Welcome to class of

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Welcome to class of

• Nucleotides and Nucleic acids
• Dr. Meera kaur

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Learning objectives

• To understand
• the names and one-letter symbols of the five
  major nitrogen bases found in nucleic acids
• two differences between the molecular composition
  of DNA and RNA
• the structure of DNA
• the process of replication, transcription and
  translation
• Concept of gene mutation and molecular disease
• Concept of recombinant DNA technology

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Introduction to nucleic acids

• In 1869, Johannes Miescher of the University of
  Germany carried out the research on elemental
  analysis of the nucleus. He studied cell
  containing large nuclei and little cytoplasm
  (white blood cells). He collected white cells
  from pus, washed from bandages of infected
  surgical patients. When he extracted the nuclei
  with basic solution and acidified the alkaline
  extract, he got a precipitate of stringy material
  that he analyzed further.
• His careful elemental analysis gave carbon,
  nitrogen and phosphorus in proportions that were
  unlike of those of carbohydrates, lipids or
  protein. Miescher named his new materials nuclein
  to reflect its nuclear origin.
• Today, we called these compound the nucleic
  acids.

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Introduction to nucleic acids

• Miescher made little progress in learning about
  nucleic acids, either their functions or
  structure. But other scientists eventually
  learned that there are two types of nucleic
  acids deoxyribonucleic acid (DNA) and
  ribonucleic acids (RNA).
• Structure of Nucleic acids
• - Nucleotides are the fundamental building
  blocks of nucleic acids.
• - DNA and RNA molecules are polynucleotides
  i.e., polymers composed of many repeating units
  of nucleotides.
• - Each nucleotide consists a sugar unit, a
  nitrogen base and a phosphate group attached to
  the sugar unit.
• The combination of a base and sugar units makes a
  nucleosides. Adding a phosphate group to the
  sugar unit of a nucleoside makes nucleotide.

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Structure of nucleic acids

• BASE SUGAR UNIT BASE---SUGAR
• A nucleoside
• BASE------SUGAR PHOSPHATE BASE
  SUGAR---PHOAPHATE
• A nucleoside A nucleotides

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Structure of the sugar units

• The sugar unit of the nucleotides strung together
  to make RNA is ? -D- ribose -- hence the name
  ribonucleic acid
• The sugar unit of DNA is ? -D-2-deoxyribose
  hence the name deoxyribonucleic acid

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Structure of the base units

• Four different nitrogen bases (heterocyclic
  amines) are found in DNA.
• Two of these bases - adenine (A) and guanine (G)
  - are derivatives of purine. They are called
  purine bases.
• The other two cytosine (C) and thymine (T) are
  derivatives of pyrimidine. They are called
  pyrimidine bases.
• Except for thymine, the same bases are found in
  RNA. Instead of thymine, uracil a pyrimidine
  base is found in RNA.

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Basic structure of nucleotide (nitrogenous base,
pentose, and phosphate)
Carbons of the sugar ring are numbered 1, 2?, 3?,
4 ? and 5?(read as one prime, Two prime and
so forth)
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Nitrogenous bases of nucleotides
The ring atoms of the nitrogen bases are numbered
as 1, 2, 3, 4, 5 and so forth
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Major purine and pyrimidine bases of nucleic acids
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Structure of nucleosides

• The base and sugar units of nucleosides are held
  together by a covalent bond between the nitrogen
  of a purine or pyrimidine bases and the ring
  carbon of the sugar unit.
• Ribonucleosides (nucleosides found in RNA) are
  similar in structure to the deoxyribonucleosides,
  except that ribose rather than deoxyribose is
  the sugar and uracil replaces thymine.
• Purine nucleosides are formed by a covalent bond
  between nitrogen 9 of the base and 1? of the
  sugar unit.
• The base and sugar of the pyrimidine nucleosides
  are joined by a covalent bond between nitrogen 1
  of the base and carbon 1? of the sugar.

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Structure of nucleotides

• Addition of a phosphate group to a sugar hydroxyl
  group forms a nucleotide.

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Some adenosine monophosphates
Examples of nucleotides
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The covalent backbone structure of DNA and RNA
In DNA and RNA molecules, nucleotides are linked
together through phosphate ester bridge between
the 3?hydroxyl group of one nucleotide and the
5?hydroxyl group of the next nucleotide in the
chain. These bridges are called phosphodiesters.
Even though two of the four oxygen attached to
the phosphorus of each bridge are tied up as
phosphate esters, and one is present in
phosphorusoxygen double bond, one oxygen is free
to lose a proton. It is the presence of many such
dissociating groups that gives DNA and RNA their
highly acidic character.
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Shorthand structures for nucleotide sequence

• DNA and RNA molecules are too complex to write in
  full. So biochemists often use a shorthand form.
• The basis for the shorthand is the differing
  order of their bases. The sugar units and the
  phosphate groups are identical in all the
  nucleotides.
• We can write the structure of an RNA by ignoring
  the sugars and the phosphodiester bridges, and by
  writing only the sequence of nitrogen bases.
  Start at the left with the end of the molecule
  that has a free 5?end and work toward the end
  that has a free 3?hydroxyl group
• UAGCUGCC dAATGTCAC
• 5? ________________ 3? 5?
  __________________ 3?
• RNA DNA

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Avery-MacLeod-McCarty experiment

• 1944
• First direct evidence that DNA is the bearer of
  genetic information
• PROBLEM not universally accepted, since protein
  impurities in the DNA could have carried the
  message

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The Avery-MacLeod-McCarty Experiment
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Adding heat killed virulent bacteria to a live
nonvirulent strain permanently transformed the
latter into lethal, virulent, encapsulated
bacteria. He concluded that a transforming factor
in the heat killed virulent bacteria had gained
entrance into the live nonvirulent bacteria and
rendered them virulent and encapsulated.
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Avery and his colleagues identified this
transforming factor as DNA.