Cell Cycle and Stages of Division

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Questions and Answers

What is the main purpose of cell division in eukaryotic cells?

To repel pathogens

To synthesize new proteins

To increase metabolism

To grow and repair tissues (correct)

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

M phase

G2 phase

G1 phase

S phase (correct)

What occurs at the end of cytokinesis?

Cell metabolism is halted

DNA is replicated

Two daughter cells are formed (correct)

Chromosomes become visible

What happens to chromosomes during interphase?

They undergo duplication Signup and view all the answers

Which statement describes the process of cytokinesis?

It leads to the separation of the cytoplasm. Signup and view all the answers

What is the main purpose of mitosis in cell division?

To create two identical daughter cells Signup and view all the answers

During which phase do chromosomes become visible as distinct structures?

Prophase Signup and view all the answers

What occurs during the prometaphase of mitosis?

The nuclear membrane dissolves and kinetochores form Signup and view all the answers

What is the role of centrioles during mitosis?

To organize microtubules for spindle fiber formation Signup and view all the answers

Which sequence correctly outlines the phases of mitosis?

Prophase, Metaphase, Anaphase, Telophase Signup and view all the answers

What is interphase primarily responsible for in the cell cycle?

Replication of genetic material Signup and view all the answers

Which statement about meiosis is correct?

Meiosis involves two rounds of division Signup and view all the answers

Which phase of mitosis is characterized by the chromosomes being pulled toward opposite poles?

Anaphase Signup and view all the answers

Which type of microtubules extend from the pole to the kinetochores during cell division?

Kinetochore microtubules Signup and view all the answers

What is the main function of polar microtubules during cell division?

To overlap the spindle apparatus Signup and view all the answers

During which phase do chromatids arrive at opposite poles of the cell?

Telophase Signup and view all the answers

In which type of cells does cytokinesis occur through the formation of a fiber ring composed of actin?

Animal cells Signup and view all the answers

What happens to chromosomes during telophase?

They disperse and become less visible Signup and view all the answers

Which of the following best describes a zygote?

A diploid cell formed from the fusion of two haploid gametes Signup and view all the answers

What is a characteristic feature of asexual reproduction?

Produces genetically identical offspring Signup and view all the answers

What defines the process of fertilization?

The combination of genetic material from two haploid gametes Signup and view all the answers

What is the role of synapsis in meiosis?

Pairing homologous chromosomes Signup and view all the answers

During which phase does crossing over occur?

Prophase I Signup and view all the answers

What is the primary outcome of meiosis I?

Two haploid cells Signup and view all the answers

Which event occurs during Anaphase II?

Sister chromatids separate Signup and view all the answers

What happens during interkinesis?

Spindle fibers are disassembled Signup and view all the answers

What is the diploid chromosome number for humans?

46 Signup and view all the answers

Which of the following best describes the primary function of meiosis?

To convert diploid cells into haploid gametes Signup and view all the answers

What is formed when homologous chromosomes find each other during prophase I?

Tetrads Signup and view all the answers

Which stage of meiosis is responsible for reducing the ploidy level from 2n to n?

Meiosis I Signup and view all the answers

What is the term used for the points where non-sister chromatids intertwine during meiosis?

Chiasma Signup and view all the answers

How many haploid cells can potentially be produced by one meiosis process?

4 Signup and view all the answers

Which of the following cell types undergoes meiosis?

Germ line cells Signup and view all the answers

Which two processes are involved in meiosis?

Meiosis I and Meiosis II Signup and view all the answers

Study Notes

Cell Cycle

The cell cycle is a sequence of growth and division.
The cycle begins at the start of one division and ends at the start of the next.
The generation time is the time required to complete one cell cycle.
Cells divide when they reach a certain size.
The division process involves mitosis and cytokinesis.
Mitosis divides the chromosomes.
Cytokinesis divides the cytoplasm.
Mitosis without cytokinesis results in multinucleate cells

Stages of Eukaryotic Cell Cycle

Interphase:
- G1 (first gap) phase: growth and metabolic activities
- S (synthesis) phase: DNA replication
- G2 (second gap) phase: preparing for mitosis
M phase:
- Mitosis: nuclear division
- Cytokinesis: division of cytoplasm

Chromosomes in Cell Division

Chromosomes contain DNA and protein.
Chromosomes carry genetic information.
Chromatin fibers are highly folded during cell division and visible in light microscopes as chromosomes.
Chromatin is extended during interphase for gene expression.

