Chapter 12 - Mitosis

Question 1

Cell Theory

Answer 1

1) All cells arise from preexisting cells

2) Every organism is composed of cells (cells are the fundamental unit of life)

Question 2

Cell cycle sequence

Answer 2

G1 => S => G2 => mitosis

G1 (first gap) : interphase

• growth of daughter cell
• occurrence of active gene expression

G0: 90% of cells go to G0 phase
-non-dividing state

S (synthesis) : interphase
-DNA replication through semiconservative replication

G2 (second gap) : interphase

• preparing for cell division
• centrosome replication

Mitosis : M phase
-cell division

Question 3

Chromatin

Answer 3

• less condensed
• packaged by histones
• form 30nm fibers in interphase

Question 4

Chromosome

Answer 4

• highly condensed

- visible through microscope

Question 5

mitosis

Answer 5

• division that involves conservation of number of chromosomes (diploid)
• prophase, metaphase, anaphase, telophase

Question 6

Homologs

Answer 6

Pair of chromosomes

• have the same lengths structure, centromere position and same genes for same characters in corresponding loci
• each chromosome is inherited from each parent

Question 7

Structure of chromosome

Answer 7

Centromere

• at the center
• holds together sister chromatids
• made of heterochromatin (not expressed)

Chromosome arm

Kinetochore

• hook-like protein in centromere
• binding site of mitotic spindle

Cohesin protein
-join 2 sister chromatids along their length
(broken down during anaphase)

Telomere

• region of non-coding, repetitive nucleotide sequences on each end of a chromosome
• protects chromosome ends from erosion

Question 8

Cohesin protein

Answer 8

-join 2 sister chromatids along their length

broken down during anaphase

Question 9

Kinetochore

Answer 9

• hook-like protein in centromere

- binding site of mitotic spindle

Question 10

Human chromosomes

Answer 10

46 chromosomes (23 pairs) 
44 autosomes (22 pairs) 
2 sex chromosomes (gametes) (1 pair)

Question 11

Stages of mitosis

Answer 11

1) Prophase
1. condensation of chromatin into chromosome
2. disappearance of nuclear envelope
3. 2 centrosomes (9+0) move to opposite poles
4. mitotic spindles extended from centrosome (aster shape)

2) Prometaphase
1. mitotic spindles (microtubules) bind to kinetochore (9+0 structure - nonmotile)
2. non-kinetochore microtubule extend and change cell shape from spherical to oval

3) Metaphase
1. duplicated chromosomes line up at the metaphase plate (equator)

4) Anaphase
1. kinetochore microtubule are shortened by ‘pac-man’ mechanism
2. separate break down cohesin protein
3. 2 sister chromatids of duplicated chromosome become individual chromosome

5) Telophase
1. decondensation of chromosome => become chromatin
2. nucleus reappears
3. preparation for cytokinesis

Question 12

Cytokinesis

Answer 12

-cytoplasmic division in cell division

1) animal cell
1. as contractile ring of microfilament shrink, forms cleavage furrow
2. pinches mother cell into 2 daughter cells

2) plant cell
1. form cell plate in the middle of cytoplasm => becomes cell wall
- cell plate is formed by fusion of cellulose-containing vesicles from Golgi complex

Question 13

Prophase

Answer 13

1. condensation of chromatin into chromosome
2. disappearance of nuclear envelope
3. 2 centrosomes move to opposite poles
4. mitotic spindles extended from centrosome (aster shape)

Question 14

Prophase

Answer 14

1. condensation of chromatin into chromosome
2. disappearance of nuclear envelope
3. 2 centrosomes move to opposite poles
4. mitotic spindles extended from centrosome (aster shape)

Question 15

Prometaphase

Answer 15

1. mitotic spindles (microtubules) bind to kinetochore (9+0 structure - nonmotile)
2. non-kinetochore microtubule extend and change cell shape from spherical to oval

Question 16

Metaphase

Answer 16

1. duplicated chromosomes line up at the metaphase plate (equator)

Question 17

Anaphase

Answer 17

1. kinetochore microtubule are shortened by ‘pac-man’ mechanism
2. separate break down cohesin protein
3. 2 sister chromatids of duplicated chromosome become individual chromosome

Question 18

Telophase

Answer 18

1. decondensation of chromosome => become chromatin
2. nucleus reappears
3. preparation for cytokinesis

Question 19

3 checkpoints

Answer 19

1) G1 checkpoint
2) G2 checkpoint
3) M checkpoint

-cell cycle stops unless there is a GO-AHEAD signal at these 3 checkpoints

Question 20

G1 checkpoint

Answer 20

• checks for growth factor, nutrients, DNA damage

- if there is no go-ahead, cells enter G0 stage (non-dividing)

Question 21

G2 checkpoint

Answer 21

-checks for cell size, number of centrosomes and amount of DNA

Question 22

M checkpoint

Answer 22

• checks for connection between mitotic spindle and kinetochore
• defect in M checkpoint causes non-disjunction of chromosome

Question 23

Cyclin

Answer 23

• protein that acts as component of go-ahead signal in cell nucleus
• constantly fluctuating concentration

Question 24

Cdk

Answer 24

Cyclin-dependent kinase