Cell Division and Mitosis Overview

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Questions and Answers

What is the main purpose of meiosis?

To replicate DNA without reducing chromosome numbers

To increase the number of chromosomes in a cell

To produce cells with a reduced chromosome number (correct)

To create identical copies of the original cell

During which phase of meiosis does crossing over occur?

Telophase II

Prophase II

Metaphase I

Prophase I (correct)

What is the outcome of Telophase I in meiosis?

Separation of chromatids into individual cells

Formation of four genetically identical daughter cells

Replication of chromosomes into 92 chromatids

Creation of two newly formed nuclei (correct)

How many chromosomes do human sperm and egg cells contain?

23 chromosomes Signup and view all the answers

During Metaphase I of meiosis, how are the chromosomes arranged?

In pairs along the equatorial line Signup and view all the answers

What process occurs during Anaphase II of meiosis?

Sister chromatids are pulled away from each other Signup and view all the answers

What are recombinant chromosomes?

Chromosomes resulting from crossing over Signup and view all the answers

Which phase of meiosis does NOT involve homologous pairing?

Prophase II Signup and view all the answers

What happens during telophase II?

The nuclei reform and the cells divide to form four cells. Signup and view all the answers

What distinguishes metaphase I from metaphase II?

Homologous pairs are present in metaphase I but not in metaphase II. Signup and view all the answers

In which phase of meiosis do chromatids separate?

Anaphase II Signup and view all the answers

How many chromosomes and chromatids would be present in prophase I if n=23?

46 chromosomes and 92 chromatids Signup and view all the answers

During which stage of gametogenesis are homologous chromosomes separated?

Anaphase I Signup and view all the answers

Which of the following statements about spermatogenesis is true?

It produces millions of sperm daily. Signup and view all the answers

What is a key feature of oogenesis compared to spermatogenesis?

It produces polar bodies. Signup and view all the answers

What describes the timing of meiosis in females?

Meiosis I completes at ovulation and Meiosis II at fertilization. Signup and view all the answers

During which phase of meiosis do cells have the least amount of chromosomal material?

Prophase I Signup and view all the answers

How is the diploid number of chromosomes restored in an organism?

Fertilization Signup and view all the answers

What is a primary characteristic of cancer cells?

They divide uncontrollably. Signup and view all the answers

What can lead to the development of cancer cells?

Exposure to toxins and radiation Signup and view all the answers

What role do transcription factors play in cell differentiation?

They determine which genes are expressed in a cell. Signup and view all the answers

Which of the following best describes stem cells?

They can become any type of cell depending on external factors. Signup and view all the answers

Which treatment method targets rapidly dividing cells in cancer?

Chemotherapy Signup and view all the answers

What can hinder cancer cells from performing normal functions?

Inability to communicate with one another Signup and view all the answers

What is the role of transcription factors in stem cells during embryonic development?

They influence the differentiation of stem cells based on their quantity and type. Signup and view all the answers

Which type of stem cell can give rise to any of the 220 cell types in the embryo?

Totipotent stem cells Signup and view all the answers

What initiates the intrinsic pathway of apoptosis?

Internal cell damage Signup and view all the answers

What occurs during the execution phase of apoptosis?

Caspases break down cellular components. Signup and view all the answers

Which of the following describes necrosis?

The cell swell due to loss of membrane integrity. Signup and view all the answers

Which step of apoptosis involves the formation of apoptotic bodies?

Execution Phase Signup and view all the answers

What triggers the extrinsic pathway of apoptosis?

Binding of death ligands to cell surface receptors Signup and view all the answers

What results from lysosomal enzyme release during necrosis?

Digestion of cell components. Signup and view all the answers

What occurs during the S phase of interphase?

DNA replication takes place. Signup and view all the answers

What is the primary role of checkpoints in the cell cycle?

To monitor DNA damage and correct errors. Signup and view all the answers

In which phase do chromosomes condense and become visible?

Prophase Signup and view all the answers

What happens during anaphase?

Chromosomes move toward opposite poles. Signup and view all the answers

What is the significance of the G0 phase in the cell cycle?

Cells stop dividing but continue to function. Signup and view all the answers

What is the final step that occurs after mitosis?

Cytokinesis Signup and view all the answers

What is the end result of meiosis?

Sperm and egg cells (gametes) Signup and view all the answers

Which structure assists in the movement of chromosomes during anaphase?

Spindle fibers Signup and view all the answers

Study Notes

Interphase

The cell grows and replicates its DNA in preparation for division.
Consists of three stages:
- G1: Cell growth
- S: DNA replication
- G2: Further cell growth
Checkpoints ensure proper cell function:
- G1 checkpoint: Checks for proper cell growth and DNA damage
- G2 checkpoint: Checks for accurate DNA replication
- M checkpoint (metaphase checkpoint): Ensures proper chromosome alignment and spindle attachment
G0: A resting phase where cells perform their functions but do not divide.
- Some cells enter temporarily due to resource limitations.
- Other cells remain permanently, never entering M phase and therefore not dividing (e.g., neurons).

Mitosis

The process of cell division that results in two genetically identical daughter cells.
Before mitosis begins:
- The cell replicates its DNA into 46 chromosomes and 92 chromatids during interphase.
Stages of mitosis:
- Prophase:
  - Chromosomes condense and become visible.
  - The nuclear envelope breaks down.
- Metaphase:
  - Chromosomes align at the cell’s equator.
  - Spindle fibers attach to the chromosomes.
- Anaphase:
  - Sister chromatids separate and move to opposite poles of the cell.
  - Spindle fibers lengthen, pulling the chromosomes apart.
- Telophase:
  - Chromosomes reach the poles and decondense.
  - The nuclear envelope reforms around the chromosomes, forming two separate nuclei.
Cytokinesis:
- Division of the cytoplasm, completing the separation into two daughter cells.

