The Cell Cycle Control system

Question 1

The cell control system

Answer 1

is regulated by both internal and external control. It has specific checkpoints where the cell cycle stops until a go-ahead signal is received

Question 2

G1 check point

Answer 2

the integrity if the DNA is assessed

Question 3

G2 check point

Answer 3

proper chromosome duplication is assessed

Question 4

M check point

Answer 4

attachment of each kinetochore to a spindle fiber is assessed

Question 5

If the cell does not receive the go-ahead signal

Answer 5

it will exit the cycle, switching into a nondividing state called G0 phase

Question 6

A chromosome consist of

Answer 6

a DNA molecule packed together with proteins

Question 7

The bacterial chromosome is

Answer 7

a double-stranded, circular DNA molecule associated with a small amount of protein

Question 8

Eukaryotic chromosomes have

Answer 8

linear DNA molecules associated with a large amount of protein

Question 9

In bacterium

Answer 9

the DNA is “supercoiled” and found in a region of the cell called the nucleotide

Question 10

supercoiled

Question 11

Chromatin

Answer 11

DNA precisely combined with proteins

Question 12

histones

Answer 12

are proteins that are responsible for the first level of packing in a chromatin

Question 13

unfolded chromatin resembles

Answer 13

beads on a string, with each “bead” being a nucleosome, the basic unit of DNA packaging

Question 14

Nuclosomes are composed of

Answer 14

two each of the four basic histone types, with DNA wrapped twice around the core of the eight histones

Question 15

the N-termini (tails) of the histones protrude from

Answer 15

the nucleosome

Question 16

Nucleosomes and histone tails are

Answer 16

involved in the regulation of gene expression

Question 17

Chromosome

Answer 17

double helix of DNA

Question 18

Chromatin fiber

Answer 18

DNA wrapped around histones

Question 19

“Beads on a string” DNA wound on nucleosomes

Answer 19

nucleosomes coiled into a chromatin fiber

Question 20

Double helix

Answer 20

further condensation of chromatin

Answer 21

duplicated chromosome

Question 22

Chromatin undergoes changes in

Answer 22

packing during the cell cycle

Question 23

at interphase some chromatin seems to be

Answer 23

organized into a 10-nm fiber, but much is compacted into a 30-nm fiber, through folding and looping

Question 24

Interphase chromosomes occupy

Answer 24

specific restricted regions in the nucleus, and the fibers of different chromosomes do not become entangled

Question 25

most chromatin is loosely packed in the nucleus during

Answer 25

interphase and condenses prior to mitosis

Question 26

euchromatin

Answer 26

• transcriptionally active
• DNA is loosely packed
• actively present in prokaryotic and eukaryotic genome
• generally active
• present at inner side of the nucleus
• stained lighter
• early replicative
• aren’t stickey
• allow gene to form a protein
• low genetic density
• consist of 2-3% part of the genome

Question 27

heterochromatin is when

Answer 27

during interphase a few regions of chromatin (centromeres and telomeres) are highly condensed

Question 28

dense packing of the heterochromatin

Answer 28

makes it difficult for the cell to express genetic information coded in these regions

Question 29

heterochromatin

Answer 29

• transcriptionally inactive
• DNA is highly packed
• only present in eukaryotic genome
• generally inactive
• present at nucleus periphery
• stained dark
• late replicative
• are usually sticky
• regulates genetic intergrity, and control gene expression
• high genetic density
• consist 97-98% of the genome

Question 30

Histones can undergo

Answer 30

chemical modifications that result in changes in chromatin condensation. these changes can also have multiple effects on gene expression