09 Cell Cycle

Overview of the Cell Cycle

• Distinction of living organisms is their ability to reproduce through cell division.

• Continuity of life relies on reproduction of cells.

Key Functions of Cell Division

• In unicellular organisms, one cell division creates an entire organism.

• In multicellular eukaryotes:

  • Development originates from a single cell.

  • Enables renewal, repair, and replacement of cells.

• Cell division is an essential part of the cell cycle, from formation to division.

Genetic Material during Cell Division

Concept 9.1: Genetically Identical Daughter Cells

• Cell division typically results in daughter cells with identical genetic information.

• DNA is transmitted from parent to daughter cells with high accuracy.

Cellular Organization of Genetic Material

• Total DNA in a cell is referred to as its genome.

• Prokaryotic cells have a single DNA molecule; eukaryotic cells have multiple.

• DNA in eukaryotic cells is organized into structures called chromosomes.

Eukaryotic Chromosomes

• Eukaryotic chromosomes consist of chromatin, a mix of DNA and protein.

• Each species has a specific number of chromosomes.

  • Somatic (non-reproductive) cells have two chromosome sets.

  • Gametes (sperm and eggs) possess one set.

Chromosome Distribution in Cell Division

• Before cell division, DNA replication occurs, leading to chromosomal condensation.

• Duplicated chromosomes have sister chromatids—identical copies joined at the centromere.

• During division, sister chromatids separate into two nuclei, becoming individual chromosomes.

Phases of the Cell Cycle

Overview of the Cell Cycle Stages

• The cell cycle consists of:

  • Mitotic (M) phase: Includes mitosis and cytokinesis.

  • Interphase: Cell growth and DNA copying in preparation for division.

Interphase Subphases

• Interphase accounts for roughly 90% of the cell cycle and consists of:

  • G1 phase: First gap, cell growth.

  • S phase: Synthesis, where DNA is replicated.

  • G2 phase: Second gap, further growth occurs.

Mitosis Stages

• Mitosis is divided into five phases:

  • Prophase

  • Prometaphase

  • Metaphase

  • Anaphase

  • Telophase

• Cytokinesis overlaps late mitosis phases.

The Mitotic Spindle

• The mitotic spindle is crucial for chromosome movement, made of microtubules and proteins.

• Centrosomes are microtubule organizing centers that replicate during interphase, migrating to opposite cell ends.

Prometaphase/Mitotic Spindle Details

• Spindle microtubules connect to kinetochores on chromosomes, facilitating movement.

• During metaphase, centromeres align at the metaphase plate.

• During anaphase, sister chromatids move towards opposite poles of the cell.

Cytokinesis

Cleavage in Animal Cells

• In animals, cytokinesis occurs via a cleavage furrow.

Plant Cell Cytokinesis

• In plant cells, a cell plate forms during cytokinesis.

Binary Fission in Prokaryotes

• Prokaryotes divide through binary fission, replicating their single chromosome and pinching into two.

Regulation of the Eukaryotic Cell Cycle

Concept 9.3: Cell Cycle Regulation

• Cell division frequency varies among cell types, controlled at the molecular level.

• Cancer cells bypass standard cell cycle controls.

Checkpoints in the Cell Cycle

• The cell cycle control system functions through checkpoints, similar to a washing machine’s timer.

• Major checkpoints include:

  • G1 checkpoint: Key for whether a cell continues cycle.

  • M checkpoint: Ensures correct chromosome attachment before anaphase.

Regulatory Signals

• Cell division is influenced by internal signals (e.g., kinases and cyclins) and external factors (e.g., growth factors).

• Cancer cells disregard growth factors and regulatory signals.

Cancer Cell Characteristics

• Cancer cells ignore cycle regulatory mechanisms, can proliferate without growth factors.

• Transformation occurs when normal cells become cancerous, leading to tumors.

  • Benign tumors: Remain localized.

  • Malignant tumors: Invade surrounding tissue and may metastasize.

Flashcards on the Cell Cycle

1. Cell Division: The process by which a parent cell divides into two or more daughter cells.

2. Unicellular Organisms: Organisms that consist of a single cell; cell division creates the entire organism.

3. Multicellular Eukaryotes: Organisms made of multiple cells; development originates from a single cell.

4. DNA Transmission: The process by which genetic information is accurately passed from parent cells to daughter cells.

5. Genome: The total DNA contained within a cell; varies between prokaryotic and eukaryotic organisms.

6. Prokaryotic Cells: Cells with a single DNA molecule, simpler in structure than eukaryotic cells.

7. Eukaryotic Cells: Cells that contain multiple chromosomes organized in structures called chromosomes.

8. Chromatin: The combination of DNA and protein that makes up eukaryotic chromosomes.

9. Somatic Cells: Non-reproductive cells in a multicellular organism, containing two sets of chromosomes.

10. Gametes: Reproductive cells (sperm and eggs) with one set of chromosomes.

11. Chromosomal Condensation: The process by which DNA becomes denser and more compact in preparation for cell division.

12. Sister Chromatids: Identical copies of a chromosome joined together at the centromere before cell division.

13. Mitotic Phase: The stage of the cell cycle where mitosis and cytokinesis occurs.

14. Interphase: The phase of the cell cycle where a cell grows and duplicates its DNA, accounting for 90% of the cycle.

15. G1 Phase: The first gap phase of interphase where the cell grows.

16. S Phase: The synthesis phase of interphase where DNA replication occurs.

17. G2 Phase: The second gap phase of interphase where further growth happens before mitosis.

18. Mitosis: The division of the nucleus into two daughter nuclei, followed by cytokinesis.

19. Mitotic Spindle: A structure made of microtubules that segregates chromosomes during cell division.

20. Centrosomes: The microtubule organizing centers that replicate during interphase.

21. Kinetochores: Protein structures where spindle microtubules attach to chromosomes.

22. Metaphase Plate: The plane where chromosomes align during metaphase.

23. Cytokinesis: The process that divides the cytoplasm of a parental cell into two daughter cells.

24. Cleavage Furrow: The indentation that forms during cytokinesis in animal cells.

25. Cell Plate: The structure that forms during cytokinesis in plant cells.

26. Binary Fission: A form of asexual reproduction in prokaryotes where the single chromosome replicates and divides.

27. Cell Cycle Regulation: Mechanisms that control the timing and occurrences of cell division.

28. Checkpoints in the Cell Cycle: Points in the cell cycle that assess whether cell division should proceed.

29. G1 Checkpoint: The checkpoint that determines whether a cell will continue through the cell cycle.

30. M Checkpoint: The checkpoint that ensures chromosomes are properly attached to the spindle before anaphase.

31. Regulatory Signals: Internal and external factors, such as kinases and cyclins, that influence the cell cycle.

32. Cancer Cells: Cells that bypass regular controls of the cell cycle, leading to uncontrolled division.

33. Transformation: The process through which normal cells become cancerous.

34. Benign Tumors: Non-cancerous tumors that remain localized.

35. Malignant Tumors: Cancerous tumors that invade surrounding tissues and may spread (metastasize).