EVERY SINGLE METABOLIC PATHWAY YOU NEED TO KNOW FOR BIOCHEMISTRY MCAT IN 30 MINUTES!!!

so the glucose molecule is at the center of all metabolism that occurs inside of a human cell so when the glucose molecule enters inside of cells these glucose molecules go through a pathway referred to us by kalus and in glycolysis we take glucose molecules and we do a bunch of chemical reactions eventually taking those glucose molecules and converting them into pyruvate molecules and keep in mind each of these chemical reactions are catalyzed by their own unique enzymes so now once we go through glycolysis and form these pyruvate molecules then they can enter inside of the

mitochondria and in the mitochondria we take these pyruvate molecules and convert them into acetylcholine molecules now once we form these cedar coin molecules they can react with oxygen as state molecules to form citrate molecules and once we form the citrate molecules again we can go through a bunch of chemical reactions eventually reforming oxaloacetate molecules which can react with new acetylcholine molecules to form new citrate molecules to go through this cycle over again so this pathway is referred to as the Krebs cycle but these two pathways glycolysis and the Krebs cycle are collectively referred to as

central metabolism because glycolysis and the Krebs cycle are at the center of all metabolism that occurs in the cell and nearly all cells in the human body go through central metabolism why well when we take glucose molecules to go through central metabolism we create ATP molecules and we know these ATP molecules are high-energy molecules which are used as a source of energy too as a source of fuel to energize all the energetic chemical reactions the cell needs to survive but not just that when we take glucose molecules to go through central metabolism we also create

these reduced cofactors like nadh and fadh2 and we know these reduced cofactors have electrons that can be donated to the electron transport chain to create even more ATP so the point is when we go through central matter we create the ATP that's needed for the cell to survive but what's interesting is yeah we can take glucose molecules to go through central metabolism but we can also take other monosaccharides to enter central metabolism for example galactose we can take galactose and convert it into this particular intermediate now once we form this particular intermediate it swoops in

to central metabolism and can be used to create ATP so the point is any molecule that can be converted into one of these intermediates can simply swoop in it and be used to create ATP and lots of different monosaccharides can be converted into intermediates and be used to create ATP so what about proteins and their component amino acids can we take these amino acids tantor central metabolism to create ATP well it depends cuz keep in mind amino acids have a carboxyl group and an aiming group but notice none of these intermediates of central metabolism have

nitrogen molecules so therefore if we want to take amino acids tantor central metabolism we must get rid of this nitrogen group but we can do that we can get rid of this nitrogen group and replace it with the carbonyl group once we do that now we have this carbon backbone and these carbon backbones can enter central metabolism and notice alanine when we get rid of the aiming group and replace it with this carbonyl group we form this molecule which happens to be pyruvate so this can simply slip in as pyruvate and enter central metabolism and

be used to create ATP so this is true for any generic amino acid with with a new R group and again it's the same idea we get rid of the aiming group replace it with the carbonyl group and now we have this carbon backbone which we refer to as an alpha keto acid and we know different amino acids will have different R groups but depending on what that R group is we can do chemical modifications to convert these keto acids into intermediates of the central metabolism and therefore enter central metabolism and be used to create

ATP but you might wonder when we take these amino acids and get this aiming group to form these carbon backbone Center central metabolism what do we do with these aiming groups because we know ammonia is toxic to the cell so so what do we do with all this ammonia well we usually have a nitrogen acceptor and the universal nitrogen acceptor is alpha ketoglutarate so this alpha ketoglutarate accepts that nitrogen so this nitrogen waste we donate to applicative glued right to form glutamate now depending on what the cell was there will be this nitrogen transporter where

we can take this nitrogen from glutamate donate it to the nitrogen transporter then this nitrogen transporter can enter the blood and transport that nitrogen to the liver hepatocytes we're then that nitrogen is donated to another alpha ketoglutarate to form glutamate which can then safely enter the urea cycle where we take that nitrogen and and convert it into the safe urea which can safely be disposed out of our body but only the liver can safely dispose of nitrogen so the point is if we have a tissue that wants to use proteins and amino acids as a

