Cell Division and Reproduction

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Questions and Answers

What occurs during the S phase of the cell cycle?

Proteins are synthesized.

Cell growth occurs.

DNA is replicated. (correct)

Cells undergo cytokinesis.

Which phase of the cell cycle directly precedes mitosis?

G2 Phase (correct)

G1 Phase

S Phase

Apoptosis

What is the main purpose of checkpoints in the cell cycle?

To monitor stages and prevent errors. (correct)

To facilitate cell death.

To enhance protein synthesis.

To ensure DNA is not replicated.

How are new cells produced through asexual reproduction?

By dividing one cell into two identical cells. Signup and view all the answers

Which of the following correctly describes binary fission in prokaryotes?

DNA replicates and each copy attaches to cell membrane. Signup and view all the answers

What defines the difference between a zygote and cells produced by mitosis?

Zygotes result from the fusion of gametes. Signup and view all the answers

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

To separate the cytoplasm of a parental cell into two daughter cells Signup and view all the answers

Which checkpoint ensures that everything is ready for DNA replication?

G1 checkpoint Signup and view all the answers

What forms the cleavage furrow in animal cells during cytokinesis?

Actin and myosin contractile ring Signup and view all the answers

What happens during telophase?

Chromatin reappears as uncondensed structures Signup and view all the answers

Which molecules act to regulate the cell cycle?

Cyclins and cyclin-dependent kinases (CDK) Signup and view all the answers

What is the consequence of losing control over the cell cycle?

Uncontrolled cell division Signup and view all the answers

Which phase follows anaphase in the cell cycle?

Telophase Signup and view all the answers

What is the role of spindle fibers during mitosis?

To pull sister chromatids apart Signup and view all the answers

During which phase of the cell cycle does chromatin condense into visible chromosomes?

Prophase Signup and view all the answers

What is the significance of the metaphase checkpoint?

To ensure proper alignment of chromosomes Signup and view all the answers

What role does the p53 gene play in normal cell function?

It halts cell division when damaged DNA is detected. Signup and view all the answers

What is the primary consequence of a defective p53 gene in cancer cells?

Ability to ignore cell cycle controlling signals. Signup and view all the answers

How does cancer development relate to cell division control?

Cancer involves unrestrained tissue growth due to cell cycle control failure. Signup and view all the answers

Which statement accurately describes necrosis compared to apoptosis?

Apoptosis is a regulated process that selectively removes unwanted cells. Signup and view all the answers

What effect do mutations have on cancer cells during DNA replication?

Mutations occur in the DNA, leading to uncontrolled proliferation. Signup and view all the answers

What happens to the communication between cells in tumor formation?

Cancer cells fail to communicate with neighboring cells. Signup and view all the answers

What triggers the start of the cell division process?

The cell reaching appropriate size and energy stores Signup and view all the answers

Which phase of the cell cycle involves the synthesis of proteins and organelles necessary for division?

G2 phase Signup and view all the answers

What is the correct order of the phases in mitosis?

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

Which of the following cells does NOT typically undergo mitosis?

Nerve cells Signup and view all the answers

What does the M phase of the cell cycle represent?

Division of the nucleus Signup and view all the answers

During which phase of the cell cycle is DNA replicated?

S phase Signup and view all the answers

What is the role of the G1 phase in the cell cycle?

Organelles duplication and protein synthesis Signup and view all the answers

What is karyokinesis commonly referred to?

Division of the nucleus Signup and view all the answers

Study Notes

Introduction

New cells are needed for growth, repair, and replacement of damaged cells.
New cells are produced by two different types of reproduction: asexual reproduction and sexual reproduction.
Asexual reproduction: one cell divides into two identical cells; examples include mitosis (in eukaryotes) and binary fission (in bacteria).
Sexual reproduction: two cells (an egg and a sperm) are joined to produce a new cell (zygote) that is not identical to the parent cells; example is meiosis.

Cell Division

Prokaryotes (Binary fission):
- Prokaryotes have a single circular DNA molecule.
- This DNA molecule replicates and each copy is attached to the cell membrane at different positions.
- The cell pulls apart, separating the replicated and original DNA molecules.
- Two identical daughter cells are formed.
Eukaryotic Cells:
- Cell division occurs when there is a need for new cells (growth, damage, etc.)
- When a cell grows too large, nutrient and waste exchange becomes difficult.
- The division process starts when the cell reaches the appropriate size and has enough protein and energy (ATP) stores.

