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15 Cards in this Set

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S vs. R strain of bacterium
smooth vs. rough, S is pathogenic and causes pneumonia, R is nonpathogenic mutant form, used in determining that DNA is the genetic material
components of DNA
double helix, antiparallel, composed of a phosphate group, deoxyribose sugar and nitrogenous base
5’ end vs. 3’ end
5’ is phosphate, 3’ is OH
number of base pairs/turn
10
each DNA molecule that forms a linear chromosome must contain:
a centromere, two telomeres, and replication origins
nucleosomes
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
histone fold
formed from three alpha helices, how the histones are held together
assembly of histone octamer
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
interface between DNA and histone
extensive, has 142 H-bonds between DNA and octamer, also (+) charged histones bind to the (-) charged DNA, histones are highly conserved
what influences where nucleosomes form in the DNA?
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
Zigzag model
theory of how nucleosomes are packed to form the 30 nm chromatin fiber
H1 histone
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
chromatin remodeling complexes
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
why would you want to remodel nucleosomes
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
covalent modifications of the Histone tails on the N-terminal
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