source of energy we must get rid of that nitrogen group but how do we get rid of that nitrogen group well again we donate that nitrogen which goes to the nitrogen transporter which can then safely donate that nitrogen to the liver and the liver can safely dispose of that nitrogen through that urea cycle so what about fatty acids can can lipids and fatty acids enter central metabolism and be used to create ATP well it's a little complicated so if we want to use fatty acids to create ATP we take the fatty acids and go through

a path that we refer to as beta oxidation and every time we go through a round of beta oxidation we create an fadh2 and an NADH and we lose two carbons in the form of acetyl co a so that happens every time we do around a beta oxidation so now we have a fatty acid that's two carbons shorter now once we form this fatty acid we can do another round a beta oxidation and again every time we do around a beta sedation we create these reduce cofactors and we lose two carbons in the form of

acetylcholine so we know these reduce cofactors can directly fuel the electron transport chain to create ATP so so therefore these fatty acids the way they are used to make ATP is directly by forming these reduce cofactors to feel the electron transport chain and again we also create these acetylcholine molecules which theoretically could enter the Krebs cycle but in reality it's a little more complicated so we'll talk about that later so we've already learned when we take glucose molecules and go in this direction to form pyruvate molecules that pathway is refer to as glycolysis however we

can also go in the reverse direction we can take pyruvate and go in the reverse direction forming glucose molecules and we can do this because each of these chemical reactions were reversible however once we take part of a and form acetyl co a this is irreversible this is a one-way street and we cannot go in the reverse direction once we form acetyl co a we cannot go in the reverse direction to form pyruvate however pyruvate we can go in the reverse direction to form glucose molecules so we when we go in this reverse direction it's

referred to as gluconeogenesis the genesis of new glucose molecules where we go in this reverse direction and we create new glucose molecules so in certain contexts we need to go in this reverse direction to form a new glucose molecules however glucose is made out of six carbons so if we want to make glucose molecules we need a source of carbons so what are those major sources of carbons well lactate has three carbons so lactate can be converted into pyruvate and once we form pyruvate we know we can go in the reverse direction to form glucose

molecules so therefore these three carbons in lactate can be used to form glucose molecules the same thing with glycerol we know we have these triglycerides which is a storage form of energy but when we hydrolyze these ester linkages and release a glycerol molecule this glycerol molecule has three carbons and glycerol can be converted into this intermediate which we know can then be used to make glucose molecules however what about keto acids like beta hydroxy butyrate can these atoms be used to Baia synthesize glucose molecules well alpha keto acids can be converted into acetyl co a

but we know once we form a seeder koi we cannot go in this reverse direction to form pyruvate molecule so we're stuck once we form acetyl co a we're we are forced to go in this direction so therefore these atoms and keto acids cannot be used to form glucose molecules so what about proteins and these amino acids can we take these atoms and amino acids to form glucose molecules well it depends for example alanine we know when we get rid of the aiming group we form this this this alpha keto acid which happens to be

pyruvate so we know this can enter as pyruvate which can be used to make glucose so therefore these atoms and alanine can go through this pathway to form Lukis molecules what about aspartate well we know we need to get rid of that aiming group so now we formed this alpha keto acid but this particular alpha keto acid just by chance happens to be oxaloacetate and something you just have to memorize is just by chance we happen to have an enzyme that can take oxaloacetate to form pyruvate and once we form pyruvate we know we can

form glucose molecules so therefore aspartate can go through this pathway to form this intermediate which is again this intermediate which can then be used to form glucose molecules but what about leucine the amino acid leucine well again we get rid of the amine group so now we form this alpha keto acid but this alpha keto acid we have the enzymes to convert it into acetyl co a and we know acetyl co a cannot be used to form glucose molecules we know it cannot go in this reverse direction it's forced to go in this direction so

it can't be used to form glucose molecules but you might wonder can't we take a seat Ocoee to go in this direction to form this guy to then be used to form glucose well no acetyl co a has theoretically two carbons that donate to form glucose molecules however once acetyl co a goes to this pathway it loses one carbon s carbon dioxide then it loses its second carbon so therefore these two carbons are lost as carbon dioxide by the time it forms this intermediate so therefore these carbons cannot be used to form glucose molecules but

