CELL REPRODUCTIONHonors Zoology

Reasons cells divide Growth and development zygote to adult Replace old cells – lining of digestive tract

and skin Repair damaged tissue – heal injuries Reproduction – make offspring

GRRR!

1 cell to 90 trillion Most animals start out as a zygote A zygote is formed by the union of an egg

and a sperm.

Mitosis The zygote divides to form genetically

identical daughter cells. They divide to form more genetically

identical cells.

The Process of Cell Replication

Interphase – 3 phases- DNA is called chromatin in interphaseG1 - 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

DNA Replication 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.

How it Works

The Good News – You do not have to memorize all of

that!What to know…

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.

What to know continued… 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

Prophase 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.

All wrapped up and let’s dance!

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.

Getting attached and dragged to the dance floor – line dance!

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.

Metaphase When the Chromosomes are lined up in

the middle.

Anaphase 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.

Telophase The opposite of prophase. The chromatids – now chromosomes

uncoil into chromatin. The nuclear membrane reforms. Spindle fibers disappear.

Cytokinesis – division of the cytoplasm

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.

The daughter cells Are genetically identical. They are clones. If the cells separate when a zygote under

goes mitosis, they are identical twins.

Control 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.

Programmed Cell Death Called apoptosis Necessary for normal growth and

development. Without it you would hae webbed fingers and a tail!

Now…

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.