The Cell Cycle

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Chapter 8

• The Cell Cycle

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8.1 Cell Division in Eukaryotes

• Prokaryotes divide in two
• Eukaryotes a more complex process to be able to
  divide in two cell cycle

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8.1 Cell Division in Eukaryotes

• Multicellular Organisms Development
• Multicellular organisms develop from a single
  fertilized egg cell. The many cell types these
  organisms are made of go through many cell cycles
  that began with that fertilized egg.

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8.1 Cell Division in Eukaryotes

• Purposes of cells division
• By dividing into many cells, surface area keeps
  up with the cells growing volume (helps for
  diffusion of materials into cell).
• Replaces cells that are damaged, worn out, or
  dead (ex skin cells).

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8.1 Cell Division in Eukaryotes

• In Plants
• Specialized regions at tips of roots stems that
  repeatedly divide ? will turn into mature tissues
  (stems, leaves, roots, etc).

• In Animals
• Cell division produce many types of cells (nerve,
  skin, blood, etc.) that coordinate organs organ
  systems.

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8.1 Cell Division in Eukaryotes

• Timing of Cell Divisions
• Cells divide at different rates times so that
  the development is coordinated with neighboring
  cells to produce organs/organ systems

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8.1 Cell Division in Eukaryotes

• Eukaryotic Cell Division Requirements
• - Accurate replication equal division of the
  cells DNA
• - Each daughter cell should receive identical
  set of chromosomes

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8.1 Cell Division in Eukaryotes

• Consequences of errors
• Error in DNA replication ? birth defects, cancer,
  serious diseases, or death

Picture of a child with Down Syndrome, which is
caused when the fertilized egg cell receives an
extra copy of the 21st chromosome.
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8.2 The Phases of the Cell Cycle
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8.2 The Phases of the Cell Cycle

• Starting Ending Products
• Starts once a new cell is formed.
• Ends as soon as that cell divides into 2
  IDENTICAL cells.
• Mitosis process of dividing nuclear material
• Interphase resting period between divisions

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8.2 The Phases of the Cell Cycle

• INTERPHASE
• Individual chromosomes are NOT visible during
  interphase.
• 3 stages of interphase
• G1 Gap 1 or prereplication
• S DNA synthesis
• G2 Gap 2 or premitosis

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8.2 The Phases of the Cell Cycle

• INTERPHASE
• Gap (G) Phases
• Cells grow
• Synthesize RNA, proteins, other molecules to
  prepare for mitosis.
• G0
• - A stopping point in G1 non-division stage
• - Cells are metabolically active but non-dividing

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8.2 The Phases of the Cell Cycle

• INTERPHASE
• Restriction Point
• - point of no return
• - the point at which a cell commits itself to
  complete the cell cycle
• Synthesis (S) Phase
• - DNA of each chromosome replicates to form an
  identical set
• - Doubles the of genes in the nucleus

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8.2 The Phases of the Cell Cycle

• INTERPHASE
• Specific events of G2
• - The specific molecules for mitosis are made

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8.2 The Phases of the Cell Cycle

• MITOSIS
• (Nuclear division)
• Each new daughter cell receives one copy of each
  chromosome
• Nucleus divides into 2 nuclei with identical
  chromosomes

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8.2 The Phases of the Cell Cycle

• CYTOKINESIS
• Division of the whole cell splitting of the
  cytoplasm
• Each cell enters G1 to start the cycle over again.

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Structure of DNA Strands are antiparallel
parallel but run in opposite directions
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8.4 DNA Synthesis

• In S phase (interphase) DNA replicates
• 3 major parts to DNA synthesis
• Binding of enzymes to existing DNA
• Unwinding of the double helix
• Synthesis of new matching strand of DNA for each
  existing strand

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8.4 DNA Synthesis

• Helicase (enzyme that unwinds DNA), an
  RNA-synthesizing enzyme, DNA polymerase (enzyme
  that makes new DNA), other enzymes/proteins
  bind to the replication origin a region on a
  chromosome
• This whole combination of the enzymes, proteins,
  DNA replisome

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8.4 DNA Synthesis

• Prokaryotes vs. Eukaryotes
• Prokaryotes only 1 replication origin
• Eukaryotes many replication origins (because
  they contain so much more DNA would take too
  long to replicate)

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8.4 DNA Synthesis

• DNA Polymerase adds nucleotides only to an
  existing strand
• Enzyme unwinds separates the DNA
• Another enzyme synthesizes a short matching RNA
  piece that acts as a primer for DNA synthesis
• Existing base sequence determines new strands
  base sequence (complementary pairing)

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(No Transcript)
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http//en.wikipedia.org/wiki/DNA
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8.4 DNA Synthesis

• Because DNA is antiparallel, we call one strand
  the leading strand (5 ? 3) and the other the
  lagging strand (3 ? 5).
• Leading strand continuous DNA synthesis DNA
  polymerase adds DNA nucleotides to the end of the
  RNA primer, moving away from the replisome (the
  RNA primer is replaced later by a different
  enzyme).

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8.4 DNA Synthesis

• Lagging Strand discontinuous addition of DNA
• WHY???
• DNA polymerase can extend the primer in only one
  direction (3 ? 5) this is the opposite way
  the replisome moves
• In lagging strand DNA synthesis occurs in
  short, unconnected segments (Okazaki fragments)
  that get joined by other enzymes following the
  replisome

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Replication Video
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8.4 DNA Synthesis

• Replisomes move along DNA in both directions.
• End result 2 identical double helices, each
  with one original strand one newly synthesized
  strand
• Called Semi-conservative DNA synthesis b/c each
  helix has an original a new strand

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8.5 DNA Repair

• New DNA strands must be EXACT complements to the
  parental strand
• Mutation - any change in the sequence of a cells
  DNA
• Can be silent, harmful, or even lethal to cells
• Ex mutations play a major role in cancers

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8.5 DNA Repair

• Processes to detect correct errors
• DNA polymerase proofreads its own work
• 1 in 10,000 bases is incorrect, but ends with
  only 1 mutation in 10,000,000 base pairs
• After adding the nucleotide it checks to see if
  the base pair is correct if not, it removes the
  incorrect one replaces it

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8.5 DNA Repair

• Mutagenic chemicals environmental factors that
  introduce or cause mutations typically cause a
  mismatched pair to occur (A-C, which cant form H
  bonds)
• Repaired by excision repair enzyme recognizes
  mismatch binds to DNA breaks the
  sugar-phosphate bonds of mismatched section,
  remove mutant DNA, DNA polymerase then fills in
  deleted DNA sequence another enzyme repairs the
  broken bonds