Cell Cycle and Division Basics
The cell cycle consists of Interphase followed by mitosis and cytokinesis. During Interphase, cells prepare for division through three phases: G1 (organelles duplicate, cell grows), S (DNA replication transforms chromatins into chromosomes), and G2 (enzymes for cell division are produced).
Mitosis divides the nucleus through four key phases. In Prophase, chromosomes condense, centrosomes with centrioles duplicate, and the nuclear membrane disappears. During Metaphase, chromosomes align at the cell's center as microtubules attach to proteins called kinetochores. Anaphase involves the separation of sister chromatids pulled to opposite sides, while in Telophase, chromosomes reach opposite poles and begin reforming nuclear membranes.
Cytokinesis (actual cell division) differs between cell types. Animal cells form a cleavage furrow using a contractile ring of microfilaments to pinch the cell in two. Plant cells instead create a cell plate from Golgi vesicles that fuses with the cell membrane, eventually forming the middle lamella and new cell walls.
Quick Tip: Remember the difference between chromosomal forms! Chromatin is the loose form of DNA, which condenses into chromatids. Sister chromatids are identical DNA copies connected by a centromere, while homologous chromosomes are matching pairs carrying genes for the same traits.
Understanding the difference between haploid cells (23 chromosomes in humans, found in gametes) and diploid cells (46 chromosomes arranged as homologous pairs, found in body cells) is crucial for grasping how genetic information passes from one generation to the next.
