Honors Zoology

 Growth and development zygote to adult  Replace old cells – lining of digestive tract and skin  Repair damaged tissue – heal injuries  Reproduction – make offspring  GRRR!

 Most animals start out as a zygote  A zygote is formed by the union of an egg and a sperm.

 The zygote divides to form genetically identical daughter cells.  They divide to form more genetically identical cells.

Interphase – 3 phases - DNA is called chromatin in interphase G1 - Most of the life of the cell. - When they do their ‘work’ S - Time when conditions are right and the signal comes for DNA synthesis to occur. G2 – Organelles reproduce in preparation for Mitosis

 During S phase of interphase a set of enzymes separate the DNA double helix and allow each side to serve as the template for synthesis of a new complementary strand of DNA.  The old molecule separates in half, gets new nucleotides paired with it to produce new DNA molecules that are ½ old and ½ new.

 DNA has 2 strands with complementary nucleotides.  Adenine pairs with Thymine and Guanine pairs with Cytosine.  Each strand is replicated in opposite directions.  DNA Polymerase is the enzyme that places the nucleotides and catalyzes their bonds.

 There are several other enzymes involved that unzip and untwist the original strand, hold it open, place RNA primers, hook/repair broken nucleotide bonds, keep it from twisting too tight, and replace the ending segments.  Actually, just know that DNA Polymerase acts in concert with several other enzymes.  The replicated strands remain attached at the centromere – as chromatids

 After DNA is replicated and repaired, it begins to coil into chromosomes.  They consists of 2 identical copies of the DNA called chromatids.  The chromatids are held together at the centromere which has a protein called the kinetochore.  The kinetochore attaches to spindle fibers during mitosis.

 DNA is not available for transcription during this time.  While the chromosomes were wrapping up, spindle fibers were growing out of the 2 centrosomes, which usually contain centrioles in animals.

 As spindle fibers form the nuclear membrane breaks apart and beads up to be divided between the daughter cells.  The spindle fibers attach to the kinetochore and the chromosome moves back and forth until it settles in the middle on the metaphase plate.

 When the Chromosomes are lined up in the middle.

 The chromatids separate at the centromere.  The chromatids move down the spindle fibers in opposite directions toward the centrosomes.  The spindle fibers without chromatids push the centrosomes apart making the cell oval shaped.

 The opposite of prophase.  The chromatids – now chromosomes uncoil into chromatin.  The nuclear membrane reforms.  Spindle fibers disappear.

 A cleavage furrow forms where the metaphase plate was. A ring of actin fibers circles the cell and interacts with other proteins to cinch the cell in half.  The infolded edges of the membrane meet and fuse.

 Are genetically identical.  They are clones.  If the cells separate when a zygote under goes mitosis, they are identical twins.

 The cycle of cell division and growth is controlled by the rise and fall of protein in the cell, especially cyclin.  Cyclin works with other proteins called cdk’s to initiate cell division.

 Called apoptosis  Necessary for normal growth and development. Without it you would hae webbed fingers and a tail!

 Use the pop beads to model mitosis for 2 chromosomes – red and yellow.  Your other supplies include yarn, string, beads, magnetic pieces, and two sheets of paper.