Cell Division and Cycle Overview

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Questions and Answers

What is the sequence of phases in the cell cycle?

S, G1, G2, M

G2, M, G1, S

M, G2, S, G1

G1, S, G2, M (correct)

Which phase of the cell cycle is primarily involved in DNA replication?

S Phase (correct)

G2 Phase

M Phase

G1 Phase

What is the main function of the G1 phase in the cell cycle?

Cell growth and preparation for DNA synthesis (correct)

Cell division

DNA replication

Chromosome separation

Which of the following is NOT a stage of mitosis?

Interphase Signup and view all the answers

What is one characteristic of asexual reproduction in cellular division?

Results in genetically identical cells Signup and view all the answers

What is the main difference between mitosis and meiosis?

Mitosis produces diploid cells, whereas meiosis produces haploid cells Signup and view all the answers

During which stage of the cell cycle is the chromosomal material duplicated?

S Phase Signup and view all the answers

What occurs during the G2 phase of the cell cycle?

Preparation for mitosis Signup and view all the answers

What triggers the start of the cell division process?

When the cell has enough proteins and energy stored Signup and view all the answers

Which phase of the cell cycle is primarily responsible for DNA replication?

S phase Signup and view all the answers

Which statement about mitosis is correct?

It results in two identical daughter cells Signup and view all the answers

What primarily occurs during the G2 phase of interphase?

Cell growth and preparation for mitosis Signup and view all the answers

Which phase of mitosis involves the alignment of chromosomes along the cell's equator?

Metaphase Signup and view all the answers

What does cytokinesis primarily involve?

Separation of the cytoplasm Signup and view all the answers

Why might nerve and brain cells not undergo mitosis?

They have reached a terminal differentiation stage Signup and view all the answers

What is the correct order of phases in mitosis?

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

What is a primary role of apoptosis during embryogenesis?

To eliminate excess cells, such as those between fingers and toes Signup and view all the answers

What is the primary purpose of cytokinesis?

To separate the cytoplasm into two daughter cells Signup and view all the answers

Which statement describes a consequence of excessive apoptosis?

Tissue atrophy and neurodegeneration Signup and view all the answers

In what situation is apoptosis particularly essential in adult tissues?

For tissue remodeling when cells are no longer needed Signup and view all the answers

Which structure forms as a result of cytokinesis in animal cells?

Cleavage furrow Signup and view all the answers

What effect does reduced apoptosis have on cell populations?

Hyperplasia leading to an overabundance of cells Signup and view all the answers

Which of the following is true about telophase?

Chromosomes reappear as chromatin Signup and view all the answers

What is apoptosis's role during the transition from a tadpole to a frog?

To remove unneeded cells during metamorphosis Signup and view all the answers

What do cyclins and cyclin-dependent kinases (CDKs) primarily regulate?

Cell cycle progression Signup and view all the answers

What is the role of checkpoints in the cell cycle?

To monitor and regulate cell cycle progress Signup and view all the answers

During which phase of mitosis do sister chromatids align at the cell equator?

Metaphase Signup and view all the answers

What structure forms from the centrioles during telophase?

Mitotic spindle Signup and view all the answers

What happens to the nucleolus during telophase?

It becomes visible again Signup and view all the answers

What is the main role of the G1 checkpoint in the cell cycle?

To ensure everything is ready for DNA replication. Signup and view all the answers

What consequence arises from a defective p53 gene in a cell?

The cell may undergo uncontrolled division. Signup and view all the answers

Which statement best describes the difference between normal cells and cancer cells?

Cancer cells do not respond to cell cycle controlling signals. Signup and view all the answers

What happens at the G2 checkpoint?

It checks for DNA damage before mitosis. Signup and view all the answers

What defines cancer in relation to cell division?

Failure to regulate tissue growth. Signup and view all the answers

Which type of cell death is described as energy-dependent and programmed?

Apoptosis. Signup and view all the answers

How do cancer cells typically differ in their communication with neighboring cells compared to normal cells?

They do not communicate and can form tumors. Signup and view all the answers

What crucial role does the p53 protein play in the cell cycle?

It halts cell division in response to DNA damage. Signup and view all the answers

Study Notes

Introduction

New cells are needed for growth, replacement of damaged cells, and increasing the number of cells.
Cells are formed using asexual reproduction where mitosis (eukaryotes) and binary fission (bacteria) are used to produce identical cells.
Sexual reproduction combines two cells to create a new cell that is not identical to the parent cells.

