2. Mitosis
 Why do cells need to divide?

4. Recap…
 Cell theory…
 Cells are the basic structural unit of life
 Cells are the functional units of life
 Cells come from pre-existing cells

5. Overview
 Why do cells need to divide?
 Repair, growth, development
 Types of reproduction
 Sexual
 Genetically different
 2 parents
 Takes time to develop, better chance of survival
 asexual
 Genetically identical
 One parent
 Many offspring very quickly

6. DNA
 Blueprint of life, nucleic acid
 Chromatin
 Granular genetic material, spread out in
nucleus of non-dividing cells
 Chromosomes
 Condensed genetic material, in dividing cells
 Sister chromatids
 Identical copies of Chromosomes joined by
a centromere (“centro-” middle)

9. Humans
 46 chromosomes
 46 sister chromatids
 One from your mom, one from your dad

10. Cell Cycle: Life of a Cell

11. Cell Cycle
 Interphase
 90 % of cell’s life, non dividing
 G1 phase
 Grows, makes organelles
 S phase
 DNA Synthesis…DNA replicates
 G2 phase
 Cell prepares to divide, makes sure it has all important
organelles for division
 M phase
 When the cytoplasm and nucleus of the cell
divides

12. 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)

13. Regulators of Cell Cycle
 Cyclins
 Protein that regulates the timing of the cell
cycle in eukaryotic cells
 Levels of cyclins rise and fall throughout the
cell cycle
 Cyclin-dependent Kinases (cdks)
 Enzymes that are activated when they bind
with cyclin and they make the cell cycle
continue

15. Regulators
 Internal
 Factors within the cell that control cell cycle
 Cyclin and CDKs
 Allow cell cycle to proceed only when certain processes
have occurred
 Replication of chromosomes
 Chromosome Attachment to spindle before anaphase
 External
 Factors Outside the cell
 Growth factorsmolecules that bind to cell surface that
signal cell to divide
 Similar cells have molecules that have opposite effect so
that when it becomes to crowded, cells stop dividing

20. M-phase
 Consists of mitosis and
cytokinesis
 Mitosis
 Process by which the
nucleus of a cell divides
 One parent cell makes two
identical daughter cells
 This is how organisms
repair tissue and grow and
develop
 Cytokinesis-division of the
cytoplasm

21. Depending on cell type…
 Mitosis can take a few minutes or a few
days
 Muscle cells (non-dividing)
 Nerve cells (non-dividing)
 Skin cells (divide all the time)
 Digestive Tract cells (divide all the time)

22. 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 6 days Can divide
intestine
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

23. Prophase
 50-60% of time
 Chromosomes become visible
 Centrioles develop in cytoplasm near nuclear
envelope
 Centrioles separate and migrate to opposite ends
of nuc. Env.
 Centrosome
 Region where Centrioles are found
 Organize the “spindle”
 Fan like microtubule structure that helps separate
chromosomes
 Plants do NOT have Centrioles

26. End of prophase
 Chromosomes coil together tightly
 Nucleolus disappears
 Nuclear envelope breaks down

27. Metaphase
 Few minutes
 Chromosomes line up in middle (M in
metaphase MIDDLE)
 Microtubules connect centromere of each
chromosome to the 2 poles of spindle

31. Anaphase
 Centromeres joining sister chromatids
separate and become individual
chromosomes
 They are dragged by fibers to opposite
poles
 Ends when chromosomes stop moving

35. Telophase
 Opposite of prophase
 Condensed chromosomes disperse into
tangle of material
 Nuclear envelope reforms
 Spindle breaks apart
 Nucleolus becomes visible
 At the end 2 identical nuclei in one cell

39. Cytokinesis
 Happens at the same time as Telophase
 Division of cytoplasm
 Animal Cells
 Cell membrane drawn inward until it pinches
off and forms 2 id daughter cells
 Plant Cells
 Cell plate forms between nuclei
 Cell Plate develops into separate membrane
 Cell wall appears

45. Regulators of Cell Cycle
 Cyclins
 Protein that regulates the timing of the cell
cycle in eukaryotic cells
 Levels of cyclins rise and fall throughout the
cell cycle
 Cyclin-dependent Kinases (cdks)
 Enzymes that are activated when they bind
with cyclin and they make the cell cycle
continue

46. Regulators
 Internal
 Factors within the cell that control cell cycle
 Cyclin and CDKs
 Allow cell cycle to proceed only when certain processes
have occurred
 Replication of chromosomes
 Chromosome Attachment to spindle before anaphase
 External
 Factors Outside the cell
 Growth factorsmolecules that bind to cell surface that
signal cell to divide
 Similar cells have molecules that have opposite effect so
that when it becomes to crowded, cells stop dividing

