Mitosis

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Mitosis
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Recap

• The cell goes through growth phases.
• G1
• S
• G2
• M phase and Cytokinesis
• Lets talk about the M phase and Cytokinesis

Interphase
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• Cell growth occurs in interphase
• During that time, DNA is loosely organized- it
  looks a bit like spaghetti.
• Remember DNA is a double-stranded molecule made
  of four different subunits called nucleotides.
• A chromosome is one long continuous thread of DNA
  that consists of numerous genes

centrioles
chromatin
nuclear envelope
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How does all the DNA fit inside the nucleus of a
cell?

• DNA wraps around proteins called histones that
  help organize and condense it.
• This process looks similar to beads on a string.
• Parts of the histones interact with each other,
  further compacting the DNA. At this stage the
  spaghetti stage the combination of DNA and
  proteins is called Chromatin.
• Recall that a chromosome is a strand of DNA, we
  have 23
• During the S phase each chromosome is copied, so
  we end up with 46 for the Mitosis phase

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Continued.

• DNA during the M-phase
• As the cell progresses, chromatin further
  condenses, it coils more and more tightly around
  organizing proteins, finally forming small thick
  rods.
• Since the chromosome has already been copied
  during the S phase, the chromosome looks similar
  to an X in which the left and
• right halves are two
• identical DNA double
• helixes

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Continued

• One half of a duplicated chromosome is called a
  chromatid.
• Together, two identical chromatids are called
  sister chromatids.
• Sister chromatids are held together at the
  centromere, a region of condensed chromosome that
  looks pinched.
• Lastly, at the ends of DNA molecules form
  structures called telomeres, which are made of
  repeating nucleotides that do not form genes.
• This prevents the ends of chromosomes from
  accidentally attaching to each other or the loss
  of genes.

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Chromosomes

• The cells of every organism have a certain number
  of chromosomes
• Fruit flies 8
• Humans 46
• Carrots 18

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Cell Division

• Once the cell is completely prepped for division,
  it enters the M phase.
• The M Phase is divided into 2 major stages
• Mitosis
• Cytokinesis

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Mitosis

• Biologists have further divided mitosis into four
  phases known as PMAT
• Prophase
• Metaphase
• Anaphase
• Telophase

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Prophase
spindle

• The nucleolus and
• nuclear membrane
• break up and temporarily disappear.
• Chromatin (spaghetti) condenses into tightly
  coiled chromosomes, each consists of two
  identical sister chromatids
• Centrosomes and Centrioles migrate to opposite
  sides of the cell
• Organized microtubules called spindle fibers grow
  from the centrioles and radiate toward the center
  of the cell.

chromosomes
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Prophase
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Metaphase

• Only a few minutes long.
• Spindle fibers attach to the centromere and align
  the chromosomes (sister chromatids)
• along the
• cell equator

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Metaphase
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Anaphase

• Sister chromatids separate from each other.
• The spindle fibers begin to shorten, which pulls
  sister chromatids away from each other and toward
  opposite sides of the cell.

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Anaphase
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Telophase

• A complete set of identical chromosomes are
  positioned at each pole of the cell.
• The nuclear envelope reforms around the
  chromosomes
• Chromosomes begin to uncoil back to
  chromatin and the spindle fibers fall apart

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Telophase
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Cytokinesis

• This phase divides the cytoplasm into two cells
  and completes a full stage of the cell cycle.
• Each cell is identical to each other

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Cytokinesis

• In animal cells, the cell membrane is pinched
  inward until the cytoplasm is separated into
  nearly equal halves.
• The pinching creates a furrow or trench.
• In plants, a cell plate is formed in the center
  of the cell and grows outward to separate the two
  cells.
• A cell wall will eventually form on each side of
  the cell plate.

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Cytokinesis
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Review The Whole Process
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Major Function of Mitosis

• In unicellular organisms, mitosis is asexual
  reproduction. A new organism is created.
• In multicellular organisms, mitosis increases the
  number of cells to help the organism grow and/or
  replace dying cells.

