Cell Division and Reproduction

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Questions and Answers

What triggers the start of the cell division process?

When the cell has doubled its size

When the cell has sufficient nutrients and appropriate size (correct)

When the cell contains enough waste materials

When the cell's DNA is fully replicated

Which phase of the cell cycle involves the synthesis of DNA?

M phase

G1 phase

G2 phase

S phase (correct)

What does the G1 phase primarily focus on?

Protein synthesis only

Separation of chromosomes

Cell growth to the appropriate size for division (correct)

DNA replication

What is mitosis also referred to as?

Nuclear division Signup and view all the answers

Which of the following cells typically do not undergo mitosis?

Nerve cells Signup and view all the answers

During which phase are chromosomes replicated to form sister chromatids?

S phase Signup and view all the answers

What is the final phase of mitosis called?

Telophase Signup and view all the answers

What collectively encompasses the G1, S, and G2 phases?

Interphase Signup and view all the answers

Which phase of the cell cycle is primarily associated with protein synthesis?

G1 Phase Signup and view all the answers

What is the primary outcome of mitosis in eukaryotic cells?

Formation of two identical daughter cells Signup and view all the answers

What type of reproduction results in cells that are not identical to their parent cells?

Sexual reproduction Signup and view all the answers

In prokaryotes, what must happen before cell division can occur?

DNA must replicate Signup and view all the answers

Which stage of mitosis involves aligning chromosomes in the center of the cell?

Metaphase Signup and view all the answers

Which of the following phases includes chromosome duplication?

S Phase Signup and view all the answers

Which checkpoint in the cell cycle is primarily responsible for checking DNA integrity before replication?

G1 checkpoint Signup and view all the answers

What distinguishes apoptosis from necrosis?

Apoptosis is a controlled process Signup and view all the answers

What does the G1 checkpoint ensure?

Cell is ready for DNA replication Signup and view all the answers

What role does apoptosis play during embryogenesis?

It eliminates excess cells between fingers and toes. Signup and view all the answers

What happens when the p53 gene is defective in a cancer cell?

The cell loses the ability to control the cell cycle Signup and view all the answers

What is a consequence of too much apoptosis in the body?

Tissue atrophy and neurodegeneration. Signup and view all the answers

Which of the following describes cancer cell behavior compared to normal cells?

Cancer cells ignore chemical signals regulating the cell cycle Signup and view all the answers

Why is apoptosis significant in adults?

It allows for cell death when cells are damaged or no longer needed. Signup and view all the answers

Which checkpoint is the p53 protein associated with?

G1/S checkpoint Signup and view all the answers

Which of the following is a major role of apoptosis in the prostate gland?

Leading to involution after late pregnancy and lactation. Signup and view all the answers

What happens if apoptosis occurs too infrequently?

It leads to hyperplasia and potential cancer development. Signup and view all the answers

What characterizes necrosis?

Unregulated cell death of most or all cells in an organ Signup and view all the answers

What is a consequence of uncontrolled cell division?

Formation of tumors Signup and view all the answers

What happens at the G2 checkpoint?

Cell ensures readiness for mitosis Signup and view all the answers

What is apoptosis?

Programmed cell death Signup and view all the answers

What is the primary outcome of telophase in cell division?

Chromosomes reappear as chromatin Signup and view all the answers

What is the role of cytokinesis in the cell cycle?

Dividing the cytoplasm into daughter cells Signup and view all the answers

What are cyclins and cyclin-dependent kinases (CDK) primarily involved in?

Regulating the cell cycle Signup and view all the answers

How do checkpoints function in the cell cycle?

They verify phase processes and DNA repair Signup and view all the answers

What does the cleavage furrow do during cytokinesis in animal cells?

Separates the cytoplasm into two daughter cells Signup and view all the answers

In telophase, which of the following structures starts to form?

Nuclear envelope Signup and view all the answers

Which of these phases follows mitosis in the cell cycle?

Cytokinesis Signup and view all the answers

What ensures the activation of target proteins in the cell cycle?

Cyclins and CDKs Signup and view all the answers

Study Notes

Introduction

Organisms require new cells for growth, reproduction, and repair.
New cells are derived from existing (ancestor) cells through two methods: asexual and sexual reproduction.

