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The Organization of
Cellular Genome
Asmarinah
Department of Medical Biology
Genome
The totality of genetic information belonging to a
cell or an organism; in particular, the DNA that
carries this information
Genomics
The science of studying the DNA sequences
and properties of entire genomes
● DNA molecules are organized into chromosome
● Chromosome: A DNA molecule with its attendant
proteins that moves as an independent units during
mitosis and meiosis
Before DNA replication, each chromosome consists of a
single DNA molecule plus protein, is called a chromatid
After replication, each chromosome consists of two
identical DNA molecule plus proteins; this are called
sister chromatids
● Chromatin: DNA plus the proteins that package it
within the cell nucleus
A
B
C
A. The principal structural features of chromosome
B. An electron micrograph of human mitotic
chromosomes
C. A diagram of various classes of human chromosomes
Centromere: The chromosomal locus that regulate the
movement of the chromosome during mitosis and meiosis
Telomere: The specialized structure at either end of
chromosomal DNA molecule that ensures the complete
replication of the chromosomal end and protects the ends
within the cell.
Chromosomes are classified based upon the position of the
centomere relative to the arms, i.e:
-Metacentric
-Submetacentric
-Acrocentric
-Telocentric
Chromatin packing
occurs on several levels
Nucleus contain two broad classes of chromatin, i.e:
● Heterochromatin
which is highly condensed throught the cell cycle
and is generally inactive in transcription
● Euchromatin
which is less condensed and contains actively
transcribed genes
Structural organization
of nucleosome
Nucleosome contains
Octameric histon protein &
DNA double helix
DNA and its building
DNA is made from subunits, called nucleotides
Each nucleotide consisting of
-Sugar (deoxyribose)
-Phosphate
-Base: Adenine
Thymine
Guanine
Cytosine
Building block of DNA
Double-stranded DNA
DNA double helix
DNA strand
The most important of chromosomes is to carry genes
A gene is defined as a segment of DNA that contains the
insctruction for making a particular protein
The Organization of human genome
Human Genome
Each human chromosome
has a unique banding
pattern
Conserved gene order in chromosome between the
human (a) and mouse (b) genome
Closely related species can have very different
chromosome numbers
Chromosomes from many eucaryotes (including human)
contain a large excess of interspersed DNA that does not
seem to carry critical information, called junk DNA
This DNA may not be important, but can play a role:
- as spacer material
- for long-term evolution of the species
- for the proper expression of genes
Bacteria and some single-celled eucaryotes have especially
compact genomes. The complete nucleotide sequence of
their genomes reveals that DNA molecules are little more
than strings of closely packed genes
The genome of E. coli
A. E.coli strain K-12 has 4.639.221
nucleotides pairs
B. A diagram of the E. coli genome.
E. Coli genome is circular that forms
a single, closed loop.
Yellow or orange bars shows
protein-coding genes
Green arrows indicate genes
encoding only RNA molecules
Genetic differences between pathogen and
nonpathogen bacteria
Example: Genetic organization of Vibrio cholerae
A. Vibrio cholerae has two circular
chromosomes, that each of its has
distinct origin of replication (oriC1 &
oriC2)
CTXφ locus carriers the gene
for cholera toxin
VPI island contains gene for
factors required for intestinal
colonization
B. Map of CTXφ locus consist of: - core region: gene for cholera toxin ctxA & ctxB
gene for involving of virulence (ace & zot)
- repeated sequence RS2 & RS1 that involved
chromosomal insertion of bacteriophage genome
Schematic drawings of several types of viral
genomes
References:
-Albert et al., 2002. Molecular biology of the cell.
4th ed.
-Albert et al., 2004. Essential of cell biology.
-Pollard and Earnshaw. 2004. Cell biology.