Chapter 11

Question 1

Telomeres prevent chromosomes from

Answer 1

being degraded at some level.

However, chromosomes become shorter with each round of replication

Question 2

Evidence shows that telomeres

Answer 2

shorten with age, and premature shortening are associated with aging features.

Hardships encountered early in life can play a part in
telomere shortening!

Children in orphanages had significantly shorter telomeres
than those in foster homes!

Question 3

E. coli –

Answer 3

has a single molecule of DNA (approximately 4.6 million base pairs).
Stretched out straight – it would be 1,000 times as long as the cell!

Human cells contain more than 6 billion base pairs of DNA!
Over 6 feet if stretched end to end!
Even the DNA in the smallest human chromosome would stretch 14,000 times the length of the cell nucleus!

Question 4

Relaxed B-DNA has

Answer 4

~ 10bp per turn of helix. (100 bp of DNA would assume ~ 10 turns)

Question 5

Supercoiling

Answer 5

• occurs when energy is used to add or remove any turns.
  Strain on the molecule, causes the helix to twist on itself!

Question 6

Positive supercoiling

Answer 6

Over-rotated molecules

Question 7

Negative supercoiling

Answer 7

Under-rotated molecules

Question 8

Topoisomerases –

Answer 8

enzymes that
add or remove rotations from the
DNA helix.
Break nucleotide strands, rotate
ends, and rejoin!

Question 9

Tertiary structure: Supercoiling

Answer 9

Bacterial and eukaryotic DNA usually fold into loops stabilized by proteins

Prevents free rotation of the ends.

Supercoiling takes place within the loops.

Question 10

Most DNA found is cells is _______supercoiled!

Answer 10

negativity

1. Supercoiled DNA can be packed into smaller space than relaxed DNA.
2. Makes the separation of strands easier for replication and transcription (requires less energy and is faster!)

Question 11

A DNA molecule 300 bp long has 20 complete rotations. This DNA molecule is

Answer 11

negativity

Question 12

The Bacterial Chromosome

Answer 12

Single circular DNA molecule

Bacterial DNA is not attached to histone proteins, but is associated with other proteins that help compress.

DNA appears as a clump called the nucleoid

Question 13

Eukaryotic Chromosomes

Answer 13

Each chromosome –consists of a single long linear DNA molecule.
Extreme folding required!

The tertiary chromosomal structure of eukaryotic DNA is not static!
Changes regularly in response to various cellular processes (Cell cycle stages, meiosis, replication, transcription, etc)

Question 14

Chromatin =

Answer 14

complex of DNA and proteins

Question 15

Euchromatin:

Answer 15

undergoes normal process of condensation and decondensation in the cell cycle

Question 16

Heterochromatin:

Answer 16

remains in a highly condensed state throughout the cell cycle, even during interphase.

Question 17

constitutive heterochromatin

Answer 17

Permanent heterochromatin at the centromeres and telomeres; and the Y chromosome as well

Question 18

facultative heterochromatin

Answer 18

May also occur at certain developmental stages;

Facultative heterochromatin occurs along one entire X chromosome in female mammals when that X becomes inactivated!

Question 19

Histones

Answer 19

The most abundant proteins in chromatin

Small, positively charged proteins, 5 major types (H1, H2A, H2B, H3 and H4). - 2 of each except H1

Positive charges attract the negative charges on the phosphates of DNA !

Question 20

Chromatin Structure

Answer 20

DNA double helix
Cont.

Question 21

Neutralizing their positive charges would have which effect on the histone proteins?

Question 22

Changes in Chromatin Structure

Answer 22

Dynamic nature was observed in polytene chromosomes.

Giant unusual chromosomes that arise when repeated rounds of DNA replication take place without accompanying cell division.

Question 23

Chromatin Modifications

Answer 23

Methylation of DNA (Ch. 10)
Use of variant histone proteins in the nucleosome
Binding of nonhistone proteins to DNA and chromatin

Although these changes don’t alter DNA sequence, they can have major changes on expression of genes.

Question 24

epigenetic changes (epigenetics)

Answer 24

Stable alterations of chromatin structure that may be passed down to descendant cells or individuals

Question 25

Nucleosome

Answer 25

~146 bp DNA + eight histone proteins (histone core)

Question 26

Chromatosome

Answer 26

~ 166 bp DNA + histone core + H1