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Medical Genetics > Cell Cycle > Flashcards

Cell Cycle Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

What are the two phases of the cell cycle?

A

– Interphase (Period between cell division)

– Mitosis (Period of actual cell division)

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2
Q

Describe interphase.

A
  • 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
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3
Q

Describe the mitotic phase

A
  • 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
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4
Q

What are labile cells?

A

Multiply throughout life.

-Cells of skin, GIT, epithelial cells

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5
Q

What are stable cells?

A 
Are quiescent (Go phase). 
Can divide if appropriately stimulated. Liver cells
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6
Q

What are the permanent cells?

A

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

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7
Q

What are the staged of interphase?

A

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

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8
Q

What are the stages of mitosis?

A 
– Prophase 
– Metaphase 
– Anaphase 
– Telophase 
– Cytokinesis (Cell division)
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9
Q

What occurs during the G1 phase?

A
  • 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
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10
Q

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

A
  • Go phase (quiescent)

- Go

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11
Q

What occurs during the S phase?

A
  • 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
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12
Q

Describe the G2 phase.

A
  • 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
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13
Q

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

A
  • G1→S

- G2→M

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14
Q

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

A
  • p53

- Rb

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15
Q

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

A

Cyclins

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16
Q

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

A
  • Growth factors stimulate cell division.

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

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17
Q

Cancers are diseases in which there is a what?

A

defect in the regulation of the cell cycle.

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18
Q

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

A
  • Tumor suppressor genes

- Checks for DNA damage before cell exit the G1 phase

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19
Q

p53 exists in ___ cells at a very low concentration.

A

non-stressed

20
Q

Under stress conditions, the p53 gene does what?

A

-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.

21
Q

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

A

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

22
Q

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

A

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

23
Q

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

A

Mitosis

24
Q

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

A

TRUE!!!

25
Q

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

A

Mitosis

26
Q

Describe the prophase stage of Mitosis

A
  • Nuclear envelope dissolves.
  • Mitotic spindle forms.
  • Chromosomes start condensing and become visible.
  • Chromosomes start binding to the spindle
27
Q

Describe the metaphase stage of mitosis.

A
  • 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
28
Q

Describe the anaphase stage of mitosis.

A
  • Sister chromatids move to the centrioles.

- Separation of the sister chromatids

29
Q

Describe the Telophase stage of Mitosis

A

-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)

30
Q

When and where does meiosis occur?

A

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

31
Q

In meiosis, the games formed are?

A

Haploid (n)

32
Q

Each gamete is genetically unique (t/f)

A

True

33
Q

Meiosis results in the formation of how many gametes?

A

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).

34
Q

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

A

2

35
Q

Define homologous recombination

A

Homologous chromosomes undergo exchange of short fragments of their genetic material

36
Q

What is responsible for the genetic variation between gametes?

A

Homologous recombination

37
Q

What are the stages of Meiosis and what occurs?

A

– Meiosis I: Homologous chromosomes separate

– Meiosis II: Sister chromatids of a chromosome separate

38
Q

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

A

Meiosis 1 (begining)

39
Q

Before meiosis occurs, what happens?

A

There is duplication of the chromosome to form two sister chromatids

40
Q

What process is responsible for trisomy after fertilization?

A

Nondisjunction

41
Q

What happens if nondisjunction occurs during Meiosis 1?

A

Homologous chromosomes do NOT separate

42
Q

What occurs if nondisjunction occurs during Meiosis 2?

A

Sister chromatids of a chromosome do NOT separate

43
Q

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

A

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.

44
Q

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

A
  • 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)
45
Q

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

A

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

Meiosis:
• Takes place only in germline cells during gametogenesis

46
Q

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

A

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)

Medical Genetics (17 decks)

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