Lecture 42: Cell divison, the cell cycle and its controllers Flashcards
What is the cell cycle?
The cell cycle is an ordered series of events that lead to cell growth, DNA replication, and cell division, producing two genetically identical daughter cells.
Why is the cell cycle important?
It ensures proper cell growth, development, and tissue repair, preventing uncontrolled cell division that could lead to diseases like cancer.
: What are the two major phases of the cell cycle?
Interphase (where the cell grows and prepares for division) and the Mitotic (M) phase (where the cell divides).
What are the three stages of Interphase?
G1 (growth and preparation), S (DNA replication), and G2 (final preparations for mitosis).
What occurs during G1 phase?
The cell grows, synthesizes proteins, and checks for DNA damage before entering S phase.
What happens in the S phase?
DNA replication occurs, producing two identical copies of each chromosome.
What is the G2 phase, and why is it important?
The G2 phase is when the cell prepares for mitosis by synthesizing proteins and organelles and ensuring DNA replication is complete.
What are the key stages of mitosis?
Prophase, Metaphase, Anaphase, and Telophase.
Describe Prophase.
Chromatin condenses into visible chromosomes, the nuclear envelope disintegrates, and spindle fibers form.
What happens in Metaphase?
Chromosomes align at the metaphase plate, and spindle fibers attach to the centromeres.
Explain Anaphase
Sister chromatids separate and move to opposite poles, pulled by the spindle fibers.
What is Telophase?
Chromosomes decondense into chromatin, the nuclear envelope reforms, and the spindle fibers break down.
What is cytokinesis, and when does it occur?
Cytokinesis is the division of the cytoplasm, occurring after telophase, to produce two separate daughter cells.
What proteins regulate the cell cycle?
Cyclins and cyclin-dependent kinases (CDKs), which control progression through checkpoints.
What is the purpose of the G1 checkpoint?
To ensure the cell has sufficient nutrients, undamaged DNA, and proper size before DNA replication.
What happens if a cell does not pass the G1 checkpoint?
The cell enters G0, a resting phase where it does not divide but may re-enter the cycle later.
What does the G2 checkpoint do?
It verifies that DNA replication was successful and that the cell is ready for mitosis.
What is the M checkpoint?
It ensures all chromosomes are correctly attached to spindle fibers before anaphase begins.
How does the tumor suppressor protein p53 regulate the cell cycle?
p53 halts the cell cycle if DNA damage is detected, allowing for repair or triggering apoptosis if damage is irreparable.
What happens when cell cycle regulation fails?
Uncontrolled cell division can occur, leading to tumor formation and cancer.
Why is the cell cycle a target for cancer treatment?
Cancer cells divide uncontrollably, so targeting specific cycle phases can inhibit tumor growth.
What are some drugs that target the cell cycle?
Chemotherapy drugs like Taxol (stabilizes microtubules) and CDK inhibitors (block cyclin-CDK complexes).
How does Taxol work?
It prevents microtubule disassembly, blocking mitosis and causing cell death.
What are CDK inhibitors, and how do they work?
They block CDK activity, halting the cell cycle and preventing cancer cell proliferation.
How do researchers analyze the cell cycle in a lab?
Techniques like flow cytometry and fluorescent microscopy help assess DNA content and cell cycle phases.
How is flow cytometry used to study the cell cycle?
It measures DNA content in cells to determine their position in the cell cycle.
What is apoptosis, and how is it linked to the cell cycle?
Apoptosis is programmed cell death, which removes damaged cells if checkpoints detect irreparable DNA damage.
How do growth factors influence the cell cycle?
Growth factors signal cells to divide by promoting cyclin and CDK activation.
How does contact inhibition affect the cell cycle?
Cells stop dividing when they come into contact with neighboring cells, preventing overgrowth.
What is the role of telomeres in the cell cycle?
Telomeres protect chromosome ends; their shortening limits cell division and contributes to aging.
What enzyme extends telomeres, and why is it significant?
Telomerase, which is active in stem cells and cancer cells, enabling continuous division.
How do oncogenes contribute to uncontrolled cell division?
Oncogenes are mutated genes that promote excessive cell growth and bypass checkpoints.
What are tumor suppressor genes, and why are they important?
They prevent uncontrolled division by repairing DNA or triggering apoptosis when necessary.
How do mutations in tumor suppressor genes lead to cancer?
Loss-of-function mutations disable the cell’s ability to halt division or repair DNA damage.
What is the significance of the Rb protein in cell cycle control?
It prevents excessive cell growth by inhibiting transcription factors required for S phase entry.
What is the role of E2F in the cell cycle?
E2F is a transcription factor that promotes DNA replication, activated when Rb is inactivated.
What is the function of mitogens in cell cycle regulation?
Mitogens stimulate cell division by promoting cyclin expression.
How does the spindle assembly checkpoint prevent chromosome missegregation?
It delays anaphase until all chromosomes are properly attached to spindle fibers.
Why do cancer cells often have chromosomal instability?
They bypass cell cycle checkpoints, leading to unequal chromosome distribution.
What is the difference between benign and malignant tumors?
Benign tumors remain localized, while malignant tumors invade tissues and metastasize.
