DNA & Chromosomes II (Lec 2)

Question 1

What are some examples of inheritance superimposed on DNA (epigenetics)?

Answer 1

DNA methylation
Chromatin Structure
Histone modification

Question 2

What are some of the challenges to the view that histones were thought to be just involved in packaging DNA?

Answer 2

mammalian chromatin contains equal mass of histone and non histone proteins

histones are highly conserved

one form of chromatin silences the genes it packages without regard to sequence and is directly inherited by daughter cells

Question 3

True or False?

Heterochromatin is very condensed.

Answer 3

true

Question 4

Where is heterochromatin highly concentrated at?

Answer 4

centromeres and telomeres

Question 5

True or False?

Heterochromatin contains a large number of genes

Answer 5

False, very few number of genes

Question 6

What is the position effect?

Answer 6

activity of a gene depends on position on chromosome; will be silenced if relocated near heterochromatin

Question 7

The less condensed form of chromatin is called?

Answer 7

euchromatin

Question 8

What part of histones are subject to a variety of covalent modifications?

Answer 8

Amino acid side chains

Question 9

Variants exist for each core histones except for __

Answer 9

H4

Question 10

When and where are major histones synthesized?

Answer 10

during S-phase and assembled into nucleosomes on daughter DNA helices just behind replication fork

Question 11

When and where are variant histones synthesized?

Answer 11

during interphase and inserted into already-formed chromatin. (requires histone exchange process catalyzed by chromatin remodeling complex)

Question 12

What does the histone code tell you?

Answer 12

determines how/when DNA is packaged in nucleosome

Question 13

What reads the histone code?

Answer 13

code reader complex; involves joint recognition of histone tail

Question 14

What does reading histone code entail?

Answer 14

involves joint recognition of marks at other sites on nucleosome along with tail recognition

Question 15

How does modified chromatin spread?

Answer 15

after modifying enzyme marks one or few neighboring nucleosomes, chain reaction can ensue; code reader-writer enzymes spread the mark over chromosome

Question 16

How does chromatin remodeling occur?

Answer 16

Complexes with ATP-dependent chromatin remodeling protein work together to either condense or decondense long stretches of chromatin as reader moves along

Question 17

What stops the spread of chromatin modifications?

Answer 17

barrier sequences: several mechanisms (physical barriers, enzymatic barriers), HS4 region which contains cluster of histone acetylase

Question 18

Why is centromeric Heterochromatin special?

Answer 18

contains centromere-specific H3 histone, CENP-A, and other proteins that pack the nucleosomes into dense arrangements to form the Kinetochore.

defined by assembly of proteins, not DNA sequence

Question 19

How is centromeric chromatin organized?

Answer 19

2 alternating types of chromatin: nucleosomes with CENP-A on the outside fold, nucleosomes with normal H3 on the inside

Question 20

What binds to the kinetcohore?

Answer 20

CENP-A

Question 21

What chromatin structures are directly inherited by the daughter strands at the replication fork?

Answer 21

H3-H4 tetramers

Question 22

What are the largest chromosomes known?

Answer 22

lampbrush chromosomes from amphibian oocytes

Question 23

In regards to chromatin movement, how does heterochromatin move?

Answer 23

preferentially associates with the nuclear lamina

Question 24

True or False?

The interior of the nucleus is very homogenous

Answer 24

false, heterogeneous

Question 25

Are mitotic chromosomes highly condensed?

Answer 25

yes

Question 26

Chromatids are held together at ____

Answer 26

centromeres

Question 27

What is the purpose of condensation?

Answer 27

disengagement of sister chromatids to allow separation for cell division, protection of fragile DNA molecule as separation occurs

Question 28

What are condensins?

Answer 28

proteins that aid in condensation; use ATP hydrolysis to coil the DNA molecules into chromatids

Question 29

What are homologues?

Answer 29

genes that are similar in both sequence and function due to common ancestry

Question 30

True or False?

Gene sequences are more tightly conserved than genome structure

Answer 30

true

Question 31

How do genomic changes occur?

Answer 31

occur as mistakes in DNA replication and repair (1/1000)

Question 32

In regards to evolution of globin gene family, duplication and mutation gave rise to what?

Answer 32

beta and alpha genes

translocation moved alpha to separate chromosome, further duplication and mutation resulted in more specialized beta molecules

Question 33

What are pseudogenes?

Answer 33

duplicated gene that has become irreversibly inactivated by multiple mutations

Question 34

True or False?

Histone modifications are transient, not permanent.

Answer 34

true

Question 35

What happens in gene duplication and divergence?

Answer 35

both copies remain functional while diverging in sequence and pattern of expression