Molecular biology

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Molecular biology

• Unit 1
• Molecular basis of life
• DNA, RNA as genetic material

By Pallavi Bohra
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Molecular basis of life

• All living organisms consist of tiny basic units
  called cells.
• Most of the cells, when viewed under the
  magnifying devices like microscopes have a darker
  staining body called nucleus which is surrounded
  with the viscous fluid cytoplasm, and is
  enveloped by a semipermeable cell membrane.
• Inside the nucleus, the genetic material DNA is
  present, which at the time of cell division
  assembles into the higher order structure called
  chromosome.
• In a human cell, the entire genetic material is
  bundled into 23 pairs of chromosomes, and is
  collectively referred as the 'human genome'

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Molecular basis of life continue.
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Molecular basis of life
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What is genetic material

• Basic Requirements for Genetic Material
• It must be stable
• It must be capable of being expressed when needed
• It must be capable of accurate replication
• It must be transmitted from parent to progeny
  without change

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Proof of DNA as genetic material

• Griffith's experiment 1928

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Avery, MacLeod and McCarty experiment 1944
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Continue..

• Paper in 1944
• Studies on the Chemical Nature of the Substance
  Inducing Transformation of Pneumococcal Types
  Induction of Transformation by a Deoxyribonucleic
  Acid Fraction Isolated from Pneumococcus Type III"

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Hershey Chase Experiment
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Chargaffs rulecontinue

• A with T the purine adenine (A) always pairs
  with  the pyrimidine thymine (T)
• C with G  the pyrimidine cytosine (C) always
  pairs with the purine guanine (G)
• The ability to form hydrogen bonds makes the base
  pairs more stable structurally
• The amount of adenine (A) in the DNA of an
  organism, the amount of thymine (T) is the same
  (Chargaff's rule). Similarly, whatever the amount
  of guanine (G), the amount of cytosine (C) is the
  same.A  T and C  G.

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Properties of DNA

• DNA stores and transmits genetic information 
• The sequence info can be converted into new DNA,
  new RNA, and protein
• DNA is copied with high-fidelity only one
  mistake per every 109 or 1010 bases
• DNA is stable
• It resistant to alkali treatment (RNA isnt)
• Resistant to low pH, however it will begin to
  hydolyze below pH 2
• Double-strandedness also shelters the bases from
  chemical attack

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