DNA Organization

Question 1

How are the backbones of DNA molecules linked?

Answer 1

By phosphodiester bonds.

Question 2

How many base pairs per turn in a DNA helix?

Answer 2

10

Question 3

What is the direction of the DNA helix turn?

Answer 3

Right handed.

Question 4

How many H bonds do C’s and G’s make?`

Answer 4

3

Question 5

How many H bonds do A’s and T’s make?

Answer 5

2

Question 6

What are nuclear pores?

Answer 6

They puncture the nuclear envelope so molecules can move between nucleus and cytosol.

Question 7

What are exons?

Answer 7

Coding sequences.

Question 8

What are introns?

Answer 8

Noncoding sequences.

Question 9

At what phase in the cell cycle are genes expressed and chromosomes replicated?

Answer 9

Interphase.

Question 10

Replication origin

Answer 10

Location where duplication begins

Question 11

Where do the kinetochores form?

Answer 11

At the centromere.

Question 12

What is a nucleosome core particle made up of?

Answer 12

2x H2A, H2B, H3 and H4 and double stranded DNA 147 nucleotides long and it includes the linker DNA.

Question 13

What is a histone fold?

Answer 13

Structural motif of 4 histone proteins formed from 3 alpha helicies connceted by 2 loops.

Question 14

What is a histone tail?

Answer 14

The N terminal end of the protein, corresponds to the beginning of that gene.

Question 15

What are the common amino acids in core histones and why?

Answer 15

Lysine and arginine because the positive charges neutralize the negative DNA backbone.

Question 16

What are the base pairs preferred on the inside of a minor groove?

Answer 16

AA, TT and TA dinucleotides.

Question 17

What are 2 results from chromatin remodeling complexes?

Answer 17

Exchange of H2A-H2B dimers or exchange of the nucleosome core

Question 18

What do chromatin remodeling complexes do?

Answer 18

Change structure of nucleosome temporarily and catalyze nucleosome sliding.

Question 19

What is the function of H1 histones?

Answer 19

They specialize in locking the nucleosome down and prevent DNA from locking up, they promote heterochromatin.

Question 20

What is the position effect?

Answer 20

When euchromatin chromosome is translocated into a region where it turns into heterochromtin and the gene is silenced.

Question 21

Where do core histone modifications occur?

Answer 21

On the N terminal of histone tails.

Question 22

What histone modifications are competing reactions?

Answer 22

Lysine acetylation and methylation.

Question 23

What are core histone modifications?

Answer 23

Covalent modifications of amino acid side chains.

Question 24

What is the result of the acetylation of lysines on the N terminal tail?

Answer 24

It loosens chromatin structure.

Question 25

How does chromatin get additional variety?

Answer 25

Through site specific insertions of small histone varients.

Question 26

What does the trimethylation of a lysine on the histone H3 tail do?

Answer 26

It attracts the heterochromatin specific protein HP1 and helps start the spread of heterochromatin.

Question 27

How are chromatin changes spread along a chromosome?

Answer 27

Through reader writer complexes.

Question 28

What do barrier sequences contain?

Answer 28

A cluster of binding sites for histone acetylase enzymes to stop the spread of heterochromatin.

Question 29

What is different about the chromatin in centromeres?

Answer 29

They contain a specific varient of histone H3, CENP-A, and additional proteins that pack the nucleosomes into dense arrangements.

Question 30

Where is heterochromatin commonly found?

Answer 30

Around centromeres and telomeres.

Question 31

How is the packing of DNA in chromatin inherited after replication?

Answer 31

Signals are left behind where there were heterochromatin proteins.

Question 32

When does gene expression shut down?

Answer 32

During mitosis.