DNA structure 3.3


Eukaryote DNA is wrapped around histone proteins. The DNA is diffuse (b) during interphase, since transcription of the genes (for protein synthesis) and DNA replication (for mitosis or meiosis) is occuring. In prophase the DNA becomes condensed (a) and transcription is repressed. The condensed DNA can be easily viewed as the chromosome structure.

Histone-deacetylase inhibitors: novel drugs for the treatment of cancer
Histone-deacetylase inhibitors: novel drugs for the treatment of cancer





external image dna-structure.jpg



This link shows DNA structure in context of the cell
http://www.brynmawr.edu/biology/franklin/genome_intro.html

THE NUCLEIC ACIDS
First isolated by Friedrich Miescher in 1869.
He isolated what he called nuclein from the nuclei of pus cells.
Nuclein was shown to have acidic properties, hence it became called nucleic acid.

Two types of nucleic acid are found
  • Deoxyribonucleic acid (DNA)
  • Ribonucleic acid (RNA)
The distribution of nucleic acids in the eukaryotic cell is interesting
DNA is found in the nucleus with small amounts in mitochondria and chloroplasts.
RNA is found throughout the cell.
DNA as genetic material: The circumstantial evidence
  1. It is present in all cells and virtually restricted to the nucleus.

  2. The amount of DNA in somatic cells (body cells) of any given species is constant (like the number of chromosomes). The RNA content varies a lot.

  3. 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.

  4. The mutagenic effect of UV light peaks at 253.7nm. This is the peak for the absorption of UV light be DNA.
NUCLEIC ACID STRUCTURE


external image 011204008.jpg





DNA IS MADE OF TWO STRANDS OF POLYNUCLEOTIDE
  • The sister strands of the DNA molecule run in opposite directions (antiparallel).
  • They are joined by the bases.
  • Each base is paired with a specific partner
  • A is always paired with T
  • C is always paired with G
  • This the sister strands are complementary but not identical
  • The bases are joined by hydrogen bonds, individually weak but collectively strong.


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The following link shows IB syllabus requirements for DNA structure
http://www.patana.ac.th/Secondary/Science/c4b/3/Chem3.3.htm


DNA Replication 3.4

This link shows IB syllabus requirements for DNA replication
http://www.patana.ac.th/Secondary/Science/c4b/3/Chem3.4.htm

This link shows DNA replication of DNA strands
http://library.tedankara.k12.tr/chemistry/vol1/biochem/trans98.jpg

This link shows zygote to inner cell mass/developing embryo
http://cache.eb.com/eb/image?id=1077&rendTypeId=4