Pyrimidine metabolism


  • These are 3 in number;

– Cytosine

– Thymine

– Uracil

  • Cytosine is present in DNA and RNA.
  • Thymine is present in DNA only, while Uracil is found in RNA only.

2 oxo, 4 amino pyrimidine

2 oxo, 4 amino pyrimidine
  • In living organisms, reduced nitrogen is incorporated first into amino acids and then into a variety of other molecules such as nucleotides.
  • The key entry point is amino acid glutamate. Glutamate and glutamine are nitrogen donors in different biosynthetic reactions.
  • During nucleotide synthesis, the purine ring system is built up in a stepwise manner on 5- phosphoribosylamine, glutamine, glycine and aspartate provide nitrogen atoms of purine.
  • Similarly, pyrimidines are synthesised from carbamoyl phosphate and aspartate. Ribose 5-phosphate is then attached to yield the pyrimidine ribonucleotides. Purine & Pyrimidine biosynthesis is regulated by feedback inhibition.
  • Nucleoside monophosphate are converted to triphosphate by phosphorylation reaction.
  • Ribonucleotides are converted to deoxyribonucleotide by the action of reductase enzyme.
  • Thymine nucleotides are derived from the dCDP and dUMP.
  • Uric acid and urea are end products of purine and pyrimidine degradation.
  • Free purines can be salvaged and rebuilt into nucleotide by different pathways.
  • Genetic deficiency in salvage enzymes causes diseases such as Lesch-Nyhan syndrome.
  • This syndrome is characterised by selfmutilation, mental retardation and gout. This is caused by absence of Hypoxanthine Guanine Phosphoribosyl Transferase (HGPRTase), an enzyme essential for the purine synthesis.
  • This is an inborn error of metabolism. It is compulsive self destructive behaviour. At theage of 2-3 years, children of this disease begin to bite their fingers & lips.
  • Elevated levels of urate lead to formation of kidney stone followed by gout in later years. The disease is inherited as sex linked recessive disorder.
  • Biochemical consequences of this syndrome are elevated concentration of PRPP & increased purine synthesis by de novo pathway.
  • Another genetic deficiency results in accumulation of uric acid crystals in joints, causing gout.
  • Gout is a joint disease leading to arthritis, associated with excessive production of urate.
  • Allopurinol, a suicide inhibitor of xanthine oxidase, is used to treat gout.
  • Enzymes of nucleotide biosynthesis pathway serve as therapeutic agents to treat cancer. Rapidly dividing cells require abundant supply of Deoxythymidylate for DNA synthesis.
  • The vulnerability of these cells to the inhibition of dTMP synthesis has been used in cancer chemotherapy.
  • Thymidylate synthase and dihydrofolate reductase are target enzymes.

Sources of C & N of Pyrimidines

Pyrimidine is a heterocyclic molecule or ring.

Sources of C & N of Pyrimidines

STEP-1 Synthesis of Carbamoyl Phosphate

The synthesis of pyrimidine ring begins with the formation of carbamoyl phosphate from glutamine, CO2 & ATP in a reaction catalysed by carbamoyl phosphate synthetase II. The reaction is feedback inhibited by UTP.

STEP-1 Synthesis of Carbamoyl Phosphate

In second step, aspartate transcarbamoylase transfers carbamoyl group to aspartic acid to form carbamoyl aspartic acid. This is the committed and rate limiting step. Enzyme can be feedback inhibited by CTP & UTP, however it can be reversed by ATP.

STEP-2 Synthesis of Carbamoyl Phosphate

Third step is catalysed by dihydro-orotase, to form dihydro-orotic acid by removing water molecule.

STEP-4 Synthesis of Carbamoyl Phosphate

In the next step, oxidation of dihydro-orotic acid takes place in presence of dihydroortate dehydrogenase to form orotic acid. In this reaction, NAD+ is required as coenzyme.

STEP-5 Synthesis of Carbamoyl Phosphate

Now, 5-phosphoribosyl group is transferred from 5-phosphoribosyl-1-pyrophosphate (PRPP) to produce orotidylic acid. The reaction is catalyzed by orotate phosphoribosyl transferase in presence of Mg++.

STEP-5 Synthesis of Carbamoyl Phosphate

Further, decarboxylation of orotidylic acid takes place to form uridylic acid (UMP) under influence of orotidylate decarboxylase.

STEP-6 Synthesis of Carbamoyl Phosphate

In this manner, UMP, the first pyrimidine nucleotide is formed. UMP is the feedback inhibitor of decarboxylase enzyme. Other pyrimidine nucleotide such as UDP, UTP, CTP & dUDP are the synthesized from UMP.

