 + C

Net result - make 2 hexoses and 1 triose from 3 pentoses. NOTE: do NOT memorize these reactions!

  1. xylulose-5-P + ribose-5-P =======> glyceraldehyde-3-P + sedoheptulose-7-P Reaction is catalyzed by transketolase which transfers a 2 C keto fragment from xylulose to ribose. ribose - aldopentose xylulose - ketopentose, and epimer of ribulose-5-P which was generated in reaction 3, the enzyme phosphopentose epimerase interconverts the C3 hydroxyl from D to L. glyceraldehyde-3-P - glycolysis intermediate Transketolase: contains a thiamine pyrophosphate (TPP) prosthetic group. Similar to pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase complexes of citric acid cycle. TPP is always present in enzymes that transfer aldehyde groups because it can form a carbanion intermediate that stabilizes aldehyde intermediate.
  1. glyceraldehyde-3-P + sedoheptulose-7-P =====> fructose-6-P + erythrose-4-P fructose-6-P is another glycolysis intermediate. catalyzed by transaldolase which transfers a 3C keto fragment from heptulose to glyceraldehyde. Transaldolase Transfers a dihydroxyacetone unit from a ketose to an aldose. No prosthetic groups. The enzyme is indiscriminant in its choice of substrates in that it will accept almost any sized ketose as the source of the three carbon fragment and any aldose phosphate as the acceptor of the three carbon fragment.
  2. xylulose-5-P + erythrose-4-P =====> glyceraldehyde-3-P + fructose-6-P also catalyzed by transketolase. products are two glycolysis intermediates. xylulose-5-P comes from epimerizing ribulose-5-P, same as before. The NON-oxidative pathway then can catalyze the alternative transfers for 2-carbon or 3- carbon ketose fragments to aldose-phosphate acceptors.

however the resulting pentose 5-phosphate must be converted back into glycolytic intermediates that can be used for ATP production. Chemotherapy : When we start studying nucleotide metabolism we will find that there are two different methods of synthesizing them. One of the methods is called the salvage pathway in which preformed bases can be reincorporated into nucleosides. In situations where there is increased cell death (chemotherapy, radiation exposure etc.) there are abundant preformed purines and pyrimidines thereby decreasing the amount of NADPH that is necessary for synthesis. However, pentoses are still required. The non-oxidative part of the PPP can be used to make the required pentose 5-phosphate from glycolytic intermediates.

Answers

  1. What is the Pentose Phosphate Pathway? Include its function and the overall reactants and products. In what cells/tissues is it active? The PPP starts with glucose-6-phosphate and produces NADPH and Ribose-5- Phosphate. NADPH is necessary for reductive biosyntheses, and ribose-5-phosphate is used in the biosynthesis of nucleic acids. This pathway is prominent in in tissues actively synthesizing fatty acids and steroids, such as the mammary gland, liver, and adipose tissue (all of which need NADPH as the reductant in anabolic pathways) and in growing and regenerating tissues, and in tumors (all of which have a need for nucleic acid synthesis for new cells).
  2. In many tissues, one of the earliest responses to cellular injury is a rapid increase in the levels of enzymes involved in the pentose phosphate pathway (PPP), up to 20- times higher than normal. Which of the following explain the need for these high levels of PPP enzymes? A. NADPH is needed for synthesis of fatty acids and cholesterol, components of cellular membranes B. Ribose-5-phosphate is necessary for synthesis of RNA and DNA C. Higher concentrations of ATP are needed D. A and B*