Overview

Question 1

what is the life cycle of organisms (meiosis, fertilization, mitosis, meiosis, fertilization,…) in eukaryotes based on?

Answer 1

based on the life cycle of the cell

Question 2

what is a cell cycle?

Answer 2

it is a series of biological events that are repeated

Question 3

Into what is the cell cycle divided? and based on what?

Answer 3

divided into 2 major phases based on cellular activities that are readily visible by light microscopy

Question 4

what are these phases?

Answer 4

the M phase or cell division (usually mitosis and cytokinesis) and the interphase

Question 5

how much does interphase last in comparison to cell division in most cells?

Answer 5

interphase lasts longer than cell division

Question 6

what is the average duration time of mitosis and interphase?

Answer 6

mitosis is about an hour whereas interphase lasts about 19 hours

Question 7

duration time varies according to what?

Answer 7

according to organism, tissue and age of the cell

Question 8

cell division and interphase are subdivided into how many stages?

Answer 8

5 and 3 stages respectively

Question 9

which cell types don’t divide, therefore they are out of the cell cycle?

Answer 9

certain cell types that are highly differentiated such as muscle fibers, red blood cells and neurons

Question 10

can such cells stay in any one of the cell cycle stages? If no, why?

Answer 10

can not stay in any one of the cell cycle stages since the cycle is stopped

Question 11

when non dividing cells leave the cell cycle, what do they enter?

Answer 11

they enter a quiescent state named G0

Question 12

what happens to certain cell types such as hepatocytes? (according to G0 and when do they leave it?)

Answer 12

enter G0 temporarily and leave it in case of liver regeneration

Question 13

in others such as neurons, what is their situation according to G0?

Answer 13

they are permanently blocked in G0

Question 14

when examining dividing cells with a microscope, what does it show? and why?

Answer 14

shows few cells in M phase. This is because interphase represents most of cell cycle duration while M phase is rapid

Question 15

what does this rule show? give example: what happens during segmentation of fertilized eggs?

Answer 15

shows many exceptions, for instance during segmentation of fertilized eggs, interphase is very short and the zygote divides many times without increasing its size

Question 16

why are the 2 phases intimately related?

Answer 16

since the events that occur during M phase would be impossible without the preparation during interphase.
That is, the biological processes that take place during interphase aim at preparing the events of M phase

Question 17

interphase is divided into how many stages? name them

Answer 17

3 stages: G1 (gap1), S (synthesis of DNA), and G2 (gap2)

Question 18

each stage is characterized by?

Answer 18

Each stage is characterized by specific processes

Question 19

What happens to the cell during interphase? What are the daughter cells supplied with?

Answer 19

the cell doubles its content (organelles, proteins, lipids, carbohydrates,…) so that the daughter cells are supplied with the necessary cellular structures organelles and components

Question 20

what happens to proteins, carbohydrates and lipids throughout the entire interphase period?

Answer 20

they are synthesized

Question 21

when does DNA replication (synthesis) occur and what does it produce

Answer 21

occurs during S phase only and produces the sister chromatids of each chromosome

Question 22

By what are these sister chromatids remain tightly joined?

Answer 22

by their centromeres and cohesion along their length

Question 23

What happens to the DNA amount during G1, S phase and G2?

Answer 23

DNA amount is constant during G1, it increases during S to reach twice the amount in G1 and finally it is constant again during G2

Question 24

During M phase, what happens to DNA quantity per cell and why?

Answer 24

DNA quantity per cell is reduced since sister chromatids are separated and distributed in 2 daughter cells

Question 25

What happens to centrioles of a centrosome as the cell makes the G1-S transition? when do they separate?

Answer 25

they duplicate as the cell makes the G1-S transition but they don’t separate from each other until late prophase

Question 26

What is centriole duplication?

Answer 26

centriole duplication is the assembly of a new centriole at right angles with respect to each old one