Cell Cycle

Question 1

What are the two phases of the cell cycle?

Answer 1

– Interphase (Period between cell division)

– Mitosis (Period of actual cell division)

Question 2

Describe interphase.

Answer 2

• Maximum time is spent in this phase. Varies from one cell type to another
• Cell grows during this phase and is ready for mitosis at the end of interphase

Question 3

Describe the mitotic phase

Answer 3

• Period when the cell actually divides to form two new daughter cells
• Time spent in mitosis is about 2-4 hours and is usually constant

Question 4

What are labile cells?

Answer 4

Multiply throughout life.

-Cells of skin, GIT, epithelial cells

Question 5

What are stable cells?

Answer 5

Are quiescent (Go phase). 
Can divide if appropriately stimulated. Liver cells

Question 6

What are the permanent cells?

Answer 6

Have lost the capacity to divide. They are permanently in Go phase.
-Neurons, Cardiac muscle cells

Question 7

What are the staged of interphase?

Answer 7

– G1 phase (Go phase)
– S phase
– G2 phase

Question 8

What are the stages of mitosis?

Answer 8

– Prophase 
– Metaphase 
– Anaphase 
– Telophase 
– Cytokinesis (Cell division)

Question 9

What occurs during the G1 phase?

Answer 9

• Newly formed cell increases in size.
• Protein synthesis is very active.
• Cell undergoes differentiation and performs its function.
• At the end of G1, the cell checks whether it is ready for division

Question 10

Some cells in G1 enter the ___. Permanent and stable cells are in__. Stable cells can reenter the cell cycle on appropriate stimulation.

Answer 10

• Go phase (quiescent)

- Go

Question 11

What occurs during the S phase?

Answer 11

• Phase of DNA synthesis/ DNA replication.
• Enzymes of replication are most active.
• The entire chromosome replicates and at the end of S phase, the chromatid number doubles.
• Each chromosome has two sister chromatids

Question 12

Describe the G2 phase.

Answer 12

• The chromatid number is double.
• The cell size increases to help the formation of two new daughter cells.
• The entire genome is scanned for any mistakes during replication.
• DNA repair mechanisms are active during this stage

Question 13

___ phase & ___ phase are important check points in a cell cycle

Answer 13

• G1→S

- G2→M

Question 14

___ &___ proteins are important at the G1→S checkpoint

Answer 14

• p53

- Rb

Question 15

____ regulate the entry of cells into various phases of the cell cycle

Answer 15

Cyclins

Question 16

In regards to the cell cycle, what are growth factors?

Answer 16

• Growth factors stimulate cell division.

- Growth factors serve as signals that tell the cell to move through the cell cycle in order to divide.

Question 17

Cancers are diseases in which there is a what?

Answer 17

defect in the regulation of the cell cycle.

Question 18

What are p53 and Rb in regards to the cell cycle?

Answer 18

• Tumor suppressor genes

- Checks for DNA damage before cell exit the G1 phase

Question 19

p53 exists in ___ cells at a very low concentration.

Answer 19

non-stressed

Question 20

Under stress conditions, the p53 gene does what?

Answer 20

-Under stress conditions, the p53 protein accumulates and induces the transcription of various genes involved in cell-cycle control, apoptosis, DNA repair, differentiation and senescence.

Question 21

The loss of p53 tumor-suppressor activity allows for what?

Answer 21

allows the proliferation of the cells that are damaged under the stress conditions.
This uncontrolled proliferation can lead to tumor development.

Question 22

The chromatid number is doubled at the end of what phase?

Answer 22

-interphase (G2)
– remember replication takes place in S phase
– each chromosome contains 2 sister chromatids

Question 23

When is there segregation of the sister chromatids and later cytoplasmic division to form two daughter cells?

Answer 23

Mitosis

Question 24

The genetic composition of the daughter cells is identical to that of the parent cell (T/F)

Answer 24

TRUE!!!

