Reproduction of Cells

1
Reproduction of Cells
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The DNA Molecule
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Chromosome Structure

• Rod shaped structure
• Made of a single DNA molecule and proteins called
  histones
• Histones maintain shape of chromosomes
• Aids in tight packing of DNA
• Seen during cell division
• Coiled and compact

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DNA and Chromosomes
double-stranded DNA molecule
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A Pair of Homologous Chromosomes
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• DNA Replication
• Each parent strand remains intact
• Every DNA molecule is half old and half new

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Chromosome structure

• Chromosome consists of two identical halves
• Each half is a chromatid
• Formed when DNA makes a copy of itself before
  cell division
• Each new cell will receive one chromatid from
  each chromosome
• Chromatids are held together by a centromere

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Chromosomal Replication
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A Chromosome After Replication
sister chromatids
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Human Chromosomes
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Human Chromosomal Pairs
23 pairs
autosomes
Sex chromosomes
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Cell Cycle
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The Cell Cycle
Centrioles replicate
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The Cell Cycle

• Interphase- 75 of cell life cycle
• G1 rapid growth
• S DNA replicates centrioles replicate.
• G2 cell prepares for cell division
  microtubular structures form.

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The Cell Cycle

• Cell Division
• Mitosis cell divides its nuclear components
  (chromosomes).
• Cytokinesis cell divides its cytoplasmic
  components.

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Stages of Mitosis

• Prophase
• Metaphase
• Anaphase
• Telophase

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Interphase
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Prophase

• Chromosomes shorten and become visible (early
  prophase)
• Chromosomes made up of 2 identical chromatin
  threads called chromatids
• Centrioles migrate toward opposite pole pulled by
  kinetochore
• Nuclear envelope disintegrates (late prophase).

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Prophase
centrioles
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Prophase
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Centrioles During Prophase
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Metaphase

• Chromosomes lined up in the middle
• Mitotic spindle complete.

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Metaphase
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Metaphase
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Chromosome at Metaphase
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Anaphase

• Sister chromatids ( identical strands of DNA)
  split from each other to form divided identical
  chromosomes.
• Kinetochore fibers shorten and pull divided
  identical chromosomes to opposite sides of the
  dividing cell.
• Polar microtubules slide past each other,
  lengthening and pushing the cell apart

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Anaphase
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Telophase

• Divided chromosomes reach opposite sides of cell
  and begin to disperse as chromatin.
• Nuclear envelopes reforms around separated
  collections of chromosomes to form two nuclei.
• Cytokinesis- completion of cell division

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Telophase

• Spindle apparatus disintegrates.
• Cytokinesis usually begins near the end of
  telophase.

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Telophase
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Cytokinesis

• Separation of cytoplasmic components to yield two
  daughter cells
• Microfilaments form a contracting ring that
  pinches the plasma membrane inward between the
  forming daughter cells

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Cytokinesis
cleavage furrow
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Cytokinesis
http//www.loci.wisc.edu/outreach/bioclips/CDBio.h
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INQUIRY

• Which cells in the body are diploid and which are
  haploid?
• During which stage does DNA replication occur?
• Which stage of mitosis is seen in this picture?
• At which stage is the cell binuclear?
• In which phase do chromosomes line up in the
  center of the cell?
• Where does the kinetochore attach?