THE NUCLEIC ACIDS 2007 Paul Billiet ODWS Friedrich
THE NUCLEIC ACIDS © 2007 Paul Billiet ODWS
Friedrich Miescher in 1869 n n isolated what he called nuclein from the nuclei of pus cells Nuclein was shown to have acidic properties, hence it became called nucleic acid © 2007 Paul Billiet ODWS
Two types of nucleic acid are found n n Deoxyribonucleic acid (DNA) Ribonucleic acid (RNA) © 2007 Paul Billiet ODWS
The distribution of nucleic acids in the eukaryotic cell n DNA is found in the nucleus with small amounts in mitochondria and chloroplasts n RNA is found throughout the cell © 2007 Paul Billiet ODWS
DNA as genetic material: The circumstantial evidence 1. 2. 3. 4. Present in all cells and virtually restricted to the nucleus The amount of DNA in somatic cells (body cells) of any given species is constant (like the number of chromosomes) The DNA content of gametes (sex cells) is half that of somatic cells. In cases of polyploidy (multiple sets of chromosomes) the DNA content increases by a proportional factor The mutagenic effect of UV light peaks at 253. 7 nm. The peak for the absorption of UV light by DNA © 2007 Paul Billiet ODWS
NUCLEIC ACID STRUCTURE n n Nucleic acids are polynucleotides Their building blocks are nucleotides © 2007 Paul Billiet ODWS
NUCLEOTIDE STRUCTURE PHOSPATE SUGAR Ribose or Deoxyribose BASE PURINES Adenine (A) Cytocine (C) Guanine(G) Thymine (T) Uracil (U) NUCLEOTIDE © 2007 Paul Billiet ODWS PYRIMIDINES
Ribose is a pentose C 5 O C 1 C 4 C 3 © 2007 Paul Billiet ODWS C 2
Spot the difference DEOXYRIBOSE CH 2 OH O C H H H C OH © 2007 Paul Billiet ODWS OH CH 2 OH C C H H OH O C H H C C C OH OH H H
THE SUGAR-PHOSPHATE BACKBONE n n The nucleotides are all orientated in the same direction The phosphate group joins the 3 rd Carbon of one sugar to the 5 th Carbon of the next in line. P P P © 2007 Paul Billiet ODWS
P G ADDING IN THE BASES P C n n The bases are attached to the 1 st Carbon Their order is important It determines the genetic information of the molecule P C P A P T P © 2007 Paul Billiet ODWS T
Hydrogen bonds P DNA IS MADE OF TWO STRANDS OF POLYNUCLEOTIDE G C P P C G A T T A P P P © 2007 Paul Billiet ODWS T A P
DNA IS MADE OF TWO STRANDS OF POLYNUCLEOTIDE The sister strands of the DNA molecule run in opposite directions (antiparallel) n They are joined by the bases n Each base is paired with a specific partner: A is always paired with T G is always paired with C Purine with Pyrimidine n This the sister strands are complementary but not identical n The bases are joined by hydrogen bonds, individually weak but collectively strong n © 2007 Paul Billiet ODWS
Erwin Chargaff’s Data (1950 -51)
Wilkins & Franklin (1952): X-ray crystallography © Norman Collection on the History of Molecular Biology in Novato, CA
Purines & Pyrimidines Adenine Guanine © 2007 Paul Billiet ODWS Thymine Cytosine
Watson & Crick Base pairing © 2007 Paul Billiet ODWS
The Double Helix (1953) © Dr Kalju Kahn USBC Chemistry and Biochemistry Public Domain image
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