Chromosome structure

2.  Chromosomes are organized structure of DNA and proteins
found in cells. they are thread-like structures located inside the
nucleus of animal and plant cells.
 Chromosomes are made up of proteins and a molecule of
deoxyribonucleic acid (DNA).
 Chromosomes are passed on from parents to offspring.
 The term chromosome is derived from a Greek word 'chroma'
which means 'color' and 'soma' which means 'body'.

3.  Chromosomes play an important role that ensures DNA is
copied and distributed accurately in the process of cell division.
 In most of the organisms chromosomes are arranged in pairs in
the nucleus of the cell.
 We have 23 pairs of chromosomes

4. TYPES OF CHROMOSOME:

5. PROKARYOTIC CHROMOSOME STRUCTURE:

6. E.COLI CHROMOSOME:
 The bulk of DNA in E.Coli cell consists of a single circular
DNA molecule of length 4.6 million base pairs.

7. DNA DOMAINS:
 When the DNA from E.Coli is isolated and observed,The DNA
consists of 50-100 domains/loops.These loops are about 50-
100kb in size.
 The ends of loops are binded to a protein member core.
SUPERCOILING OF GENOME:
 The E.Coli chromosome as a whole is negatively
supercoiled.(ΔLK/LK°=-0.06).
 Some domains may not be supercoiled because the DNA has
become broken in one end.
 The attachment of the DNA to the protein member core may
act as a barrier to rotation of DNA.

8. DNA BINDING PROTEINS:
 Proteins HU-a small basic,positively charged,dimeric protein
which binds DNA non specifically.
 H-NS protein(formally protein H1)-A monomeric neutral
protein which binds DNA non specifically(Also called histone
like proteins-it has the effect of compacting the DNA,which is
essential for packing of DNA into nucleoid.)

9. HU PROTEIN H-NS PROTEIN

10. EUKARYOTIC CHROMOSOME STRUCTURE:

11. DIFFERENCE BETWEEN PROKARYOTIC &
EUKARYOTIC CHROMOSOMES:

12. CHROMATIN STRUCTURE:
 Chromatin is comprised of histones and DNA: 147 base
pairs of DNA wraps around the 8 core histones to form the
basic chromatin unit, the nucleosome.

13. HISTONE PROTEINS:

22. NUCLEOSOMES:
 The histone octomer(made of core histone) forms a wedge
shaped disk,around when the 146bp of double helix DNA is
wrapped in 1.8 turns in a left handed direction.
 The left handed wrapping of the DNA around the nucleosome
corresponds to negative supercoiling.
 Nucleosome is a basic unit of chromatin.
 Nucleosomes are separated by spacer DNA to which histone H1
is attached.This continous string of nucleosomes represents
beach on a string forms chromatin.

24. ROLE OF H1:
 One molecule of histone H1 bind to the nucleosomes and act to
stabilise the point at which the DNA enter and leaves the
nucleosome core.
 In presence of H1 a further 20bp of DNA is protected from
nuclease digestion.
 A nucleosome core plus H1 is known as chromatosome.
 The larger the size of H1 compared with core histones is due to
presence of an additional c-terminal tail,which stabilises the
DNA between the nucleosome core.

25. LINKER DNA:
 The beads on a string structure,comprises globular
particles(nucleosomes) connected by thin strand of DNA
 These thin strands are known as linker DNA.
 The average length of linker DNA between core particles is
55bp.

26. HIGHER ORDER STRUCTURE:
 The 10nm fiber is further coiled to produce 30nm fiber which
has a solenoid structure with 6 nucleosomes,in every turn.
 These 30nm fibers are further organised into non condensed
loops (300nm) and then into condensed form of
chromosome(700nm)metaphase chromosome(1400nm).
 Chromatins are believed to operate directly through the histone
proteins which carry out packaging.

28. GENOME COMPLEXITY:
 Genome- The total DNA(genetic information) contained in an
organism or a cell is regarded as the genome.Thus the genome
is the store house of biological information.
 Genomics-The study of the structure and function of genome.
 It includes the chromosome in the nucleus and DNA in
mitochondria and chloroplasts.

29.  The genome of most eukaryotes are more complex and larger
than prokaryotes.
 It contains
a) Functional genes(coding sequence of DNA)
b) DNA sequence that does not code for protein.
 Coding sequence are extrons and non coding sequence are
introns.

30. FLOW OF GENETIC INFORMATION:
 The biological information from DNA to RNA and form
proteins.
 The DNA is trascriped to an RNA molecule(mRNA)
 And then the message is translated into a protein sequence
according to genetic code.