the pentose phosphate pathway is a very important biochemical process that takes place inside the cytoplasm of our cells now this process is important for two different reasons number one is the pentose phosphate pathway gives us a way to actually generate five carbon pencil sugar molecules and we use these pentose sugar molecules to basically generate generate biological molecules such as DNA molecules RNA molecules ATP molecules nadh and fadh2 generate coenzyme a on top of that the second reason why the pentose phosphate pathway is important is because it gives us a way to generate reducing agent molecules molecules we call NADPH which stands for the reduced version of nicotine and nicotine MI adenine dinucleotide phosphate now this molecule is used in by synthetic processes such as the building of fatty acids the building of cholesterol molecules the building of nucleotide molecules and so forth we also use the NADPH molecules in different detoxification processes that take place inside our cell so in this lecture I'd like to focus on the first phase of the pentose phosphate pathway and recall that the first phase of this pentose phosphate pathway is the oxidative phase this is where we actually oxidize glucose we transform it into a pentose molecule as we'll see in just a moment in the process we release a carbon dioxide and we generate the much-needed reducing agent molecules that NADPH molecule so the first phase of the pentose phosphate pathway is the oxidative breakdown of glucose to release carbon dioxide and generate NADPH molecules so let's see exactly how this takes place so essentially we can break down the first phase into four steps and let's begin with reaction one step one so in the first step the end on that catalyze the first step is known as glucose 6-phosphate dehydrogenase why well because the substrate molecule is a glucose 6-phosphate and this is actually a dehydrogenase reaction so what happens is we have this nadp+ molecule that will act as an electron acceptor so we essentially extract two electrons from this particular glucose 6-phosphate and those two electrons are picked up by this molecule in addition and h ion is picked up by this molecule as well and we generate the reduced version of nicotinamide adenine dinucleotide phosphate we also release the H+ ion and we produce the six phosphor glucan o delta lactone molecule so this is essentially an ester bond that we form and so this is known as an intramolecular ester molecule and this bond here will be broken in step two as we'll see in just a moment so the important part of this step is we generate the much-needed reducing agent molecule this molecule here we also form the ester bond here that will be broken down in step two so the oxidative phase begins with the dehydrogenation of the glucose 6-phosphate at the first carbon so dehydrogenation simply means we're removing h ions so an enzyme called glucose 6-phosphate dehydrogenase catalyzes the transfer of a hydride ion so that's an H+ ion and two electrons from the glucose and onto the end of the nad plus carrier molecule so this is the electron acceptor that picks up two electrons and that H+ ion and we also release a hydrogen ion so we formed this intramolecular ester molecule known as six phosphor glucose Delta lacked Delta lactone now let's move on to step two so in step two what we want to basically do is we want to prepare the molecule for a decarboxylation in reaction and the way that we prepare the molecule is by opening up the ring structure we open up that ring structure via a hydrolysis reaction which is catalyzed by an enzyme known as Latin a so Latin ease catalyzes the hydrolysis of this ester bond and so we transform the six phospho glucose into a six phosphor glucose the H+ ion as shown here so once we open up this molecule it's now ready to undergo a decarboxylation reaction now along with releasing the carbon dioxide in step three we also actually oxidize this the six phosphoglucomutase EEP Loess molecule nadp+ molecule this is the oxidized version of nicotine amide adenine dinucleotide phosphate so essentially we remove carbon one along with these two oxygens so we form the carbon dioxide in the process we extract two electrons from the sugar molecule place them unto this molecule in addition we take an H+ I and place it onto this and we form the rib ulos five phosphate molecule as well as another NADPH molecule so the net amount of NADPH molecules that are formed when one glucose 6-phosphate undergoes the first phase of the pentose phosphate pathway is two one is formed in step one and the other one is formed in step three so we have an enzyme called six phosphor gluconate dehydrogenase again it's a dehydrogenase because we're essentially extracting the two H+ ions along with those two electrons which are picked up by this electron carrier molecule so this enzyme catalyzes the oxidative decarboxylation so oxidative means we have an oxidation reduction reaction going on where this is oxidized and this is reduced and we also have a decarboxylation reaction taking place where this carbon number one along with these two oxygen atoms are essentially removed and so we form this rebel OHS 5 phosphate molecule so we kick off a carbon dioxide molecule we form a pentose sugar a five carbon sugar so we have 1 2 3 4 5 6 carbons here while we have only 1 2 3 4 5 carbons here and we also form that reducing agent molecule that can be used by the cell in a variety of different ways now once we form that the RHIB ulis 5 phosphate we had the final reaction taking place that is really an isomerization reaction in which we have the enzyme phosphatase isomerase basically transforms this ketose regulates 5 phosphate into an aldose the d ribose 5-phosphate so the derivative is transformed to the d ribose 5-phosphate via the activity of phosphor pantos isomerase so we see that in the first phase of the pentose phosphate pathway we basically have four steps in step one we undergo an oxidative reaction and oxidation reduction reaction which we generate that first and adp h molecule in the second step we open up this molecule to basically prepared for step 3 because in step 3 we want to generate yet another NADPH molecule as well as release that carbon dioxide to generate a pentose sugar and the final step we transform the RHIB ulos 5 phosphate into its isomer form the ribose 5-phosphate which can then be used in the second phase of pentose phosphate pathway the non oxidative phase that we're going to focus on in the next several lectures