Cell Biology: Nucleus and Cell Cycle

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Questions and Answers

What is the role of MPF in the cell cycle?

It regulates gene shuffling during meiosis.

It triggers the process of cytokinesis.

It initiates mitosis by phosphorylating proteins. (correct)

It promotes the synthesis of cyclin.

What causes cancer cells to divide uncontrollably?

They produce excessive amounts of MPF.

They are unaffected by external chemical signals.

They lack normal controls like contact inhibition. (correct)

They have increased levels of growth factors.

During which phase is cyclin concentration highest?

G1 phase

S phase

G2 phase (correct)

M phase

What happens to cyclin levels during mitosis according to the control of cell division?

They decrease abruptly. Signup and view all the answers

Which of the following accurately describes contact inhibition?

Normal cells stop proliferating upon contact with each other. Signup and view all the answers

What is the primary outcome of the process of meiosis?

Generation of haploid gametes Signup and view all the answers

During which stage of meiosis do homologous chromosomes separate?

Anaphase 1 Signup and view all the answers

What ensures that the chromosome count remains consistent at 46 in humans after fertilization?

The reduction of gamete chromosome count to 23 Signup and view all the answers

What is the significance of crossing over during meiosis?

It promotes genetic diversity Signup and view all the answers

Which of the following accurately describes the gametes produced by meiosis?

Haploid cells with 23 chromosomes Signup and view all the answers

What is the term for the exact pairing of homologous chromosomes during meiosis?

Synapsis Signup and view all the answers

What occurs during the second meiotic division?

Separation of sister chromatids Signup and view all the answers

What is NOT a special event during meiosis?

DNA synthesis Signup and view all the answers

What is the primary function of the cell nucleus?

Controlling cellular activities Signup and view all the answers

During which phase of the cell cycle does DNA replication occur?

S phase Signup and view all the answers

Which of the following phases has the longest duration in the interphase?

G1 phase Signup and view all the answers

Which process divides the cytoplasm of the mother cell to create two daughter cells?

Cytokinesis Signup and view all the answers

What happens at the end of the G2 phase?

Centriole replication is completed Signup and view all the answers

Which of the following is NOT a phase of mitosis?

Cytokinesis Signup and view all the answers

What term describes cells that have permanently ceased dividing?

Go phase cells Signup and view all the answers

Which stage of the cell cycle includes the cell's active growth and preparation for division?

Interphase Signup and view all the answers

What happens to chromatin during the S phase?

It is replicated Signup and view all the answers

Which term refers to the highly condensed form of genetic material?

Heterochromatin Signup and view all the answers

Study Notes

Cell Nucleus

The nucleus is a cell organelle that functions as the control center of the cell.
The nucleus contains chromosomes, the genetic material of the cell.
Chromatin in the nucleus exists in two states: heterochromatin, which is highly condensed, and euchromatin, which is less condensed.

Cell Cycle

The cell cycle encompasses two major periods, interphase and cell division (mitotic phase).
Interphase is the period of cell growth and carries out usual activities, including protein synthesis and organelle production.
Cell division (mitotic phase) is when a cell divides into two cells.

Interphase

Interphase is the period of cell growth and preparation for division, subdivided into three subphases: G1, S, and G2.
During the G1 (gap 1) phase, cells actively grow, synthesize proteins, and carry out metabolic activities.
The S (synthetic) phase is when DNA replication occurs, ensuring that both daughter cells receive identical copies of genetic material.
The G2 (gap 2) phase prepares the cell for division by synthesizing necessary enzymes and proteins.

DNA Replication

DNA replication occurs during the S phase of interphase.

Mitosis

Mitosis is the division of the nucleus, occurring in somatic cells (diploid cells).
Mitosis is a continuous process, with four phases: prophase, metaphase, anaphase, and telophase.
Mitosis produces two identical daughter cells with the same number of chromosomes as the original cell.

Meiosis

Meiosis is cell division that occurs in germ cells (sex cells).
Meiosis produces haploid (n) gametes, which are the egg and sperm cells.
During meiosis, diploid (2n) germ cells undergo two cell divisions, reducing the chromosome count to 23.

Significance of Meiosis

Meiosis ensures the constancy of the chromosome number in each generation by reducing the chromosome number from diploid (2n) to haploid (n).
It also ensures random assortment of maternal and paternal chromosomes between the gametes.
Lastly, it allows relocation of segments of maternal and paternal chromosomes by the crossing over of chromosome segments, which shuffles the genes and produces a recombination of genetic material.

Control of Cell Division

Two key factors influence when cells divide:
- Chemical signals released by other cells, such as growth factors and hormones.
- The availability of space, with normal cells stopping proliferation when they touch, referred to as contact inhibition.
A key protein complex called MPF (M-phase promoting factor) influences the cell cycle.
MPF is a cyclin-dependent kinase complex that triggers mitosis at the G2 phase.
MPF activity fluctuates based on the level of cyclin in the cell.

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Description

Explore the foundational concepts of cell biology, including the structure and function of the cell nucleus and the stages of the cell cycle. This quiz covers the states of chromatin, the interphase phases, and the process of cell division. Test your understanding of these essential biological processes.