Mitosis
 Why do cells need to
divide?
Terms To Know
 Diploid
 Having two sets of chromosomes (one from each parent)
 Haploid
 Having one set of chromosomes
 Somatic Cell
 Normal body cell
 Diploid
 2 sets of chromosomes = 46 chromosome (humans)
 Gamete
 Reproductive cell
 Haploid
 1 set of chromosomes = 23 chromosomes (humans)
 Zygote
 Cell formed when two gametes fuse; will develop into morula, blastula,
gastrula, embryo after many rounds of mitotic cleavage
 Mitosis
 Division of the nucleus; maintains
chromosome number
 DNA replicated followed by 1 round of division
 Parent cell  2 genetically ID daughter cells
 Meiosis
 Reduction division of the nucleus
 DNA replicated followed by 2 rounds of
division
 1 cell  4 genetically DIFFERNET cells with
half the # of chromosomes
Diploid
 Di= two sets
 Literally means “cells that
contain 2 sets of
chromosomes”
 Cell that contains both sets of
homologous chromosomes
 Cell contains
 2 complete sets of
chromosome
 2 complete sets of genes
 Represented by 2N
Haploid
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Means “one set”
Refers to cells that
contain only one set of
chromosomes
Gametes
(reproductive cells)
Represented by N
Created by MEIOSIS
Eukaryotic Cells
 Nucleus contains genetic info (DNA)
 MUST replicate all this genetic info to create identical daughter
cells
 All your body cells are genetically identical
 Exception: GAMETES (reproductive cells)
 All cells derived from ONE cell ZYGOTE
 Formed when 2 gametes from your parents fuse
Why Cells Divide (Mitosis)
 Growth
 Replacement of cells and repair of
tissues
 Asexual reproduction
 Cloning
Growth
 Parent cell divides into two
identical daughter cells
 CLONES
 Same in number of
chromosomes and arrangement
of genes on chromosomes
 Allows unicellular zygotes to
develop into multicellular
organisms
 Two types of growth:
 Over entire body
(development in animals)
 Over specific regions
(meristematic growth in plant
cells)
Replacement of Cells & Repair
of Tissue
 Cells constantly dying
 Life spans of different types of
cells (even in same organism)
vary
 Cells must be replaced w/
identical cells
 Regeneration of re body parts
in some organisms
 Starfish
 Salamander
Life Span of Some Human
Cells
Cell type
Life span
Cell division
Lining of esophagus
2-3 days
Can divide
Lining of small intestine
1-2 days
Can divide
Lining of the large
intestine
6 days
Can divide
Red blood cells
Less than 120 days
Cannot divide
White blood cells
10 hours to decades
Many do not divide
Smooth muscle
Long-lived
Can divide
Cardiac (heart) muscle
Long-lived
Cannot divide
Skeletal muscle
Long-lived
Cannot divide
Neurons (nerve) cells
Long-lived
Most do not divide
Asexual Reproduction
 Production of new single species from
one single parent organism
 New individuals are produced from a single
parent without the act of fusion of
gametes
 Occurs in unicellular and multicellular
organisms
 Amobea (unicellular protista)
 “Budding” in Hydra and Plants
(multicellular organism)
 New individuals produced when they bud
off the parent organism in various ways
(Hydra and plants)
 Plants’ vegetative propagation:
Regeneration of new plants from portions of
vegetative organs (“budding”)
 Bud grows from stem of parent plant, eventually
drops off, become individual plant
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Cloning
White blood cells for immune response
B- lymphocytes (B cells)
 Produced in bone marrow
 Comes in contact with invader and it is
activated helper T cell:
 divides into plasma cells (produce
antibodies) and memory cell (long lifespan
to remember invader)
T-lymphocytes (T cells)
 2 types: helper T cells and killer T cells
 Helper T cells activate B cells and killer T
cells
 Activated by macrophage or dendritic
cell that has engulfed invader
 Killer T cells once activated, destroy specific
invaders
 Precursor of T cells produced in bone marrow
and mature into T-cells in thymus
More on immunity in a few weeks….
