HL 1 Biology

2.5a Cell Cycle

Cell cycle: cell division of pre-existing cells occur in all living organisms, to produce new cells.

  • In prokaryotic cells: Binary fission (asexual reproduction)
    • replication of single circular chromosome
    • the 2 copies shift to opposite ends of the cell
    • cytokinesis: division of cytoplasm, produce two cells
  • In eukaryotic cells: Mitosis (form 2 genetically identical nuclei)
    • Before mitosis= DNA replication: conversion of all chromosomes from single DNA molecule into 2 identical DNA molecules(chromatids)
    • 1 chromatid passes to each daughter nucleus
        • thus, daughter nuclei genetically identical to each other + to original parent nucleus
    • 2 daughter cells can each receive one nuclei, since mitosis occurs before cytokinesis (split in cytoplasm)

Interphase and Cell Cycle

  • Cell cycle: events between a cell division and in eukaryotic cell; roughly divided into interphase and cell division

Interphasean active period in cell’s life when many metabolic reactions occur (protein synthesis, DNA replication and increase in number of mitochondria and/or chloroplasts) and cell grows larger

  • indefinite; not a preparation for mitosis; some cells stay in interphase
  • 3 phases: GI phase, S phase and G2 phase
    • GI phase: period of growth, DNA transcription + protein synthesis; cellular contexts except chromosomes are duplicated
    • S phase: each chromosomes(all DNA in nucleus) are duplicated
    • G2 phase:  preparation for mitosis

Mitosis: process when nucleus divides to form 2 genetically identical nuclei

  • involved whenever cells with genetically identical nuclei are necessary in eukaryotes:
      • during growth, embryonic development, tissue repair and asexual reproduction
  • Divided into four phases:prophase, metaphase, anaphase and telophase 
  • Start interphase after cell completed mitosis and cytokinesis


1 (a01:00 = most DNA replication during S phase

(b) 05:00 and about 03:00

2) G1: when most of the increase in cell size is occurring

3) The timing of the cell cycle in Emiliania huxleyi is an adaptation to take advantage of light resources as the phytoplankton produce energy from photosynthesis with the sun light and during the night, would use these stored energy for processes such as cell division and mitosis. As these cells take advantage of the light during the day, the relative cell size increases whereas during the night the cell size decreases because of the division in the cell.  Since the cells have already underwent cell division, these new cells would be able to use the light to produce energy once again.

One thought on “2.5a Cell Cycle

  1. Grade 7 A consistent and thorough understanding of the required knowledge and skills, and the ability to apply them almost faultlessly in a wide variety of situations.

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