Download Chapter 10: Cell Division

Chapter 5: Cell Growth and
Division
MRS. WILLIAMS
FRESHMAN BIOLOGY - HONORS
SEMESTER TWO
Origin Statement – November 18th, 2013
 If you’re a cell, is it better to be small or large?
 Justify your answer!
 How do organisms grow? Do the cells that they have
get bigger or do they grow more cells?
 In your own words, describe “cell division”.
Introduction
 Intro to the Cell Cycle with Bill Nye
Cell Growth
 Most living things grow by producing more cells.
 Cells don’t necessarily get larger, there are just more
of them.
 As cells get bigger, their volume increases much
faster than their surface area.
 Reasons why cells DIVIDE rather than grow larger:
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The bigger the cell, the more demands the cell places on the
DNA
The bigger the cell, the more trouble the cell has moving
enough nutrients and wastes across the cell membrane
The bigger the cell, the more quickly food and oxygen are used
up
RA Activity
 Turn to page 136 in the Alligator text
 Read “Cell Size is Limited” (second half of page 136 through
page 137) with your partner and do a Think Aloud.
 Focus on the ratio of surface area to volume in cells and
discuss how that relates to cell growth
 Think, Pair, Share
Chromosomes
 In eukaryotic cells, genetic info that is passed from
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one generation to the next is carried on
chromosomes
Made up of DNA and proteins
Each cell has a specific number of chromosomes
(humans have 46)
Before cell division, each chromosome is copied in to
two sister chromatids that hold identical genetic info
One chromatid goes to each of the new cells
Diploid vs. Haploid
 Diploid (2n) cells have two
sets of chromosomes

One inherited from mom;
one from dad
 All somatic (body) cells are
diploid (all cells except sex
cells)
 Humans’ diploid number is
46, but other species have
other numbers.
 The chromosomes that are
alike from each set are
called homologous
chromosomes.
 Haploid (1n) cells have one
set of chromosomes
 Gametes (sex cells) are
haploid
 Humans’ haploid number
is 23, but other species
have different numbers.
 When fertilization occurs,
the organism will again be
diploid.

23 chromosomes from male
parent + 23 chromosomes
from female parent = 46
total (diploid)
Chromosome Structure
Chromosome Structure Continued
 Before replication
 Each chromosomes is a single strand
 After replication
 Each chromosome is made of two identical copies stuck
together by a centromere

Each copy is called a sister chromatid
The Cell Cycle
 A series of events that
cells go through as they
grow and divide
 During the cell cycle, a
cell:
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Grows
Preps for division
Divides to form two
daughter cells (has
nothing to do with
gender!)
Phases of the Cell Cycle
 There are three main phases of the cell cycle
 1. Interphase
G1
S
 G2