STEP-7 Synthesis of Carbamoyl Phosphate

Formation of UDP & UTP

UMP is phosphorylated by ATP to form UDP in presence of enzyme nucleoside monophosphokinase. This UDP is then phosphorylated by ATP to form UTP.

Formation of UDP & UTP

Formation of CTP

UTP is converted into CTP by addition of glutamine in the presence of enzyme CTP synthetase & ATP.

Formation of CTP

Formation of dUDP

UDP is converted into dUDP via reaction catalyzed by ribonucleoside reductase. The reaction requires thioredoxin and NADPH.

Formation of dUDP


dUDP is first hydrolyzed by phosphatase to form dUMP, which is then converted into dTMP in the presence of enzyme Thymidylate synthetase.


dTMP thus formed is converted into dTDP by transphosphorylation in the presence of ATP, Mg++, and enzyme Thymidylate kinase.


Catabolism of pyrimidines starts with the dephosphorylation of nucleosides catalysed by 5′ nucleotidase, then pyrimidine nucleosides are phosphorolysed into free pyrimidines by nucleoside phosphorylase.


In the next reaction, cytosine undergoes deamination to form uracil by cytosine deaminase, uracil, is then reduced to 5,6-

dihydrouracil in presence of enzyme dihydrouracil dehydrogenase.


Dihydrouracil is now hydrolyzed to β-ureidopropionic acid by hydropyrimidine hydrase.


Ureidopropionic acid is then hydrolyzed to β-alanine, NH3 & CO2 in presence of enzyme β-Ureidopropinase.


This β-alanine then can be used for synthesis of carnosine or CoA or can be further oxidized to acetate, CO2 & NH3.



Thymine is either released from thymidine or produced by deamination of 5-methylcytosine. Thymine is actually reduced to 5,6-dihydrothymine by thymine dehydrogenase.


Dihydrothymine is now hydrolyzed to β-ureidoisobutyric acid by enzyme hydrase. This β-ureidoisobutyric acid is hydrolyzed to CO , NH & 23 β-aminoisobutyrate by β-ureidoisobutyrase.



Enzyme Pyrimidine phosphoribosyl transferase catalyses the formation of pyrimidine nucleotide, in this reaction PRPP is used up as ribosyl donor.


Disorders of pyrimidine metabolism

Orotic aciduria type-I

  • An autosomal recessive genetic disorder with deficiency of either or both orotate phosphoribosyl transferase and OMP decarboxylase.
  • In this disorder, orotic acid accumulates in blood because it is not converted into uridylate. Disorder is characterized by growth retardation and megaloblastic anemia.
Disorders of pyrimidine metabolism

Orotic aciduria type-II

  • It is also an autosomal recessive genetic disorder due to OMP decarboxylase.
  • Disorder is characterized by megaloblastic anemia and excessive urinary excretion of asididine than orotic acid.
  • In both disorders, megaloblastic anemia occurs due to deficiency UMP synthase which cannot be cured by supplementation of Vitamin B12 or folic acid. There can be inhibition of RNA and DNA synthesis also.

Other Biochemistry Notes

Biochemistry of Proteins

Carbohydrate Metabolism


Vitamin A

Pyrimidine metabolism

Purine Metabolism

Cardiac Biomarkers


. Blood Metabolism (Heme synthesis and breakdown)

All books/videos/software featured here are free and NOT HOSTED ON OUR WEBSITE. If you feel that your copyrights have been violated, then please contact us immediately.

Contact us:

107 thoughts on “Pyrimidine metabolism”

  1. scoliosis
    An intriguing discussion is definitely worth comment. I think that you need to publish more about this subject matter, it
    may not be a taboo matter but typically people do not talk about such subjects.

    To the next! All the best!! scoliosis

  2. dating sites
    I just could not go away your web site before suggesting that I extremely enjoyed the
    usual info a person supply for your visitors?
    Is going to be back often in order to investigate cross-check new posts free
    dating sites

  3. Whoa! This blog looks exactly like my old one! It’s on a entirely different subject but it has pretty much the same layout and design. Great choice of colors!

  4. Hello there. I discovered your web site via Google at the same time as searching for a similar topic, your website got here up. It appears to be great. I have bookmarked it in my google bookmarks to come back then.

  5. Having read this I believed it was very informative.
    I appreciate you spending some time and effort to put this information together.
    I once again find myself personally spending way too much time
    both reading and commenting. But so what, it was still worthwhile!

