Chromosome Structure

Question 1

What is chromatin?

Answer 1

Is a DNA molecule and the proteins that are associated with it.

Question 2

what protein is about one-third of all proteins within the chromatin? what charge are these things?

Answer 2

Histones

Question 3

what are the two important functions of histones?

Answer 3

they attach to the DNA molecule and help compact it into a smaller size, they also help regulate the activity of genes within the chromosome.

Question 4

how many different histones are there and what are they?

Answer 4

there are five different histones which are H1, H2A, H2B, H3, & H4

Question 5

which histones interact to form a spherical particle called a histone octamer?

Answer 5

the latter four histones being H2A, H2B, H3, & H4)

Question 6

what does a histone octamer contain?

Answer 6

two H2A, two H2B, two H3, and two H4 proteins

Question 7

What does a histone octamer associate with, how big is it, what does it do do?

Answer 7

with a small part of the DNA molecule it is around 146-147bp, it is wrapped around twice on the outside of the histone octamer.

Question 8

what does a histone octamer and the DNA that it wraps form?

Answer 8

a nucleosome

Question 9

what are nucleosomes separated by? what is this type of DNA called?

Answer 9

They are separated by a short length of DNA that is not a part of a nucleosome called linker DNA.

Question 10

how long is linker DNA? what is it associated with?

Answer 10

Linker can be 20-100bp in length it is associated with H1 protein.

Question 11

What do linker histones and nonhistone proteins do?

Answer 11

They help organize adjacent nucleosomes and have a role in compaction.

Question 12

what happens to the length of a DNA molecule that is organized into a nucleosome?

Answer 12

It is reduced in length about seven fold

Question 13

what inhibits gene expression in nucleosomes?

Answer 13

closely spaces nucleosomes inhibit gene expression

Question 14

to express a gene what needs to be done? what is the protein that catalyzes this reaction?

Answer 14

Nucleosomes need to be either moved farther apart or removed altogether, the proteins that form ATP-dependent chromatin-remodeling complexes.

Question 15

what is compaction for DNA?

Answer 15

the process of making the DNA molecule within a chromosome smaller.

Question 16

what is the first step in the compaction process?

Answer 16

organizing the DNA into nucleosomes

Question 17

Nucleosomes within chromatin are coiled into _____. What does this coiling require?

Answer 17

30nm fibers, it requires linker histone

Question 18

what are the 30nm fibers arranged into? what binding factor is it?

Answer 18

loop domains, the binding factor is CCCTC (CTCF) or SMC protein

Question 19

what are chromosomes that occupy distinct locations within the nucleus?

Answer 19

Chromosome territories

Question 20

what are translocations?

Answer 20

chromosomal abnormalities

Question 21

what are the advantages of loop domains?

Answer 21

it helps compact the DNA so it will fit in the nucleus, but it doesn’t compact it to much.

Question 22

what are the highly compacted structures in loop domains called?

Answer 22

heterochromatin

Question 23

what are less compacted structures in loop domains called?

Answer 23

euchromatin

Question 24

where is most of the heterochromatin located at?

Answer 24

centromere and telomeres

Question 25

where are most genes located at?

Answer 25

euchromatin

Question 26

what happens in cell division? (think of heterochromatin), what are a advantage of this?

Answer 26

all regions of a chromosome becomes as compact as heterochromatin

Question 27

what is a draw back in compact chromosomes during cell division?

Answer 27

DNA replication and transcription are inhibited in these compact chromosomes

Question 28

what does euchromatin become after cell division is completed?

Answer 28

it becomes less compact