Biology Cell Division and Cycle

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Questions and Answers

What cellular structures form during telophase to help in separating the daughter cells?

Actin and myosin (correct)

Spindle fibers

Kinetochore fibers

Centrioles

What is the primary function of cyclins in the cell cycle?

To regulate the progression of the cell cycle (correct)

To aid in cytokinesis

To check the cell's environment

To repair DNA damage

What is the role of the G2 checkpoint in the cell cycle?

To check the overall cell size

To ensure DNA replication is complete (correct)

To confirm spindle fibers are attached

To prepare the cell for anaphase

During which phase do chromosomes reappear as uncondensed chromatin?

Telophase Signup and view all the answers

What initiates the cleavage furrow during cytokinesis in animal cells?

Contractile ring Signup and view all the answers

What happens if a cell loses control of its cell cycle?

It can cause uncontrolled cell division Signup and view all the answers

Which phase of the cell cycle is primarily concerned with the alignment of chromosomes at the cell equator?

Metaphase Signup and view all the answers

What occurs to the nuclear envelope during telophase?

It begins to reform Signup and view all the answers

Which checkpoint ensures the spindle fibers are properly attached to chromosomes?

Metaphase checkpoint Signup and view all the answers

What is the role of cyclin-dependent kinases (CDKs) in the cell cycle?

To activate or deactivate target proteins Signup and view all the answers

What is the primary purpose of cell division in organisms?

To create new cells for growth, repair, and maintenance Signup and view all the answers

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

S Phase Signup and view all the answers

Which of the following stages is NOT a part of mitosis?

S Phase Signup and view all the answers

What occurs during binary fission in prokaryotes?

DNA is replicated and separated before cell division Signup and view all the answers

Which type of reproduction produces new cells that are identical to the parent cells?

Asexual reproduction through mitosis Signup and view all the answers

What describes the outcome of sexual reproduction?

It generates a zygote that is genetically distinct from both parents. Signup and view all the answers

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

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

What may occur as a result of mutations in DNA during the cell cycle?

Tumors can form due to uncontrolled growth. Signup and view all the answers

Which of the following best characterizes necrosis?

It is the unregulated death of cells in a tissue or organ. Signup and view all the answers

How does a cancer cell with a defective p53 gene behave compared to a normal cell?

It ignores signals to stop the cell cycle. Signup and view all the answers

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

Uncontrolled tissue growth may result. Signup and view all the answers

In the context of cancer, what is the significance of the G1/S checkpoint?

It is where p53 exerts its control to halt cell division. Signup and view all the answers

What is the primary purpose of the G1 phase in the cell cycle?

The cell grows and prepares for division. Signup and view all the answers

Which phase follows the S phase in the cell cycle?

G2 phase Signup and view all the answers

What happens during the anaphase of mitosis?

Sister chromatids are pulled apart to opposite poles. Signup and view all the answers

Which of the following statements is true regarding mitosis?

It involves four distinct phases. Signup and view all the answers

What occurs during the G2 phase of the cell cycle?

All cell structures needed for division are synthesized. Signup and view all the answers

Which of the following types of cells typically do not undergo mitosis?

Nerve and brain cells Signup and view all the answers

What is the overall outcome of the cell cycle?

One cell divides into two identical daughter cells. Signup and view all the answers

What is the correct sequence of phases during mitosis?

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

Study Notes

Introduction

Organisms need new cells for growth, replacement of damaged or lost cells
New cells are derived from ancestor cells
New cells are produced by asexual and sexual reproduction

Cell division

Prokaryotes
- Single circular DNA molecule
- Replicated DNA is attached to cell membrane
- Cell pulls apart, separating DNA
- Two identical daughter cells are formed
Eukaryotes
- Division initiated when cell has reached appropriate size and has enough protein and energy stores.