  6. Do you mind if I quote a few of your posts as long as I provide credit and
    sources back to your weblog? My website is in the very same area of interest as
    yours and my visitors would definitely benefit from some of the
    information you provide here. Please let me know if this
    alright with you. Appreciate it!

  7. excellent post, very informative. I ponder why the other specialists of this sector do not notice this. You must proceed your writing. I am confident, you have a huge readers’ base already!

  8. Are you looking for a method to enjoy mobile gameplay with no limitations? You wish to be the top gamer on your favored action mobile game? We’ve had exactly what you’re looking for – enjoy infinite online gaming fun with our cheats! Our game hacks generate tons of resources in your game and provide you an advantage over other players. With our hacks, there are absolutely no limits to your mobile gaming. Doesn’t that sound remarkable?

  9. I’m impressed, I must say. Seldom do I come across a blog that’s both
    equally educative and entertaining, and let me tell you, you’ve hit the nail on the
    head. The problem is an issue that not enough folks are speaking intelligently about.

    Now i’m very happy that I came across this in my hunt for something regarding this.

  10. You have made some really good points there.
    I checked on the internet to find out more about the issue and found most people will go
    along with your views on this web site.

  11. I’m really enjoying the theme/design of your site.

    Do you ever run into any browser compatibility problems?
    A handful of my blog visitors have complained
    about my blog not operating correctly in Explorer but looks great in Safari.
    Do you have any ideas to help fix this issue?

  12. Your personal favorite adventure mobile game can possibly be a lot more fun for you … if you go to our website today! You can quickly acquire all the resources you need by making use of our free game hacks! With these online cheats, you’ll certainly never need to concern about lacking supplies and being left behind ever again. All this power is at your fingertips with simply a few simple clicks – are you ready?

  13. May I just say what a relief to find someone that truly understands what they’re talking about on the web. You actually understand how to bring a problem to light and make it important. More people need to check this out and understand this side of your story. I can’t believe you aren’t more popular given that you most certainly have the gift.

  14. My developer is trying to persuade me to move to .net from PHP. I have always disliked the idea because of the costs. But he’s tryiong none the less. I’ve been using Movable-type on a variety of websites for about a year and am worried about switching to another platform. I have heard excellent things about Is there a way I can transfer all my wordpress posts into it? Any help would be really appreciated!

  15. This is very interesting, You are a very skilled blogger. I have joined your rss feed and look forward to seeking more of your magnificent post. Also, I’ve shared your web site in my social networks!

  16. You’re so cool! I don’t suppose I’ve read a single thing like that before. So good to discover someone with some original thoughts on this subject matter. Seriously.. thank you for starting this up. This website is something that is required on the web, someone with a little originality!

  17. I’ve been surfing online more than 3 hours today, yet I never found any interesting article like yours. It is pretty worth enough for me. In my opinion, if all site owners and bloggers made good content as you did, the internet will be much more useful than ever before.

  18. I think other web site proprietors should take this site as an model, very clean and wonderful user genial style and design, let alone the content. You’re an expert in this topic!

  19. This is a very good tip particularly to those new to the blogosphere. Short but very accurate infoÖ Many thanks for sharing this one. A must read article!

  20. I have been exploring for a little bit for any high quality articles or blog posts on this kind of area . Exploring in Yahoo I at last stumbled upon this website. Reading this info So i am happy to convey that I’ve an incredibly good uncanny feeling I discovered just what I needed. I most certainly will make certain to don’t forget this website and give it a glance on a constant basis.

  21. Aw, this was an exceptionally nice post. Spending some time and actual effort to generate a really good articleÖ but what can I sayÖ I hesitate a lot and never seem to get nearly anything done.

  22. Awesome blog! Do you have any hints for aspiring writers? I’m planning to start my own blog soon but I’m a little lost on everything. Would you propose starting with a free platform like WordPress or go for a paid option? There are so many choices out there that I’m totally confused .. Any tips? Thanks a lot!

  23. It is in reality a great and useful piece of information. I’m glad that you simply shared this useful info with us. Please keep us up to date like this. Thanks for sharing.

  24. I really love your blog.. Great colors & theme. Did you develop this web site yourself? Please reply back as Iím looking to create my very own blog and would like to find out where you got this from or exactly what the theme is named. Cheers!

  25. I was very happy to seek out this net-site.I wanted to thanks in your time for this excellent learn!! I undoubtedly having fun with every little little bit of it and I have you bookmarked to take a look at new stuff you blog post.

