EUKARYOTIC GENOME
INTRODUCTION:
A 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.
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.
GENOME SIZE AND COMPLEXITY :
Eukaryotic genomes are diverse in size, ranging from ∼10 Mb in some fungi to
>100 000 Mb in certain plants, salamanders, and lungfishes. Because they can be so
large, eukaryotic genomes are usually expressed as ‘C-value’ (where ‘C’ stands for
‘constant’ referring to the fact that the genome size is constant from cell to cell in a
given organism or species). C-value is the mass of DNA in picograms (1 pg ≈ 1 billion
base pairs or 1000 Mb of DNA) in a haploid set of chromosomes (often measured
from gametes). The relationship between genome size and gene number is weaker in
eukaryotic genomes than in prokaryotic genomes.
EUKARYOTIC GENOME ORGANISATION :
Eukaryotic genomes include two characteristics that pose a significant information processing
problem.
1. The standard multicellular eukaryotic cell has a substantially larger genome than a
prokaryotic cell.
2. 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
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 primary proteins that comprise chromatin are called histones and DNA is wrapped
around these histone proteins. There are five main histone classes connected to the eukaryotic
INTRODUCTION:
A 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.
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.
GENOME SIZE AND COMPLEXITY :
Eukaryotic genomes are diverse in size, ranging from ∼10 Mb in some fungi to
>100 000 Mb in certain plants, salamanders, and lungfishes. Because they can be so
large, eukaryotic genomes are usually expressed as ‘C-value’ (where ‘C’ stands for
‘constant’ referring to the fact that the genome size is constant from cell to cell in a
given organism or species). C-value is the mass of DNA in picograms (1 pg ≈ 1 billion
base pairs or 1000 Mb of DNA) in a haploid set of chromosomes (often measured
from gametes). The relationship between genome size and gene number is weaker in
eukaryotic genomes than in prokaryotic genomes.
EUKARYOTIC GENOME ORGANISATION :
Eukaryotic genomes include two characteristics that pose a significant information processing
problem.
1. The standard multicellular eukaryotic cell has a substantially larger genome than a
prokaryotic cell.
2. 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
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 primary proteins that comprise chromatin are called histones and DNA is wrapped
around these histone proteins. There are five main histone classes connected to the eukaryotic