Cell cycle

Represents stages from when a cell divides into two daughter cells until those daughter cells divide again.
Divided into three phases:
- G1: primary growth phase
- S: DNA replication occurs
- G2: secondary growth phase
- G1, S, and G2 are collectively called interphase
Mitosis: Nuclear division
Cytokinesis: Division of cytoplasm

Interphase

G1 phase:
- Cell grows
- Increases supply of proteins needed for division
- Increases number of organelles like mitochondria
- Protein synthesis occurs
S phase:
- DNA quantity is doubled
- Chromosomes replicated into two sister chromatids
G2 phase:
- Second growth phase after DNA duplication
- Cell synthesizes structures needed for division
- Completed interphase results in a cell that can start mitosis

Mitosis

Occurs only in eukaryotes
Some cells do not undergo mitosis, like nerve and brain cells
Divided into four phases:
- Prophase: Chromatin condenses into chromosomes, nucleolus and nuclear membrane disappear, mitotic spindle forms
- Metaphase: Chromosomes attach to kinetochore fibers and line along cell equator
- Anaphase: Spindle fibers pull sister chromatids apart; each pole of the cell has a complete set of original genes
- Telophase: Chromosomes reappear as chromatin, nuclear envelope starts to form, nucleolus is visible, spindle breaks apart

Cytokinesis

Physical process of cell division
Divides cytoplasm into two daughter cells
Actin and myosin contractile ring forms a cleavage furrow, separating the cytoplasm

Regulation of cell cycle

Aims to control cell division to prevent uncontrolled cell growth
Regulatory molecules involved: cyclins and cyclin-dependent kinases (CDK)
Cyclin and CDK form a heterodimer, phosphorylating and activating or deactivating target proteins
Checkpoints: Monitor and regulate the progress of the cell cycle, allowing for verification of necessary phase processes and repair of DNA damage
- 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 division

Uncontrolled cell cycle results in tumor formation
Damaged/defective p53 gene causes loss of information needed to respond to control signals
Cancer cells with defective p53 cannot respond to cell cycle controlling signals, leading to uncontrolled division

Normal cell versus cancer cell

Normal cell:
- DNA replicated properly
- Chemical signals start and stop cell cycle
- Cells communicate with each other to avoid overcrowding
Cancer cell:
- DNA mutations occur during replication
- Chemical signals that control the cell cycle are ignored
- Cells do not communicate with each other leading to tumor formation

Cancer

Failure of cell division control leading to uncontrolled tissue growth
P53 gene plays key role in G1/S checkpoint, halting cell division if damaged DNA is detected
All cancer cells have to shut down p53 activity

Cell death

Necrosis:
- Unregulated cell death
- Death of most or all cells in an organ or tissue due to disease, injury, or lack of blood supply
Apoptosis:
- Regulated cell death
- Energy-dependent programmed cell death for removing unwanted individual cells

Necrosis vs. Apoptosis

Necrosis: Unregulated, accidental cell death often causing inflammation and damage.
Apoptosis: Regulated, controlled cell death important for development, tissue remodeling, and removal of dysfunctional cells.

Apoptosis in physiologic situations

In the human body, about 100,000 cells are produced every second by mitosis and a similar number die by apoptosis.
Embryogenesis:
- Morphogenesis, removal of excess cells between fingers and toes
- Metamorphosis of a tadpole into a frog
Adults:
- Tissue remodeling, removal of cells no longer needed
- Virgin mammary gland, Late pregnancy, lactation, Involution
- Prostate gland: Apoptosis regulated by testosterone

Apoptosis in disease

Too Much: Tissue atrophy, neurodegeneration, thin skin
Too Little: Hyperplasia, atherosclerosis

Question

Cells divide rather than simply increase in size, as it maintains cellular function by addressing issues like:
- Surface area to volume ratio: As cells enlarge, surface area to volume ratio decreases, limiting nutrient uptake and waste removal. Division maintains a favorable ratio for efficient functions.
- Complexity of cell processes: Division ensures each daughter cell receives a full set of genetic material and organelles, enabling specific functions to be performed efficiently. Enlarging a cell would strain its ability to perform complex tasks effectively.
- Replication and repair: Division allows for replication of genetic material and organelles ensuring the correct functioning of new cells. It also allows for repair mechanisms to be distributed across daughter cells, helping to maintain the integrity of tissues.

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Description

Explore the fascinating processes of cell division and the cell cycle in this quiz. Learn about the differences between prokaryotic and eukaryotic cell division, as well as the stages of the cell cycle, including interphase and mitosis. Perfect for biology students looking to reinforce their understanding of cellular processes.