what about methionine well again we get rid of the aiming group so we form this alpha keto acid and this particular alpha keto acid can be converted into this particular intermediate which again can enter this pathway and be used to form glucose molecules so therefore certain amino acids can be used to form glucose molecules and the amino acids that can be used to form glucose molecules or for twisted gluco genic amino acids however other amino acids can not be used to form glucose molecule so there were four twice ketogenic because they can be used to

form ketone bodies so what about fatty acids can these atoms and fatty acids be used to create glucose molecules well we know when we go through rounds about oxidation we create acetylcholine molecules and we already explained these carbons in acetyl co a cannot be used to form glucose molecules because those carbons are lost as carbon dioxide however if you happen to to end up with three carbons in your final fatty acid this just by chance can be converted into this intermediate so and it can it be used to form glucose molecules so these last three

carbons can be used to form glucose molecules so these two carbons in acetyl co a are incredibly important and yeah even though these two carbons cannot be used to form glucose molecules they can be used for other purposes for example we can take these two carbons in the seeder co2 biosynthesize free fatty acids like pal medic acid through the process of fatty acid synthesis now once we form this pol medic acid it it can react with the moiety of glycerol where we take one of MOA T of glycerol two moieties of PAL medic acid and

one inorganic phosphate to form these phospholipids and we know these phospholipids key components of our cell membranes but not just that we can take one motive glycerol and three moieties of PAL medic acid to form try a so glycerides through the process of lipogenesis and we know these triglycerides are the primary storage form of energy our bodies use for example when we're in the fed state so we've just eaten a big meal we know when we eat a big meal our bodies will have lots of glucose proteins and fatty acids that we got from our

meal so we want to store those molecules for example all those glucose molecules we enter through a process of glycogenesis where we take those glucose molecules and store them in the form of glycogen which we know is just a storage form of glucose molecules so we take excess glucose molecules and store them in the form of glycogen and in all those excess proteins and those amino acids we use to replace already existing enzymes and structural proteins and peptide wormans however eventually we're going to to fill up our glycogen stores where we filled up our glycogen

stores and we've replaced all of the enzymes and structural Herrmann's and and proteins so once we do that what do we do with all these excess glucose and protein molecules for example let's say we've been in a very big meal so what do we do with all the excess glucose and proteins well we enter them through central metabolism and use the energy in these molecules to form try it try so glycerides so we convert the excess glucose and proteins in to try so glycerides just as a stored form of energy so we know these tries

to glycerides is a primary storage form of energy our bodies use but also it's pretty interesting is we can take the atoms and serine and react it with these atoms and how Minik acid to form this fing go scene backbone and we know the sphingosine backbone is very important to form other important lipids for example we take the sphingosine backbone and we react a free fatty acid to this amine group where we add a free fatty acid to the saving group to form ceramide the ceramide molecule and we know with this my molecule we can

use it to form lots of important molecules for example we take ceramide and we add a phospho group to this hydroxyl head group to form bingo violin and we know the sphingomyelin is a key component of the myelin sheaths of our neurons also what we can do is we can take the ceramide and we can add a carbohydrate to this hydroxyl head group to form cerebro size and also we can add more carbohydrates to form gangliosides so that's what happens during the fed state but what about the fasted State for example let's say we haven't

eaten a meal for a couple days what is the source of energy we don't eat well we can use these try so glycerides as a storage form as a source of energy where we hydrolyze these ester linkages releasing free fatty acids and we know we can take free fatty acids and go through rounds of beta-oxidation and every time we do around a beta oxidation we create reduced cofactors and acetylcholine molecules and we know these reduced cofactors can feel the electron transport chain to create ATP so this is one way we create ATP during a fasted

