 Between cell divisions DNA is not tightly coiled into chromosomes-called chromatin  Regions uncoil to be read to direct cell’s activities  Prokaryotes have only 1 chromosome attached to the inside of the cell membrane, still compact to fit in cell but in a loop

 When a eukaryotic cell prepares to divide, the DNA and the proteins associated with the DNA coil into a structure called a chromosome

 Histones-aid in tight packing of DNA and help maintain the shape of the chromosome  Nonhistone proteins are involved in controlling the activity of specific regions of the DNA

 The 2 exact copies of DNA that make up each chromosome are called chromatids  The 2 chromatids of a chromosome are attached at the centromere

 The chromatids separate during cell division and are placed into each new cell  Each new cell will have the same genetic information as the original cell

 Each species has a characteristic number of chromosomes

 Sex chromosomes determine the sex of an individual –XY  Autosomes are all other chromosomes  Chromosomes come in pairs – one member from each parent  Chromosome pairs carry genes for the same traits  Chromosome number (n) tells how many of each type of chromosome is present in a cell; 2n is diploid

 Sperm and egg cells are haploid (1n)-have only ½ the number of chromosomes of diploid cells- why?  Karyotype-a picture of the condensed chromosomes of an individual

 Three reasons why cells reproduce by asexual reproduction: 1. Growth 2. Repair 3. Replacement Cell Division You make about 2 trillion new cells per day!

Mitosis-eukaryotic nuclear division- leads to the equal distribution of DNA to 2 new nuclei of daughter cells Prokaryotic cells reproduce asexually (only 1 parent) by an entirely different mechanism called binary fission

G1 (Growth 1) G1 (Growth 1) –cell carries out routine functions S (Synthesis) S (Synthesis) - DNA copied, each chromosome is 2 chromatids attached at the centromere G2 (Growth 2) G2 (Growth 2) - cell prepares for division, microtubules rearranged

Mitosis Mitosis – nucleus divided into 2 nuclei Cytokinesis Cytokinesis – cytoplasm divides G 0 phase-cell does not copy DNA or prepare to divide

 Interphase  Prophase  Metaphase  Anaphase  Telophase & Cytokinesis

Chromosome # doubles Chromosomes appear as threadlike coils (chromatin)

Animal Cell Plant Cell

Mitosis (cell begins to divide)DNA tightens into chromosomes, nuclear membrane breaks down and disappears Centrosomes-dark spots that appear next to the nucleus and begin to move to opposite end of the cell-if an animal-then has a pair of centrioles Spindle fibers made of microtubules, form between the poles-mitotic spindle-to equally divide the chromatids

 Kinetochore fibers-attach to centromeres-extend to the centrosomes  Polar fibers-extend across cell from pole to pole, do not attach to chromosomes

Animal CellPlant Cell

 Kinetochore fibers move chromosomes to the center of the cell

Animal Cell Plant Cell

 Chromatids separate and begin to move to opposite ends of the cell.

Animal CellPlant Cell

Two new nuclei form Chromosomes appear as chromatin (threads rather than rods) Mitosis ends

Animal Cell Plant Cell

 Cell membrane moves inward to create two daughter cells – each with its own nucleus with identical chromosomes

Interphase Prophase Metaphase Anaphase Telophase Interphase

Prophase Metaphase Anaphase Telophase Interphase