Nucleic Acids: Structure, Digestion, and Absorption in the Body

1. By: Micheal, Robert, & Narjes Nucleic Acids (DNA, RNA)

2. Nucleic Acids (NA) are nonessential nutrients, because they can be synthesized in the body. • Nucleic Acid: polymeric macromolecules made from nucleotide monomers • Nucleotide are Building block of nucleic acid, The two DNA strands are made of two monomer units called nucleotides. Consists of purine/pyrimidine base , ribose/deoxyribose and phosphates. • Nucleoside: Consist of purine or pyrimidine base, and ribose or deoxyribose • Purines and Pyrimidinesare nitrogenous bases that make up the two different kinds of nucleotide bases in DNA and RNA. • adenine and guanine are purines • thymine, uracil and cytosine are pyrimidines

4. Purine: A nitrogen-containing substance derived from uric acid Purine bases: Adenine and Guanine Pyrimidine: A nitrogenous base with a six-sided structure Pyrimidine bases: Cytosine, Thymine, Uracil • Base Paring in DNA: A=T, C=G • Base Pairing in RNA: A=U, C=G • Main functions: • 1. DNA/RNA Replication • Short Term energy storage of ATP

5. Mouth: Responsible for mechanical digestion - Mastication and deglutition Esophagus: Responsible for transportation of the bolus to the stomach - Deglutition and Peristalsis. Stomach: Responsible for denaturation of Nucleic Acids and beginning chemical digestion Small Intestine: Responsible for completing chemical digestion by way of enzyme release via pancreatic juice

6. Digestion in the Stomach • It has been found that human gastric juice is able to significantly digest ingested NAs. Further study demonstrates that the dominant enzyme in gastric juice, pepsin, was responsible for this activity. • The harsh pH of the stomach is responsible for denaturing the DNA strands into individual strands. • From there, Pepsin digests NAs at specific sequences, leaving them in fragments with a 3′-phosphate end and a 5′-OH end. • The active site for cleaving phosphodiester bonds is believed to be the same as that used for digesting peptide bonds in proteins. • Some research would argue then that chemical digestion starts in the stomach rather than the small intestine as others would suggest.

7. Digestion in Small Intestine

8. Nucleic acid fragments then enter the small intestine from the stomach dissolved in gastric chyme • As gastric chyme enters the duodenum, the pancreas delivers two enzymatic nucleases: • Ribonuclease (RNAse) • Deoxyribonuclease (DNAse) • There are two types of nucleic enzymes: • Endonucleases & Exonucleases Enzymes that break apart a polynucleotide chain by cleaving successive nucleotides from the ends of the polynucleotide molecule. Enzymes that break apart a polynucleotide chain by cleaving the phosphodiester bonds between nucleotides within a polynucleotide chain.

9. Ribonuclease: catalyzes the breakdown of RNA into ribonucleotides. Deoxyribonuclease: catalyzes the breakdown of DNA into deoxyribonucleotides. These individual ribo- and deoxyribonucleotides are still too large and are required to be broken down into smaller components until they can be absorbed in the small intestine.

10. Brush Border Enzymes Further digestion occurs at the microvilli in the S.I. from two enzymes: Phosphatases - catalyze the cleavage of a phosphate group from a nucleotide to form a nucleoside and a phosphate ion. Nucleosidases - catalyze the breaking of the covalent bond between the nitrogenous base and the pentose sugar of a nucleoside. These Enzymes are responsible for breaking nucleotides into their individual absorbable components: phosphate ions, nitrogenous bases & pentose sugars

11. Nucleic acid absorption Nucleic acid Absorption end products: mainly occur in the duodenum and jejunum of the small intestine, at the intestinal villus. • All nucleic acid are absorbed as: • Nitrogenous bases • Pentose sugar • Phosphate ions

12. Membrane transport proteins carry the products of nucleotide digestion into epithelial cells from the lumen. Some involve active transport, other involved secondary active transport(direction of its concentration gradient).Through diffusion , the products of nucleotide digestion are transported from the intestinal epithelial cells: • Across the basolateral membrane • Into the interstitial fluid • And finally into the blood capillaries of the intestinal villi

14. The nucleotide digestion products are transported by blood circulation to the liver and other tissues where they undergo further degradation. Uric acid which is the end product of purine degradation exist as sodium ureate in plasma. Maximum amount of sodium ureate that can dissolve in the blood plasma is about 7 mg/100 ml. At this point there will be saturation of blood with sodium ureate.

