1. Section 2 Molecular and Morphological Structure of Chromosomal DNA
Experiments proving that Chromosomes Posses the DNA:
Chemical analysis (Ris & Marasky)
Feulgen’s reaction
Ultraviolet absorption
Enzymatic digestion Lambproush chromosomes
Autoradiography

2. Section 2 Molecular and Morphological Structure of Chromosomal DNA
1- Enzymatic Digestion of Lampbrush Chromosomes:
A Lampbrush chromosome is the largest chromosome known and is found in the amphibian oocytes (immature eggs).
Lampbrush chromosomes occur during the diplotene stage of meiosis I. They are meiotic bivalents, each consisting of 2 sister chromatids. Lampbrush chromosomes are clearly visible even in the light microscope, where they are seen to be organized into a series of large chromatin loops emanating from a linear chromosomal axis.
Rnase +proteinase
Dnase
Matrix disappeared
Chromosome lyses

3. Section 2 Molecular and Morphological Structure of Chromosomal DNA
2- Feulgen’s Reaction
a specific staining procedure for DNA: mild acid hydrolysis makes the aldehyde group of deoxyribose available to react with schiffs reagent to give a purple colour.
Warm and diluted Acid
Schiff’s reagent +
Nucleic Acid Source
(CHO- Ribose)
magenta or purple color develops
DNA hydrolysis

4. Section 2 Molecular and Morphological Structure of Chromosomal DNA
3- Ultraviolet Absorption DNA can absorb UV waves in 2600 Å (260n.m) wave length due to the cyclic structure of the nitrogen bases.
High radiation
Low radiation uv

5. The secondary compound
Chemical Analysis (Ris and Marasky)
Animal
( Cow)
Thyroid
glands
10 %
The secondary compound
90 %
The main compound
14 % RNA
2.6 % DNA
80 % Non Histone Proteins
45 % DNA
55 % Histone proteins

6. Autoradiography

7. Genome Organization Eukaryotes Vs. Prokaryotes Genome Haploid Diploid

9. Eukaryotic Chromosome

10. DNA Packaging Why package DNA? Levels of Packing: 1-Nucleosome
2-30 nm fiber/Solenoid
3-Loops
4-Rossettes
5-Chromosome

11. A nucleosome core particle contains:
Chromosomes
Nucleosome (Level 1)
A nucleosome core particle contains:
146 base pairs of supercoiled DNA
Around a core of eight histone molecules
Histone core
Two copies of H2A, H2B, H3 and H4
Octamer
H1 resides outside of core
Linker histone
Binds to linker DNA
Connecting one nucleosome core particle to next