Recap…
 Cell theory…
1. Cells are the basic structural and functional unit
of life (Hooke)
2. All living things (plants, animals, fungi, bacteria,
protista) are made of cells (Schleiden,
Schwann, Van Leewoehoek)
3. Cells come from pre-existing cells (Rudolf
Virchow, 1855)
Overview
 Types of reproduction
 Sexual Reproduction
 Genetically different
 2 parents
 Takes time to develop,
better chance of survival
 More chance of mutation
 Process begins by making
gametes…Uses MEIOSIS
 Asexual
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Genetically identical
One parent cell
Many offspring very quickly
Less chance of mutations
(by MITOSIS)
DNA
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Blueprint of life, nucleic acid
2 nm wide
Total length of all 46 chromosomes (DNA molecules) in hmnas = 1.8 meters
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Packed into nucleus with a diameter of 6 um
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Chromatin
Granular genetic material, spread out in nucleus of nondividing cells
Exists in 2 forms
 Euchromatin  loosely coiled DNA (DNA is like this
during INTERPHASE)
 Where active genes are located
 Heterochromatin  tightly coiled DNA
 Contain inactive genes
Chromatin is mostly condensed during METAPHASE of
cell cycle
 Makes it easier to separate evenly into 2 new cells
DNA wound around proteins called HISTONES (prevents
tangling)
 Histones are BASIC and can easily interact with
ACIDIC DNA
DNA coils around histones, then super coils, then is further
looped, coiled and packed away creating NUCLEOSOMES
Nucleosome
 Cylindrical in shape
 11 nm wide x 6 nm long
 Composed of 8 histone molecules
 DNA coils around 1 and 2/3 times (147 base pairs)
and then links to next nucleosome
 Nucleosomes line up making a fiber 10 nm wide (fiber
is further coiled)
 Chromosomes
 Condensed genetic material, in
dividing cells
 Made of one molecule of DNA
 Chromatids (sister chromatids)
 One DNA molecule and its
identical copy (during s-phase of
mitosis)
 centromere (“centro-” middle)
 Narrow region found anywhere on
chromatid; place where they are
attached
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NON-dividing cell chromosomes NOT
visible
DIVIDING cell chromosomes visible
 Due to stains give intense color to
chromosomes
 “chromo” = color
 “some” = body
Chromosome number unique to each
species
All Cells Must Reproduce
 Must pass off copies of their genes to
“daughter” cells
 Process precisely controlled
 Cannot lose vital genetic info
 2 parts:
 Nuclear division (mitosis)
 Cell Division (cytokinesis)
Karyotype/Karyogram
 photograph of a
person's
chromosomes,
arranged according to
size
 Created by cutting
individual
chromosomes from a
picture and
rearranging them in
order
 Taken from either a
dividing cell or nondividing cell
 Homologous chromosomes
 The matching pairs of chromosomes in a
Karyotype
 Distinguished by:
 Size
 Shape
 Distinctive banding when stained with certain dyes
 In the original human zygote:
 Two sets of 23 chromosomes
 One set of 23 from mother
 One set of 23 from father
 Autosomes
 Chromosomes 1-22 (excludes sex chromosomes)
 Sex chromosomes
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Not numbered
Determine sex of individual
XX female
XY male
Cell Cycle: Life of a Cell
3 Stages of Cell Cycle
1. Interphase
 90 % of cell’s life, non dividing
 G1 phase
 Grows, makes organelles, does its job (protein factory)
 Cell makes RNA, enzymes, and proteins needed for growth
 @ end commitment made as to whether or not cell will divide
 S phase
 Short
 DNA Synthesis…DNA replicates
 Once it enters S, cell is committed to complete cycle
 G2 phase
 Cell prepares to divide, makes sure it has all important organelles for division
 Sharp increase in production of TUBULIN protein in microtubule  make
up mitotic spindle
 Cell grows in size
 New DNA is checked for any errors
2. M phase
 When the nucleus of the cell divides
3. Cytokinesis
 When the cytoplasm divides
M-Phase
 Growth temporarily stops
 M  mitosis
 Nucleus divides into 2
 After M-Phase  Actual cell divides
 Division of cytoplasm  CYTOKINESIS
Length of Cell Cycle
• Variable
• Depended on 2 things:
1. Type of cell
2. Environmental conditions
• Examples:
• Root tip cells of onion's divide every 20 hrs
• Epithelial cells of human intestines  divide every 10 hrs
Cell Cycle
 There are check points in
G1, S, and G2
 Make sure cell is ready to move
onto the next phase (has all
necessary organelles, copied
DNA, etc.)
 Once the cell has past the
G1 checkpoint, it will
complete the cell cycle
 Some cells stay in the G1
phase all their life (muscle
cell, brain cells)
M-phase
 Mitosis (PMAT)
 Process by which the
nucleus of a cell divides
 One parent cell makes two
identical daughter cells
 Prophase, metaphase,
anaphase, telophase