Eukaryotes By prof Sawsan Sajid AL Jubori transcription and its regulation in prokaryotics is much simpler But the eukaryotes have to transcribe and then have a process for mRNA processing like capping splicing and adding ply adenine tail and then have a special mec ID: 934780
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Slide1
Gene regulation in prokaryotes and Eukaryotes
By prof
Sawsan
Sajid
AL-
Jubori
Slide2Slide3transcription and its regulation in prokaryotics is much simpler. But the eukaryotes have to transcribe and then have a process for mRNA processing like capping, splicing and adding ply adenine tail, and then have a special mechanism to transport the processed mature mRNA to the cytoplasm from the nucleus.Because
prokayotes
don't have a nuclear membrane, transcription and translation can occur at opposite ends of the mRNA molecule at the same time. This is not true for eukaryotes.
Transcription is responsible for most gene regulation in prokaryotes but in
eukaryotes
gene regulation is more complicated and genes are regulated before and after transcription
And another difference is that eukaryotes don't express their genes all at once; they express one at a time. Prokaryotes do.
Prokaryotes don't contain
introns
. So splicing of introns and joining of exons are not needed. But in
eukaryotics
, splicing of introns and joining of exons is needed
.
Slide4Slide5How do bacteria adapt so quickly to their environments? Part of the answer to this question lies in clusters of co regulated genes called operons.
Bacteria are typically exposed to an ever-changing environment in which nutrient availability may increase or decrease radically. Bacteria respond to such variations in their environment by altering their gene expression pattern; thus, they express different enzymes depending on the carbon sources and other nutrients available to them. It would be wasteful to synthesize, for example, lactose-metabolizing enzymes in the absence of lactose. However, when lactose is the only available carbon source, bacteria must quickly induce lactose-metabolizing enzymes, or else they will die. In bacteria, this sort of genetic regulation is mediated at the level of
transcription
.
Bacterial Operons Are
Co-regulated
Gene Clusters
Bacterial genes are organized into operons, or clusters of
coregulated
genes. In addition to being physically close in the genome, these genes are regulated such that they are all turned on or off together. Grouping related genes under a common control mechanism allows bacteria to rapidly adapt to changes in the environment.
The best-studied examples of operons are from the bacterium
Escherichia coli
(
E. coli
), and they involve the enzymes of lactose metabolism and tryptophan biosynthesis
Slide6Apoptosis
(
"falling off") is a process of programmed cell death that occurs in
multicellular
organisms
Biochemical events
lead to characteristic cell changes (
morphology
) and death. These changes include
,
cell shrinkage,
nuclear fragmentation
,
chromatin condensation
,
chromosomal DNA fragmentation
, and global
mRNA
decay. Between 50 and 70
billion
cells die each day due to apoptosis in the average human
adult
]
For an average child between the ages of 8 and 14, approximately 20 billion to 30 billion cells die a day
.
Slide7Slide8Slide9Slide10Slide11Slide12Slide13Slide14Slide15Slide16Slide17Slide18Slide19Slide20Slide21Slide22Slide23Slide24Slide25Slide26Slide27Slide28Slide29Slide30Slide31Slide32Exon shuffling
is a molecular mechanism for the formation of new genes. It is a process through which two or more
exons
from different genes can be brought together
ectopically
, or the same
exon
can be duplicated, to create a new
exon-intron
structure.
[1]
There are different mechanisms through which
exon
shuffling occurs:
transposon
mediated
exon
shuffling, crossover during sexual recombination of parental genomes and illegitimate recombination.
Exon
shuffling follows certain splice frame rules.
Introns
can interrupt the reading frame of a gene by inserting a sequence between two consecutive codons
(phase 0 introns), between
the first and second nucleotide of a codon (phase 1 introns), or between the second and third nucleotide of a codon (phase 2 introns). Additionally
exons
can be classified into nine different groups based on the phase of the flanking
introns
(symmetrical: 0-0, 1-1, 2-2 and asymmetrical: 0-1, 0-2, 1-0, 1-2, etc
.
Intron
and
exon
classes.
Introns
can be classified into phase 0, phase 1, and phase 2 depending on their position relative to the reading frame.
Exons
can be classified into 9 groups depending on the phases of their flanking
introns
.
Slide33Slide34Slide35Slide36Slide37Crossover during sexual recombination of parental genomesEvolution of eukaryotes is mediated by sexual recombination of parental genomes and since
introns
are longer than
exons
most of the crossovers occur in
noncoding
regions. In these
introns
there are large numbers of transposable elements and repeated sequences which promote recombination of
nonhomologous
genes.
There
is a mechanism for the formation and
shuffling
.
This mechanism is divided into three stages. The first stage is the insertion of
introns
at positions that correspond to the boundaries of a protein domain. The second stage is when the "
protomodule
" undergoes tandem duplications by recombination within the inserted
introns
. The third stage is when one or more
protomodules
are transferred to a different
nonhomologous
gene by
intronic
recombination. All states of modularization have been observed in different domains such as those of
hemostatic
proteins
Slide38Slide39LINEs are a group of genetic elements that are found in abundant quantities in eukaryotic genomes.
LINE-1 is the most common LINE found in humans. It is transcribed by
RNA polymerase II
to give an
mRNA
that
codes for two proteins: ORF1 and ORF2, which are necessary for
transposition.Upon
transposition, L1 associates with 3' flanking DNA and carries the non-L1 sequence to a new genomic location.
The
donor DNA sequence remains unchanged throughout this process because it functions in a copy-paste manner via RNA intermediates; however, only those regions located in the 3' region of the L1 have been proven to be targeted for duplication
..
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