Exam 2: Chromatin and Chromosomes

Question 1

in interphase, DNA is…

Answer 1

decondensed and coiled around protein spools

Question 2

nucleosome “beads on a string”

Answer 2

protein spool that DNA of eukaryote chromosomes are always spooled around

left handed spiral

eukaryotes only

Question 3

nucleosome core

Answer 3

roundish disk made of 8 histones

150 base pairs of dsDNA in 2 loops

allows chromosomes to be condensed in length

Question 4

what proteins are nucleosomes made of

Answer 4

histones (100-200 AAs)

25% lysine and arginine to help bind to acidic phosphates on DNA

Question 5

each core is wrapped in ____ turns of DNA

Answer 5

~1.7, almost 2

Question 6

between nucleosomes there is additional ____

Answer 6

unspooled linker DNA

this all forms a repeating unit of roughly 200 bp

150 bp nucleosome DNA and 50 bp linker DNA

Question 7

each nucleosome core is an ____

Answer 7

octamer

8 histone molecules

Question 8

if you mix histones together…

Answer 8

they will spontaneously assemble into nucleosome cored

Question 9

if you mix DNA with nucleosome cores…

Answer 9

the DNA naturally coils around the cores

Question 10

what happens during s-phase

Answer 10

a ton of nucleosome cores are made

newly replicated DNA wraps around immediately

Question 11

nucleosomes shorten DNA by a factor of _

Answer 11

7; 3 feet to 5 inches

the nucleosome packing shortens DNA by another 7

total packing is by a factor of 49/50

Question 12

nucleosomes don’t only stick to DNA…

Answer 12

they stick to each other making disk-like structures

a strand about 30nm called chromatin fiber (next level of supercoiling) involving histone tails

Question 13

scaffold proteins and loops

Answer 13

central core of skeleton for the chromosome

chromatin fibers form loops and are attached to the scaffold

loops exist in interphase and metaphase chromosomes

Question 14

matrix associated region

Answer 14

AT-rich regions of DNA attached to scaffold protein

attach bases of DNA loops

MAR=SAR (scaffold associated region)

Question 15

the final shortening of chromosomes occurs during _____

Answer 15

prophase

highest level of chromatin packing

Question 16

how do we number the human karyotype

Answer 16

number the autosomes from longest to shortest

divide into groups A-G based on shapes

sex chromosomes are simply X and Y

Question 17

what is the smallest chromosome

Answer 17

chromosome 21

it’s out of order~

Question 18

most chromosomes have regions of….

Answer 18

constitutive heterochromatin near the centromeres

large heterochromatic centromeric bands on 1, 9, 16

Question 19

acrocentric autosomes include…

Answer 19

13, 14, 15, 21, 22

all have ribosomal genes on the short arms

Question 20

chromatin contains

Answer 20

both DNA and protein

more protein than DNA

Question 21

nonhistone proteins in chromatin include both

Answer 21

structural and regulatory proteins

Question 22

differences between euchromatin and heterochromatin

Answer 22

the amount of packing

Question 23

heterochromatin

Answer 23

more condense, less active, late-replicating, dark staining

constitutive is always hetero

facultative is sometimes hetero

Question 24

euchromatin

Answer 24

decondensed and active

facultative is sometimes euchromatin

Question 25

constitutive heterochromatin

Answer 25

always hetero

tails of Y’s, all centromeric regions

especially 1, 9, 16

Question 26

facultative heterochromatin

Answer 26

goes between hetero and euch

barr body

female’s x chromosome

Question 27

Giemsa stain

Answer 27

G-bands are alternating light and dark bands on chromosomes when a staining technique is used

bands are large and contain many genes

numbered to ID regions, blocks of genes, deletions

tell chromosomes apart

Question 28

with careful banding techniques…

Answer 28

recognize same chromosome in diff generations

this is b/c some parts of chromosomes are more variable, esp in heterochromatic regions

Question 29

if you remove histones from a mitotic chromosome what fraction of the original weight of the chromosome does this remove?

Answer 29

50%

1/3 remaining mass is other proteins including scaffolds

resulting structure is loose, relaxed DNA still attached in large loops to the scaffold