BBT 302 unit 4 (1).pdf

BBT 302: Molecules of Life Mrs. Mary David, Asst. Professor, SBB, DYPU Unit IV Nucleic acids and Vitamins  Lecture 14 Nucleic acids, nucleotides, functional groups , formation of phosphodiester linkage, structure of...

BBT 302: Molecules of Life Mrs. Mary David, Asst. Professor, SBB, DYPU Unit IV Nucleic acids and Vitamins  Lecture 14 Nucleic acids, nucleotides, functional groups , formation of phosphodiester linkage, structure of DNA (Watson – Crick model),  Nucleic Acids Nucleic acids are molecules that store information for cellular growth and reproduction. There are two types of nucleic acids: - deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) These are polymers consisting of long chains of monomers called nucleotides A nucleotide consists of a pentose sugar (ribose in RNA with an OH at the 2’ C atom and deoxyribose in DNA with an H at the 2nd C atom), a nitrogen base and a phosphate group. The C-atoms in the sugar are numbered as 1’,2’, 3’,4’, 5’ so that they can be distinguished from the members of the nitrogen base 4 Nucleosides nucleotides and Nucleic acids http://biology-forums.com/gallery/33_23_06_11_4_12_30.jpeg  The Nitrogen bases The nitrogen bases in nucleotides are planar. They can therefore be stacked. They are of two types. The bicyclic purines, Adenine (A) and Guanine (G) The monocyclic pyrimidines, Cytosine (C), Thymine (T) and Uracil (U) 5 Introduction to nucleosides nucleotides and Nucleic acids http://www2.samford.edu/~djohnso2/44962w/333/chapt10/10_07_bases.jpg  Tautomeric forms of bases in DNA https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcRy3rZ_XkP8gk- 6 Nucleosides nucleotides and Nucleic acids ItNvtVhkjhVuN58lVUq8qBmQnHTQTNxURQ9KnMg  Base pairing in tautomeric forms of bases in DNA https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcSiHmyXmycGG0I0487hKRacrBw2- 7 Nucleosides nucleotides and Nucleic acids 0VKn5DWD0DczCqQlLH937gHLA  Modified bases Nucleic acids also contain unusual or modified bases Unusual bases are the additional purines and pyrimidines which are included by nucleic acids at considerably smaller quantities 5-methyl cytosine → DNA N6-methyl adenine → DNA N6,N6-dimethyl adenine → RNA 5-OH methyl cytosine → DNA Pseudouracil → RNA 7-methylguanine → RNA N2-methylguanine → DNA 8 Nucleosides nucleotides and Nucleic acids  Modified bases 9 Nucleosides nucleotides and Nucleic acids http://4.bp.blogspot.com/-WlQzLBDWlHM/TitaYLGyn8I/AAAAAAAALOQ/4Pd93o5JyeI/s1600/tmp.bmp  Modified bases http://mol-biol4masters.masters.grkraj.org/html/Ribose_Nucleic_Acid3A-Transfer_RNA_files/image016.gif 10 Nucleosides nucleotides and Nucleic acids  Modified bases – functions They serve important functions in oligonucleotide recognition in DNA and RNA. The presence of specific methylated nucleotide bases allows the bacterial DNAses arising from viral infection in bacteria to distinguish between native and foreign oligonucleotides Methylated cytosine in the promoter region in both prokaryotes and Eukaryotes typically is responsible for repressing gene expression. Unusual bases play role in regulation of half-life of RNAs Methylated purines in plants: Theophylline → Dimethylxanthine → Tea Caffeine → Trimethylxanthine → Coffee Theobromine → Cocoa 11 Nucleosides nucleotides and Nucleic acids  Modified bases – Hypoxanthine and Xanthine They are intermediates in the catabolism of purines. They can be produced by spontaneous deamination of adenine and guanine, respectively and be a cause for mutation 12 Nucleosides nucleotides and Nucleic acids  Nucleosides and Nucleotides A nucleoside consists of a nitrogen base linked by the N9 of a purine or N1 of a pyrimidine by a glycosidic bond to the C1’ of a ribose or deoxyribose. Nucleosides are named by changing the the nitrogen base ending to -osine for purines and –idine for pyrimidines A nucleotide is a nucleoside with a phosphate group attached by a phosphate ester bond to the C5’ OH group of ribose or deoxyribose. Nucleotides are named using the name of the nucleoside followed by 5’- monophosphate https://upload.wikimedia.org/wikipedia/commons/thumb/e/e2/Nucleotides_1.svg/ 700px-Nucleotides_1.svg.png http://www.mikeblaber.org/oldwine/BCH4053/Lecture18/nucleoside01.jpg 13 Nucleosides nucleotides and Nucleic acids  Names of Nucleosides and Nucleotides 14 Nucleosides nucleotides and Nucleic acids http://images.slideplayer.com/15/4643010/slides/slide_12.jpg  The different nucleotides 15 Nucleosides nucleotides and Nucleic acids http://www.bio.miami.edu/dana/pix/nucleotides.jpg  Syn and Anti- conformations of nucleotides The nucleosides in the DNA duplex adopt the anti conformation (there are very few exceptions to this rule, one of which is guanosine monophosphate, in which the guanine base adopts the syn conformation about the glycosidic bond) especially in Z DNA when purines may be in syn conformation and pyrimidines in anti conformation, giving Z DNA its characteristic zig-zag form. 16 https://upload.wikimedia.org/wikipedia/commons/thumb/6/69/Adenosine_syn_anti_conformation.svg/620px- 16 Nucleotides and Nucleic acids Adenosine_syn_anti_conformation.svg.png  Properties of Nucleotides Nucleotides absorb uv light at 260nm, a property which can be attributed to the cyclic nitrogen bases. This property is used to quantitate DNA and also to check its purity. Nucleotides have a negative charge on account of its phosphate group. This property is taken advantage of in gel electrophoresis of nucleic acids. 17 Nucleosides nucleotides and Nucleic acids Thank You