Cell Cycle Flashcards
Prokaryote binary fission steps:
Replication of DNA with partition:
What is the purpose of the cell cycle?
Copy the genome and partition copies equally between daughter cells.
• Enable growth of a multicellular organism.
• Maintain total cell number by replacing lost or damaged cells.
How do prokaryotes divide?
Prokaryotes divide by binary fission.
• Two pathways must be coordinated:
- DNA replication
- Cytokinesis (FtsZ ring forms, contracts, and separates the cell)
What is multifork replication in prokaryotes?
Multifork replication occurs because DNA replication takes longer than cell division.
• Multiple replication forks can be active at the same time, allowing DNA replication to continue even as the cell divides.
• At least one round of DNA replication is completed before cytokinesis.
What are the key phases of the eukaryotic cell cycle?
• G1 (Gap 1): Growth phase, organelles and proteins double, enzymes for replication synthesized.
• S (Synthesis): Chromosome duplication, sister chromatids held together by cohesin.
• G2: Preparation for mitosis.
What happens during mitosis?
Chromosome condensation: Chromosomes become visible and compact.
- Mitotic spindle formation: Spindle apparatus forms and pulls chromosomes apart.
- Cohesin cleavage: Sister chromatids separate.
- Cytokinesis: Division of cytoplasm. In plant cells, a phragmoplast guides division.
What is the difference between early embryonic cycles and somatic cells?
Early embryonic cycles: Division without growth, producing smaller cells, 20x faster than somatic cells.
• Somatic cells: Normal cell division cycle with growth.
What is the difference between open mitosis and closed mitosis?
Open mitosis: Occurs in multicellular organisms, nuclear envelope breaks down.
• Closed mitosis: Occurs in unicellular organisms, nuclear envelope remains intact.
: What is cell polarity in cell division?
Asymmetric division: Segregates cell fate determinants to one side, resulting in one daughter cell differentiating while the other remains a stem cell.
What regulates the cell cycle?
Cyclin-dependent kinase (CDK): Active when bound to cyclin, drives cell cycle progression.
• Cyclin levels rise and fall, coordinating different phases.
• Protein complexes ensure phases occur in proper order.
What are checkpoints in the cell cycle?
Ensure that previous phases are completed before the next begins.
• G1 checkpoint (restriction point): Positive signal required for cell division.
• G2 checkpoint and spindle checkpoint ensure correct progression and segregation.
What happens if checkpoints fail?
Failure can lead to mutations and possible cancer.
• In cancer, the cell cycle is deregulated, contact inhibition is lost, and checkpoints do not operate correctly.
What is the role of cyclin in the cell cycle?
Cyclin directs CDK to specific target proteins and is degraded at the end of the cell cycle phase.
• This degradation terminates the phase and coordinates the transition to the next phase.
How do cell-fusion experiments support the coordination of the cell cycle?
Cell fusion experiments show that if an S-phase cell is fused with a G1-phase cell, the G1 cell is instructed to enter the S phase.
• This demonstrates that the cell cycle is coordinated and regulated by signals between phases.