15. Purine Catabolism

16. Nucleotides are absorbed into intestinal mucosa cells, where they are degraded to three components: Base, Pentose, and phosphate. Pentose is absorbed but base is degraded and excreted. Duodenum and Jejunum absorb the products in the epithelial cells. The end product of purine catabolism is uric acid in humans.

18. Hyperuricemia •An abnormally high level of uric acid in the blood. •High levels of uric acid in the blood can lead to gout, which is a medical condition characterized by recurrent attacks of acute inflammatory arthritis. Gout

19. Absorption Occurs in duodenum and jejunum of small intestines Absorbed at the intestinal villus. Goes from lumen to epithelial cells then across the basolateral membrane into the interstitial fluid into the blood and then to the liver and other tissues for further degradation.

20. 1- De Novo Synthesis The Main synthesis pathway of nucleotides. De Novo synthesis creates purine nucleotides through anabolism. Can be Divided into two phases

21. Stage one of De Novo Synthesisformation of inosine monophosphateRequires five moles of ATP, two moles of glutamine, one mole of glycine, one mole of CO2, one mole of aspartate and two moles of formate. PRPP SynthetaseR5P+ATP--------------------->PRPP+AMP amidophosphoribosyltransferaseH2O+PRPP+Glutamine---------------------->PRA+ Glutamate+ PPiGlutaminase domain: Glutamine --> NH3+GlutamatePhosphoribosyltransferase domain: PRPP+ NH3 → PRA+PPi

22. 10 step reaction for IMPPRPP+H20+glutamine------->Glutamate+Pi2. Glycine+ATP+PRA------------------------->Glycinamide ribotide+ADP+Pi 3. GAR+N10-formyl-THF-------------------->THF +Formylglycinamide ribotide4. FGAR+ATP+Glutamine----> Formylglycinamine ribotide+ADP+Pi+Glutamate5. FGAM+ATP------------------------>ADP+Pi+5 aminoimidazole ribotide6. AIR+CO2-------------------------> Carboxylaminoimidazole ribotide7. Aspartate+ATP---->ADP+Pi+5-aminoimidazole-4 (N-Succinylocarboxamide) ribotide8.SAICAR--------->Fumerate+5-aminoimidazole-4-carboxylamide ribotide9.AICAR+ N10 formyl-THF-------------> THF+ FAIRCAR10. FAICAR+H20 IMP

23. Stage two: conversion of IMP to either AMP or GMPRoute one IMP to GMP Adenylosuccinate synthetase(ADSS)Aspartate+GTP+IMP----------------------> GDP+Pi+ Adenylosuccinate Adenylosuccinate lyase (ADSL)Adenylosuccinate----------------------> Fumerate+ AMPRoute Two IMP to GMPIMP dehydrogenase 1IMP+H20+NAD+--------------->NADH+H+Xanthylate GMP SynthetaseXanthylate+ Glutamine+ATP---------------> AMP+PPi+ Glutamate +GMP

24. De Novo Pathway PRPP IMP UMP UDP GMP AMP DUDP CTP DUMP DTMP

25. De Novo Pathway SummaryPurine ring is built from one or a few atoms at a time and attached to the ribose ring throughout the process.Pyrimidine ring is synthesized from orotate and attached to the ribose phosphate.Ribose phosphate is converted to common pyrimidine nucleotidesThe enzymes involved in De-novo synthesis are present as large multienzyme complexes.