Reproduction

Asexual reproduction: involves only mitosis, producing genetically identical offspring.
Sexual reproduction: involves the combination of two haploid sex cells (gametes) to produce a zygote.
Gametes are haploid, containing a single set of chromosomes.
The zygote is diploid, containing two sets of chromosomes.

Meiosis

Meiosis converts a diploid cell into haploid gametes.
The purpose of meiosis is to create genetic diversity in offspring.
Meiosis involves two distinct divisions: Meiosis I (reduces ploidy level from 2n to n) and Meiosis II (divides remaining chromosomes).

Mitosis

Mitosis is nuclear division accompanied by cytokinesis.
Mitosis produces two identical daughter cells.
The stages of mitosis include:
- Prophase
- Metaphase
- Anaphase
- Telophase

Detailed Stages of Mitosis

Prophase:
- Chromatin condenses into visible chromosomes
- Nucleolus disappears
- Centrioles move to opposite poles
- Microtubules form the mitotic spindle
Prometaphase:
- Nuclear membrane dissolves
- Proteins attach to centromeres, forming kinetochores
- Microtubules attach to kinetochores, and chromosomes begin moving
Metaphase:
- Spindle fibers align chromosomes at the metaphase plate (middle of the cell nucleus)
- Polar microtubules extend to the equator
- Kinetochore microtubules extend from poles to kinetochores
Anaphase:
- Paired chromosomes separate at kinetochores
- Chromosomes are pulled by kinetochore microtubules towards opposite poles, forming a "V" shape.
Telophase:
- Chromatids reach opposite poles
- New nuclear membranes form around daughter nuclei
- Chromosomes disperse and become invisible
- Spindle fibers disperse
- Cytokinesis begins
Cytokinesis:
- In animal cells, a contractile ring of actin pinches the cell into two daughter cells.
- In plant cells, a new cell wall forms between the two daughter cells.

Diploid Cells

Contain two sets of chromosomes per cell.
Homologous chromosomes: similar in length, shape, and carry similar attributes. One is maternal, the other paternal.

Haploid Cells

Contain only one member of each homologous chromosome pair.

Different Cell Types

Somatic (vegetative) cells: produced by mitosis.
Germ line cells: become gametes.
Most cell divisions in the human body are mitotic, with meiosis restricted to gonads.

First Meiotic Division (Meiosis I)

Prophase I:
- The spindle appears
- Nuclear envelopes disappear
- DNA condenses, chromosomes become visible
- Homologous chromosomes pair and synapse to form a tetrad
- Crossing over may occur between non-sister chromatids within a tetrad
Metaphase I: Tetrads line up along the equator.
Anaphase I: Homologous pairs separate, cells become haploid.
Telophase I: Nuclear envelopes reappear, spindle disappears.
Interkinesis: brief pause between Meiosis I and Meiosis II, no DNA synthesis occurs.

Second Meiotic Division (Meiosis II)

Prophase II: Spindle reappears, nuclear membrane fragments.
Metaphase II: Chromosomes align at equator.
Anaphase II: Sister chromatids separate.
Telophase II: Nuclear envelopes reappear, resulting in four haploid cells.

Gametogenesis

Germ line cells undergo gametogenesis to form gametes.
Spermatogenesis produces sperm.
Oogenesis produces eggs, usually one ovum and two or more polar bodies.

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Description

Explore the essential concepts of the cell cycle, including its stages and the processes involved in cell growth and division. Understand the roles of interphase and mitosis, as well as the structure and function of chromosomes during cell division.