Pentose Phosphate Pathway Flashcards
What is the main enzyme in PPP?
Glucose 6 phosphate dehydrogenase
What does PPP start with?
Glucose 6 phosphate
What is made in the PPP?
Ribose and NADPH
Where is the PPP located in the cell?
Cytosol
How many NADPH are made in the PPP from each glucose 6 phosphate?
2
What else is made from the irreversible reaction in PPP besides NADPH?
Ribose 5 phosphate
What is another named for the PPP?
Hexose monophosphate pathway
Is ATP produced or consumed in the PPP?
Neither! (Unique)
What are the two purines?
Guanine and adenine
What are the two pyrimidines?
Thymine and cytosine (for DNA) & uracil and cytosine (for RNA)
What is a nucleoside?
Nitrogenous base + sugar
What is a nucleotide?
Nitrogenous base + sugar + phosphate
What do we need ribose 5 phosphate for?
ATP, coenzyme A, NAD, FAD, nucleic acids
What stimulates PPP overall?
Anything that consumes ribose 5 phosphate
What do we use NADPH for?
Reductive biosynthesis, free radical elimination (antioxidant regeneration), detoxification, respiratory bursts
Is NADPH an electron donor or acceptor?
Donor
Is the first irreversible reaction of PPP oxidative or reductive?
Oxidative
What are products of the reversible, non-oxidative reactions of PPP?
Products that can be utilized in glycolysis if we need energy (G3P, fructose 6 phosphate, etc…)
Dehydrogenation of what substance occurs in the first step of PPP?
Glucose 6 phosphate
Hydrolysis of what substance occurs in the second step of PPP?
6 phosphate gluconate alpha lactone (6-phosphogluconolactone)
What occurs in the third step of oxidative decarboxylation in PPP?
Occurs to 6-P gluconate to yield ribulose 5 phosphate
What occurs in the fourth isomeric action step in PPP?
Ribulose 5 phosphate to ribose 5 phosphate
What are the reactants for the enzyme glucose 6 phosphate dehydrogenase?
Glucose 6 phosphate and NADP+
What is the product of the enzyme glucose 6 phosphate dehydrogenase?
NADPH
What enzyme is responsible for the oxidization of glucose 6 phosphate in the first step of PPP?
Glucose 6 phosphate dehydrogenase (main enzyme of PPP)
What effect does NADPH have on glucose 6 phosphate dehydrogenase?
Inhibition (because it’s a product)
What enzyme is responsible for the hydrolysis reaction that is the second step of PPP?
Lactonase
What compound is used during the hydrolysis reaction in PPP using lactonase?
H20 (water)
What enzyme is responsible for the third step of PPP, the oxidative carboxylation?
6-phosphogluconate dehydrogenase
What is an extra product of the third step of PPP, besides the ribulose 5 phosphate and NADPH?
CO2 (carbon dioxide)
In which two steps of PPP is NADPH made?
Step one - dehydrogenation & step three - oxidative decarboxylation
In which step of PPP is a glycolysis like intermediate made?
Step four - isomerization
If there is low energy in the cell, where are the intermediates of PPP, such as G3P, going to go?
Glycolysis (to make energy)
What do the fat synthesis and cholesterol pathways use up that eventually stimulates PPP?
NADPH
What enzymes make up the reversible reactions of PPP that provide linkages with this pathway and glycolysis?
Transketolases and transaldolases
What is reductive biosynthesis?
Building things by adding electrons (donated from NADPH) like fat, cholesterol, steroid hormones, bile salts
Where in fat synthesis is NADPH used?
Reductions steps of “CRDR” (fatty synthase)
What is the process of detoxification?
Making toxins more water soluble for excretion through the urine by adding electrons (from NADPH)
What is added to toxins during detoxification to make them more water soluble?
Hydroxyl groups (OH)
What system of enzymes is used for detoxification?
The liver’s P450 monooxygenase system
What other substance must join with the extra electrons from NADPH to make toxins more water soluble?
O2 (oxygen) to make the final OH group
Where is the location of the cytochrome P450 monooxygenase system?
