October 25, 2011 Mitosis!

Brainteaser You enter a dark room. You have only one match. There is an oil lamp, a furnace, and a stove in the room. Which would you light first?

Lets’ Review In DNA replication, what protein unwinds or cuts apart the hydrogen bonds holding the nitrogenous bases together? Replication is thought to be ____-________ What are the four nucleotide bases? What are the complementary bases?

Cell Growth and Reproduction Mitosis

Mitosis produces identical offspring (2N---2N)

Cell Growth and Reproduction So how does cell division take place? Scientists recognized that just before cell division, short stringy structures appeared in nucleus These structures are called chromosomes in form of chromatin

Cell Growth and Reproduction Before cell division, chromosome is in spaghetti-like CHROMATIN state As cell division begins, chromosomes take on a new tightly packed shape Genes are found on chromosomes DNA makes up Genes DNA is made up of base pairs. A - T G - C

Cell Growth and Reproduction INTERPHASE: DNA has replicated, but has not formed the condensed structure of chromosome. They remain as loosely coiled chromatin. The nuclear membrane is still intact to protect the DNA molecules from undergoing mutation.

Cell Growth and Reproduction MITOSIS: As cell gets to the maximum size, it begins to undergo MITOSIS (cell division) FOUR PHASES: Prophase Metaphase Anaphase Telophase

Cell Growth and Reproduction PROPHASE – 1st Stage of Mitosis Long stringy chromatin coils up into visible chromosomes Spindle fibers Disappearing nuclear envelope Doubled Chromosome

Cell Growth and Reproduction PROPHASE – 1st stage of Mitosis Towards end of Prophase, nucleus begins to disappear as nuclear envelope and nucleolus disintegrate. The nuclear membrane and nucleolus are no longer visible. Centrioles begin to migrate to opposite ends of cells

Cell Growth and Reproduction PROPHASE: Let’s break it down Chromosomes coil up Sister Chromatids form Nucleolus and Nuclear Envelope disintegrates Centrioles migrate to opposite ends Spindles form between Centrioles

Cell Growth and Reproduction 2nd Phase of Mitosis: METAPHASE The spindle fibers attach themselves to the centromeres of the chromosomes The chromosomes align at the equator or middle plate.

Cell Growth and Reproduction 2nd Phase of Mitosis: METAPHASE One sister chromatid’s spindle fiber extends to one pole while other spindle fiber extends to opposite pole.

Cell Growth and Reproduction 2nd Phase of Mitosis: METAPHASE What is the importance? This arrangement of the chromatids ensures that each new cell receives identical and complete set of chromosomes (DNA)

Cell Growth and Reproduction 3rd Phase of Mitosis: ANAPHASE Beginning of sister chromatid separation Centromeres split Chromosomes separate from each other spindle fibers shorten and pull apart chromatids to opposite poles

Cell Growth and Reproduction 4th Phase of Mitosis: TELOPHASE Begins once chromatids reach opposite poles Chromosomes begin to unwind and return to chromatin Spindle fibers breaks down

Cell Growth and Reproduction 4th Phase of Mitosis: TELOPHASE Nucleolus and nuclear envelope reappears around new set of chromosomes Double membrane forms between two new nuclei Two daughter cells formed

Cell Growth and Reproduction Cytokinesis: After Telophase, cell’s cytoplasm divides Animal Cells: At end of Telophase, plasma membrane pinches off forming two separate cells. Plant Cells: Cell plate laid across cell’s equator—there is no pinching off. Cell membrane forms around each cell and new cell walls form on each side of cell plate

plant cytokinesis

Cell Growth and Reproduction Cytokinesis:

Cell Growth and Reproduction What are the results of Mitosis? Single Cell organism remains a single cell but has replicated itself Multicellular organisms have grown or created another cell that will work together as tissue to perform a certain function

Cell Growth and Reproduction Recall BIOLOGICAL ORGANIZATION: Cells Tissues Organs Organ System Organisms

Cell Growth and Reproduction Section Quiz: The stringy structures in the cell nucleus that contain DNA are __________. Centromeres Chromatin Genes Chlorophylls