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The Cell Cycle
Review
Text – page 201
Animal Cell
Plant Cell
Cell Size Limitations
 Text - Ch 7
 Wide variety of sizes and shapes
 RBC
(1 um) to nerve cells (1 m)
 Egg yolk (ostrich)
 Most are 2-200 um
 cell scale
Diffusion limits cell size
 Selectively permeable membrane
I.e. Nutrients in and wastes out
 Becomes slow and inefficient as
distance between organelles and
membrane increases
DNA limits cell size
 DNA supports protein needs of cell
 More than one nucleus
Surface area-to-volume ratio
 As cell grows the volume increases faster
than the surface area
 If cell doubles
 Nutrients
requirements increase 8-fold
 Waste also increases 8-fold
 Surface area only increases 4-fold
 The cell, therefore, will either starve to
death or be poisoned.
Cell Reproduction
 Cells divide before they become too
large.
 Recall: all cells come from pre-existing
cells
The Redi Experiment
Pasteur’s
swan neck
flask
experiment
Chromosomes Discovered
 Become visible just before cell division
 Vanish soon after cell division
 Contain DNA
 Chromosome (X’me) number varies
 Humans
46
Chromosomal Structure
 Exist as chromatin most of cell’s life
 Long
strands of DNA
 Wrapped around proteins called
histones
 Appear as beads on a string
 Reorganize before cell division
The Cell Cycle
Def’n: Sequence of growth and division
 about 3 000 000 cells die in your body
every minute.
 Cells die due to damage or when they
don’t get enough food or oxygen.
 Regeneration - Healing of damaged tissue
or the replacement of body parts is called
regeneration.
Mitosis
 Mitosis is responsible for the cell
division that all plants and animals
require for:


Growth
Repair (and replacement) of body cells
Characteristics of Mitosis
 Always only one parent
 Offspring identical to parents (fast,
convenient, safe)
I.e. asexual reproduction
Phases of the Cell Cycle
IPMAT
Interphase
 Most of cell’s life

Longest and busiest phase
 DNA in thin strands called Chromatin
replicate.
 Chromatin coils up to form double
stranded X’mes.
Interphase
 A Centromere connects the original
chromatin with its identical replicate.
 The cell has a complete extra copy of
DNA.
http://www.pitt.edu/~super1/lecture/lec19281/004.htm
Chromosome
Prophase
Prophase
 Duplicate DNA is easily seen under
microscope.
 Nucleolus and Nuclear Membrane
disappear.
 Centrioles move to opposite sides of the
cell.
 Spindle fibres (like a scaffold) grow out of
each centriole and attach to centromere.
Metaphase
http://www.madsci.org/posts/archives/2000-11/974783537.Cb.1.jpg
Metaphase
 Spindle fibres pull on centromeres
 double X’mes pulled into a line across
the middle
 Shortest phase
Anaphase
Anaphase
 Spindle fibers contract fully
 Centromeres are pulled apart
 1 copy of DNA goes to each side of the
cell
Telophase
Telophase
 A complete set of X’mes arrives at each




centriole.
Two daughter cells have formed
Spindle fibers disappear
Nuclei/nucleoli and nuclear membrane
form.
X’mes uncoil into thin chromatin.
Telophase (cont’d)
 Animal cells
 Cleavage furrow – cytokinesis (cell
membrane pinches off)
 Plant cell
 A cell plate grows across the cell
Parent Cell
Daughter Cells
Animations
 NOVA Online | Life's Greatest Miracle | How
Cells Divide: Mitosis vs. Meiosis (Flash)
 mitosis = cell division
 hybridmedical-mitosis
 hybridmedical-mitosis youtube
 DNA repl'n & spindle