Cell Cycle

Represents the different stages from the moment a cell is divided into two distinct daughter cells until they are dividing themselves into new cells.
Divided into three phases: G1, S, G2, and M.
Interphase (G1, S, and G2 phases):
- G1 (Primary Growth Phase):
  - Cell grows to appropriate size for division.
  - Increases its supply of proteins needed for division and number of organelles like mitochondria and ribosomes.
- S (Synthesis Phase):
  - DNA amount doubles.
  - Chromosomes replicate, forming two sister chromatids.
- G2 (Secondary Growth Phase):
  - 2nd growth phase after DNA duplication.
  - All cell structures needed for division are made (e.g., centrioles).
  - Proteins and organelles needed for division are synthesized.
M (Mitosis) Phase:
- Division of the nucleus.
- Happens only in eukaryotes.
- Some cells, like nerve and brain cells, do NOT undergo mitosis.
C (Cytokinesis) Phase:
- The physical process of cell division that divides the cytoplasm of a parental cell into two daughter cells.
- After mitosis, the cytoplasm of the newly formed cells is separated by the aid of actin and myosin contractile ring, which forms a cleavage furrow.

Mitosis Stages

Prophase:
- Chromatin condenses into chromosomes.
- Nucleolus and nuclear membrane disappear.
- Mitotic spindle forms from centrioles.
Metaphase:
- Chromosomes attached to kinetochore fibers are lined up along the cell equator.
- Each pole has a whole set of original genes.
Anaphase:
- Spindle fibers pull sister chromatids apart at their centromeres.
Telophase:
- Chromosomes reappear as chromatin (uncondensed).
- Nuclear envelope starts to form.
- Nucleolus is visible.
- Spindle breaks apart.

Regulation of Cell Cycle

Aims to control cell cycle to prevent uncontrolled division of cells.
Regulatory molecules involved are called cyclins and cyclin-dependent kinases (CDK).
Cyclin (regulatory subunit) and CDK (catalytic subunit) form a heterodimer that phosphorylates and activates or deactivates target proteins.
Checkpoints of Cell Cycle are used to monitor and regulate the progress of the cell cycle, ensuring necessary processes are completed and DNA damage is repaired.
- G1 Checkpoint: Ensures everything is ready for DNA replication.
- G2 Checkpoint: Ensures the cell is ready for mitosis.
- Metaphase Checkpoint: Ensures the cell is ready to complete cell division.

Uncontrolled Cell Cycle: Tumor Formation

Uncontrolled cell division is a hallmark of tumor formation.
A damaged/defective p53 gene causes loss of information needed to respond to control signals.
Cancer cells with defective p53 do not respond to cell cycle controlling signals, resulting in uncontrolled division.

Normal Cell vs. Cancer Cell

Normal Cell:
- DNA is replicated properly.
- Chemical signals start and stop the cell cycle.
- Cells communicate with each other to prevent overcrowding.
Cancer Cell:
- Mutations occur in the DNA when it is replicated.
- Chemical signals that start and stop the cell cycle are ignored.
- Cells do not communicate with each other, leading to tumor formation.

Cancer: Failure of Cell Division Control

Cancer is essentially a failure of cell division control, causing unrestrained, uncontrolled tissue growth.
p53 gene plays a key role in the G1/S checkpoint.
- p53 protein halts cell division if it detects damaged DNA.
- All cancers have to shut down p53 activity.

Cell Death

Necrosis (Unregulated Cell Death): Death of most or all of the cells in an organ or tissue due to disease, injury, or failure of the blood supply.
Apoptosis (Regulated Cell Death): An energy-dependent programmed cell death for removal of unwanted individual cells.

Necrosis vs. Apoptosis

Necrosis involves swelling of the cell and rupture of the cell membrane, releasing cellular contents into the surrounding area, potentially causing inflammation.
Apoptosis involves a cascade of cellular events that lead to the dismantling of the cell without releasing cellular contents, minimizing inflammation or damage to surrounding cells.

Apoptosis in Physiologic Situations

About 100,000 cells are produced every second by mitosis and a similar number die by apoptosis in the human body.
Apoptosis during Embryogenesis:
- Morphogenesis (Eliminates excess cells): Removal of unnecessary cells between fingers and toes.
Apoptosis during Metamorphosis:
- Eliminates cells no longer needed as an organism undergoes a change in form (example: tadpole to frog).

Apoptosis in Adults

Tissue Remodeling (eliminates cells no longer needed):
- Virgin Mammary Gland: Apoptosis occurs during late pregnancy and lactation and again during involution (when the gland returns to its non-pregnant state).
- Prostate Gland: Apoptosis is regulated by testosterone levels.

Apoptosis and Disease

Too Much Apoptosis:
- Tissue Atrophy: Diminished size and function of an organ or tissue due to loss of cells.
- Neurodegeneration: Progressive loss of structure and function of neurons, leading to neurological disorders.
Too Little Apoptosis:
- Hyperplasia: Abnormal increase in the number of cells in an organ or tissue.
- Athersclerosis: Buildup of plaque in arteries, often leading to heart disease.

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Description

This quiz covers the processes of cell division, including asexual and sexual reproduction. It highlights the mechanisms of mitosis in eukaryotes and binary fission in prokaryotes. Test your knowledge on how new cells are formed for growth and repair.