572770707-Structure-of-Eukaryotic-Genome.pdf

sequence of four nucleotides arranged in a certain pattern, encoding information, constitutes an organism’s genetic material or DNA (deoxyribonucleic acid). The linear arrangement of DNA components and their partition into chromosomes is referred to as a genomic organisation. “Genome organisation” can also refer to the arrangement of DNA sequences inside the nucleus and the three-dimensional structure of chromosomes.

Eukaryotic genomes are linear and follow the Watson-Crick Double Helix structural model. They are contained within chromosomes, bundles of DNA and proteins (Histone) known as nucleosomes. The protein-coding genes in eukaryotic genomes are organised in exons and introns, which represent the coding sequence and intervening sequence, respectively, indicating the functionality of the RNA section of the genome.

Also, read: Double Helix Structure of DNA

Table of Contents
Eukaryotic Genome Configuration
Eukaryotic Genome Organisation
Gene Expression in Eukaryotes
Frequently Asked Questions (FAQs)
Eukaryotic Genome Configuration
The eukaryotic genome configuration consists of protein-coding regions, gene regulatory regions, gene-related sequences, and intergenic DNA or extra genic DNA, which comprises low copy number and moderate or high copy number repetitive sequences. The configuration is shown in the flowchart below.

Eukaryotic Genome Organisation
Basic facts on eukaryotic nuclear genomes are as follows:

Eukaryotic genomes include two characteristics that pose a significant information processing problem.
The standard multicellular eukaryotic cell has a substantially larger genome than a prokaryotic cell.
Many genes can only be expressed in certain types of cells due to cell specialisation.
A huge amount of DNA that does not direct the synthesis of RNA or protein is included in the reported 35,000 genes in the human genome.
The eukaryotic DNA is intricately organised. The DNA-protein complex known as chromatin is not only linked to proteins but is also structured at a higher structural level than the DNA-protein complex in prokaryotes.
Eukaryotic cells have a significantly higher concentration of DNA in their nuclei than prokaryotic cells.
Structure of the Chromatin
Chromatin is the intricate structure of DNA and protein that comprises chromosomes and consists of linear unbroken double-stranded DNA. There are two types of chromatin:

Euchromatin
Heterochromatin
Chromatin
Euchromatin: It is a lightly packed chromatin that is enriched in genes, and is often under active transcription (but not always). Euchromatin contrasts sharply with heterochromatin, which is densely packed and much less available for transcription. The euchromatic region constitutes 92% of the human genome.

Heterochromatin: It is a densely compacted form of DNA or compressed DNA, which comes in multiple variants. These variants fall somewhere between facultative heterochromatin and constitutive heterochromatin. Both are involved in how genes are expressed.

The pr

1. Structure of Eukaryotic genome

2. The Genome
•Refers to the entire genetic material or genetic makeup of an
organism.
•Consists of DNA in both prokaryotes and eukaryotes;
•RNA viruses are exceptions to this rule.
•Bacterial genome consists of a single molecule of DNA usually
dispersed in the cytoplasm; some contain extra chromosomal
DNA (plasmids).
•Eukaryotic genome consists of a complete set of DNA in the
nucleus; chloroplasts and mitochondria contain DNA.

3. Prokaryotic and Eukaryotic Genomes
•The genome of eukaryotes contain far more genetic
information than prokaryotes.
•DNA in eukaryotes have more structural organization
than prokaryotes.
•The DNA is associated with basic proteins called
histones.
•The genes are contained in the nuclei bound by
nuclear membranes.

4. Prokaryotic Genomes
•Prokaryotic genomes are
made of DNA.
•Prokaryotic
chromosomes can be
circular or linear.
•Prokaryotic cells do not
contain organelles.
•Genomes float freely inside the
cell.
Transmission electron
micrograph of
E. coliO157:H7 showing
flagella. (Courtesy of the CDC)

5. Eukaryotic Genomes
•The genomes of eukaryotic
organisms are made of
DNA.
•The genomes of eukaryotic
organisms contain introns.
•Eukaryotic genomes frequently
include several to many linear
chromosomes.
Human epithelial cells
stained with
DAPI (blue, to show the
nucleus) and
phallotoxin (red, to show F-
actin in the cell body)
Courtesy of RL Alford, PhD

6. Viral Genomes
•Some viral genomes are
made up of DNA; others
are RNA.
•Some viral genomes are
single-stranded; others are
double-stranded.
•Some viruses integrate
their genetic material into
the host cell’s genome;
others do not.
HIV-1 virus budding from a
cultured lymphocyte
(Transmission electron micrograph courtesy of CDC)
Hantaviruses that cause Hantavirus
pulmonary syndrome are carried in
rodent droppings
(Transmission electron micrograph courtesy of CDC )

7. The Gene
•Genetic information (information on the blueprint for
the organism) is organized into genes/cistrons.
•The gene is the unit of heredity.
•Genes are located on the chromosomes.
•A gene is a sequence of DNA (a finite sequence of
nucleotides) capable of independent expression.
•Its major function is to specify the sequence of amino
acids in a protein; it determines the protein structure.