47. MEIOSIS

48.  Gregor
Mendel
 1822
 Austrian monk
 University of
Vienna
 In charge of
the Garden

49. What Gregor Mendel
Knew…
 Each organism must inherit a single copy
of every gene from each of its “parents”
 Each of the organisms gametes must
contain just one set genes
 When gametes are formed, there must be a
process that separates the 2 sets of genes
so each gamete gets one set

50. Karyotype
 A photograph of a organism’s
chromosomes, arranged according to
size

55. Chromosome Number
 Homologous chromosomes
 Chromosome that has a corresponding
chromosome from the opposite-sex parent
 Fruit fly has 8 chromosomes
 4 from mom
 4 from dad

56. Diploid
 Di= two sets
 Cell that contains both sets of homologus
chromosomes
 Cell contains
 2 complete sets of chromosome
 2 complete sets of genes
 Number of chrms in diploid cell represented
by 2N
 For Drosophilia (fruit fly) 2N=8
 Mendel said:
 Each adult cell contains two copies of each gene

57. Haploid
 Means “one set”
 Refers to cells that contain only one set
of chromosomes
 Gametes (sex cells)
 Represented by N
 Drosophilia fruit fly
 N=4

58. How are
haploid (N)
gametes made
from diploid
(2N) cells?

59. Meiosis
 Process of reduction division in which the
number of chromosomes per cell is cut in
half through the separation of
homologous chromosomes in a diploid
cell

60. Meiosis
 2 distinct stages
 Meiosis I
 A diploid cell enters here
 Meiosis II
 At the end of this, the diploid cell that
entered meiosis has become 4 haploid cells

63. Meiosis I
 Before meiosis 1, each chromosome is
replicate
 Then they divide like in mitosis
 What happened in mitosis?
 PMAT
 Tetrad
 STRUCTURE MADE WHEN EACH
CHROMOSOME PAIRS UP WITH ITS
HOMOLOGOUS CHROMOSOME
 4 CHROMATIDS IN A TETRAD

64. Prophase 1
 Each chromosome pairs with its
homologous chromosome making a
tetrad
 As they pair up in tetrads, chromosomes
exchange portions of their chromatids in
the process …. CROSSING OVER

65. Crossing Over

67. Metaphase1
 Spindle fibers attach to chromosomes
Anaphase 1
• The spindles pull homologous
chromosomes apart to opposite
poles/ends
Telophase 1
• Nuclear membranes form and cell
separates into two new cells

69. Now what do we have?
 2 new daughter cells
 Are they identical to the parents?
 No
 The parent has 4 chromosomes
 Each daughter cell has 4 chromosomes but they
are different because of crossing-over
 Each daughter cell has a set of chromosomes
and alleles different from each other and
different from the parent diploid cell

70. Meiosis II
 Unlike Mitosis, Neither cell goes through
a round of chromosome replication
 Each cell’s chromosome has 2
chromatids

71. Prophase II
 Meiosis I resulted in 2 “seemingly” diploid
cells
 Remember they are genetically different b/c
of crossing over in prophase I
 We still need to cut this number in half to
reach our goal of 4 haploid cells

72. Metaphase 2
 Chromosomes line up in middle
Anaphase 2
• Sister chromatids separate and move to
opposite poles
Telophase 2
• Meiosis II results in 4 haploid (N)
daughter cells
• 4 daughter cells contain haploid number
of chromosomes, just 2 each

75. Gamete Formation
 Male
 Haploid gametes produced by meiosis are called
sperm
 Female
 Haploid gamete produced by meiosis is called an
egg
 Cell divisions at the end of meiosis one and two
are uneven so one cell gets most of the cytoplasm
(the EGG) and the other three are called polar
bodies (don’t participate in reproduction)

81. Mitosis vs. Meiosis
 Mitosis
 Results in the production of two genetically
identical DIPLOID cells
 Daughter cells have sets of chromosomes
identical to each other and to parent cell
 MITOSIS allows body to grow and replace other
cells
 Asexual reproduction
 Meiosis
 Results in four genetically different HAPLOID cells
 MEIOSIS is how sexually reproducing organisms
make gametes

85. Genes

88. Microscope Lab Analysis
 Mitosis/Meiosis
Microscope Lab
 Lab notebooks Title
“Cell Division
Microscope Lab”
 MUST sketch each
stage and label the
power
 Label slide name
 Stage of mitosis or
meiosis
 Power of the objective
used to observe cell
 Need to observe each
stage of mitosis and
meiosis