State we use our our trace or glycerides our stored form of energy as a source of energy but we know when we go through around to beta oxidation we also create these acetylcholine molecules so what do we do with these acetylcholine molecules well we can react three acetylcholine molecules with each other to form this hmg-coa and this hmg-coa is a very important molecule because in the liver in hepatocyte so we can take hmg-coa and go through a process referred to as ketogenesis we reform these ketone bodies like beta hydroxy butyrate and acetoacetate so during a

fasted state with the fasted state hormones and with a lot of acetylcholine molecules that we get from beta oxidation we can form h mg go away and go through ketogenesis to form these keto acids in the liver but why is the liver forming all these keto acids well these keto acids can leave the liver enter the blood and enter into other tissues and these other tissues can take these keto acids and convert them into C taquoia molecules and then these tissues can use these acetic oil molecules to enter the krebs cycle to create reduced cofactors

to kill the electron transport chain to create ATP so this is what happens during the fasted State however this hmg-coa is really important and can enter other pathways so again in a fasted State with the hormones during a fasted State we take a hmg-coa to form keto acids through ketogenesis but in other contexts for example during a fed state we can take hmg-coa and use it to form these five carbon units these these five carbon units which can be used as building blocks to build larger organic carbon based molecules for example we can take two

of these five carbon units react them with each other to form a 10 carbon unit then we take a 10 carbon unit reacted with the 5 carbon unit to form a 15 carbon unit then we react two of those to two of those 15 carbon units to form a 30 carbon unit which is referred to as squalene so this squalene has free rotation among some of these bonds so the squalene can fold and get in a particular conformation where it can react with itself to form land Estoril which can then be used to form cholesterol

but notice this is pretty interesting as long as we have glucose molecules we can take these atoms and glucose molecules to form acetylcholine molecules which can form hmg-coa which can form these five carbon units which can be used to form larger organic molecules like cholesterol so we can biosynthesize cholesterol and that's good because we know cholesterol is super important and is used to create lots of important hormones for example we can take cholesterol reacted with some energy from sunlight and then reacted with delivering the kidney to form different derivatives of vitamin D which is an

important hormone we can also take cholesterol and enter and use it to make lots of other important steroid hormones for example in the testes we can go through this pathway to form testosterone in the ovaries we can go through this pathway to form estradiol in different parts of the adrenal cortex we can go through different pathways to form cortisol and aldosterone these important steroid hormones and in the liver we can take cholesterol to form these bile salts which are needed to emulsify and absorb fats from our diet but what's pretty cool is we can take

these intermediates of central metabolism and use them to form amino acids but we know amino acids have nitrogens and none of these intermediates of central metabolism have nitrogens so therefore to take these intermediates to form amino acids we need a source of nitrogen and that nitrogen usually comes from glutamate which is a universal nitrogen donor so what are some examples well we can take oxaloacetate which is an intermediate of central metabolism so we can take this oxaloacetate and use it to form aspartate and we can do that because glutamate has a nitrogen that it donates

toxo a state to form aspartate so that's pretty cool we took this intermediate of central metabolism and formed aspartate another examples we can take this particular intermediate of central metabolism and form alanine and again we know we were able to do that because we have glutamate which can donate nitrogens to these intermediates of central metabolism to form certain amino acids so that's pretty cool we can take these intermediates of central metabolism to biosynthesized certain amino acids and here's a comprehensive list of all the amino acids we can form for example this intermediate of central metabolism

can be used to form serine which can then be used to form cysteine and glycine this intermediate can be used to form aspartate which can be used to form asparagine and also all these amino acids with these red stars we make and with very low efficiency we take this intermediate and form phenylalanine with very low efficiency so therefore most of the fat all most of these essential amino acids we need to get from our diet but a lot of amino acids we can buy synthesize which is pretty neat and we know these amino acids are

super important to form proteins to form enzymes and hormones and transcription factors in etc so we're already explained how we can take this intermediate of glycolysis to form serine but this serine amino acid is really important because it has this carbon which is used as a carbon donor to build larger molecules so how do we do this well we take this carbon and we donated two tetrahydrofolate to form this methylated form of tetrahydrofolate then we can take this carbon to donate it to homocysteine so now homocysteine gains that carbon to form the thiamine now methionine

reacts with ATP ATP to form this s adenosylmethionine the Sam molecule which is the universal methyl donor in the body so again if we want to build molecules we need carbons so a lot of the times those carbons come from Sam and also if we want to methylate DNA those carbons come from sim so this Sam is the universal methyl donor where it has these carbon groups that can donate for anabolism but also keep in mind this tetra or folate also has a carbon that can donate for anabolism so these are the two Universal Carbon

