EUKARYOTIC GENE. BAHAY GÜLLE* FATIH UNIVERSITY ART & SCIENCE FACULTY BIOLOGY DEPARTMANT 4 TH YEAR STUDENT. Eukaryotes have a complex intracellular organization with internal membranes, membrane bond-organelles, a nucleus and a welled organized cytoskeleton.
FATIH UNIVERSITY ART & SCIENCE FACULTY BIOLOGY DEPARTMANT 4TH YEAR STUDENT
Eukaryotes have a complex intracellular organization with internal membranes, membrane bond-organelles, a nucleus and a welled organized cytoskeleton.
Eukaryotic cells have several linear chromosomes in their nuclei . In each of the chromosomes there is a very long DNA molecule packaged by histones and other proteins.
The number and DNA content of chromosomes are different among different species.
Human genome : 3x109 nts
Onion : 15x109 nts
Lily : 90x109 nts
low gene density
high gene density
no introns (or splicing)
no RNA processing
Eukaryotic genomes may be so large, in part, because most eukaryotic genes in higher eukaryotic organisms are interrupted by introns.
The main proportion of DNA in the genomes are non-coding sequences, thus gen density is low in eukaryotic genomes.(The total number of gene in human is estimated to be 30,000-40,000
Most eukaryotic genes are DNA sequences that are never translated into polypeptides. These noncoding regions, called introns, alternate with regions called exons that are expressed in the polypeptide sequence.
-the basal or core promoter located within about 40 bp of the start site
-an "upstream" promoter, which may extend over as many as 200 bp farther upstream
The transcription start is usually associated with an AT rich DNA sequence about 25 bp away from the initiation - the TATA box
Upstream anywhere from 50 to 100 bases from the TATA box is another sequence associated with transcription initiation - the CAAT box. This sequence may not be necessary in all genes.
Eukaryotic Gene ControlEukaryotic control sites include promoter consensus sequences similar to those in bacteria.
In eukaryotes the splicing process of a pre-mRNA can lead to different ripe mRNA molecules and therefore to different proteins. This phenomenon is called alternative splicing.
When the pre-mRNA has been transcribed from the DNA, it includes several introns and exons. But what is an intron and what is an exon is not decided yet. This decision is made during the splicing process.