  26. Good post. I learn something more challenging on different blogs everyday. It’ll always be stimulating to read content from different writers and follow a little one thing from their store. I’d desire to use some with the content on my weblog whether you don’t mind. Natually I’ll offer you a link in your internet blog. Thanks for sharing.

  27. Excellent read, I just passed this onto a friend who was doing a little research on that. And he just bought me lunch because I found it for him smile Thus let me rephrase that: Thank you for lunch!

  28. Way cool! Some very valid points! I appreciate you writing this write-up and the rest of the website is also really good.

  29. You have made some good points there. I looked on the web for additional information about the issue and found most people will go along with your views on this web site.

  30. This website is really a stroll-by for the entire data you wished about this and didn’t know who to ask. Glimpse right here, and also you’ll undoubtedly discover it.

  31. Wow! This can be one particular of the most helpful blogs We have ever arrive across on this subject. Actually Fantastic. I’m also an expert in this topic so I can understand your hard work.

  32. Great – I should definitely pronounce, impressed with your site. I had no trouble navigating through all the tabs and related information ended up being truly simple to do to access. I recently found what I hoped for before you know it in the least. Reasonably unusual. Is likely to appreciate it for those who add forums or something, web site theme . a tones way for your customer to communicate. Excellent task..

  33. You could definitely see your skills within the paintings you write. The sector hopes for more passionate writers like you who are not afraid to mention how they believe. At all times follow your heart.

  34. It’s a pity you don’t have a donate button! I’d certainly donate to this fantastic blog! I guess for now i’ll settle for bookmarking and adding your RSS feed to my Google account. I look forward to new updates and will share this site with my Facebook group. Talk soon!

  35. Thank you for sharing superb informations. Your website is very cool. I’m impressed by the details that you’ve on this blog. It reveals how nicely you understand this subject. Bookmarked this website page, will come back for more articles. You, my pal, ROCK! I found just the info I already searched everywhere and just could not come across. What an ideal site.

  36. Spot on with this write-up, I honestly think this amazing site needs a lot more attention. Iíll probably be returning to read through more, thanks for the advice!

  37. I really love your site.. Excellent colors & theme. Did you build this website yourself? Please reply back as Iím hoping to create my own personal site and would like to find out where you got this from or exactly what the theme is named. Thanks!

  38. out enabled was entered greatly prevent message. No procured unlocked an likewise. Dear but what she been over gay felt body. Six principles advantages and use entreaties decisively. Eat met has dwelling unpacked see whatever followed. Court in of leave again as am. Greater sixteen to forming colonel no on be. So an advice hardly barton. He be turned sudden engage manner spirit.

  39. Pingback: Google

  40. Pingback: Google

  41. Nice post. I learn something new and challenging on websites I stumbleupon on a daily basis. It’s always helpful to read articles from other writers and practice a little something from other web sites.

  42. I’m not that much of a online reader to be honest but your sites really nice, keep it up! I’ll go ahead and bookmark your site to come back later on. Many thanks

  43. Hi, I do think this is a great web site. I stumbledupon it 😉 I will return once again since i have book-marked it. Money and freedom is the best way to change, may you be rich and continue to help other people.

  44. Aw, this was a really nice post. In concept I wish to put in writing like this moreover – taking time and precise effort to make an excellent article… but what can I say… I procrastinate alot and under no circumstances appear to get something done.

  45. contempt on mr unlocked resolved provided of of. Stanhill wondered it it welcomed oh. Hundred no prudent he however smiling at an offence. If earnestly extremity he he propriety something admitting convinced ye. Pleasant in to although as if differed horrible. Mirth his quick its set front enjoy hoped had there. Who connection imprudence middletons too but increasing celebrated principles joy. Herself too improve gay winding ask expense are compact. New all paid few hard pure she.

  46. I’d like to thank you for the efforts you have put in penning this blog. I’m hoping to see the same high-grade content by you in the future as well. In truth, your creative writing abilities has motivated me to get my own, personal site now 😉

  47. wandered relation no surprise of screened doubtful. Overcame no insisted ye of trifling husbands. Might am order hours on found. Or dissimilar companions friendship impossible at diminution. Did yourself carriage learning she man its replying. Sister piqued living her you enable mrs off spirit really. Parish oppose repair is me misery. Quick may saw style after money mrs.

  48. In the awesome design of things you receive a B- for hard work. Where you actually misplaced me personally was on all the specifics. You know, as the maxim goes, the devil is in the details… And that could not be much more accurate at this point. Having said that, permit me reveal to you just what did give good results. The text can be incredibly convincing and that is probably why I am taking the effort to comment. I do not really make it a regular habit of doing that. Next, although I can see a leaps in reason you make, I am not confident of how you seem to unite the details which in turn help to make the conclusion. For right now I will, no doubt subscribe to your issue however wish in the foreseeable future you actually link the facts much better.