donors the two universal methyl donors what's also pretty neat is we can take certain amino acids and other sulfur containing compounds from our diet and use them to form sulfate once we form sulfate we can react it with a ATP using this enzyme to form this particular intermediate then we can react it with another ATP molecule using this enzyme to form this three phosphate dynast in five phosphorous sulfate this PAP's molecule which is the universal sulfur donor so we need to build molecules that need salt for molecules they usually come from this universal sulfur donor

so for example we know there are lots of different monosaccharides our bodies use for lots of different purposes for example we sometimes buy costly lipids so we need different carb monosaccharides to glycosylated ease lipids also proteins get glycosylated so these proteins get glycosylated with lots of different monosaccharides and we also know red blood cells have proteins that get glycosylated and that's the basis of blood type so we know there are lots of different monosaccharides that that our bodies used for lots of different purposes but how do we create these monosaccharides well usually they come from

these intermediates of glycolysis and if you're interested here's the here are the pathways I know this looks really complicated but the point is we can take this intermediate of glycolysis to go through this pathway to form all of these monosaccharides and again notice this monosaccharide has a sulfur where does they get that sulfur well again we already explained perhaps as a universal sulfur donor so once we have this intermediate we take this perhaps to donate a sulfur to form this sulfated glucosamine and also we can take this intermediate of central metabolism and throw on a

nitrogen from glutamine to form this this monosaccharide with the nitrogen group which can then enter different pathways to form lots of different monosaccharides and again whenever a monosaccharide has a sulfur you know got it from paps so I know this looks complicated but the point is there are lots of different monosaccharides we can biosynthesize and usually they come from these intermediates of central metabolism we can also take this particular intermediate of glycolysis to enter a pathway refer to as the pentose phosphate pathway and in this pentose phosphate pathway we produce two important products one we

create ribose 5-phosphate and also we create these reduced NADPH cofactors and these reduced NADPH cofactors are really important because they have electrons and essentially they can use these electrons and these hydrides as a source of electrons for anabolism because we know if we want to build larger molecules we need electrons to form these bonds so these electrons usually come from NADPH which has electrons but also these NADPH can take their electrons and donate them to this oxidized glutathione to form reduced glutathione and this reduced glutathione is an endogenous antioxidant this is an antioxidant so if

we have reactive oxygen species and if we have free radicals we know these are toxic molecules they're super reactive cuz they have these unpaired electrons so they're toxic they react with biomolecules and destroy them so these reactive oxygen species and free radicals are toxic however fortunately we have this endogenous antioxidants glutathione to donate electrons so now this unpaired electrons gets paired to form a neutralized safe molecule so that's pretty neat essentially what we can do is we can take these electrons from glucose go through this pathway take those electrons and eventually donate them to NADPH

which can donate those electrons to glutathione to form an antioxidant which can then take those electrons to donate them to free radicals to neutralize those free radicals so we have this endogenous antioxidant system which is pretty neat and we know this is important because our electron transport chain in our mitochondria is constantly producing free radicals even if you're healthy young whatever you're our mitochondria are constantly producing free radicals which get metabolized into other toxic free radicals and these free radicals for example hydroxyl radical is extremely dangerous and toxic it can react with free fatty acids

which react with these hydroxyl radicals to form this peroxy radical which goes through a very nasty free radical chain reaction which forms more free radicals and conform carcinogens and this is a very toxic pathway however fortunately we have this reduced glutathione which got its electrons from glucose so this reduced glutathione is an antioxidant it can donate electrons to vitamin C which can then donate that electron to vitamin E which can then donate that electron to this peroxy radical stopping that toxic chain reaction so that's pretty neat we have this endogenous antioxidant system so it's important

to have a strong endogenous antioxidant system by having lots of vitamin C and vitamin E and also having the right minerals that's needed for these enzymes and is this pathway for example selenium and magnesium and copper and zinc these are important minerals to allow a very strong endogenous antioxidant system however what about this ribose 5-phosphate well we can take this ribose 5-phosphate and we can add a nitrogenous group to form this nucleic acid precursor where these atoms came from aspartate and these atoms came from glutamate to form this nucleic acid precursor which can be used

