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Cell Reproduction/Mitosis
Chapter 12
What you need to know!
• Mitotic Cell division results in
genetically identical daughter cells
• The mitotic phase alternates with
interphase in the cell cycle
Overview
I. Cell Division Overview
II. The Cell Cycle
III. Mitosis – nuclear
division/cytokinesis
IV. Stages of Mitosis
Cell Division
• Life depends on the ability of cells to
reproduce/copy
• Cell Division = 1 cell divides into 2
• Unicellular organisms cell division =
reproduction
– Prokaryotes, Protists
– Bacteria = binary fission
Cell Division
•
Multicellular organisms cell division =
growth and development, repair and
replace.
– Protists, fungi, plants and animals
•
2 types of multicellular organism
cells:
1. Somatic Cells: Body cells of an
organism that do all the daily
function of the organism
2. Germ Cells: reproductive cells (eggs
and sperm)
Cell Cycle
• G0: the cell spends its life working and
growing (i.e. breaking down sugars, making
ATP, enzymes)
• Sometimes a cell will prepare to divide
– 1 mother cell  2 daughter cells
• Interphase
– G1 (Gap1): Growth, development, organelle
production, etc. Cell must enter reproduction (S
phase) or not (G0)
– S (Synthesis): DNA replication
– G2 (Gap2): continued growth and preparation
for division (centrosomes/centrioles duplicate)
Cell Cycle
• Mitosis (M): nuclear division
• Cytokinesis: division of cytoplasm
and cell membrane/cell wall
DNA
• Chromatin: spread out DNAprotein complex. In Eukaryotes
the proteins are histones. Human
cells have 3 billion base pairs.
• Chromosomes: condensed
strands of DNA distinct in number
and length for each organism.
One chromosome is made up of
30 to 150 million base pairs.
DNA
• Humans have 46 chromosomes (23
pairs).
• Each chromosome contains a few
thousand genes that code for cellular
proteins
DNA
• Diploid indicates that our somatic
(body) cells have 23 pairs of
chromosomes (2n)
• Haploid indicates that our gametes
(sex cells) have 23 chromosomes (1n
or n)
Mitosis: Division of the Nucleus
• Problem: distribution of one exact
copy of each of their chromosomes to
each new cell.
• Each chromosome contains
thousands of genes, each necessary
to the proper functioning of the
organism.
• Humans have ~120,000 genes spread
over 46 chromosomes in each
somatic cell.
Mitosis
• During Mitosis all access to the DNA
stops as chromatin coils up and
condenses into visible chromosomes
• Each replicated chromosome is
composed of 2 identical parts (sister
chromatids) held together by a
centromere.
Mitosis
• Sister chromatids are pulled apart
during mitosis, and partitioned into 2
daughter cells
• Result of mitosis & cytokenesis: 2
daughter cells genetically identical to
the parent cell.
IV. Stages of Mitosis
• Prophase: Chromosomes condense,
centrosomes are pushed apart by
growing spindle, nuclear envelope
disintegrates
Stages of Mitosis
• Prometaphase: the 2 centromeres of
each chromosome attach to one
kinetochore spindle fiber;
centrosomes move to opposite poles
Kinetochore
spindle fiber
Non Kinetochore
spindle fiber
Stages of Mitosis
• Metaphase: Chromosomes line up at
the metaphase plate (equator);
centrosomes are at opposite poles
Stages of Mitosis
• Anaphase: Chromosomes separate
due to shortening of kinetochore
spindle fibers; cell elongates due to
lengthening of non-kinetochore
spindle fibers
Non Kinetochore
spindle fiber
Kinetochore
spindle fiber
Stages of Mitosis
• Telophase: Chromosomes
immediately uncoil and resume
transcription activities; spindle
proteins disassemble; nuclear
envelope reassembles
Mitosis Animation
• http://vcell.ndsu.nodak.edu/animations
/mitosis/movie-flash.htm
Cytoskeleton Creates
Chromosome Migration
•
•
Spindle fibers are microtubules
made of tubulin proteins that are
always present in the cytoplasm
Enzymes assemble and
disassemble spindle fibers
Centromere region contains
1. Centromere protein clamp, holding
the 2 sister chromatids together;
deactivated during anaphase
2. Kinetochore motor protein; 1 on each
sister chromatid
Kinetochore microtubule
• Several microtubules attach to each
kinetochore motor protein
• Motor protein starts moving (walks
along the spindle fibers); kinetochore
microtubules shorten, pulling
chromsomes (at the metaphase plate)
apart
– ATP hydrolysis powers the motion
Non Kinetochore Microtubules
• Microtubules lengthen, pushing the
two poles apart (cell expands)
Non Kinetochore
spindle fiber
Kinetochore
spindle fiber
Cytokinesis
Animal:
• Cleavage furrow
– Made by microfilaments (actin fibers)
– A drawstring around the middle of the
cell
• Cell pinches off into 2 daughter cells
Mitosis & Cytokinesis in
Plant Cells
• Plants have centrosomes w/out
centrioles
• No cleavage furrow
– plant cells cannot separate due to cell
wall
• Cell plate grows through divided cell
Duration of the Cell Cycle
• Prokaryotic Cells – 20 minutes
• No DNA/Histone complex + fast DNA
replication (500 NT/sec)
• No spindle fibers, no mitosis
• 2 DNA rings are attached to 2 spots of
the plasma membrane which grows
apart
• 1 plasmid
Duration of the Cell Cycle
• Eukaryotic Cells – 12-48 hrs
• Longest phase of the cell cycle is
interphase
• Longest phase of mitosis is prophase
Frequency of Cell Cycles
• Depends on cell type:
Cell type
Life span/frequency
Esophagus, epidermis 2-3 days
Small intestine
1-2 days
Large intestine
6 days
Red blood cells
3 months
White blood cells
Up to 10 years
Nerve cells
Lifetime (G0)