BCHM-3050 Lecture Notes - Lecture 4: Noncoding Dna, Satellite Dna, Genome Size
23 May 2018
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Bacterial genome
Chromosomal compaction occurs by negative supercoiling
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Nucleoid: compacted structure of chromosomes
Exist in cytosol
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Each loop of DNA is bound to protein
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Genome sizes
No simple relationship b/w organismal complexity and genome size
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Eukaryotic genome: larger
Diploid
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Introns: noncoding segments of genome
Most of eukaryotic protein coding genes
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Prokaryotic genome: smaller
Haploid
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Repetitive Sequences
Roy Britten and David Kohne: early indication that euk chromosomes
contain noncoding DNA
Develop technique for analyzing DNA reassoc kinetics
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Method #1: general analyzation of DNA reassoc kinetics
Total DNA is cut into pieces and heated to cause strand separation
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Pieces are slowly cooled
Allow complementary strands to reassociate
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Results: multiple copies reassociate quickly and single sequences
reassociate slowly
With single sequences abundance is low
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Method #2: Analyzation of Bovine DNA
Result: most DNA reassoc more rapidly than expected for single
copy sequence
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Satellite DNA
Satellite DNAs: clusters of repeated sequences
Make up 10-20% of total genome
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AT rich sequences: lower density then avg composition DNA
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GC rich sequences: even denser
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Highly concentrated near centromeres of chromosome
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Chromatin
Histones: proteins apart of formation of nucleosomal structure
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Eukaryotic chromatin: DNA complex of histones and nonhistones
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Histone and Nonhistone chromosomal proteins
Histones are building blocks of chromatin structure
Small basic proteins made up of lysine and arginine
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Fundamental building blocks of chromatin structure
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Bacterial cells have proteins assoc w their DNA
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Higher order chromatin structure in the nucleus
Euchromatin: transcriptionally active chromatin
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Heterochromatin: transcriptionally inactive
Compacted
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Restriction and Modification
Widespread among bacteria
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Chapter 21
Sunday, May 20, 2018
2:51 PM
