Mitosis and Meiosis

It is a highly regulated process. Why would it be important to regulate this type of cell division?

-        We don’t want to make mistakes when we copy the DNA  mutations

-       We don’t want to make more cells than we need  tumors

Overview of DNA

• In cell division, DNA must be copied and then distributed to the new daughter cells. The daughter cells will then have set DNA.

• DNA is a polymer (macromolecule) that is composed of nucleotides monomers.

• All life on Earth uses DNA to store information and pass it along to the next generation.

• DNA is double stranded. A double helix is two strands of DNA which are held together by hydrogen bonds.

• The structure of a double helix is often referred to as a ladder where the sugar and phosphates serve as the backbone and the bases serve as the rungs.

· What does the term complementary base pairing mean?

-       A goes with T

-       C goes with G

Eukaryotic DNA Organization

·       Most of the time, the DNA in your cells associates with proteins called histones and exists as thin unraveled fibers called chromatin.

·   Eukaryotic chromosomes are linear and contain genes and are housed inside the nucleus.

Chromosomes

Human somatic cells contain somatic chromosomes or 46 pairs.  How many are from mom? 23 Dad? 23

·       Homologous pair: “matching chromosomes” from mom and dad; two chromosomes containing the same genes

Chromosomes can be detected via a light microscope.

What is a telomere on a chromosome?

-       Protective caps at the end of chromosomes

-       After every cell division, the telomere gets a little shorter

How do telomeres relate to cellular aging? – the older a cell, the shorter is telomeres

How many cell divisions occur for a typical human cell? – 50 to 70

What are some major differences you notice between prokaryotic and eukaryotic chromosomes?

Prokaryotic Cells: Chromosomes is circular, located in the nucleoid region, DNA is not associated with histone proteins

Eukaryotic Cells: Chromosome is linear, located within the nucleus, DNA is associated with histone proteins (chromatin)

Start of Interphase:                                                                                       

-       Chromosomes are in unduplicated form

-       At the end of this process, cells will be identical to this cell

End of Interphase:

-       G1, S, and G2 must occur

-       Chromosomes were duplicated

M Phase:                                                                                                       

1.   Prophase:

-     Chromosomes are fully coiled and condensed

-     They are in duplicated form

-     The nuclear membrane starts breaking down

-     Spindle fibers start to form

-     We have 4 duplicated chromosomes

2.   Metaphase:

-       Chromosomes align down the center of the cell

-       The spindle fibers assist

-       The order in which chromosomes line up is not important

-       We still have 4 duplicated chromosomes

3.   Anaphase:

-       The spindle fibers pull from each side

-       The sister chromatids are pulled apart

-       We now have 8 unduplicated chromosomes (the number has temporarily doubled)

4.   Telophase (with cytokinesis):

-       The chromosomes are now divided up

-       Nuclear membranes need to reform

-       Cytokinesis must occur

-       End result: 2 daughter cells, each has 4 unduplicated chromosomes (note: they look identical to what we started with)

How many homologous pairs does each cell have? – 23 pairs

Are the daughter cells at the end identical? – Yes, during mitosis, the two resulting daughter cells are genetically identical to each other and to the original parent cell