to form perimeters like citing and urine these nucleic acids so so that's pretty cool and another example is we can take this ribose 5-phosphate at a different nitrogenous group to form this nucleic acid precursor where these atoms came from glycine these atoms came from glutamate and these atoms came from aspartate and then these two carbons came from tetrahydrofolate which is a methyl donor but then we form this intermediate which we know can be used to form a purine nucleic acids like adenosine and Guana Swanson so that's pretty cool we can bio synthesize these nucleic acids

as long as we have glucose to go through this pathway to form our bus by phosphate which makes this component and as long as we can form these amino acids to donate the items for this nitrogenous base we have everything we need from central metabolism to biosynthesize nucleic acids so so that's pretty cool but also we can degrade these nucleic acids for example gtp we can degrade it where we get rid of the phosphate groups then then we hydrolyze this bond releasing this nitrogenous base which we can then catabolized to form uric acid which can

safely be disposed in our urine and the same thing with the perimeters we can degrade these perimeters to form these end products which can for example co2 we can simply breathe out ammonia gets converted into urea which can be safely exposed of and and these compounds can also be safely exposed of so we can bio synthesize these these nucleic acids but we can also do safely degrade them and get rid of these waste products we can also use these intermediates of central metabolism to bias in the size of neurotransmitters for example we can take this

intermediate to form a phenylalanine and the truth is we do this with a very low efficiency so most of the phenylalanine we need for died but once we happen alanine we can form tyrosine which can be used to form l-dopa which can be used to form dopamine so that's how he buys synthesized dopamine but we can also go step further if we need norepinephrine and we can also go another step further if we need epinephrine so this is how we buy synthesize a lot of neurotransmitters there are other pathways for example we take a seat

of koay and react it with this choline molecule to form acetylcholine which is a really important neurotransmitter we take this particular intermediate to form a glutamate which can be used to form gaba and glutamine these are two important neurotransmitters we can form tryptophan with very low efficiency so mostly tryptophan we need from our diet but once we have tryptophan we can then form serotonin or go step further to form melatonin and we can also take histidine to form histamine so that's how we biosynthesize a lot of these important neurotransmitters but a lot of them come

from these intermediates of central metabolism also we can take this intermediate to eventually form glycine which we can react with cecile Co a to form this particular intermediate then we take two of these guys and react them with each other to form this compound then we take four of these guys react them with each other to form this porphyrin ring and we know this porphyrin ring with this with this iron group can be used this Parfitt ring can be used to form hemoglobin or myoglobin or the cytochromes important for for metabolism or the electron transport

chain so that's pretty cool we can form this porphyrin ring from these intermediates of central metabolism so now you can see why glycolysis and the Krebs cycle are collectively referred to as central metabolism because these two pathways are at the center of all metabolism that crews in the cell all these different metabolic pathways stem from these intermediates of central metabolism and if you're interested in the link below I have a different link for each of these pathways in more detail for example I have a separate link dedicated for amino acid biosynthesis and another link dedicated

to ketogenesis in other link dedicated to fatty acid synthesis I have different links dedicated to each of these chemical reactions so one last final note yeah we can take these intermediates of central metabolism tebah synthesize lots of important compounds however there are limitations to central metabolism for example by definition we cannot buy synthesized vitamins we cannot take glucose and these intermediates to biosynthesize vitamins for example vitamin b3 niacin yeah this may be a very simple molecule however we simply don't have the enzymes to take these intermediates to by synthesize niacin so therefore this vitamin we

need to get from our diet so that's true for all vitamins we by definition cannot bio synthesize them so these vitamins we must get from our diet then the same thing with minerals with electrolytes for example sodium and potassium and chromium we cannot take these intermediates we can't take glucose with these carbons and oxygens and hydrogen's and transmutate these elements to form sodium ions or potassium ions so therefore these minerals we must get from our diet so so all these with all these elements in purple are the the minerals we must get from our diet

and these minerals are really important some of these minerals for example chromium is really important for certain enzymes to function properly so there are limitations to what we can do with central metabolism