D’YOUVILLE COLLEGE
BIOLOGY 102 - INTRODUCTORY BIOLOGY II
LECTURE # 19
CELL CYCLE, MITOSIS
1. Introduction to Cell Division: cellular reproduction – cell division, a process that precisely duplicates & distributes genetic information (genome) of a ‘parent’ cell to two ‘daughter’ cells, such that offspring are genetically identical to parent (fig. 12 – 2)
• reproduction of unicellular organisms; in prokaryotes, cell division occurs by simple fission (fig. 12 – 12 & ppt. 1)
• proliferation of cells, e.g., growth from zygote to multicellular organism,
regeneration of tissue in healing
• cell renewal systems, e.g. bone marrow, epidermis
2. Organization of Genetic Material:
• chromatin: nucleic acid (usually DNA) combined with protein
(nucleoprotein); dispersed as fine network of fibers in nucleus of eukaryotic cells; chromatin represents the genetic material (genome) of the cell
- supercoiling of nucleoprotein – special histone proteins form spool-like shapes for winding of DNA: nucleosomes, looped domains (fig. 16 – 22 & ppt. 2)
• chromosomes (figs. 12 – 4, 12 – 5 & ppt. 3): supercoiled chromatin organized into threadlike bodies; appear during cell division
- characteristic species # (usually paired); pairs represent two
homologous sets (maternal & paternal = diploid # = 2n)

Bio 102 lec. 19 - p. 2
• chromosome duplication: chromosome # is duplicated prior to cell division producing double-stranded chromosomes; centromere connects sister chromatids
& facilitates spindle attachment (kinetochore) (fig. 12 – 5 & ppt. 3)
• two types of nuclear division: mitosis & meiosis – each involving exquisite maneuvers of chromosomes & each followed by cytoplasmic division (cytokinesis)
3. Cell Cycle (fig. 12 – 6 & ppt. 4): variable length (10 - 30 hr.) in different organisms; interphase followed by mitosis followed by cytokinesis
• interphase: non-dividing stage
- three subdivisions: G
1
, S, & G
2
, characterized by metabolism & growth
- gap periods (G
1
& G
2
) involve mainly respiration & protein synthesis
- period of DNA synthesis (S) involves duplication of genetic material
- cell cycle is controlled by chemical signals (internal or external) that act at
specific checkpoints (figs. 12 – 15, 12 – 16 & ppt. 5)
- internal control is coordinated by enzymes, Cdks (cyclin dependent
kinases); one type of Cdk is activated by Mcyclin & forms MPF (maturation promoting
factor), which initiates mitosis (fig. 12 – 17 & ppt. 6)
- non-mitotic cells stop in G
1 cells (G
0
)
( fig. 12 – 16), e.g. nerve cells, skeletal muscle
- external control is coordinated by growth factors, e.g., platelet derived
growth factor (PDGF) (fig. 12 – 18 & ppt. 7)
- controls are absent or fail in cancer cells - divide uncontrollably (figs. 12 –
19, 12 – 20, ppts. 8 & 9)

Bio 102 lec. 19 - p. 3
4. Mitosis: (figs. 12 – 7, 12 – 11, p. 245, ppts. 10, 11, 14 & 15)
• prophase: duplicated centrosomes separate & chromatin condenses
(supercoiling) into visible chromosomes (inactive in gene expression)
- radiating microtubules emanate from migrating centrosomes
• prometaphase: nuclear envelope & nucleoli disperse; polar (non-kinetochore)
& chromosomal (kinetochore) microtubules establish spindle apparatus (figs. 12 – 8,
12 – 9, ppts. 12 & 13)
• metaphase: chromosomes assemble in equatorial ring, each doublestranded & attached by kinetochores to a spindle fiber from each pole
• anaphase: centromeres divide (separation of sister chromatids); spindle fibers pull chromosomes (now single-stranded) to opposite poles
• telophase: reversal of prophase; chromatin disperses; interphase nuclear morphology restored; cytokinesis begins
• cytokinesis (fig. 12 – 10 & ppt. 16): animal cells develop equatorial cleavage
furrow (directed by microfilaments); plant cells develop equatorial cell plate (new cell wall)