Genomes are larger due to less gene density -Introns dilute density -Intergenetic regions dilute...
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Transcript of Genomes are larger due to less gene density -Introns dilute density -Intergenetic regions dilute...
![Page 1: Genomes are larger due to less gene density -Introns dilute density -Intergenetic regions dilute density -Bacteria use one intergenetic region to regulate.](https://reader035.fdocuments.in/reader035/viewer/2022062409/5697bfbc1a28abf838ca191b/html5/thumbnails/1.jpg)
Genomes are larger due to less gene density
-Introns dilute density
-Intergenetic regions dilute density
-Bacteria use one intergenetic region to regulate several correlated genes. In humans only ~5% of transcribed DNA gets translated - 95% consists of introns
![Page 2: Genomes are larger due to less gene density -Introns dilute density -Intergenetic regions dilute density -Bacteria use one intergenetic region to regulate.](https://reader035.fdocuments.in/reader035/viewer/2022062409/5697bfbc1a28abf838ca191b/html5/thumbnails/2.jpg)
DNA is wrapped around histones to form a nucelosome - first step of DNA packaging
Packaging:
-Allows DNA to fit into a cell (reduces length 10,000X)
-Protects DNA
-Makes transmission to daughter cells possible
-Restricts transcription
-Nucleosomes only reduce length 6x
-Highly conserved structure in eukaryotes
![Page 3: Genomes are larger due to less gene density -Introns dilute density -Intergenetic regions dilute density -Bacteria use one intergenetic region to regulate.](https://reader035.fdocuments.in/reader035/viewer/2022062409/5697bfbc1a28abf838ca191b/html5/thumbnails/3.jpg)
2 copies of 4 sub units make a histone core
-Each histone protein has an N-terminal tail that is not necessary for nucleosome formation
-Proteins are lysine and argenine rich - positively charged
![Page 4: Genomes are larger due to less gene density -Introns dilute density -Intergenetic regions dilute density -Bacteria use one intergenetic region to regulate.](https://reader035.fdocuments.in/reader035/viewer/2022062409/5697bfbc1a28abf838ca191b/html5/thumbnails/4.jpg)
“Histone fold” domain assists in self assembly of tetramers and dimers
-Each histone core protein has 3 alpha-helices separated by an unstructured loop
-Nucleosome assembly is initiated by H3/H4 tetramer binding, followed by two H2A/H2B dimers
-~40 hydrogen bonds are formed between histone proteins and the DNA backbone and minor groove
-Helices fit into major groove, associate with DNA due to electrostatic charges
![Page 5: Genomes are larger due to less gene density -Introns dilute density -Intergenetic regions dilute density -Bacteria use one intergenetic region to regulate.](https://reader035.fdocuments.in/reader035/viewer/2022062409/5697bfbc1a28abf838ca191b/html5/thumbnails/5.jpg)
Functionally, why is it important that histones only interact with the phosphate backbone and the minor groove of DNA?
- There is no sequence specific binding: Nucleosomes can form with any stretch of DNA (if it hasn’t been modified in some way)
![Page 6: Genomes are larger due to less gene density -Introns dilute density -Intergenetic regions dilute density -Bacteria use one intergenetic region to regulate.](https://reader035.fdocuments.in/reader035/viewer/2022062409/5697bfbc1a28abf838ca191b/html5/thumbnails/6.jpg)
Nucleosomes alter linkage number locally and facilitate unwinding
![Page 7: Genomes are larger due to less gene density -Introns dilute density -Intergenetic regions dilute density -Bacteria use one intergenetic region to regulate.](https://reader035.fdocuments.in/reader035/viewer/2022062409/5697bfbc1a28abf838ca191b/html5/thumbnails/7.jpg)
Histone 1 coils DNA tighter
H1 absentH1 present
![Page 8: Genomes are larger due to less gene density -Introns dilute density -Intergenetic regions dilute density -Bacteria use one intergenetic region to regulate.](https://reader035.fdocuments.in/reader035/viewer/2022062409/5697bfbc1a28abf838ca191b/html5/thumbnails/8.jpg)
Angles of DNA entry and exit from nucleosomes generates a 30nm fiber of DNA
Larger structure formation is also dependent on histone tails
![Page 9: Genomes are larger due to less gene density -Introns dilute density -Intergenetic regions dilute density -Bacteria use one intergenetic region to regulate.](https://reader035.fdocuments.in/reader035/viewer/2022062409/5697bfbc1a28abf838ca191b/html5/thumbnails/9.jpg)
Packaging into nucleosomes and 30nm fibers shorten DNA 40x
- Need to shorten 1,000-10,000x to fit into a nucleus
![Page 10: Genomes are larger due to less gene density -Introns dilute density -Intergenetic regions dilute density -Bacteria use one intergenetic region to regulate.](https://reader035.fdocuments.in/reader035/viewer/2022062409/5697bfbc1a28abf838ca191b/html5/thumbnails/10.jpg)
DNA is looped into a nuclear scaffold
- 1 loop is 40-90kb
![Page 11: Genomes are larger due to less gene density -Introns dilute density -Intergenetic regions dilute density -Bacteria use one intergenetic region to regulate.](https://reader035.fdocuments.in/reader035/viewer/2022062409/5697bfbc1a28abf838ca191b/html5/thumbnails/11.jpg)
Histone tails may be modified to allow easier access to DNA
![Page 12: Genomes are larger due to less gene density -Introns dilute density -Intergenetic regions dilute density -Bacteria use one intergenetic region to regulate.](https://reader035.fdocuments.in/reader035/viewer/2022062409/5697bfbc1a28abf838ca191b/html5/thumbnails/12.jpg)
![Page 13: Genomes are larger due to less gene density -Introns dilute density -Intergenetic regions dilute density -Bacteria use one intergenetic region to regulate.](https://reader035.fdocuments.in/reader035/viewer/2022062409/5697bfbc1a28abf838ca191b/html5/thumbnails/13.jpg)
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