2. Mitosis
Prophase
 Metaphase
 Anaphase
 Telophase
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3. Cytokinesis
Interphase
 Interphase: divided into three phases – G1, S, G2
 G1
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 S
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Gap phase
Cell grows and carries out normal function
Some cells may stay in G1 indefinitely (called G0)
Synthesis phase
Chromosomes replicate
DNA synthesis takes place
 G2
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Gap phase
Cell grows and carries out normal functions
Other organelles replicate
Cell Division
 Happens in two stages:
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Mitosis
Cytokinesis
 Mitotic reproduction is
asexual since the new
cells produced are
genetically identical to
the parent cell
Origin Statement – 11/20/13
 What are the three major stages of the cell cycle?
 Draw a picture showing the following:
 A chromosome before replication
 A chromosome after replication
 Sister chromatids
 Centromere
 What is the difference between haploid and diploid
cells?
 What happens during S phase of interphase?
Exit Slip
 Without the use of your notes, answer the
following on a scrap piece of paper that you
CAN turn in:
 1. What is the difference between a haploid
and a diploid cell?
 2. Name the three stages of interphase and
describe what happens during each.
Review (from exit slips)
 Haploid
 One SET of chromosomes – not one chromosome!
 Diploid
 Two SETS of chromosomes – not two chromosomes!
 Not all organisms have 46 chromosomes per cell!
 Stages of Interphase
 G1 – Cell grows and carries out normal function
 S – DNA is replicated/synthesized
 G2 – Cell grows, carries out normal function, and organelles
are replicated
Cell Division
 Mitosis
 Division of the nucleus
 Occurs in somatic cells (body cells, NOT sex cells)
 One division with 4 phases, creating 2 identical daughter
cells
 Cells start diploid and end diploid!
 Cytokinesis
 Division of the cytoplasm
Mitosis
 Four Phases
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Prophase
Metaphase
Anaphase
Telophase
 Refer to page 141 in your
“Alligator” text for great
pictures!
Mitotic Phases in Detail: Phase One
 Prophase
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Chromatin condenses into
chromosomes
Centrioles separate
Spindle begins to form
Nuclear envelope breaks
down
Mitotic Phases Detailed: Phase Two
 Metaphase
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Chromosomes line up
across the center of the
cell
Each chromosome is
connected to a spindle
fiber at its centromere
Mitotic Phases Detailed: Phase Three
 Anaphase
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Spindle fibers shorten and
pull apart the sister
chromatids
Individual chromosomes
are moved apart
Mitotic Phases Detailed: Phase Four
 Telophase
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Chromosomes gather at
opposite ends of the cell
and lose their distinct
shapes
Two new nuclear
envelopes form
Mitosis Online Lab
Mitosis with Tim & Moby
Cytokinesis
 NOT part of mitosis; last
step of cell cycle
 During cytokinesis:
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The cytoplasm pinches in
half
End product: 2 daughter
cells that are IDENTICAL to
the parent cell (so if parent
has 46 chromosomes, each
daughter cell has 46
chromosomes!)
Varies slightly in animal and
plant cells
Cytokinesis in Plant and Animal Cells
 Animals
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In most animal cells, the
cell membrane is drawn
inward until the
cytoplasm is pinched into
two nearly equal parts
Each part contains its own
nucleus and organelles
 Plants:
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A cell plate forms midway
between the divided nuclei
Cell plate gradually
develops into a separating
membrane
Cell wall begins to appear
in the cell plate
Cell Division Controls and Problems
 Generally, when cells
come into contact with
other cells, they stop
growing
 Timing of cell growth
regulated by proteins
called cyclins
 See fig. 5.10, page 146
 Sometimes cells don’t respond
to the signals that regulate the
growth of most cells
 This can lead to cancer – a
disorder in which some of the
body’s own cells grow out of
control
 p53 is a gene that halts the cell
cycle until all chromosomes are
replicated; found to have
mutations in cancer patients
 These cells grow uncontrollably
and form masses called tumors
Cell Cycle Flow Map
 Create a Flow Map showing the 6 major steps of the
cell cycle
 Each large box should have a picture of what the cell
looks like in that stage
 The small boxes beneath should describe what
happens during that step!
Meiosis
CHAPTER 6, SECTIONS 1 & 2
Comparing Mitosis and Meiosis
 During the video, take notes comparing the two
processes
 These notes will be useful for a later activity, so be
thorough!
 Mitosis/Meiosis Video
Characteristics of Meiosis
 Meiosis occurs in gametes (sex cells) ONLY
 TWO divisions with 4 phases each (8 phases total)
creating 4 unique cells
 Cells start out diploid and end haploid
Meiosis I: Prepping for Meiosis
 Interphase I
 Cells replicate DNA ONCE, forming duplicate chromosomes
 There will only be ONE interphase during the whole
process of meiosis.
 Meiosis I has four stages:
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Prophase I
Metaphase I
Anaphase I
Telophase I
 Cytokinesis
 Page 174-175, figure 6.5 (A)
Meiosis I: Stage One
 Prophase I
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Each chromosome (2
sister chromatids) pairs
with its corresponding
homologous chromosome
to form a tetrad
Crossing-over occurs

Results in the exchange of
alleles between
homologous chromosomes
and produces new combos
of alleles
Meiosis I: Stage Two
 Metaphase I
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Spindle fibers attach to
the chromosomes
Still attached at the
centromere
Meiosis I: Stage Three
 Anaphase I
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Spindle fibers pull apart
homologous chromosomes
toward opposite ends of
the cell
Meiosis I: Stage Four and Cytokinesis
 Telophase I
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Nuclear membranes form
 Cytokinesis
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The cytoplasm separates
(just like in mitosis)
Cell splits into two haploid
(n) cells
Meiosis II
 Meiosis II is very similar to mitosis; however there is NO
chromosome replication that takes place before it begins
(no interphase II)
 Both haploid (n) cells created in meiosis I divide
 Ends with four new haploid (n) cells
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Sperm or egg cells
 Four stages:
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Prophase II
Metaphase II
Anaphase II
Telophase II
 Cytokinesis
Meiosis II: Stage One
 Prophase II
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The two haploid (n)
daughter cells that were
produced at the end of
meiosis I have half the
number of chromosomes
as the original cell
NO REPLICATION OF
CHROMOSOMES
happens during meiosis II
Meiosis II: Stage Two
 Metaphase II
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Chromosomes line up in
the center of each cell
Spindle fibers are attached
at centromeres of sister
chromatids
Like metaphase in mitosis
Meiosis II: Stage Three
 Anaphase II
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Spindle fibers shorten
Sister chromatids separate
and move toward opposite
ends of each cell
Meiosis II: Stage Four and Cytokinesis
 Telophase II
 Nuclear envelopes reform in
both cells
 Cytokinesis
 The cytoplasm in both cells
splits to form 4 haploid (n)
daughter cells with HALF the
number of chromosomes as
the original cell
 So if parent cell has 46
chromosomes, each cell at
the end of meiosis II would
have 23 chromosomes.
Origin Statement – November 26th
 What are the steps of the cell cycle, in order?
 What two steps make up what is referred to
as “cell division”?
 What type of reproduction is mitosis?
Meiosis?
 List three similarities and three differences
between mitosis and meiosis.
Spermatogenesis & Oogenesis
 Spermatogenesis
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Formation of sperm
Starts at puberty
Forms 4 sperm during each
meiosis
Men will make 5 to 200
million sperm per day!!
 Oogenesis
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Formation of the egg
Meiosis starts inside the
womb and continues in some
during every cycle after
puberty
1 egg and 3 polar bodies are
created after every meiosis
The egg must contain a lot of
cytoplasm to support the
developing embryo after
fertilization
Fig. 6.6, page 176