Meiosis

A type of cell division that produces four genetically diverse haploid cells (gametes).
Haploid cells: contain only one set of chromosomes (23 in humans).
Before meiosis:
- Interphase occurs, where the cell grows and replicates its DNA into 46 chromosomes and 92 chromatids
Meiosis I: (reduction division)
- Prophase I:
  - Chromosomes condense and pair up with their homologous counterparts.
  - Crossing over occurs, exchanging genetic material between homologous chromosomes, creating recombinant chromosomes.
- Metaphase I:
  - Homologous chromosome pairs align at the cell’s equator.
- Anaphase I:
  - Homologous chromosome pairs separate and move to opposite poles of the cell.
- Telophase I:
  - The nuclear envelope reforms around the chromosomes, forming two separate nuclei.
- Cytokinesis:
  - The cytoplasm divides, resulting in two daughter cells.
Meiosis II: (equational division)
- Prophase II:
  - Chromosomes condense.
  - Spindle fibers form.
- Metaphase II:
  - Chromosomes align at the cell’s equator.
- Anaphase II:
  - Sister chromatids separate and move to opposite poles of the cell.
- Telophase II:
  - The nuclear envelope reforms around the chromosomes, forming four separate nuclei.
- Cytokinesis:
  - The cytoplasm divides, resulting in four haploid daughter cells.

Differences between Metaphase I and Metaphase II

Metaphase I: Homologous chromosomes are in pairs at the equator.
Metaphase II: Sister chromatids are aligned individually at the equator.

Differences between Anaphase I and Anaphase II

Anaphase I: Homologous chromosomes separate, reducing the chromosome number to 23.
Anaphase II: Sister chromatids separate, resulting in 46 chromatids.

Expected Number of Bivalents, Chromosomes, and Chromatids in Prophase I

Bivalents: 23
Chromosomes: 46
Chromatids: 92

Stages of Gametogenesis

Anaphase I: Homologous chromosomes separate.
Anaphase II: Sister chromatids separate.

Stage of Gametogenesis Where Chromosomes Become Haploid

Telophase II: The daughter cells have 23 chromosomes each (haploid).

Differences between Spermatogenesis and Oogenesis

Feature	Spermatogenesis	Oogenesis
Location	Testes	Ovaries
Start time	Puberty	Fetal development
End time	Continues throughout life	Menopause
Duration	Continuous with a cycle of 64-72 days	Cyclical and can take years
Primary product	Four haploid sperm cells	One haploid egg cell and polar bodies
Cytokinesis	Equal division of cytoplasm	Unequal division of cytoplasm; the egg receives most of the cytoplasm
Cell output	Millions of sperm cells daily	One mature egg per menstrual cycle
Timing of meiosis	Continuous once started	Meiosis I completed at ovulation, Meiosis II upon fertilization
Resource allocation	Sperm are small with few stored resources	Eggs are large and nutrient-rich

Phase with Least Chromosomal Material

Prophase I: Chromosomes are condensed and paired, but they have not yet separated.

Restoring Diploid Chromosome Number

Fertilization: The fusion of a haploid sperm cell and a haploid egg cell results in a diploid zygote with 46 chromosomes.

Cancer Cells

Uncontrolled Cell Division:
- Cancer cells divide frequently and without regulation.
Abnormal Cell Behavior:
- May not communicate properly with other cells, perform normal functions, or securely anchor themselves.
Secretion of Growth Hormones:
- Cancer cells can produce their own growth factors, promoting their growth and survival.
Blood Vessel Diversion:
- Cancer cells attract blood vessels, which supply them with nutrients and take nutrients away from healthy cells.
Risk Factors:
- Genetic predisposition, exposure to toxins, radiation, or excessive UV light.
Tumors:
- Uncontrolled growth of cancer cells can result in tumors, which may be localized or invasive.
Treatments:
- Radiation and chemotherapy aim to destroy cancer cells, targeting cells that divide frequently.

Cell Differentiation

Stem Cells:
- Unspecialized cells that can differentiate into various cell types in the body.
- Totipotent: can give rise to all cell types in the embryo
- Pluripotent: can give rise to all cell types except the placenta
- Multipotent: can give rise to a limited number of cell types
Transcription Factors:
- Proteins that regulate gene expression, determining which genes are activated in a cell.
- Play a critical role in cell differentiation.
Internal and External Cues: Internal cues include transcription factors and location within the embryo. External cues include signaling from neighboring cells and environmental factors.

Cell Aging

As cells age, they undergo changes, including:
- Reduced DNA repair capacity: Accumulation of DNA damage.
- Changes in protein synthesis: Increased accumulation of misfolded proteins.
- Cellular senescence: Cells stop dividing due to age or stress.

Cell Death

Apoptosis: Programmed cell death, a natural process for removing damaged or unwanted cells.
- Initiation: Intrinsic pathway triggered by internal damage, extrinsic pathway triggered by external signals.
- Signal transduction: Activates pro-apoptotic proteins and caspase enzymes.
- Execution phase: Breakdown of cellular components.
- Formation of apoptotic bodies: Cell fragments are engulfed by other cells.
Necrosis: Unprogrammed cell death caused by injury or stress.
- Cell injury: Damage to the cell membrane.
- Loss of membrane integrity: Swelling and disruption of cellular processes.
- Organelle swelling and dysfunction: Loss of function of organelles.
- Enzyme release: Lysosomal enzymes digest cellular components.

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Description

This quiz covers the stages of interphase and mitosis, focusing on the processes of cell growth, DNA replication, and cell division. Understand the checkpoints that ensure cellular integrity and the significance of the G0 phase. Test your knowledge of the intricate steps involved in mitosis.