26. Salvage pathway Used to recover the Nucleosides and bases that formed from the degradation of DNA and RNA

27. Purine salvage pathway RNA or DNA GMP IMP AMP Purines AMP GMP Adenosine HGPRT (Hypoxanthine-guanine phosphoribosyltransferase) Adenosine Deaminase Hypoxanthine Hypoxanthine & Guanine Inosine

28. Product pathways GMP IMP AMP Guanosine adenosine Guanine inosine hypoxanthine xanthine uric acid

29. Defecation Reflex • After electrolytes and H2O have been absorbed, the waste passes to the rectum from the sigmoid colon. • This causes an increase in rectal pressure, and stretch receptors send a signal to the spinal cord causing the urge to defecate. • leads to contraction of sigmoid colon, and rectum and relaxation of internal anal sphincter muscles. • Voluntary muscle response occurs due to habit either allowing or disallowing defecation. If it is convenient to do so external sphincter muscles relax.

30. Defecation Reflex •During defecation the longitudinal rectal muscles contract to increase pressure. • •Defecation is normally assisted by taking a deep breath and trying to expel this air against a closed glottis causing contraction of abdominal and pelvic skeletal muscles. • This forced defecation is a similar sensation to lifting a heavy object or performing the valsalva maneuver.

31. Valsalva Maneuver •Forcefully expulsing air while plugging your nose and closing your mouth •Clears pressure in the middle ear (air travel, scuba diving, pressurization of a space suit) •The Valsalva Maneuver aids in creating pressure in the chest such that the thorax exerts pressure on the digestive tract in the abdomen •Used clinically in a variety of ways: diagnosis of cardiovascular, neurological or urogenital issues, palpating subclavicular lymph nodes, etc.

32. 4 stages: Initial Pressure Rise - pressure rises in the chest forcing blood out of pulmonary circulaiton = slight increase in stroke volume Reduced Venous Return and Compensation - return of blood to the heart is impeded by pressure in the chest = CO and SV falls Pressure Release - pressure on chest is released allowing pulmonary vessels and aorta to return to reexpand = venous blood can enter the heart and chest Return of Cardiac Output - rapid increase in CO peaking above baseline and returning to normal after a brief stint at elevated levels Valsalva Maneuver and the heart

33. Valsalva Maneuver Cont. • Any deviation from this normal pattern would suggest abnormal heart function or perhaps improper autonomic nervous control of the heart. • The valsalva maneuver can be used to diagnose issues with cervical nerves. The pressure build up can often times cause radiating pain and help to identify a nerve impingement • subclavicular lymph node enlargement is usually an indicator of cancers. Having a patient perform a valsalva maneuver pushes the lungs up making lymph nodes more accessible for palpation. • Forcing yourself to urinate of defecate is a similar pressure felt to valsalva maneuver, and urogenital leakage during such demonstration could be indicative of sphincter deficiency.

34. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4500949/figure/f6/https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4500949/figure/f6/ https://www.ncbi.nlm.nih.gov/pubmed/26168909 http://www.johnwiley.net.au/highered/interactions/media/Energy/content/Energy/dig6a/bot.htm http://science-forums.com/index.php?action=gallery;sa=slideshow;id=776 Fox, Stuart I., Human Physiology 13th ed., New York, NY: McGraw-Hill 2013 Pgs. 619-659 Works Cited

35. Checklist: Group 4 Requirements: Digestion of Nucleic Acids (DNA and RNA):Chemical Structures; Function/Digestion in Mouth?; Esophagus?; Stomach?; Small Intestine?;Absorption: where? how? all enzymes? fate?Topics to mention and terms to define for the class: pyrimidine; purine; base; endonuclease; nucleotide; nucleoside; exonuclease; nucleotidases; de-novo synthesis; salvage pathway; purine degradation into uric acid (gout) and hyperuricemia.Defecation Reflex;Valsalva’s maneuver;