chemistry of nucleoproteins

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Chemistry of Nucleoproteins

• M.Prasad Naidu
• MSc Medical Biochemistry, Ph.D,.

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• Structure of DNA
• Watson Crick model
• Double stranded helix
• Both strands are polar 5 and 3end
• 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 Chargaffs rule

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• STRUCTURE OF
  DNA
• The structure of DNA was proposed by Watson and
  Crick.
• Salient features
• 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.

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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
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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 .
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Base Pairing
A T Weak Two Hydrogen bonds
G C Strong Three Hydrogen bonds
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9.CHARGOFFs 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.
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• Coding strand the DNA strand that
• gives the genetic information. Also called as
  non-template
• Template strand the DNA strand the
• forms the mRNA.

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• 5end coding strandDNA
  3end
  
• AGTC-----------------------------------
  -
• TCAG-----------------------------------
  -
  
  
  
  
• template
  strandDNA
• AGUC-----------------------------------
  ----
• RNA

DNA
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• Structure of DNA Watson Crick model
• Double stranded helix
• Both strands are polar 5 and 3end
• Both strands are Anti-parallel
• Both strands are complimentary .
• Strands are composed of A, T, C, G
• Strands are held by phosphodi-ester/ H bonds
• Deoxy ribophosphates outside and bases inside
  
• Obeys base pair rule
• Obeys chargaffs rule
• Stores genetic message on coding strand.

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• 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

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DNA structure
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Each strand has hydrophilic deoxyribose phosphate
back bone on periphery and hydrophobic bases
stacked inside

• .

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• 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.

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• 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.

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• RENATURATION OF DNA
• Separated strands of DNA reassociate when
• appropriate physiologic temperature and salt
• conditions are achieved , a process called
• as Renaturation (Reannealing)

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RIBONUCLEIC ACID (RNA) RNA is
a polymer of ribonucleotides in a single chain
linked by phosphodiester bonds. 3 TYPES mRNA,
tRNA, rRNA
.
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• 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.
• .

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• 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.

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Post transcriptional modifications

• 51 Capping and 31 Poly-A tailing
• primary transcript m RNA
• 51 ---------------------- 31 hn RNA
• 7-methyl guanosine51 -----------------------------
  ---- 31 AAAAA
• capping
  mature RNA tailing

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• 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.

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Structure of t RNA Clover leaf model
with 5 arms
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• tRNA
• Acceptor arm at 3 'end Carries the aminoacid.
• 2. Anticodon arm recognises codon present in
  mRNA
• 3. Pseudouridine arm (T?C) binds t RNA to
  ribosomes.
• 4. D arm recognition site for amino acid
• 5. Variable arm Most variable arm
• .

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RIBOSOMAL RNA
(rRNA) Ribosomes provide necessary infrastructure
for mRNA , tRNA, and aminoacids to interact with
each other for translation process.
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Eukaryotic 80s ribosome
60s
40s
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• Differences between DNA and RNA
• DNA
  RNA
• SITE NUCLEUS
  CYTOPLASM
• STRAND DOUBLE
  Single strand
• SUGAR DEOXYRIBOSE
  RIBOSE
• BASES THYMINE
  URACIL

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DNA
RNA

• Chargaffs rule obeys do not
  obey
• Alkalihydrolysis stable
  susceptible
• Function genetic information protein
  synthesis
• protein synthesis
• Types A,B, and Z mRNA, tRNA, rRNA

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