Exam 2: Ch 6 Organization of Eu Chromo and Functional Elements Flashcards Preview

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Flashcards in Exam 2: Ch 6 Organization of Eu Chromo and Functional Elements Deck (51):
1

the packing of DNA is crucial

to cell architecture

to prevent tangles in long DNA during cell division

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histones

abundant nuclear proteins that compact and organize chromosomal DNA

3

chromatin

complex of histones and DNA (1/2ea)

dispersed in interphase

4

further folding and compaction of chromatin during mitosis produces...

visible metaphase chromosomes

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the structural organization of _______ allows vast DNA length to be compacted into the microscopic constraints of the nucleus

chromatin

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5 major types of histone proteins

H1, H2A, H2B, H3, H4

rich in pos charged aa that interact with neg charged phosphate on DNA

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extracted chromatin appearance depends on

salt concentration

low = beads on a string

physiological = condensed fiberlike form 30nm in diameter

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beads on a string

nucleosomes connected by linker DNA

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nucleosomes

primary structural units of chromatin

about 10nm in diameter

less susceptible to nuclease digestion than linker DNA

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structure of a histone

DNA wrapped around octamer histone protein core

2 copies of each histone (not H1) into a disk like structure

11

when is DNA assembled into nucleosomes

during cell replication after the replication fork passes

uses histone chaperones

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structure of 30nm fiber

chromatin zig-zag ribbon

two strands of stacked nucleosomes wound into a left handed double helix

contains H1

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30nm fiber purpose

chromatin in chromosomal regions not being transcribed or replicated

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modifications of _____ ______ control chromatin condensation and function

histone tails

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histone tail

flexible n-terminus and C-terminus in H2A and B extending from histone octamer core

required for chromatin to condense from beads on a string to 30nm fiber

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histone tail modification

post-translational modifications like acetylation, methylation, phosphorylation, and ubiquitination

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histone code

the different combinations of tail modification

alter binding sites on chromatin-associated proteins

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histone acetylation

tail lysines undergo reversible acetylation by enzymes acting on N-terminus

acetylation neutralizes lysine's positive charge --> beads on a string (increases transcription and replication)

correlated with increased chromatin digestion by nucleases

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histone methylation

prevents acetylation to maintain positive charge on lysine

makes chromatin less available

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heterochromatin

dark staining condensed regions of chromatin

remains compacted after mitosis

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examples of heterochomatin

centromeres, telomeres, transcriptionally inactive genes

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euchromatin

light staining loose chromatin

most transcribed regions of DNA

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histone code of modified aas in tails is "read" b proteins that...

bind to modified tails and promote condensation or decondensation

forms open or closed chromatin structures as judged by their sensitivity to DNase I digestion

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proteins that read histone code have a _______

chromodomain that binds histone tails when they're methylated at specific lysines

25

example of a histone code reading protein

HP1 heterochromatin protein I

has a 2nd domain called chromoshadow domain that helps spread methylation into heterochromatin

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bromodomain

binds to acetylated histone tails in euchromatin

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TFIID

a transcription factor with a bromodomain

histone acetylase activity

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x-chromosome inactivation in females

epigenetic gene control through repression by heterochromatin

half of cells have inactive Xmom and inactive Xdad

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dosage compensation

process that ensures cells of females express same level of proteins encoded on x-chromosomes as cells as males who only have 1

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Polycomb in dosage compensation

binds methylated histone tails and contains histone methyl transferase activity

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epigenetic process

affects expression of specific genes and is inherited by daughter cells w/o being result of a change in DNA sequence

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nonhistone proteins organize....

long chromatin loops

scaffold associated regions (SARs) or matrix attachment regions (MARs)

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SARs/MARs

located at bases of DNA loops

found between transcription units

insulate neighboring genes

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insulators

DNA sequences that separate transcription units from each other

35

can proteins regulating transcription of one gene influence the transcription of a neighboring gene separated by an insulator?

no

36

structural maintenance of chromosome proteins (SMCs)

hold bases of chromatin loops in place in interphase

nonhistone proteins that a crucial for maintaining structure of condensed chromatin in mitosis

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chromonema fiber

100-130nm fiber condenses during prophase

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middle prophase chromatid

200-250nm structure made from a chromonema fiber

folds into 500-750nm chromatids observed in metaphase

39

interphase and metaphase chromosomes contain...

proteins other than histones that regulate transcription and replication

transcription factors in interphase

high mobility group proteins (HMG) assist binding of TFs

40

each metaphase chromosome consists of two sister _____ that are linked at the centromere

chromatids

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karyotype

number, sizes and shapes of the metaphase chromosomes

different for each species

human: 22 autosomes 1 pair of sex chromosomes

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FISH

chromosomes painting that differentiates chromosomes os similar size and shape

probes specific for sites scattered along length of chromosome

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how does FISH work

probes labeled with different fluorescent dyes are hybridized to chromosomes

observed with fluorescence microscope

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what is FISh used for

detect abnormal number of chromosomes, translocations

finer structure analysis to reveal deletions or duplications or chromosomal regions

reveal evolution of chromosomes

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conserved synteny

genes occurring in the same order on a chromosome in 2 different species

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polytene chromosome

enlarged interphase chromosomes with a large number of reproducible well-demarcated bands

salivary glands of fruit flies

precisely locate specific DNA sequences, translocations, and inversions (immunostaining)

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3 functional elements required for replication and correct segregation

replication origins where DNA polymerase + other proteins initiate synthesis

centromere (proper segregation)

telomeres

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kinetochore

complex protein structure that assembles at centromeres and uses mitotic spindle fibers

49

telomere

repeat sequence TTAGGG at end of chromosomes to prevent shortening

lagging strand not replicated by DNA polymerase in its entirety so lose end of chromo

50

telomerase

specialized form of reverse transcriptase that carries an internal RNA template to direct DNA synthesis

adds telomeres to ends of chromosomes

51

telomerase is active/inactive in...

active: cancer, germ/stem cells

inactive: cells of adult tissues that replicate a limited number of times or never again (postmitotic)