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

Question 1

the packing of DNA is crucial

Answer 1

to cell architecture

to prevent tangles in long DNA during cell division

Question 2

histones

Answer 2

abundant nuclear proteins that compact and organize chromosomal DNA

Question 3

chromatin

Answer 3

complex of histones and DNA (1/2ea)

dispersed in interphase

Question 4

further folding and compaction of chromatin during mitosis produces…

Answer 4

visible metaphase chromosomes

Question 5

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

Answer 5

chromatin

Question 6

5 major types of histone proteins

Answer 6

H1, H2A, H2B, H3, H4

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

Question 7

extracted chromatin appearance depends on

Answer 7

salt concentration

low = beads on a string

physiological = condensed fiberlike form 30nm in diameter

Question 8

beads on a string

Answer 8

nucleosomes connected by linker DNA

Question 9

nucleosomes

Answer 9

primary structural units of chromatin

about 10nm in diameter

less susceptible to nuclease digestion than linker DNA

Question 10

structure of a histone

Answer 10

DNA wrapped around octamer histone protein core

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

Question 11

when is DNA assembled into nucleosomes

Answer 11

during cell replication after the replication fork passes

uses histone chaperones

Question 12

structure of 30nm fiber

Answer 12

chromatin zig-zag ribbon

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

contains H1

Question 13

30nm fiber purpose

Answer 13

chromatin in chromosomal regions not being transcribed or replicated

Question 14

modifications of _____ ______ control chromatin condensation and function

Answer 14

histone tails

Question 15

histone tail

Answer 15

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

Question 16

histone tail modification

Answer 16

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

Question 17

histone code

Answer 17

the different combinations of tail modification

alter binding sites on chromatin-associated proteins

Question 18

histone acetylation

Answer 18

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

Question 19

histone methylation

Answer 19

prevents acetylation to maintain positive charge on lysine

makes chromatin less available

Question 20

heterochromatin

Answer 20

dark staining condensed regions of chromatin

remains compacted after mitosis

Question 21

examples of heterochomatin

Answer 21

centromeres, telomeres, transcriptionally inactive genes

Question 22

euchromatin

Answer 22

light staining loose chromatin

most transcribed regions of DNA

Question 23

histone code of modified aas in tails is “read” b proteins that…

Answer 23

bind to modified tails and promote condensation or decondensation

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

Question 24

proteins that read histone code have a _______

Answer 24

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

Question 25

example of a histone code reading protein

Answer 25

HP1 heterochromatin protein I has a 2nd domain called chromoshadow domain that helps spread methylation into heterochromatin

Question 26

bromodomain

Answer 26

binds to acetylated histone tails in euchromatin

Question 27

TFIID

Answer 27

a transcription factor with a bromodomain histone acetylase activity

Question 28

x-chromosome inactivation in females

Answer 28

epigenetic gene control through repression by heterochromatin half of cells have inactive Xmom and inactive Xdad

Question 29

dosage compensation

Answer 29

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

Question 30

Polycomb in dosage compensation

Answer 30

binds methylated histone tails and contains histone methyl transferase activity

Question 31

epigenetic process

Answer 31

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

Question 32

nonhistone proteins organize....

Answer 32

long chromatin loops scaffold associated regions (SARs) or matrix attachment regions (MARs)

Question 33

SARs/MARs

Answer 33

located at bases of DNA loops found between transcription units insulate neighboring genes

Question 34

insulators

Answer 34

DNA sequences that separate transcription units from each other

Question 35

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

Answer 35

no

Question 36

structural maintenance of chromosome proteins (SMCs)

Answer 36

hold bases of chromatin loops in place in interphase nonhistone proteins that a crucial for maintaining structure of condensed chromatin in mitosis

Question 37

chromonema fiber

Answer 37

100-130nm fiber condenses during prophase

Question 38

middle prophase chromatid

Answer 38

200-250nm structure made from a chromonema fiber folds into 500-750nm chromatids observed in metaphase

Question 39

interphase and metaphase chromosomes contain...

Answer 39

proteins other than histones that regulate transcription and replication transcription factors in interphase high mobility group proteins (HMG) assist binding of TFs

Question 40

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

Answer 40

chromatids

Question 41

karyotype

Answer 41

number, sizes and shapes of the metaphase chromosomes different for each species human: 22 autosomes 1 pair of sex chromosomes

Question 42

FISH

Answer 42

chromosomes painting that differentiates chromosomes os similar size and shape probes specific for sites scattered along length of chromosome

Question 43

how does FISH work

Answer 43

probes labeled with different fluorescent dyes are hybridized to chromosomes observed with fluorescence microscope

Question 44

what is FISh used for

Answer 44

detect abnormal number of chromosomes, translocations finer structure analysis to reveal deletions or duplications or chromosomal regions reveal evolution of chromosomes

Question 45

conserved synteny

Answer 45

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

Question 46

polytene chromosome

Answer 46

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)

Question 47

3 functional elements required for replication and correct segregation

Answer 47

replication origins where DNA polymerase + other proteins initiate synthesis centromere (proper segregation) telomeres

Question 48

kinetochore

Answer 48

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

Question 49

telomere

Answer 49

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

Question 50

telomerase

Answer 50

specialized form of reverse transcriptase that carries an internal RNA template to direct DNA synthesis adds telomeres to ends of chromosomes

Question 51

telomerase is active/inactive in...

Answer 51

active: cancer, germ/stem cells inactive: cells of adult tissues that replicate a limited number of times or never again (postmitotic)