Question 25

Which stage of the cell cycle takes place during growth of the embryo and in all somatic cells capable of cell division

Answer 25

Mitosis

Question 26

Describe the prophase stage of Mitosis

Answer 26

- Nuclear envelope dissolves. - Mitotic spindle forms. - Chromosomes start condensing and become visible. - Chromosomes start binding to the spindle

Question 27

Describe the metaphase stage of mitosis.

Answer 27

- Chromosomes condense and are maximally visible. - Chromosomes align at the equator. - Time at which they are visualized by karyotyping. - The microtubules attach to the centromere kinetochores during cell division

Question 28

Describe the anaphase stage of mitosis.

Answer 28

- Sister chromatids move to the centrioles. | - Separation of the sister chromatids

Question 29

Describe the Telophase stage of Mitosis

Answer 29

-Sister chromatids move to opposite poles. -Nuclear envelope starts forming. -Chromosome become less condensed. -Division of the cell to form two new daughter cells (Cytokinesis) • The daughter cells have the same genetic composition as the parent cell (2n)

Question 30

When and where does meiosis occur?

Answer 30

Takes place only in the gamete forming cells of ovary or testis (germline cells), final stages of gametogenesis

Question 31

In meiosis, the games formed are?

Answer 31

Haploid (n)

Question 32

Each gamete is genetically unique (t/f)

Answer 32

True

Question 33

Meiosis results in the formation of how many gametes?

Answer 33

four gametes, each of which has only 23 chromosomes: one of each kind of autosome and either an X or a Y (23X or 23Y in males, 23X in females).

Question 34

During meiosis, each chromosome is duplicated before meiosis to form how many sister chromatids?

Answer 34

2

Question 35

Define homologous recombination

Answer 35

Homologous chromosomes undergo exchange of short fragments of their genetic material

Question 36

What is responsible for the genetic variation between gametes?

Answer 36

Homologous recombination

Question 37

What are the stages of Meiosis and what occurs?

Answer 37

– Meiosis I: Homologous chromosomes separate – Meiosis II: Sister chromatids of a chromosome separate

Question 38

Meiotic crossing over - homologous recombination, occurs during what phase of the cell cycle?

Answer 38

Meiosis 1 (begining)

Question 39

Before meiosis occurs, what happens?

Answer 39

There is duplication of the chromosome to form two sister chromatids

Question 40

What process is responsible for trisomy after fertilization?

Answer 40

Nondisjunction

Question 41

What happens if nondisjunction occurs during Meiosis 1?

Answer 41

Homologous chromosomes do NOT separate

Question 42

What occurs if nondisjunction occurs during Meiosis 2?

Answer 42

Sister chromatids of a chromosome do NOT separate

Question 43

What are the significant difference in gametogenesis between males and females?

Answer 43

o Male meiosis produces four sperm cells per round. o Female meiosis produces one egg and three polar bodies. o Mitotic division of cells occur at different times in males and females. o Females have undergone all mitotic division by birth.

Question 44

What are the defects if maternal or paternal age is increased??

Answer 44

* There is a higher risk of non-disjunction (non separation of the homologous chromosomes/ sister chromatids) in the meiotic divisions in a female greater than 35 years, resulting in a higher risk of trisomy (chromosomal abnormality) in the fetus * Higher the paternal age, greater is the risk of development of new dominant single gene mutations (errors during replication)

Question 45

In regards to the differences between Mitosis and Meiosis, where do each take place?

Answer 45

Mitosis: • Takes place in all dividing somatic cells, & during embryogenesis & initial stages of gametogenesis Meiosis: • Takes place only in germline cells during gametogenesis

Question 46

What are the differences in genetic composition between the products of Mitosis and Meiosis?

Answer 46

Mitosis: - The genetic composition of the daughter cells is same as the parent (46,XX or 46,XY) Meiosis: • The gametes formed have a unique genetic composition due to meiotic crossover • The gametes are haploid (23,X or 23,Y)