Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
The Cell Cycle: A continuous sequence of events divided into interphase (, , and ) and the phase (mitosis and cytokinesis).
Interphase: The most active phase where the cell carries out normal functions. (growth), (DNA replication resulting in sister chromatids), and (preparation for mitosis).
Mitosis: The division of the nucleus into two genetically identical daughter nuclei, involving four stages: Prophase, Metaphase, Anaphase, and Telophase.
Prophase: Chromosomes undergo supercoiling to become visible; the nuclear envelope breaks down and spindle fibers begin to form from microtubule organizing centers ().
Metaphase: Spindle fibers attach to the centromeres of each chromosome; chromosomes align along the equator (metaphase plate) of the cell.
Anaphase: Centromeres divide and spindle fibers contract, pulling sister chromatids toward opposite poles; once separated, they are considered individual chromosomes.
Telophase: Chromosomes reach the poles and uncoil; nuclear membranes reform around each set of chromosomes, and the spindle apparatus disappears.
Cytokinesis: The division of the cytoplasm. In animal cells, a cleavage furrow forms via a contractile ring of actin and myosin. In plant cells, vesicles fuse to form a cell plate, eventually becoming a new cell wall.
Cyclins: A group of proteins that regulate the cell cycle by binding to cyclin-dependent kinases (), which then phosphorylate target proteins to trigger specific cell cycle stages.
Oncogenesis: The process by which normal cells turn into cancer cells due to mutations in proto-oncogenes. These mutations can be triggered by mutagens such as radiation or certain chemicals.
📐Formulae
💡Examples
Problem 1:
In a sample of onion root tip cells, cells were found to be in prophase, in metaphase, in anaphase, and in telophase. Calculate the Mitotic Index () for this tissue.
Solution:
Explanation:
The Mitotic Index is calculated by dividing the sum of all cells in any stage of mitosis () by the total number of cells observed. The result indicates that of the cells are currently dividing.
Problem 2:
If a diploid cell () contains chromosomes, how many DNA molecules and how many chromosomes are present at the end of the phase and after anaphase?
Solution:
End of phase: chromosomes, DNA molecules. After Anaphase: chromosomes, DNA molecules.
Explanation:
During the phase, DNA replication occurs. Each chromosome now consists of two sister chromatids ( chromosome = DNA molecules). In anaphase, sister chromatids are pulled apart and are then defined as individual chromosomes, thus doubling the chromosome count temporarily within the single cell until cytokinesis is complete.