Honors Biology

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Honors Biology

• Chapter 8
• Cell Cycle

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Homework

• Read Chapter 8
• Page 230 231
• Reviewing Ideas 3, 6, 10
• Using concepts 1, 2, 4

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Cell Growth

• Limits to Cell Growth
• As cells grow, it is more difficult for the cell
  to move nutrients and wastes and to defend itself
  from pathogens
• Most cells are between 2 µ and 200 µ in diameter
  (µ micron or 1E-6 meters)
• In addition, it is difficult for the DNA in the
  nucleus to meet the needs of a very large cell
• Thus there is a physical limitation to the size
  of a cell
• Ratio of surface area to volume changes with cell
  size
• Smaller the cell size, greater the ratio
• Larger the cell size, smaller the ratio
• Helps determine efficiency of cellular processes

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Prokaryotic Cell Division

• Occurs in bacteria
• Called binary fission
• Replication of DNA
• Replication of cell membrane
• Pinching off
• Replication of cell wall (if present)

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Eukaryotic Cell Division

• DNA is contained in 2 identical sister
  chromatid strands
• They are attached at the centromere
• They appear as chromosomes (denser form of
  chromatids) during mitosis
• Autosomes not involved in sex determination
• Sex chromosomes are involved in sex
  determination

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Eukaryotic Cell Division

• Cell Cycle and Mitosis
• Interphase portion of cell cycle between
  divisions
• G1 cell growth, increased number of organelles
• S chromosome replicate into sister chromotids
• G2 cell makes organelles and substances
  required for cell division

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Interphase
G1
S
Telophase
Anaphase
Mitosis
G2
Metaphase
Prophase
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chromosome (unduplicated) in cell at interphase
same chromosome (duplicated) in interphase prior
to mitosis
Mitosis, Cytoplasmic Division
chromosome (unduplicated) in daughter cell at
interphase
chromosome (unduplicated) in daughter cell at
interphase
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Cell Division

• Cell division
• Mitosis cell divides the nucleus
• Prophase chromatids thicken, nucleolus and
  nuclear envelope disappear
• Metaphase chromosomes move to center of cell by
  spindle fibers, sister chromatids radiate from
  opposite ends of cell
• Anaphase centromeres of each chromosome are
  pulled to the ends of the cell
• Telophase new nuclei form around the
  chromosomes at each end of the cellcell membrane
  begins to pinch the cell into two separate cells
• Cytokinesis cell divides the cytoplasm

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G1, S, G2
Mitosis
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End of Mitosis
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Animal Cell
Mitosis is over, and the spindle is now
disassembling.
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Plant Cell
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Regulating the Cell Cycle

• Biologists noted that cells will continue to
  divide until there is a resource limitation
• Biologists also noted cell will divide if they
  are wounded
• What turns on and off cell division?
• A protein called cyclin, regulates the timing of
  cell division in eukaryotic cells
• More than 20 other proteins have subsequently
  been discovered that play a role in mitosis

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Regulating the Cell Cycle

• There are two types of cell regulators
• Internal regulators respond to events within the
  cell to continue or stop cell division
• Usually based on the action of specific proteins
• External regulators respond to events outside
  the cell to continue or stop cell division
• Protein growth factors

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Regulating the Cell Cycle

• Cancer cells are cells that have lost the ability
  to have controlled growth and division
• Some cancer cells do not respond to internal
  regulators, while others do not respond to
  external regulators
• Environmental exposures may trigger the formation
  of cancer cells
• Smoking
• Radiation
• Pollution
• Viruses

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Mitosis - Summary

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DNA Replication

• Since mitosis produces a cell with the exact same
  chromosome complement as the parent cell, how is
  the DNA in each chromosome replicated (copied)?
• While we will discuss this later, DNA consists of
  four bases
• Adenine (A)
• Thymine (T)
• Guanine (G)
• Cytosine (C)
• There is also a five-carbon sugar, deoxyribose
  and a phosphate group
• In DNA, A always bonds with T and G always bonds
  with C

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Overview Structure of DNA

• Nucleotides in DNA backbone are bonded from
  phosphate to sugar between 3? 5? carbons
• DNA molecule has direction
• complementary strand runs in opposite
  direction

5?
3?
3?
5?
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How does DNA Replicate?

• During the S phase of mitosis the DNA is copied
• This process involves more than 20 enzymes, the
  most important being DNA polymerase (replisome)
• Energy from ATP is used to unzip the DNA
• DNA polymerase copies continuously on the leading
  strand and discontinuously on the lagging strand
• Copying is always done from the 5 to 3 end of
  the strand

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How Does DNA Replicate?
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Mutation

• Any time there is a mistake in a DNA strand this
  is called a mutation
• During replication there is about 1 error in
  every 10 million bases copied
• Some mutations are caused by environmental
  factors, including chemicals, radiation and
  viruses
• There are a group of proteins whose role in DNA
  replication is to remove and correct any errors