Cell Division

Prokaryotes: Have a single circular DNA molecule that replicates and attaches to the cell membrane.
Eukaryotes: Division is triggered when a cell reaches an appropriate size and has enough protein and energy stores, to prevent the cell from becoming too large, making nutrient and waste exchange difficult.

Cell Cycle

The cell cycle is a series of stages that occur from when a cell divides into two cells until those daughter cells divide as well.
Includes:
- Interphase:
  - G1 Phase: Cell grows in size, and increases its supply of proteins and organelles for division.
  - S Phase: DNA replicates, resulting in two sister chromatids per chromosome.
  - G2 Phase: Second growth phase, all structures needed for division are created, including centrioles, and protein, and organelle synthesis.
- M Phase: Mitosis, or karyokinesis, where the nucleus divides. Occurs in eukaryotes only, some cells such as nerve and brain cells, do not undergo mitosis.
- C Phase: Cytokinesis, the physical process of cell division where the cytoplasm divides into two daughter cells with the help of actin and myosin contractile rings that form a cleavage furrow.
Mitosis:
- Consists of four stages (PMAT):
  - Prophase: Chromatin condensates into chromosomes, the nucleolus and nuclear membrane disappear, and the mitotic spindle formation begins from centrioles.
  - Metaphase: Chromosomes attach to kinetochore fibers and line up along the cell equator.
  - Anaphase: Spindle fibers pull sister chromatids apart to opposite poles, each pole with a full set of original genes.
  - Telophase: Chromosomes reappear as chromatin, the nuclear envelope begins to form, the nucleolus is visible, and the spindle breaks apart.
Cell division assists in growth, repair, and replacement of damaged cells within tissues.

Regulation of Cell Cycle

Aims to control cell division to prevent uncontrolled cell division and tumor formation.
Regulatory molecules: cyclins and cyclin-dependent kinases (CDK)
- These molecules form a heterodimer that activates or deactivates target proteins through phosphorylation.
Checkpoints ensure proper cell cycle progression:
- G1 Checkpoint: Verifies that everything is ready for DNA replication.
- G2 Checkpoint: Checks that the cell is ready for mitosis.
- Metaphase Checkpoint: Ensures that the cell is ready to complete cell division.
Loss of Cell Cycle Control leads to tumor formation.
- A damaged or defective p53 gene causes a loss of information needed to respond to control signals. Cancer cells with faulty p53 lack responsiveness to cell cycle control signals, leading to uncontrolled cell division.
- Normal Cells: DNA replicates correctly, chemical signals start and stop the cell cycle, cells communicate to prevent overcrowding.
- Cancer Cells: DNA replicates with mutations, chemical signals for starting and stopping the cell cycle are ignored, cells don't communicate, leading to the formation of tumors.
Cancer: Essentially a failure of cell division control.
- All cancers require a shutdown of p53 activity, which plays a key role in the G1/S checkpoint and halts cell division if damaged DNA is detected.

Cell Death

Necrosis: Unregulated cell death caused by disease, injury, or lack of blood supply.
Apoptosis: Regulated cell death for the removal of unwanted cells. This is an energy-dependent process.
Necrosis VS Apoptosis:
- Necrosis is a massive, uncontrolled event, while apoptosis is a controlled, individual cell process.
- Necrosis causes cell swelling, while apoptosis leads to cell shrinking.
- Necrosis results in inflammation, whereas apoptosis prevents inflammation.
Apoptosis in Physiological Situations:
- About 100,000 cells are produced each second by mitosis, with a similar number dying by apoptosis.
- Embryogenesis: Apoptosis plays a role in morphogenesis to eliminate excess cells, for example, between fingers and toes.
- Metamorphosis: Apoptosis assists in the transformation of a tadpole into a frog.
Apoptosis in Adults:
- Tissue Remodeling: Apoptosis eliminates unwanted cells through tissue renewal. Example: the mammary glands.
- Prostate Gland: Testosterone controls the level of apoptosis in the prostate gland.
Apoptosis in Disease:
- Too Much Apoptosis: Tissue atrophy, neurodegeneration.
- Too Little Apoptosis: Hyperplasia, athersclerosis.

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Description

Explore the essential concepts of cell division and the cell cycle in this quiz. Understand the differences between prokaryotic and eukaryotic cell division, the stages of the cell cycle, and the processes of mitosis and binary fission. Test your knowledge on how cells grow, replicate, and prepare for division.