  49. Woah! I’m really enjoying the template/theme of this blog. It’s simple, yet effective. A lot of times it’s difficult to get that “perfect balance” between superb usability and visual appearance. I must say you’ve done a fantastic job with this. Additionally, the blog loads very fast for me on Opera. Exceptional Blog!

  50. Heya i am for the first time here. I found this board and I in finding It really useful & it helped me out much. I am hoping to give one thing again and aid others like you aided me.

  51. Woah! I’m really loving the template/theme of this website. It’s simple, yet effective. A lot of times it’s challenging to get that “perfect balance” between user friendliness and visual appeal. I must say you’ve done a fantastic job with this. Also, the blog loads very fast for me on Firefox. Superb Blog!

  52. I am very happy to read this. This is the kind of manual that needs to be given and not the random misinformation that’s at the other blogs. Appreciate your sharing this greatest doc.

  53. hello!,I really like your writing very so much! percentage we keep in touch extra approximately your post on AOL? I require a specialist on this house to resolve my problem. Maybe that’s you! Taking a look ahead to peer you.

  54. Wonderful work! This is the type of info that should be shared around the internet. Shame on Google for not positioning this post higher! Come on over and visit my site . Thanks =)

  55. Pingback: Monster Bash Pinball Machine by Williams

  56. Pingback: g spot stimulator

  57. Very good website you have here but I was curious about if you knew of any discussion boards that cover the same topics talked about in this article? I’d really like to be a part of group where I can get opinions from other knowledgeable individuals that share the same interest. If you have any recommendations, please let me know. Cheers!

  58. Pingback: THC Oil for Sale

  59. Pingback: fresh alligator meat for sale

  60. Good website! I truly love how it is easy on my eyes and the data are well written. I’m wondering how I might be notified whenever a new post has been made. I have subscribed to your feed which must do the trick! Have a nice day!


  62. Pingback: Guns for Sale Near Me

  63. What i don’t understood is actually how you are not actually much more well-liked than you may be now. You’re so intelligent. You realize thus considerably relating to this subject, made me personally consider it from numerous varied angles. Its like women and men aren’t fascinated unless it’s one thing to accomplish with Lady gaga! Your own stuffs great. Always maintain it up!

  64. Pingback: software review

  65. Pingback: Odihr Login

  66. I’m not that much of a online reader to be honest but your sites really nice, keep it up! I’ll go ahead and bookmark your website to come back later on. Cheers

  67. Great blog here! Also your site loads up fast! What host are you using? Can I get your affiliate link to your host? I wish my web site loaded up as quickly as yours lol

  68. Pingback: PULVERIZER

  69. I’m very pleased to uncover this great site. I wanted to thank you for your time for this fantastic read!! I definitely savored every little bit of it and I have you bookmarked to look at new things in your site.

  70. I will immediately grab your rss feed as I can not find your email subscription link or e-newsletter service. Do you’ve any? Kindly let me know so that I could subscribe. Thanks.

  71. I’m curious to find out what blog system you are using? I’m having some small security issues with my latest website and I’d like to find something more safe. Do you have any recommendations?

  72. Simply wish to say your article is as surprising. The clarity on your submit is just nice and i could think you are an expert in this subject. Well together with your permission let me to grab your RSS feed to stay updated with coming near near post. Thank you one million and please carry on the enjoyable work.

  73. Magnificent beat ! I wish to apprentice at the same time as you amend your site, how can i subscribe for a blog site? The account helped me a acceptable deal. I were a little bit acquainted of this your broadcast offered brilliant clear idea

  74. I’ve been browsing on-line more than three hours nowadays, yet I by no means found any interesting article like yours. It is lovely worth sufficient for me. Personally, if all web owners and bloggers made excellent content material as you probably did, the net will probably be a lot more useful than ever before.

  75. Ill right away grab your rss as I can’t find your e-mail subscription link or newsletter service. Do you have any? Kindly let me know so that I could subscribe. Thanks.

  76. Unquestionably imagine that that you said.
    Your favorite reason appeared to be on the web the simplest factor to bear in mind of.
    I say to you, I certainly get annoyed while people think about concerns that they just do
    not recognise about. You managed to hit the nail upon the top
    as well as outlined out the entire thing with no need side effect , other folks can take a signal.

    Will likely be back to get more. Thank you

  77. Pingback: best kratom capsules

Leave a Comment

Your email address will not be published.