Endoplasmic reticulum of the liver
The cytochrome p450 monooxygenase system adds hydroxyl groups to what types of compounds?
Aromatic and aliphatic
What is respiratory burst?
Creating “harsh chemistry” by using electrons from NADPH to kill off non-self things like bacteria
Why is it called respiratory burst?
White blood cells take in more oxygen
What reactive molecules are made during respiratory burst to kill off bacteria in a vesicle?
Oxygen and electrons from NADPH
What enzyme makes hypochlorus acid (HOCl) from hydrogen peroxide during respiratory burst?
Myeloperoxidase
What other molecule is made during respiratory burst to kill off bacteria?
H2O2 (hydrogen peroxide)
What enzyme in respiratory burst changes O2- to H2O2?
Superoxide dismutase
What is antioxidant regeneration?
Adding electrons (from NADPH) to antioxidants to keep them protecting the body from free radicals
What has the ability to inactivate reactive molecules?
Antioxidants
What is an antioxidant?
A substance that inhibits oxidation and is capable of counteracting the damaging effects of oxidation in body tissue
What is a free radical?
An atom or molecule that has one or more unpaired electrons
What types of free radicals are referred to as ROS or RNS?
Those containing oxygen or nitrogen
What does ROS stand for?
Reactive oxygen species
What does RNS stand for?
Reactive nitrogen species
Do reactive species always have to be free radicals?
No
Are free radicals always reactive species?
Yes
What is O2-?
Superoxide
What is e-OH?
Hydroxyl
Is hydrogen peroxide considered a radical?
No, but it is a reactive species
Why are free radicals and reactive species bad?
They attack polyunsaturated fat in phospholipids, attack protein in cells, and attack nucleic acids in DNA
What is quenching in reference to reactive species?
The process by which electronically excited molecules are inactivated
How is quenching usually established?
By an antioxidant giving an electron to a free radical
Antioxidant regeneration give what power back to the antioxidant?
Reducing power
When antioxidants are being regenerated, are they being oxidized or reduced?
Reduced; electrons are being added to them
During antioxidant regeneration, is NADPH being oxidized or reduced?
Oxidized
What else may quench free radicals?
Enzymes such as superoxide dismutase, catalase, and glutathione peroxidase
What does catalase quench specifically?
Hydrogen peroxide
What is the location of superoxide dismutase?
Extracellular, cytoplasm, mitochondria
What is the function of superoxide dismutase?
Eliminate superoxide and produce hydrogen peroxide
What is the extra product of the reaction with superoxide dismutase creating hydrogen peroxide?
O2
Superoxide dismutase requires what cofactors?
Zinc and copper (along with manganese in the mitochondria)
What is formed when an electron is added to a superoxide radical?
Molecular oxygen
Where is O2- created?
Catecholamine/oxygen reactions, folate or THF/oxygen reactions, mitochondrial production (ETC), cytochrome p450, and white blood cells
Is O2- lipid soluble?
No; therefore, it does not travel far from the site of production
How is O2- created in the mitochondria during ETC?
Due to leakage of electrons from coenzymeQ to O2
What can increase the effect of superoxide formation during the ETC?
Exercise
What is the location of catalase?
Mostly in cell peroxisomes; smaller amounts in the cytoplasm, mitochondria, and microsomes
What is the function of catalase?
Eliminates hydrogen peroxide
What type of cell has a lot of catalase?
Neutrophils (respiratory bursts)
What occurs in cell peroxisomes?
Oxidation of very long fatty acids
What is a cofactor of catalase?
Iron
What is the end result of catalase on hydrogen peroxide?
Water and oxygen
Most hydrogen peroxide is removed by what enzyme?
Glutathione peroxidase
Where is glutathione peroxidase located?
Cytosol and mitochondria
What is the cofactor of glutathione peroxidase?
Selenium
What reactive species does glutathione peroxidase quench?
Hydrogen peroxide
What is used to regenerate glutathione peroxidase?
Electrons from NADPH and the enzyme glutathione reductase
Because NADPH is needed for antioxidant regeneration, what enzyme is therefore stimulated?
Glucose 6 phosphate dehydrogenase
