L8 Chromosome Structure and Function

Question 1

Define chromsome

Answer 1

structure composed of DNA complexed with specific proteins, which is the form that genetic information is encoded, maintained, and transmitted

Question 2

What are the important functions of the chromosome

Answer 2

condense DNA into a smaller space, protect the genome, regulate all processes that require access to DNA

Question 3

Define Chromatin

Answer 3

the DNA-protein complex that makes up chromosomes (the uncondensed form of chromosomes)

Question 4

What is the first packaging stage of DNA

Answer 4

the binding of positively charged histones which are rich in lysine and arginine which aid in stabilization

Question 5

What are some important details to consider in regards to histone and DNA structure

Answer 5

Histones interact with the minor groove of DNA and forms supercoils that facilitates strand displacement

Question 6

How many core histones are there

Answer 6

4 conserved histones that are crucial for survival

Question 7

What is H1 and what is its function

Answer 7

it is a linker histone that bind to the linker DNA helping in compaction; neutralizes charge to facilitate folding of DNA

Question 8

Why is CENP-A important

Answer 8

it serves as a marker for the kinetochore to recognize the centromere

Question 9

What is a nucleosome

Answer 9

H2A/H2B dimers x 2, H3/H4 tetramer; Octamer and DNA

Question 10

Nucleosome Core Particle smallest turn and winding direction

Answer 10

1.67 turns, it winds left. Once the histone is removed it produces a negative supercoil (making strand separation easier which is required for replication and transcription

Question 11

Describe the process of chromatin packing

Answer 11

first level is a 10nm fiber due to nucleosome association (beads on string), in vitro only it then folds into a 30nm fiber which involves histone H1, the 30nm fiber is then compacted into chromosomes which forms large loops anchored to the central scaffold

Question 12

define euchromatin

Answer 12

relatively extended and open chromatin that is potentially active (light)

Question 13

define heterochromatin

Answer 13

very condensed DNA in which DNA is mostly inaccessible (dark)

Question 14

Where is heterochromatin localized

Answer 14

it prefers to localize in the nucleolus and nuclear membrane

Question 15

Which regions are rich in heterochromatin

Answer 15

telomeres, centromeres, regions with highly repetitive DNA sequences

Question 16

Functions of heterochromatin

Answer 16

inhibits transcription, delays replication timing, inhibits recombination

Question 17

why is inhibiting recombination an important process for heterochromatin

Answer 17

it protects parts of the genome that are replicative

Question 18

Not all euchromatic regions. . .

Answer 18

are actively transcribed (ex: a euchromatic gene translocated to a heterochromatic region can actively prevent transcription

Question 19

Chromatin is organized into TADs

Answer 19

topologically associated domains; chromatin has a level of organization in the cell defined by boundary proteins and crosslinks between specific regions

Question 20

Why is cohesin and condesin important in DNA structure

Answer 20

the result in the boundary domains in TADs during interphase, and compact during mitosis