• Cells have distinct phases of growth, reproduction and normal
functions
• The cell cycle
has four main
stages
– Regular
pattern of
growth, DNA
replication,
and cell
division
• Main Stages- gap 1,
synthesis, gap 2, and mitosis
– Gap 1 (G₁): cell growth and
normal functions
– DNA synthesis (S): copies DNA
– Gap 2 (G₂): additional growth
– Mitosis (M): includes division
of the cell nucleus (mitosis)
and division of the cell
cytoplasm (cytokinesis)
• Do all cells divide at the
same rate?
• Why do you think skin cells
only have a life span of
about 2 weeks?
• Some cells divide
only rarely- G₀
phase
•
Cell size is limited
– Volume increases faster than surface area
•
•
•
•
Which cell has the largest surface area?
Which cell has the largest surface area-to-volume ratio?
Which has the larger ratio of surface area to volume, a tennis ball or a soccer ball?
Why is a suitable cell size important?
• Cells divide during mitosis and cytokinesis
• Chromosomes condense at start of mitosis
• DNA wraps around proteins
(histones) that condense it
• Chromatin- DNA plus proteins
• Chromatid- half of a
duplicated chromosome
• Centromere- hold sister
chromatids together
• Telomeres- found on end of
DNA molecules and protect
them
• Mitosis and cytokinesisproduce two genetically
identical daughter cells
• Interphase prepares the
cell to divide
– DNA is duplicated
• Mitosis divides the cell’s
nucleus in four phases
– Prophase, Metaphase,
Anaphase, Telophase
• Mitosis 1 video
• Mitosis divides the cell’s nucleus in four phases
– Prophase- chromosomes condense and spindle fibers form,
nuclear envelope breaks down
• Metaphase- chromosomes line up in the middle of
the cell
– Chromosomes are connected to spindle fiber
• Anaphase- sister
chromatids separate to
opposite sides of the
cell
• Telophase- new nuclei
form and chromosomes
begin to uncoil
– Two new nuclear
envelopes will form
• Cytokinesis- division of
cytoplasm
– Usually occurs at same
time of telophase
• Cytokinesis differs in
animal and plant cells
– Animal- membrane
pinches closed
– Plant- cell plate forms
• Mitosis 2 Video