Lectures 21 and 22: The regulation and mechanics of cell division • Today - cell cycle (regulation of cell division) – Cell proliferation – The eukaryotic cell cycle – Measuring the cell cycle – Models of the cell cycle: from fungi to frogs – The cell cycle is regulated by cyclin-dependent kinases • Next time - mechanisms of cell division
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Lectures 21 and 22: The regulation and mechanics of cell division Today - cell cycle (regulation of cell division) –Cell proliferation –The eukaryotic.
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Lectures 21 and 22: The regulation and mechanics of cell division
• Today - cell cycle (regulation of cell division)
– Cell proliferation
– The eukaryotic cell cycle
– Measuring the cell cycle
– Models of the cell cycle: from fungi to frogs
– The cell cycle is regulated by cyclin-dependent kinases
• Next time - mechanisms of cell division
A cell cycle is one round of growth and division
mitosis
cytokinesis
Growth and division must be carefully regulatedUnregulated cell growth = cancer
Cells only come from pre-existing cells
Division occurs in “M-phase:” “mitosis” and “cytokinesis” (<1 hr)
Most cell growth occurs during “G1” (6-20+ hrs; duplicate organelles, double in size)
DNA replication occurs during “S-phase” (4-10+ hrs)…
“G2” prepares cells for division (1-6+ hrs)…
G1+S+G2=“Interphase”
Division = “M-phase”
A “typical” cell cycle for animal cells is 24-48 hrs long, but varies…
The eukaryotic cell cycle is partitioned into four “phases”
ECB 18-2
2C(unreplicated DNA,diploid chr #)
4C(DNA replicated,diploid chr #)
4C 2C
2C 4C
Cell cycle times vary
Adapted from MBoC figures17-5 and 17-6
DNA content (arbitrary units)1 2
Num
ber
of
cells
Cells in G1
Cells in G2/M
Cells in S
Can determine phase of cell cycle from DNA content
Where are cells in G1, S, G2 and M on plot?
Which phase has most cells in it?Lasts longest?
ECB 18-2
Transition from one phase to another is triggered
We will take a historical perspective to ‘triggers’
Regulating the eukaryotic cell cycle: studies in four model organisms
• Marine invertebrates:– Surf clam (Spisula)
– Sea urchins and starfish
• Frog eggs and embryos:– Rana pipiens (Northern leopard frog)
Apoptosis: A tale of tadpole tails and mouse pawswhat do they have in common?
Both processes involve “programmed cell death (apoptosis)”
Tadpole tails are resorbed during metamorphosis
ECB figure 18-19
Paws develop from “paddles”
ECB figure 18-18
ECB - “programmed cell death is a commonplace, normal, and benign event. It is the inappropriate proliferation and survival of cells that presents real dangers”
Necrosis (cell death following injury) often results in lysis, spilling the contents into the surrounding space and causing inflamation
During apoptosis (“programmed cell death”), cells remain intact and condenseCorpses of apoptotic cells are often engulfed by their neighbors or specialized phagocytic cells
Apoptosis is visibly distinct from necrosis
ECB 18-20
Apoptosis is mediated by a “caspase cascade”“Caspases” are proteases; inactive precursors activated by proteolysis
Presence of suicide signals and/or withdrawal of needed survival factor activates first caspase in cascade