GENOME ORGANIZATION IN EUKARYOTES DOWNLOAD
GENOME ORGANIZATION IN EUKARYOTES DOWNLOAD!
Organization and control of eukaryotic genomes. Gene expression in eukaryotes has two main differences from the same process in prokaryotes. The typical multicellular eukaryotic genome is much larger than that of a bacterium. Cell specialization limits the expression of many genes to specific cells. The hereditary material i.e. DNA(deoxyribonuclic acid) of an organism is composed of a The vast expansion of the genome with noncoding and repetitive DNA in higher eukaryotes implies more extensive epigenetic silencing mechanisms. [Genome organization in eukaryotes]. The main (euchromatic) part of the genome is considered as the totality of separate functional units (chromomere, gene loci), which have in the average a higher excess of DNA compared to the sized of the structural gene.
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- Genomic organization - Wikipedia
- Organization and control of eukaryotic genomes
- [Genome organization in eukaryotes].
- [Genome organization in eukaryotes].
- Presentation Description
This can populate the eukaryotic genome with multiple copies of its sequence. Major rearrangements of at least one set of genes occur during immune system differentiation. B lymphocytes produce immunoglobins, or antibodies, that specifically recognize and combat viruses, bacteria, and other invaders.
Each differentiated cell produces one specific type of antibody that attacks a specific invader. Functional antibody genes are pieced together from physically separated DNA regions. Each immunoglobin consists of four polypeptide chains, each genome organization in eukaryotes a constant region and a variable region, giving each antibody its unique function.
As a B lymphocyte differentiates, one of several hundred possible variable segments is connected to the constant section genome organization in eukaryotes deleting the intervening DNA. The random combinations of different variable and constant regions create an enormous variety of different polypeptides, which combine with others genome organization in eukaryotes form complete antibody molecules.
As a result, the mature immune system can make millions of different kinds of antibodies from millions of subpopulations of B lymphocytes. The Control of Gene Expression Each cell expresses only a small fraction of its genes Are continually turned on and off in response to signals from their internal and external environments.
Gene expression must be controlled on a long-term basis during cellular differentiation. Highly specialized cells express only a tiny fraction of their genes. Problems with gene expression and control can lead to imbalance and diseases, including cancers. The control of gene expression can occur at any step in the pathway from gene to functional protein.
Chromatin packing modifications Genes of densely condensed genome organization in eukaryotes are usually not expressed.
Chemical modifications of chromatin play a key role in chromatin structure and transcription regulation. For example, the inactivated mammalian X chromosome in females is heavily methylated. Methylation enzymes correctly methylate the daughter strands.
This accounts for genomic imprinting in which methylation turns off either the maternal or paternal alleles.
Histone acetylation and deacetylation appear to play a direct role in the regulation of gene transcription. Acetylated histones grip DNA genome organization in eukaryotes tightly, providing easier access for transcription proteins in this region.
Some of the enzymes responsible for acetylation or deacetylation are associated with or are components of transcription factors that bind to promotors.
DNA methylation and histone deacetylation may cooperate to repress transcription. Initiation of transcription is the most important and universally used control point in gene expression. Control elements are noncoding DNA segments that regulate transcription by binding transcription factors.
One transcription factor recognizes the TATA box. Distal control elements, enhancers, may be thousands of nucleotides away from the promoter or even downstream of the gene or within an intron.
GENOME ORGANISATION in EUKARYOTES |authorSTREAM
Bending of DNA enables transcription factors, activators, bound to enhancers to contact the protein initiation complex at the promoter.
Eukaryotic genes also have repressor proteins that bind to DNA control elements called silencers.
Repression may operate mostly at the level of chromatin modification.