chromatin and gene regulation

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compaction ratio in human genome
Chr22 goes from 1.5cm to 2um - 10,000 fold.
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Three roles of chromatin
package the DNA into a small volume to fit into the cell, regulate access to the DNA sequence for transcription and translation. and lock in patterns of gene expression.
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What are nucleosomes
The first and most basic level of DNA packaging, made up of nucleosomes. A nucleosome core particle and adjacent linker DNA
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Describe the structure of a nucleosome core
2x H2A-H2B dimers, plus a H3-H4 tetramer. Histone H1 binds to the linker region
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Structural motif of the histone proteins
they all share a histone fold, formed from three a helixes connected by two loops.
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How many hydrogen bonds between DNA and histone
142
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The two forms of chromatin
heterochromatin and euchromatin.
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Which is heretochromatin?
The highly condensed form - INACTIVE
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Which is euchromatin
less condensed - ACTIVE
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How often does DNA in a nucleosome unwind and rewind
four times a second
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An example of chromatin remodelling complexes
SWI/SNF
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What do all chromatin remodelling complexes contain
an ATP hydrolysis region, which can use energy to change how tightly the DNA is bound, and promotes the exchange of histones
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Modification of histones - which ones and where
The N terminal tails of histones in the nucleosome core can be modified
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Which amino acid can be acetylated
Lysines. by Histone acetyltransferases, or histone deacetylases.
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What amino acids can be methylated
lysines and arginines. by histone methyltransferases.
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What amino acids can be phosphorylated
serines and threonines
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Another way histones can be modified
Histone variants - H3 variant CENPA-A is 46% the same as h3 and in involved in organising chromatin at the centromere
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How does chromatin become open
Hyperaceytlation of histones, methylation of some specific lysines
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How does chromatin become inactive
methylation of sone specific lysines associated with inactive chromatin
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How does methylated DNA lead to inactive chromatin
Methylated DNA binds to MeCP2, which recruits HDAC which leads to inactive chromatin
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Card 2

Front

Three roles of chromatin

Back

package the DNA into a small volume to fit into the cell, regulate access to the DNA sequence for transcription and translation. and lock in patterns of gene expression.

Card 3

Front

What are nucleosomes

Back

Preview of the front of card 3

Card 4

Front

Describe the structure of a nucleosome core

Back

Preview of the front of card 4

Card 5

Front

Structural motif of the histone proteins

Back

Preview of the front of card 5
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