Cell Division and Cell Cycle

Question 1

What is the cell division?

Answer 1

An integral part of the cell cycle consist of a series of growth and developmental steps results in genetically identical daughter cells from a mother cell.

Question 2

Which are the major phases of the cell cycle?

Answer 2

Interphase and Mitotic Phase

Question 3

What is the interphase and how it is divided?

Answer 3

The interphase is the non-dividing state that consist of 3 stages:
1. G1- The cell grows physically larger and copies organelles
2. S- The cell synthesizes a complete copy of the DNA in its nucleus ( genome replication ) and it also duplicates the centrosomes.
G2- secondary growth

Question 4

What are the centresomes?

Answer 4

Microtubules- organizing structure that help separate the DNA during M phase.

Question 5

What is the mitotic phase and how it is divided?

Answer 5

During the M phase the cell divides its copied DNA and cytoplasm (cytokinesis) to make 2 new cells. In Mitosis Diploid cells divide. Each new cell receives one copy of every chromosome that was present in the original cell. Number of diploid cells is preserved ( 46 chromosomes ).

Question 6

What does the cell when it is not dividing?

Answer 6

DNA Molecules in extended, uncondensed form, relaxed. Cell can only use DNA in this state.

Question 7

What does the cell when is preparing for division?

Answer 7

DNA Molecules condense to form compact DNA (easier to sort into daughter cells) prior division. Each chromosome is a single molecule of DNA.

Question 8

What are the condensins?

Answer 8

They are protein complexes that help to promote chromosome to condense and prepare for duplication.

Question 9

What are haploid cells?

Answer 9

Unlike somatic cells, sperm and egg cells are
haploid cells, containing only one set of
chromosomes. At sexual maturity the ovaries and testes
produce haploid gametes by meiosis

Question 10

When a duplicated chromosome is known a sister chromatids?

Answer 10

When their centromeres are attached.

Question 11

What is a centromere?

Answer 11

The centromere is a constricted region of the chromosome containing a specific DNA sequence, to which is bound 2 discs of protein called kinetochores.

Question 12

What is a kinetochore and what it does?

Answer 12

Kinetochores ,discs of protein, serve as points of attachment for microtubules that move the chromosomes during cell division

Question 13

What is a chromatid?

Answer 13

A chromatid is one half of a replicated chromosome.

Question 14

What happen in the G2 phase?

Answer 14

The cell has 2 centrosomes, each with 2 centrioles, and DNA has been copied. Chromosomes, duplicated
during S phase, cannot be seen individually because they have not yet condensed.

Question 15

What is a centrosome

Answer 15

An organelle that will play a key role in mitosis.

Question 16

Describe the Prophase

Answer 16

• The chromatin fibers become more tightly coiled, condensing into discrete chromosomes
• The nucleoli disappear.
• Each duplicated chromosome appears as two identical sister chromatids joined together.
• The mitotic spindle begins to form. It is composed of the centrosomes and the microtubules that extend from them. The radial arrays of shorter microtubules that extend from the centrosomes are called asters (“stars”).
• The centrosomes move away from each other, apparently propelled by the lengthening microtubules between them.

Question 17

Describe Metaphase

Answer 17

The centrosomes are now at opposite ends of the cell.
•The chromosomes convene on the metaphase plate, an imaginary plane that is equidistant between the spindle’s two poles. The chromosomes’ centromeres lie on the metaphase plate.
• For each chromosome, the kinetochores of the sister chromatids are attached to kinetochore microtubules coming from opposite poles.
• The entire apparatus of microtubules is called the spindle
because of its shape.

Question 18

Describe Telophase

Answer 18

• Two daughter nuclei begin toform in the cell.
• Nuclear envelopes arise fromthe fragments of the parent cell’s nuclear envelope and other portions of the endomembrane system.
• The chromosomes become less condensed.
• Mitosis, the division of one nucleus into two genetically identical nuclei, is now complete.

Question 19

Abnormalities in cell division can occur due?

Answer 19

Due to chromosomal, genetic or environmental factors , or combination of these

Question 20

What regulate the cell cycle?

Answer 20

The cell cycle control system, molecules that trigger and coordinate key events in the cell cycle.

Question 21

How many checkpoints we have in the cell cycle?

Answer 21

three found in G1, G2 and M phases.

Question 22

Why the G1 checkpoint is the most important?

Answer 22

If the cell receives a go-ahead signal, it usually completes the cell cycle and divides.
• If it does not receive a go-ahead signal, the cell exits the cycle and switches to a nondividing state, the G0 phase. Most human cells are in this phase.
• Liver cells can be “called back” to the cell cycle by external cues (growth factors), but highly specialized nerve and muscle cells never divide.