Download The Cell Cycle

The Cell Cycle
Early Observations
● All living things have a life
cycle
● Cell cycle- a pattern of
eukaryotic cell growth &
division
● Early observations saw 2 stages
○ mitosis (cell division)
○ interphase (not division)
Improved Observations
● Better tools and
observations led to 4
stages.
○ Gap 1 (G1)
○ Synthesis (S)
○ Gap 2 (G2)
○ Mitosis (M)
Gap 1/Growth 1 (G1)
● Cell growth
● Normal cell
function
● Creates organelles
and proteins
● Longest stage of
the cell
Synthesis (S)
● Cell copies its DNA
in the nucleus to
prepare for
division
● 2nd longest stage
of interphase
Gap 2/Growth 2 (G2)
● More normal
functions
● Cell grows for cell
division
● More organelles
made for cell
division
Mitosis (M)
● Division of the cell
nucleus & its contents
● Cytokinesis- divides
the cell’s cytoplasm
○ 2 identical
“daughter cells”
produced
Chemical Checkpoints
● Exist at the ends
of G1 & G2 and in
the middle of
mitosis
● Makes sure that the
cell is ready for
the next stage
Human Cell Cycle
● On average, cells go through the S, G2, & M
stages in 12 hours
● G1 time differs by cell type
○ Shorter for cells that are worn down
quickly or during fast growth
■ embryonic cells
■ stomach cells
■ skin cells
Human Cell Cycle
● G1 differs by cell type
○ Longer G1 for internal organs that have
less wear and tear
■ lung cells
■ kidney cells
■ liver cells
G Zero Stage (G0)
● Cells that rarely divide
but continue with normal
cell function
● No S, G2, or M stages
● Only certain cells have
this stage
○ neurons
○ heart muscle cells