Asexual Reproduction

A single parent cell divides into two identical daughter cells.
Examples include mitosis (in eukaryotes) and binary fission (in bacteria).

Sexual Reproduction

Two parent cells (egg and sperm) combine to form a new cell (zygote) that is not identical to the parent cells.
Example is meiosis.

Cell Division in Prokaryotes (Binary Fission)

Prokaryotes have a single circular DNA molecule.
DNA replicates, and each copy attaches to the cell membrane at different positions.
The cell elongates, pulling the DNA copies apart.
The cell membrane pinches inward, dividing the cell into two identical daughter cells.

Cell Division in Eukaryotes

Cell division is triggered when cells reach a certain size and have sufficient resources.
The cell cycle dictates the stages of cell division.

Cell Cycle

The cell cycle represents the distinct stages a cell undergoes from division to the point where its daughter cells divide again.
Consists of three phases:
- Interphase: includes G1, S, and G2 phases.
- Mitosis (M phase)
- Cytokinesis (C phase)

Interphase

G1 phase: cell grows, increases protein production, generates organelles.
S phase: DNA replication occurs, forming two sister chromatids per chromosome.
G2 phase: cell prepares for mitosis, synthesizes proteins and organelles.
Interphase prepares the cell for mitosis.

Mitosis (M Phase)

Division of the nucleus, occurs only in eukaryotes.
Some cells, like nerve and brain cells, do not undergo mitosis.
Consists of four phases:
- Prophase: chromatin condenses into chromosomes, nuclear envelope and nucleolus disappear, mitotic spindle forms from centrioles.
- Metaphase: chromosomes align at the cell equator, attached to microtubules (kinetochore fibers) from the mitotic spindle.
- Anaphase: sister chromatids are pulled apart to opposite poles by the spindle fibers.
- Telophase: chromosomes uncoil into chromatin, nuclear envelope reforms, nucleolus reappears.
Mitosis results in two daughter cells with the same genetic information as the parent cell.

Cytokinesis (C Phase)

Physical division of the cytoplasm, forming two separate daughter cells.
In animal cells, a cleavage furrow forms, constricting the cell membrane.
In plant cells, a cell plate forms, dividing the cell.

Regulation of the Cell Cycle

Controls cell division to prevent uncontrolled growth.
Cyclins and cyclin-dependent kinases (CDKs) regulate the cell cycle.
Cyclins and CDKs form a complex that phosphorylates and activates or deactivates target proteins.

Checkpoints

Monitor and regulate cell cycle progression.
Prevent cell cycle progression at specific points, ensuring necessary processes occur and damage is repaired.
G1 checkpoint: checks for readiness for DNA replication.
G2 checkpoint: checks if the cell is ready for mitosis.
Metaphase checkpoint: ensures the cell is ready to complete cell division.

Uncontrolled Cell Division and Cancer

Uncontrolled cell division results in tumor formation.
Damaged or defective p53 gene can lead to uncontrolled cell division.
p53 gene plays a crucial role in the G1/S checkpoint, halting cell division if DNA damage is detected.
Cancer cells often have inactive p53 activity, leading to uncontrolled growth.

Cell Death

Necrosis: unregulated cell death caused by injury or disease.
Apoptosis: regulated cell death programmed for the removal of unwanted cells.

Apoptosis in Physiological Situations

Approximately 100,000 cells are produced and die by apoptosis each second in the human body.
Plays important roles in:
- Embryogenesis: eliminates excess cells (e.g., between fingers and toes).
- Metamorphosis: removes unnecessary cells (e.g., tadpole to frog).
- Tissue remodeling: eliminates cells no longer needed (e.g., mammary gland, prostate gland).

Apoptosis in Disease

Too much apoptosis: tissue atrophy, neurodegeneration.
Too little apoptosis: hyperplasia, atherosclerosis.

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Description

Explore the fascinating processes of asexual and sexual reproduction in organisms. This quiz covers cell division methods such as mitosis, meiosis, and binary fission, and highlights the differences between prokaryotic and eukaryotic cell division. Test your knowledge on how organisms grow, reproduce, and repair cells.