Chromatin o Compaction of the large DNA molecules and the control of gene expression in eukaryotes are achieved by having the dna complexed with a set of special proteins to form the protein-DNA complex called chromatin. The DNA-binding proteins of chromatin are histones, and nonhistone
•Compaction of the large DNA molecules and the control of gene expression in eukaryotes are achieved by having the DNA complexed with a set of special proteins to form the protein–DNA complex called chromatin. The DNA-binding proteins of chromatin are histones, and nonhistones. Chromatin
Histones vs nonhistone Histones are small, very basic proteins rich in lysine and arginine. The histones are the basic building blocks of chromatin structure. The nucleoids of prokaryotic cells also have proteins associated with dna, but these proteins are quite different from the histones and do not seem to form a comparable chromatin structure Nonhistone chromosomal proteins- The histones are accompanied by a much more diverse group of DNA binding proteins called nonhistone chromosomal proteins
Histones vs Nonhistone • Histones are small, very basic proteins rich in lysine and arginine. The histones are the basic building blocks of chromatin structure. The nucleoids of prokaryotic cells also have proteins associated with DNA, but these proteins are quite different from the histones and do not seem to form a comparable chromatin structure. • Nonhistone chromosomal proteins - The histones are accompanied by a much more diverse group of DNAbinding proteins called nonhistone chromosomal proteins
Chromosomes Bacterial chromosome- Almost all of the dna of a typical prokaryote like E coli is contained in a single, large, supercoiled circular DNA molecule, with a minor fraction present in small plasmids Eukaryotic chromosomes- The typical eukaryotic cell genome is divided into several or many chromosomes, each of which contains a single, very large, linear DNa molecule. These DNa molecules are commonly of the order of 10 to 10 bp in length. The number of eukaryotic chromosomes ranges from l(in an Australian ant)to 190(in a species of butterfly). Ploidy- Some eukaryotic cells are highly polyploid, carrying many copies of each chromosome
Bacterial chromosome - Almost all of the DNA of a typical prokaryote like E. coli is contained in a single, large, supercoiled circular DNA molecule, with a minor fraction present in small plasmids. Eukaryotic chromosomes - The typical eukaryotic cell's genome is divided into several or many chromosomes, each of which contains a single, very large, linear DNA molecule. These DNA molecules are commonly of the order of 107 to 109 bp in length. The number of eukaryotic chromosomes ranges from 1 (in an Australian ant) to 190 (in a species of butterfly). Ploidy - Some eukaryotic cells are highly polyploid, carrying many copies of each chromosome. Chromosomes
Eukaryotic chromosome Eukaryotic chromosome DNA A eukaryotic chromosome set Gene locus Chromosome
Eukaryotic chromosome
Considerations in eukaryotic chromosomes The enormous amount of dna in eukaryotic cells poses the following obstacles to cells. 1. Compaction- The length of the total DNA content of a human cell is nearly 3 meters, yet it must be packed into a nucleus about 10-5 m in diameter 2. Selective transcription-In a typical differentiated eukaryotic cell, only a small fraction of the DNA (5%-10%o)is ever transcribed. Many genes that do undergo transcription do so only in certain cell lines in particular tissues, and then often only under special circumstances. To maintain and regulate such complex programs of selective transcription, the accessibility of the dna to RNa Polymerases must be under strict control
Considerations in eukaryotic chromosomes The enormous amount of DNA in eukaryotic cells poses the following obstacles to cells: 1. Compaction - The length of the total DNA content of a human cell is nearly 3 meters, yet it must be packed into a nucleus about 10-5 m in diameter. 2. Selective transcription - In a typical differentiated eukaryotic cell, only a small fraction of the DNA (5%-10%) is ever transcribed. Many genes that do undergo transcription do so only in certain cell lines in particular tissues, and then often only under special circumstances. To maintain and regulate such complex programs of selective transcription, the accessibility of the DNA to RNA Polymerases must be under strict control