Eukaryotic Cell Chromosome: Molecule to Chromosome

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Eukaryotic Cell Chromosome Molecule to
Chromosome
One Very Long, Linear DNA Molecule Representing
Thousands of Genes, the Units that Specify
Inherited Traits
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Eukaryotic Chromosomes Have the Following
Characteristics

• Supercoils of DNA-protein called CHROMATIN.
• Each chromosome consists of the following
• DNA molecule that is long, double-stranded
  segments of which are called GENES.
• Various proteins maintain chromosome structure
  or help with gene expression, DNA replication and
  DNA repair.
• Exist in species-specific numbers (e.g. 46).
• Exist in different states (visible in mitosis
  invisible in interphase)

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EUKARYOTIC CHROMOSOMES

• 46 chromosomes in human somatic cells... all
  but reproductive cells.
• 23 chromosomes in human reproductive cells
  (sperm or egg), thus half as many chromosomes.

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Preparation for Eukaryotic Cell Division..

• Complete Genome is duplicated.
• This forms SISTER CHROMATIDS.
• Sister chromatids are identical copies of
  chromosomal DNA.
• Sister chromatids are initially attached at the
  CENTROMERE.
• CELL DIVISION IN TWO STEPS
• Nuclear Division (Mitosis)
• Cytoplasmic Division (Cytokinesis)

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FIGURE 11.5 THE CELL CYCLE
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THE CELL CYCLE Mitosis Alternates with
Interphase

• A cell copies its entire genome by duplicating
  each chromosome.
• After replication (duplication), each chromsome
  consists of two SISTER CHROMATIDS

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THE CELL CYCLE

• A CENTROMERE holds the two chromatids together.
• In MITOSIS (division of nucleus), the sister
  chromatids are pulled apart repackaged as
  complete sets of two nuclei (at each end of cell).

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THE CELL CYCLE

• CYTOKINESIS- division of cytoplasm follows
  mitosis, where there was one cell, now there are
  two cells.

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THE CELL CYCLE

• Each cell is genetically equivalent to the
  parent cell....chromosome number remains the
  same (e.g. human somatic cell ?)

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THE CELL CYCLE

• Mitosis is only one part of the cell cycle...the
  M Phase (Mitosis Cytokinesis) is the shortest
  in duration.

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THE CELL CYCLE

• INTERPHASE 90 of cell lifetime Cell grows
  copies its chromosomes in preparation for cell
  division.

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THE CELL CYCLE

• INTERPHASE consists of three growth periods
• G1 Phase - Cell Growth
• S Phase - Copies Chromosomes
• G2 Phase - Cell Grows in Prep. for Cell Division.

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Mitosis M Phase

• M Phase (not interphase) Division

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CELL CYCLE OVERVIEWG2 INTERPHASE

• Late interphase well defined nucleus with one or
  several nucleoli.
• Additional centrosome formed (2) with CENTRIOLES
  (animals only).
• ASTERS (not flowers) are forming from centrioles.
• Chromsomes have already duplicated in S Phase but
  are not visible yet.

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G2 of Interphase
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CELL CYCLE OVERVIEW MITOTIC PROPHASE

• Nucleoli disappear
• Chromatin fibers become more tightly coiled into
  discrete chromsomes
• Each duplicated chromosome is joined at the
  centromere to form two sister chromatids

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Mitosis CD Clip..
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Keep in Mind.........Chromosomal Features
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METAPHASE Bowties in a Line
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MITOTIC SPINDLEA Closer look (Figure 12.6)
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CELL CYCLE OVERVIEWMITOTIC ANAPHASE

• Paired centromeres of each chromosome separate
  -liberate sister chromatids.
• Each chromatid is now a CHROMOSOME!

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MITOTIC ANAPHASE

• The sisters move along microtubules towards
  opposite poles.
• Two poles now have complete sets of chromosomes.

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ANAPHASE Headed to the Poles
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MITOTIC TELOPHASE CYTOKINESIS

• Mitosis is complete when identical nuclei are
  formed...cytokinesis is ongoing separates the
  cytoplasm for two daughter cells.

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Know this scheme in detailUse your Interactive CD
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(No Transcript)
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Cleavage furrow vs. Cell plate
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What Controls the Cell Cycle? EXTERNAL INTERNAL
CUES

• Cells grown in artificial cultures are
  stimulated or inhibited by certain chemical
  physical factors.
• Essential nutrients required for division.

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Control of Cell Division

• Some mammalian cells only divide if medium has
  specific regulatory substances called GROWTH
  FACTORS.
• e.g. fibroblasts (connective tissue cells)
  require platelet-derived growth factor (PDGF).

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Control of Cell Division

• Binding of PDGF to receptors stimulates cell
  division when platelets (blood cells) fragment
  release PDGF during an injury to help in wound
  healing.

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Control of Cell Division

• Cell density regulates division. Crowding
  inhibits cell division, which is called
  DENSITY-DEPENDENT INHIBITION.