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Friday in Biology
Get out journal
 Pick up scissors and glue

First page of Journal
____your name’s __________
Biology Journal
Biology Wikipage
http://willimon-phs-biology.wikispaces.com/
THE CELL CYCLE and Mitosis:
Cells at Work!!
Review: DNA &
Chromosomes
DNA – the molecule that carries the
genetic information
Ex. The toilet paper
Gene – a section of DNA that codes
for a protein/trait
Ex. A small piece of toilet paper
Histone – Proteins that the DNA
wraps around to form chromosomes
Ex. The toilet paper roll
Chromosome – a long DNA molecule
found in the nucleus
Ex. The toilet paper on the toilet
paper roll
Chromosome
Structure
Sister
chromatids –
duplicated
chromosomes
that are
attached to each
other
Centromere –
narrow waist
where sister
chromatids are
attached
Chromosome
Structure
Telomeres – ends
of chromosomes
that protect DNA
from damage
(hard hats)
Kinetochores –
disc-shaped
proteins that
attach
chromosomes to
the spindle
(handles)
Chromosomes vs. Chromatin
Chromosomes
Chromatin
-Toilet paper on the
toilet paper rolls
-Organized for
distribution
(information cannot
be used)
-Mitosis
-large pile of toilet
paper unwound off
the roll
-information in DNA
can be used by cell
-Interphase
What is the cell cycle?
 Continuous
sequence of growth and division
of a cell. 2 parts: Interphase & Mitosis
 Busiest and longest section is INTERPHASE
 After DNA is replicated (during Interphase),
mitosis can begin
Cell Cycle
Interphase: first phase of
Cell Cycle
G1 phase – cell grows, makes proteins
and other products, and does its cell
business
 S phase – “synthesis” phase, when
chromosomes (DNA and histone proteins)
are replicated
 G2 phase – cell prepares for division

Centrosomes and centrioles replicate
 Proteins associated with division accumulate

Cell Cycle – Mitotic Phase

Mitosis –
division of
the nucleus
and the
chromosom
es within it

Cytokinesis
– division of
the
cytoplasm
What is Mitosis??
Part of the cell cycle
 Nuclear cell division during which
chromosomes are equally distributed
to the 2 identical daughter cells that
are formed
 Results in growth
 Continuous process
 4 stages

Stage 1: Prophase
•Chromatin coils up into
chromosomes
•Nucleus begins to
disappear
•Centrioles migrate to
opposite ends of cells
and spindle forms
Stage 2: Metaphase
•Chromosomes attach
to spindle fibers
•Chromosomes line up
along the equator of
the spindle
•Very short phase
Stage 3: Anaphase
•sister chromatids
separate
•Centromeres split
apart
•Chromatids are
pulled to opposite
poles of the cell
Stage 4: Telophase
•chromatids reach the
poles
•Chromosomes unwind
and spindle breaks
down
•New nuclei form
around each set of
chromosomes
•Plasma membrane
separates
Cytokinesis: Division of the
cytoplasm



Animal cell
Plasma membrane
pinches along
equator
Forms a cleavage
furrow that
deepens until the
cell is pinched in
two



Plant cell
Plasma membrane
does not pinch in
b/c of rigid cell
wall
Cell plate forms at
the equator that
divides the
cytoplasm
I Pour Milk And Tea





I—Interphase “The Xerox phase”
P—Prophase “Cell PREPARES and
chromosomes become visible”
M—Metaphase “The chromosomes line
up in the MIDDLE”
A—Anaphase “The chromosomes pull
APART”
T—Telophase “The TWO identical
daughter cells separate”
Purpose of Mitosis (Cell Division)
DNA makes an exact copy of itself so
that AFTER mitosis, the 2 new daughter
cells will be identical.
 The process of mitosis ensures that
each new cell receives the correct
number of chromosomes for that
organism (Humans = 46 chromosomes)
 23 from mom, 23 from dad
 When both sets of chromosomes are in
a cell, it is said to be diploid.
 All somatic (body) cells are diploid.

Cell Cycle Regulation
Cell Cycle
Regulation
Internal check
points
External cues
Cyclin and
kinases (proteins)
that are made
during G2 phase
Cancer
Cancer cells do
not respond to
cell cycle signals
– they divide
continuously
divide or they
stop and start
dividing at
random places in
the cell cycle