DNA & RNA

DNA & RNA for MBBS course

1. DNA & RNA Dr. Farhana Atia Assistant Professor Department of Biochemistry Nilphamari Medical College, Nilphamari Email: [email protected]

2. Traits DNA RNA Denote Deoxyribonucleic acid Ribonucleic acid Location Nucleus & mitochondria Nucleus & cytoplasm Pentose sugar Deoxyribose sugar Ribose sugar Base AGCT AGUC Double stranded deoxyribosephosphate backbone Strands are antiparallel Single strand No backbone Complementary base pairing No

3. DNA RNA Can not be hydrolyzed due to absence of 2’ hydroxyl group Can be hydrolyzed by alkali due to presence of 2’ OH group. Alkali liability of RNA is used in diagnostic & analytic purpose. Molecular size- Large Smaller Function- Chemical basis of heredity & fundamental unit of genetic information. Protein synthesis.

4. FUNCTIONS OF DNA Chemical basis of heredity & fundamental unit of genetic information. Genetic information stored in nucleotide sequence of DNA serve two purpose Source of information for synthesis of all protein molecule of cells & organism. DNA molecule serve as a template for transcription of information of RNA. Provide information inherit by daughter cell/ offspring. Replicate information into daughter DNA molecule.

5. Watson & Crick Model o f DNA Structure Introduction: DNA is a poly deoxyribonucleotide that contains many mono deoxyRNT . Covalently linked by 3 ′ 5 ′ phosphodiester bond. Double stranded molecule Two strands wind around anti- parallelly each other forming a double helix.

6. Salient features Right handed double helix 3 ′ 5 ′ phosphodiester bond Base pairing rule H bonding Anti parallel Other feature

7. Right handed double helix The two strands are twisted around a central axis in the form of right handed double helix similar to a spiral staircase. Right handed : as one looks down the double helix- clockwise direction Hand rail : Sugar & Phosphate group Steps : Bases jutting inside Base : perpendicular to helix axis Sugar : Right angle to the axis

8. Right handed double helix

9. 3 ′, 5 ′- phosphodiester bond Join the 5’ OH group of on the d-pentose of one nucleotide to 3’ OH group on d-pentose of another nucleotide through a P bond . Possesses a polarity; one end has a 5’ OH or P terminal while the other has a 3’ OH or P terminal.

10. Base pairing rule The 2 strands are always complementary to each other A of one strand are in pair with T of opposite strand, while G with C. The base pairing is called Chargaff’s rule. Chargaff’s rule : no of purine is equal to the no of pyrimidine . Stabilize the structure of double helix.

11. H Bonding Strands are held together mainly by H bond between purine & pyrimidine bases. A-T : 2 H bonds G-C : 3 H bonds, stronger [more resistant to melting] Stabilize structure of double helix.

12. Anti-parallel The two strands run anti-parallel. One strand runs in 5’ to 3’ direction Another runs in 3’ to 5’ direction . Other Each strand act as a template for the synthesis of opposite strand during replication process.

13. Template strand : genetic information resides in sequence of NT of one strand. It copied during RNA synthesis. So called non-coding strand . Coding strand : Opposite strand which matches the sequence of RNA transcript that encode protein [contain U instead of T ] A single turn of double helix : 10 bp [34 A] WIDTH- 20 A

14. Denaturation of DNA Separation The loss of helical structure is called denaturation. The double strand of DNA may be denatured & separated by heat. This is called melting of DNA. Melting temperature [Tm] is the temperature when half of the helical structure is denatured. Annealing : Melted structures are re-associated at lowering of temperature.

15. Denaturation & Annealing

16. DNA Transcription Translation Trait RNA Protein The “Central Dogma” of Genetics RNA processing

17. RNA Unbranched polymeric molecule composed of mono-nucleotide joined together by phospho -di-ester bond Contain ribose sugar & pyrimidine base uracil instead of deoxy -ribose & thymine in DNA Different types of RNA differs from each other in terms of size, function & special structural modification

18. Classes of eukaryotic RNA RNA Abundance Function in Function Ribosomal ( rRNA ) 80% of total Cytoplasm Structural framework for ribosome Machinery for protein synthesis Messenger (mRNA) 2-5% of total Nucleus, migrates to ribosome in Cytoplasm Transfer of genetic information from nucleus to cytoplasm or from gene to ribosome Transfer ( tRNA ) 15% of total Cytoplasm Transfer of amino acid to ribosome & correct sequence insertion Small RNAs Small nuclear ( snRNA ) <1% of total Processing of rRNA & mRNA Involved in gene regulation Micro ( miRNA ) <1% of total Inhibition of gene expression

19. hn RNA [heterogeneous nuclear RNA] Precursor RNA sc RNA [small cytosolic RNA] Selection of protein for export Other small RNA [ important role in gene regulation] Micro RNA [mi- RNA] Small interfering RNA [ si RNA]

20. rRNA Found in association of a number of different protein as a component of ribosome The complex structure served as the site of protein synthesis Size species of RNA Prokaryotic cell- 23s, 16s, 5s Eukaryotic cytosol - 28s, 18s, 5.8s, 5s Eukaryotic mitochondria- 23s, 16s, 5s

21. rRNA

22. tRNA Smallest of 3 major species (molecular wt-4s) Length 74-95 NTs Allow extensive folding & intrastrand complementarity to generate a secondary structure Each tRNA molecule carries a specific aa to the site of protein synthesis At least 1 specific type of tRNA for each of 20 amino acid that commonly found in protein So minimum 20 RNA present in every cell

23. 4 main arm Acceptor arm Terminates in CCA-OH (added post- transcriptionally ) Amino acid attached/ charged (onto 3 ΄ OH of A) Anticodon arm- Recognize triplet codone of mRNA D arm ( dihydrouracil ) T ψ C arm- Contain sequence of T, C, pseudouridine

24. tRNA

25. mRNA Most heterogenous type in terms of size (500-6000NT) & base sequence Carry genetic information from DNA to cytosol where it used as a template for protein synthesis PolyA tail: a long sequence of adenine nucleotide of 3 ΄ end of RNA chain A cap on 5 ΄ end consists 7-methyl guanosine attached backward (5 ΄ - 5 ΄ ) to a tri-phosphate linkage

26. mRNA

27. Thank You