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Cell Cycle
includes
M phase (Mitosis)
Interphase
is divided into
is divided into
G1 phase
S phase
Prophase
G2 phase
Metaphase
Telophase
Anaphase
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Why do cells divide rather than continuing to grow indefinitely? The larger the cell becomes, the more demands it places on the DNA The cell has trouble moving enough nutrients and wastes across the cell membrane
What are the three limits to cell growth? Diffusion DNA Surface area to volume ratio
What is cell division? The process by which 2 new cells are produced from one cell.
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What are the 4 phases of the cell cycle? 1. G1 Phase 2. S Phase 3. G2 Phase 4. M Phase
What happens during the G1 Phase? Cell Growth the cell increases in size and synthesizes new proteins and organelles.
What happens during the S Phase? DNA Replication a new set of DNA is created from the original and proteins associated with DNA are synthesized.
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What happens during the G2 phase? Prep for Mitosis Organelles and molecules required for cell division are produced.
What happens during the M phase? Mitosis and Cytokinesis - Cell division occurs
In what form does genetic information take in eukaryotes? DNA deoxyribonucleic acid
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During what phase does cell growth occur? Interphase
What is chromatin? The granular material made up of DNA bound to protein.
What are the three parts of Interphase? G1, S, and G2 phases
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What are sister chromatids? The original chromosome joining with the copied chromosome.
How are the two sides of the chromatids joined together? centromere
What are the two parts of the M Phase? Mitosis and Cytokinesis
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What are the four phases of Mitosis? Prophase Metaphase Anaphase Telophase
What happens during Prophase? The nucleolus and nuclear membrane break up and temporarily disappear. Centrioles duplicate and separate to opposite sides of the cell. The mitotic spindle begin to form near the centrioles.
What happens during Metaphase? The chromosomes line up across the center of the cell on an imaginary line called the metaphase plate. Microtubules attach to the centromere of each chromosome from both poles of the spindle.
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How are plants cells different in prophase? Plant cells do not have centrioles but still form a spindle to organize cell division.
What happens during Anaphase? The centromeres are broken and the sister chromatids separate. Each sister chromatid is now called a chromosome. The chromosomes continue to move until they have separated into two groups near the poles of the spindle.
What happens during Telophase? Chromosomes begin to unwind back to chromatin. The nuclear envelope reforms around the chromosomes. a nucleolus becomes visible in each daughter nucleus The spindle breaks apart.
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What happens during cytokinesis for animal cells? - The cell membrane is pinched inward until the cytoplasm is separated into nearly equal halves.
What happens during cytokinesis for plant cells? - A cell plate is formed in the center of the cell and grows outward to separate the two cells.
What is the major function of mitosis for unicellular organisms? - mitosis is asexual reproduction so a new organism is created.
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What is the major function of mitosis for multi-cellular organisms? Mitosis increases the number of cells to help the organism grow and/or replace dying cells.
What is this phase and what is happening? Interphase - G1, S, G2, Cell growth, and replication of DNA and organelles.
What is this phase and what is happening? Prophase The nucleolus and nuclear membrane break up and temporarily disappear. Centrioles duplicate and separate to opposite sides of the cell. The mitotic spindle begin to form near the centrioles.
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What is this phase and what is happening? Metaphase The chromosomes line up across the center of the cell on an imaginary line called the metaphase plate. Microtubules attach to the centromere of each chromosome from both poles of the spindle.
What is this phase and what is happening? Anaphase The centromeres are broken and the sister chromatids separate. Each sister chromatid is now called a chromosome. The chromosomes continue to move until they have separated into two groups near the poles of the spindle.
What is this phase and what is happening? Telophase Chromosomes begin to unwind back to chromatin. The nuclear envelope reforms around the chromosomes. a nucleolus becomes visible in each daughter nucleus The spindle breaks apart.
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What are stages of the cell cycle? 1. G1 Phase 2. S Phase 3. G2 Phase 4. M Phase Prophase, Metaphase, Anaphase, Telophase