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Chemistry of nucleoproteins

Chemistry of nucleoproteins







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    Chemistry of nucleoproteins Chemistry of nucleoproteins Presentation Transcript

    • M.Prasad Naidu MSc Medical Biochemistry, Ph.D,.
    • Structure of DNA  Watson & Crick model  Double stranded helix  Both strands are polar [5’ and 3’end]  Both strands are Anti-parallel  Both strands are complimentary .  Strands are composed of A, T, C, G  Strands are held by phosphodi-ester and Hydrogen bonds  Obeys base pair rule  Obeys Chargaff’s rule
    • STRUCTURE OF DNA The structure of DNA was proposed by Watson and Crick. Salient features 1. DNA is a double stranded helix. DNA has two chains , twisted around each other on a common axis. It is commonly a right handed helix . 2. The 2 strands are polar with 5’ and 3’ ends. 3. The two strands are antiparallel, one strand runs in 5‘ to 3' and another in 3' to 5' direction. 4. The two chains are not identical but complementary to each other due to base pairing.
    • 5. Each turn of helix is 3.4 nm , with 10 pairs of nucleotides , each pair placed at a distance of 0.34nm. 6. Each strand has hydrophilic deoxyribose phosphate back bone on periphery and hydrophobic bases stacked inside. 7. The two strands of helix are held by both hydrogen bonds between bases and by vanderwaals and hydrophobic interactions between adjacent base pairs
    • 8. Obeys base pair rule: Adenine always pairs with Thymine and Guanine with Cytosine Two purines , they would not fit into allowable space Two pyrimidines – too far to form H- bonds. So, purine always pairs with pyrimidine .
    • A T Weak Two Hydrogen bonds G C Strong Three Hydrogen bonds Base Pairing
    • 9.CHARGOFF’s RULE: Concentration of adenine = thymine , and concentration of guanine = cytosine. 10. Genetic information is present on coding strand. the other strand is called as non coding strand.
    •  Coding strand : the DNA strand that gives the genetic information. Also called as non- template  Template strand: the DNA strand the forms the mRNA.
    • 5`end coding strand[DNA] 3`end AGTC------------------------------------ TCAG------------------------------------ template strand[DNA] AGUC--------------------------------------- RNA DNA
    • Structure of DNA : Watson & Crick model 1. Double stranded helix 2. Both strands are polar [5’ and 3’end] 3. Both strands are Anti-parallel 4. Both strands are complimentary . 5. Strands are composed of A, T, C, G 6. Strands are held by phosphodi-ester/ H bonds 7. Deoxy ribophosphates outside and bases inside 8. Obeys base pair rule 9. Obeys chargaff’s rule 10.Stores genetic message on coding strand.
    • TYPES OF DNA A DNA B DNA Z DNA • Helix handedness right right left • Base pairs per Turn 11 10 12 • Pitch ( turn ) 2.46 nm 3.4 nm 4.56 nm •Major groove present present convex shape •Minor groove present present deep cleft
    • DNA structure
    •  . Each strand has hydrophilic deoxyribose phosphate back bone on periphery and hydrophobic bases stacked inside
    • Denaturation of DNA • The double stranded structure of DNA can be separated into two component strands (melted) in solution by increasing temperature or decreasing salt concentration. • This phenomenon of loss of helical structure is called denaturation. • Disruption of hydrogen bonds occur. • •PDE bonds not broken.
    •  Melting temperature (Tm) :  It is defined as temperature at which half of helical structure is lost.  Tm is influenced by base composition and by salt concentration of solution. DNA rich in G-C pairs melts at higher temperature than A-T pairs.
    • RENATURATION OF DNA • Separated strands of DNA reassociate when appropriate physiologic temperature and salt conditions are achieved , a process called as Renaturation (Reannealing)
    • RIBONUCLEIC ACID (RNA) RNA is a polymer of ribonucleotides in a single chain linked by phosphodiester bonds. 3 TYPES: mRNA, tRNA, rRNA .
    • Messenger RNA •m RNA is present in nucleus •m RNA receives genetic information from DNA • m RNA is the most heterogenous in size and stability. • hnRNA on processing liberates functional mRNA which enter cytoplasm and take part in protein synthesis. .
    •  The mRNA formed from DNA is called the primary transcript or hnRNA.  It undergoes extensive modifications to become active and mature mRNA. These modifications are called as post transcriptional modifications.
    • Post transcriptional modifications51 Capping and 31 Poly-A tailing primary transcript [m RNA] 51 ---------------------- 31 [hn RNA] 7-methyl guanosine51 --------------------------------- 31 AAAAA [ capping ] mature RNA [ tailing ]
    • Transfer RNA (soluble RNA): • At least 20 species of tRNA in every cell , corresponding to each of 20 aminoacids required for protein snythesis. • Apart from regular nucleotides it has pseudouridine and thymine. • The primary structure of t-RNA allows extensive folding to generate secondary structure --- CLOVER LEAF MODEL.
    • Structure of t RNA : Clover leaf model with 5 arms
    • tRNA 1.Acceptor arm at 3 'end: Carries the aminoacid. 2. Anticodon arm : recognises codon present in mRNA 3. Pseudouridine arm (TψC): binds t RNA to ribosomes. 4. D arm : recognition site for amino acid 5. Variable arm : Most variable arm
    • RIBOSOMAL RNA (rRNA) Ribosomes provide necessary infrastructure for mRNA , tRNA, and aminoacids to interact with each other for translation process.
    • Eukaryotic 80s ribosome 60s 40s
    •  Chargaffs rule obeys do not obey  Alkalihydrolysis stable susceptible  Function genetic information protein synthesis protein synthesis  Types A,B, and Z mRNA, tRNA, rRNA DNA RNA