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15 Cards in this Set
- Front
- Back
S vs. R strain of bacterium
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smooth vs. rough, S is pathogenic and causes pneumonia, R is nonpathogenic mutant form, used in determining that DNA is the genetic material
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components of DNA
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double helix, antiparallel, composed of a phosphate group, deoxyribose sugar and nitrogenous base
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5’ end vs. 3’ end
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5’ is phosphate, 3’ is OH
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number of base pairs/turn
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10
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each DNA molecule that forms a linear chromosome must contain:
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a centromere, two telomeres, and replication origins
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nucleosomes
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are the basic unit of eukaryotic chromosome structure, composed of DNA (146 nucleotides long) wrapped around a protein core formed from histones (8 total histones, 2 molecules of H2A, H2B, H3 and H4) connected to other nucleosomes by linker DNA, left handed coil, DNA wrapped 1.65 turns
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histone fold
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formed from three alpha helices, how the histones are held together
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assembly of histone octamer
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H3 and H4 make a H3-H4 dimer and H2A and H2B make a dimer themselves, two H3-H4 dimers form to form a tetramer, and this tetramer binds to two H2A-H2B dimers to form the histone octamer
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interface between DNA and histone
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extensive, has 142 H-bonds between DNA and octamer, also (+) charged histones bind to the (-) charged DNA, histones are highly conserved
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what influences where nucleosomes form in the DNA?
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1. the difficulty of bending the DNA double helix into two tight turns around the outside of the histone octamer, this requires substantial compression of the minor groove, favors A-T rich sequences (DNA flexibility)
2. the presence of other tightly bound proteins on the DNA, some favor nucleosome formation, others don’t nucleosomes can therefore occupy any one of a number of positions relative to the DNA sequence |
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Zigzag model
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theory of how nucleosomes are packed to form the 30 nm chromatin fiber
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H1 histone
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used in properly condensing the nucelosomes into chromatin fibers, one binds to each nucleosome, changes the path of the DNA as it exits the histone
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chromatin remodeling complexes
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protein machines that use the energy of ATP to change the structure of nucleosomes temporarily so that DNA becomes less tightly bound to the histone core, thought to have an affect on the H2A-H2B dimmers since the H3-H4 dimers are relatively stable, some are inactivated by phosphorylation
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why would you want to remodel nucleosomes
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1. it permits ready access to nucleosomal DNA by other proteins in the cell
2. remodeling complexes can catalyze changes in the positions of nucleosomes along DNA, can even transfer a histone core from one DNA molecule to another |
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covalent modifications of the Histone tails on the N-terminal
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can lead to major changes in chromatin, acetylation of lysines, methylation of lysines and phosphorylation of serine, modifications normally occur after their synthesis in the cytosol but before assembly, those that occur after assembly occur in the nucleus, can cause further compaction of the nucleosome or improve access to the DNA, may be directly linked to chromatin remodeling complexes
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