1. 10/20/08
Lecture 18 – Cell Cycle 1
 DNA replication: DNA is distributed equally to the two daughter cells.
 Functions of cellular replication
1. Reproduction
 single celled organisms
2. Growth and development
 single celled –cell devision→ multicellular organism
 zygote (fertilized egg)
3. Repair and maintenance
 wounds
 many cells divide regularly
 The prokaryotic cell
 Consist of the bacteria and archeae kingdoms.
 Divide by binary fission.
 Replication takes place at the origin.
 Two origins → each move to the opposite ends of the cell.
 Cell membrane grows across the cell.
 The eukaryotic cell
 Each chromosome has a DNA molecule.
 Eg. Humans – 46 chromosomes, 46 DNA molecules.
 In a cell that is not dividing, the DNA is stretched out into a long thin fiber (chromatin).
 During cellular division, the DNA folds into the chromosome shape.
 Diploid (2n): Having two of the basic sets of chromosomes in the nucleus.
 Haploid (n): A single set of chromosomes (half the full set of genetic material).
 All cells are diploid except gametes.
 The cell cycle: the process of a dividing cell.
 Overview
 The phases
 Mitotic phase (M phase)
 Mitosis (division of the nucleus).
 Positioning of the chromosomes into two daughter cells.
 Cytokinesis (physical division of the cell).
 Interphase (between division)
 G1 phase – Gap I
 S phase (DNA replicated)
 G2 phase – Gap II (getting ready for the next M phase)
 In-depth (in the animal cell)
 G2 phase
 Nuclear envelope intact.
 Nucleoli present.
 Centrosome has replicated.
 Chromosomes are duplicated (double-stranded).
 Prophase
 Chromosomes condense.
 Spindle of the microtubules being to form.
 Centrosome move to the poles of the cell.
 Nucleoli beings to disappear.
 Prometaphase
 Nuclear membrane breaks down.
 Spindle microtubules interact with each chromosome at the centromere (some don't interact)

2.  Kinetochore (where microtubules connect with the chromosome).
 Metaphase
 Centrosome are at the poles
 Chromosome line up at the equator of the cell
 Spindle is fully formed
 Anaphase
 Sister chromatids separate at the centromere.
 Single-stranded chromosome.
 A set moves of chromosomes move to each pole of the cell.
 Cell elongates for cytokinesis.
 Telophase
 Two new nuclei form (nucleoli and nuclear membrane)
 Chromosomes decondense (stretch out)
 Cleavage furrow (cytokinesis: cells pinch into two).