L8: Cell cycle and cell division

Question 1

What is the cell cycle?

Answer 1

the series of events that take place in a cell involving cell growth and cell division and produce two daughter cells.

Question 2

What are the stages of the cell cycle?

Answer 2

Interphase and cell division

Question 3

Why is interphase called the resting stage and is it the longest part of the cell’s life cycle?

Answer 3

It is called by this name because the cell doesn’t divide in it and yes it is the longest phase in the cell’s life cycle.

Question 4

What is interphase?

Answer 4

It is the period between two successive cell divisions.

Question 5

What are the stages of interphase?

Answer 5

G1 (1st gap) stage.
• S (synthesis) stage.
• G2 (2nd gap) stage.

Question 6

What is the def. of G1?

Answer 6

It is the gap between previous mitosis and s-stage

Question 7

What are the events that take place in G1?

Answer 7

Growth of the newly formed daughter cell, After growth: cells pass to (S).

Question 8

What is the number of chromosomes in G1?

Answer 8

46 S-chromosome

Question 9

What is the definition of S-stage?

Answer 9

It is the stage of chromosomal duplication.

Question 10

What are the events that take place in S-stage?

Answer 10

DNA duplication

Question 11

What is the number of chromosomes in the S-stage?

Answer 11

92 S-chromosome

Question 12

What is the definition of the G2 stage?

Answer 12

It is the stage between S-stage and the next mitosis.

Question 13

What are the events that take place in G2?

Answer 13

The pairing of each two identical s-chromosomes and the duplication of centrioles.

Question 14

What are the steps of cell division?

Answer 14

Cell division consists of two phases: karyokinesis (a nuclear division that divides the genetic material in the nucleus), followed by cytokinesis (cytoplasmic division).

Question 15

What are the types of cell division?

Answer 15

1)Mitosis (indirect cell division)
2)Meiosis (reduction cell division).

Question 16

Mitosis

Answer 16

-happens in somatic cells

-Gives 2 daughter cells

-have the same numbers of chromosomes which is 46 s-chromosome

Question 17

Meiosis

Answer 17

-happens in germ cells of testes and ovaries

-gives 4 daughter cells

-each of them has half the number of chromosomes in parent cells which is 23 S-chromosome

Question 18

What is mitosis?

Answer 18

It is the type of division in which there is production of two daughter cells, each has the same number of chromosomes as the mother cell (46 s - chromosomes)

Question 19

What are the stages of mitosis?

Answer 19

1)Prophase.
2)Metaphase.
3)Anaphase.
4)Telophase.

Question 20

What are the events that happen In the Early prophase?

Answer 20

Fragmentation of ER, Golgi, and disassembly of the cytoskeleton.
* Mitotic spindle formation: Continuous microtubules arise between the pairs of centrioles (MTOCs) and grow gradually causing:
A)Formation of an eccentric spindle.
B) Gradual elongation of the cell.

Question 21

What are the events that happen in the Late prophase of mitosis?

Answer 21

Nuclear membrane breaks.

Nucleoli disintegrates

The spindle becomes central.

The d -chromosomes lie in the inter-tubular spaces of the spindle.

They become more condensed with the appearance of kinetochores.

Question 22

What are the events of the metaphase of mitosis?

Answer 22

Formation of chromosomal microtubules.

Single chromosomes arrange in the center or equator of the cell and show the highest degree of condensation.

Question 23

What are the events that take place in the anaphase of mitosis?

Answer 23

Splitting of the sister chromatids of each d-chromosome at the centromere.

Movement of each set of chromosomes toward the opposite pole of the cell.

Question 24

What are the events that take place in the telophase of mitosis?

Answer 24

Cytokinesis: Formation of Contractile ring and cleavage furrow which deepens gradually until the separation of the two daughter cells

Nuclear membrane forms at each end of the cell around the chromosomes.

Nucleolus reform.

Chromosomes become less tightly coiled & appear as chromatin again.

The net result is the production of two daughter cells, each having 46 s – chromosomes.

Question 25

What is the definition of meiosis?

Answer 25

It is the type of division in which there is production of 4 cells, each one has (haploid) number of chromosomes (23 s - chromosomes).

Question 26

What are the stages of meiosis?

Answer 26

1. 1st Meiotic division.2. 2nd Meiotic division: the same as mitosis.
   N.B: no S stage in the interphase between both meiotic divisions.

Question 27

What are the substages of prophase I of meiosis?

Answer 27

A) Leptotene phase: D-chromosomes appear as thin threads.

B) Zygotene phase: Homologous d-chromosomes are paired with formation of synaptonemal complex and called bivalents.

C) Pachytene phase:
-Chromosomes condense and become thicker and shorter.- Crossing over occurs between chromatids to allow exchange of genetic material.

D) Diplotene phase:
-Chromosomes are more condensed and appear as tetrad.
- Chromosomes are separated except at chiasmata

E) Diakinesis: * Disappearance of nuclear envelope & nucleoli. * Formation of the spindle.

Question 28

Compare between mitosis and first meiosis

Answer 28

Question 29

Compare between the three categories of specialized cells and give examples.

Answer 29

Question 30

What is the result of meiosis?

Answer 30

In ♂: production of 4 viable spermatids.In ♀: production of one viable ovum and 3 non-viable polar bodies.