Lecture 9- Mitosis

Question 1

State the stages of the cell cycle (with Mitosis considered 1) and how long they take relatively in human cells

Answer 1

Mitosis (<1 Hour) G1 ( 5-6 hours) S phase (10-12 hours) G2 ( 4-6 hours) In total about 24 hours

Question 2

What is apoptosis?

Answer 2

Programmed cell death by cell’s own enzymes, when body finds an error in the cell or when it grows old

Question 3

*Describe the events of apoptosis

Answer 3

• Cyclins (internal proteins find a problem in the cell
• Nucleus collapses
• Chromatin and nucleus fragments condense
• Plasma membrane blisters, and blebs form
• Blebs leave the damaged cell
• Cell fragments are phagocytized by WBC

Question 4

How many main cell checkpoints are conducted in a cell cycle, where are they, and what conducts them?

Answer 4

3 main checkpoints by cyclins (nternal proteins enzymes) In G1, G2, and M )Late metaphase/ Early anaphase))

Question 5

*Is it true that only 3 checkpoints are conducted in cell cycle?

Answer 5

No! There are 3 main checkpoints, but checkpoints in general are conducted throughout the cell cycle

Question 6

What is the cellular genome?

Answer 6

The collection of DNA, in the human body, mainly the 46 chromosomes

Question 7

What are somatic cells?

Answer 7

Non sex cells (contain diploid number of chromosomes)

Question 8

What are the 5 stages of mitosis?

Answer 8

Prophase Prometaphase Metaphase Anaphase Telophase

Question 9

What does a chromatid contain?

Answer 9

A DNA double helix and histone proteins ∴ 2 DNA strands with histone proteins

Question 10

How many chromosomes do gamete cells have?

Answer 10

half that of somatic cells (23 for humans)

Question 11

At which point in the human cell cycle are there 92 functional chromosomes?

Answer 11

At no point are there 92 functional chromosomes

Question 12

What events take place at Early prophase?

Answer 12

• centrosome duplication (1->2)

Question 13

What events occur at prophase?

Answer 13

• condensation of chromatin fibers, now observable with light microscope ∴ Histone proteins deassocate with chromosomes
• Nucleolous disappear
• formation of mitosis spindle and asters
• centrosome begin to move away, propelled by lengthing microtubules

Question 14

What events occur at prometaphase?

Answer 14

• Nuclear envelope fragments
• kinetochore develops at each chromatid
• beginning of attachment of kinetiochore microtubules to kinetochores
• Non kinetochore microtubules interact with those in opposite pole( never directly touch)

Question 15

What happens at Metaphase?

Answer 15

• Centrosome are now at the poles of the cell
• the chromosomes are now at the metaphase plate
• each kinetochore now has microtubules attached to it
• there are still non kinetochore microtubules

Question 17

What is the function of non-kinetochore microtubules?

Answer 17

Elongate the cell and keep the cell integrity

Question 18

What happens during Anaphase?

Answer 18

• Sister chromatids move apart at a rate of 1 μm/min (now
• Cell elongates as the non kinetochore microtubules lengthen
• by the end, two ends of the cell have the complete collection of chromosomes

Question 19

What happens during Telophase?

Answer 19

• 2 daughter nuclei begin to form
• Nuclear envelopes arise from fragments of nuclear envelopes and portions of the endomembrane system
• chromosomes decondense
• mitotic spindles are broken down
• mitosis is now complete

Question 20

What is cytokinesis and when does it start and end?

Answer 20

it is the division of the cytoplasm

Anaphase–> G1

Question 21

Explain the differences in cytokinesis between plant and animal cells

Answer 21

in animal cells, a cleavage furrow is formed (indentation of membrane between 2 daughter nuclei), it is deepened by actin filaments contractile ring

in plant cells, cell walls prevent formation of cleavage burrow, instead, Golgi apparatus vesicles form the cell plate

Question 22

What is the shortest phase in the cell cycle?

Answer 22

Anaphase

Question 23

What is the longest phase?

Answer 23

Metaphase