8. Alleles
•A gene can exist in different forms
called alleles
i.Dominant& Recessive,
ii.Genotype: combination of alleles in
organism
iii.Phenotype: visible expression of
genotype
Heterozygotes& Homozygotes
Diploid pair showing
Dominant or Recessive
genotypes.

9. DNA
•Genes are composed of deoxyribonucleic acid (DNA).
Monomers of DNA are called Nucleotides.
(E.g. Deoxyadenosine phosphates, dAMP, dADP, & dATP).

10. Nucleotides
•Nucleotides have 3 parts:
i.Phosphate
ii.5-carbon sugar (deoxyribose)
iii.One of 4 Nitrogenous bases
Adenine (A), Guanine (G),
Thymine (T), Cytosine (C)
A & G (purines –2 rings);
C & T (pyrimidines –1ring)
Purine and Pyrimidine bases in DNA & RNA

11. Nucleosides
•Nucleotides minus phosphate
are known as Nucleosides.
Base Nucleoside
(RNA)
Deoxynucleoside
(DNA)
Adenine Adenosine Deoxyadenosine
Guanine Guanosine Deoxyguanosine
Cytosine Cytidine Deoxycytidine
Uracil Uridine Not usually found
Thymine Not usually
found
Deoxythymidine

12. Base Pair
•Chargaff’s Chemical study (1950)
Total Purines (A + G) =
Total Pyrimidines (C + T)
Therefore, A pairs with Twhereas
Gpairs withCalways.
A = T
G ≡ C

13. Phosphodiester Bond
•Watson & Crickin 1953 proposed:
•DNA = double-stranded helix
•Nucleotides linked by Phosphodiester
bond
Phosphate = bridge between adjacent
nucleotides.
DNA molecule has polarity: 5’phosphate
at top & free 3’ hydroxyl at bottom end
where new nucleotide can be added.
Trinucleotide showing Phospho-
diester bonds, 5’ & 3’

14. Gene Location
•Genes are not distributed randomly in a genome.
•Each is located on specific region of the
chromosome.
•Maps are used to describe the location of a
particular gene on a chromosome.
•Cytogenetic location: based on unique pattern of bands
seen when chromosome is stained with certain
chemicals.
•Molecular location: based on the sequence of
nucleotides (base pairs) that make up the chromosome.

15. Cytogenetic location
Gene location based on the
unique pattern of bands
seen when chromosomes
are stained with certain
chemicals.

16. Genetic Code
•Genetic information is encoded in a triplet of bases
called codons.
•Codons specify amino acids to be incorporated into a
growing protein chain and also chain termination.
•There are 64 codons:
•61 codons specify amino acids
•3 codons specify chain termination
•Codons are on the mRNA while each tRNAhas the
specific anticodon for a specific codon.

17. THE CODONS

43. Prokaryotic Genomes
•Prokaryotic genomes are
made of DNA.
•Prokaryotic
chromosomes can be
circular or linear.
•Prokaryotic cells do not
contain organelles.
•Genomes float freely inside the
cell.
Transmission electron
micrograph of
E. coliO157:H7 showing
flagella. (Courtesy of the CDC)

44. Eukaryotic Genomes
•The genomes of eukaryotic
organisms are made of
DNA.
•The genomes of eukaryotic
organisms contain introns.
•Eukaryotic genomes frequently
include several to many linear
chromosomes.
Human epithelial cells
stained with
DAPI (blue, to show the
nucleus) and
phallotoxin (red, to show F-
actin in the cell body)
Courtesy of RL Alford, PhD

45. Viral Genomes
•Some viral genomes are
made up of DNA; others
are RNA.
•Some viral genomes are
single-stranded; others are
double-stranded.
•Some viruses integrate
their genetic material into
the host cell’s genome;
others do not.
HIV-1 virus budding from a
cultured lymphocyte
(Transmission electron micrograph courtesy of CDC)
Hantaviruses that cause Hantavirus
pulmonary syndrome are carried in
rodent droppings
(Transmission electron micrograph courtesy of CDC )

46. The Human Genome (I)
•Consists of 23 pairs
of chromosomes.
•Chromosomes 1
through 22 are
called autosomes.
•The X and Y
chromosomes are
the sex
chromosomes.
•Males are XY.
•Females are XX.
2005 VisiScience Corporation.All rights reserved.

47. The Human Genome (II)
•The haploid human genome
contains 3 billion base pairs of
DNA.
•Only 1.5-3% of the human
genome codes for proteins.
•Humans have 35,000-100,000
genes.
•Humans are 99.9% identical at
the DNA level.
The Living Genome:
Reading the Book of Life,
Houston Museum of
Natural Science

48. Chromatin and DNA Packaging
•The DNA contained
within each human
cell would be 5.8 feet
long if it were
stretched out
lengthwise.
•To fit into the tiny
cell, each
chromosome is
subjected to several
levels of packaging.
•Packaged DNA is
called chromatin.
Courtesy of Helmut Schiessel,