Chromosome Strucutre and Chromatin

Question 1

What is chromatin?

Answer 1

the material of which chromosomes are made of

Question 2

What is a chromatid?

Answer 2

one of the two copies of a replicated chromosome that is joined at the centromere to the other copy

Question 3

What is the centromere?

Answer 3

the chromosomal region that holds sister chromatids together and where the kinetochores forms

Question 4

What is a kinetochore?

Answer 4

a protein complex that forms on chromosome centromeres during M phase that binds microtubules and directs chromosome movement in mitosis

Question 5

What are telomeres?

Answer 5

the ends of chromosomes

Question 6

Where are the chromosomes?

Answer 6

the nucleus

Question 7

What proteins form chromatin?

Answer 7

histones

Question 8

What are genes transcribed to produced?

Answer 8

the RNA molecules needed to programme translation in the cytoplasm

Question 9

What encode proteins and genetic traits?

Answer 9

the sequence of bases in the DNA

Question 10

What is genetic material split into in eukaryotic cells?

Answer 10

individual long pieces of double stranded DNA (chromosomes)

Question 11

How many chromosomes in humans?

Answer 11

46

Question 12

Why does DNA take up little space in the nucleus?

Answer 12

DNA is a naturally helical molecule and is supercoiled using specialised enzymes

Question 13

When are chromosomes active?

Answer 13

all the time

Question 14

How many histone pieces are in a nucelosome?

Answer 14

8

Question 15

Metaphase chromosomes:

Answer 15

(in mitosis) highly condensed and compacted

Question 16

Interphase chromosomes:

Answer 16

visible less distinct and exhibit variable levels of compaction depending on their activity

Question 17

Euchromatin:

Answer 17

largely de-compacted and potentially active in gene expression

Question 18

Heterochromatin:

Answer 18

highly compacted and transcriptionally inactive(in general)

Question 19

What do centromeres and telomeres contain?

Answer 19

repetitive DNA sequences

Question 20

What des electron micro graphing show?

Answer 20

‘unfolded’ chromatin: ‘beads on a string’

Question 21

‘Beads on a string’:

Answer 21

beads are nucleosomes and string is DNA

Question 22

Why is the wrapping loose in euchromatin?

Answer 22

so that the raw DNA may be accessed

Question 23

What process allows chromatin to become more compact?

Answer 23

condensation

Question 24

What does protein does chromatin condensation involve?

Answer 24

histone H1

Question 25

Where do individual chromosomes tend to concentrate?

Answer 25

within discrete territories with limited intermingling

Question 26

What types of chromatin is visible during interphase?

Answer 26

1. euchromatin
2. heterochromatin

Question 27

Describe euchromatin

Answer 27

diffuse and light staining; actively transcribed genes; tend to concentrate to the middle of the nucleus

Question 28

Describe heterochromatin

Answer 28

condensed, dark staining, genes not transcribed; repetitive sequences; tend to concentrate at the peripery

Question 29

What is a method by which gene expression can be controlled?

Answer 29

DNA accesibility

Question 30

Why must gene expression be regulated?

Answer 30

to ensure proper timing and location of protein production

Question 31

Can regulation occur at multiple points?

Answer 31

yes

Question 32

What is chromatin remodeling?

Answer 32

the alteration of chromatin structure

Question 33

Why do nucleosomes contain DNA and histones in a tight complex?

Answer 33

it compacts, making DNA less accessible

Question 34

Can transcription factors bind to DNA in the nucleosome?

Answer 34

yes

Question 35

What do eukaryotic cells have a large variety of?

Answer 35

histone modifying enzymes that covalently modify chromatin structure and ATP-dependant chromatin remodelling complexes, to permit DNA replication and transcription

Question 36

What do each histone have at it N terminus?

Answer 36

a positively charged amino acid “tail”

Question 37

What can histone acetyltransferases(HATs) do?

Answer 37

change their tails charge by adding acetyl groups to lysine residues (HDAC’s remove them)

Question 38

Possible mechanisms for increased local access include?

Answer 38

1. nucleosome sliding
2. nucleosome displacement
3. partial histone displacement
4. replacement of octamer subunits with histone variants