Human body makes more than 20 billion new cells every day Human body makes more than 20 billion new cells every day. Over the course of 7 years, all body cells have been replaced (except nerve cells). How does your body make all these new cells?

Cell Cycle Notes Cell Division — process by which a cell divides into 2 new cells Why do cells need to divide? Living things grow by producing more cells, NOT because each cell increases in size Repair of damaged tissue If cell gets too big, it cannot get enough nutrients into the cell and wastes out of the cell to maintain homeostasis

I. DNA – Deoxyribonucleic acid; located in nucleus A. Long and thread-like DNA in a non-dividing cell – chromatin B. Thick, short, coiled doubled DNA in a dividing cell – chromosome

chromosome consists of 2 parts: a. chromatid b. centromere – protein tab that holds 2 sister chromatids together

2. chromosomes are divided into segments called – genes

coils up into chromosomes C. Illustration: chromatin to chromosomes duplicates itself chromatin coils up into chromosomes Why does DNA need to change from chromatin to chromosome? More efficient division

II. Cell Cycle – the repeating sequence of growth and II. Cell Cycle – the repeating sequence of growth and division of a eukaryotic cell A. The cell spends most of its time in – Interphase 1. Interphase: cell grows, DNA is loosely wound, and cell carries out normal functions

cell grows and matures – G1 (first growth) 2. 3 phases: cell grows and matures – G1 (first growth) chromatin duplicates – S (synthesis) organelles replicate and cell prepares for division – G2 (second growth) G1 phase S phase G2 phase

B. Division of the nucleus – mitosis

C. Division of the cytoplasm and organelles – cytokinesis Occurs quickly 1. In animal cells the cytoplasm pinches in (Cleavage Furrow) 2. In plant cells a cell plate forms Cell plate D. After mitosis and cytokinesis, the cell returns to Interphase

III. Mitosis – division of the nucleus into 2 nuclei, each with the same number and kind of chromosomes A. HANDOUT

nuclear envelope breaking apart Prophase duplicated chromosomes nuclear envelope breaking apart spindle fibers form

Metaphase (middle) spindle fibers centriole

Anaphase (away) individual chromosomes

nuclear envelope reforming chromosomes unwind into chromatin Telophase (two) nuclear envelope reforming chromosomes unwind into chromatin

Cytokinesis

Interphase centrioles nuclear envelope chromatin

B. 4 phases PMAT 1. chromosomes condense, nuclear envelope breaks down, spindle fibers form – Prophase 2. chromosomes line up along equator -- Metaphase 3. chromatids separate, centromere divides, and move to opposite poles – Anaphase 4. chromosomes uncoil, new nuclear envelope forms spindle fibers break down – Telophase

What Phase Of the Cell Cycle Is It? B C Anaphase Telophase Cytokinesis D E F Interphase Metaphase Prophase

2 Daughter Cells Parent Cell C. Mitosis occurs only in body cells, or – somatic cells D. 2 new cells formed have same number and kind of chromosomes as original 1. original cell called – parent cell 2. cells formed are known as – daughter cells 2 Daughter Cells Parent Cell

E. Many organisms, especially unicellular E. Many organisms, especially unicellular organisms, reproduce by means of cell division-- called asexual reproduction ex: bacteria

Summary: Cell Cycle Interphase Mitosis (PMAT) Cytokinesis ** Daughter cells genetically identical to parent cells

F. Chromosome Number 1. number of chromosomes each organism has in its cells varies from species to species example: human = 46 lettuce = 18 dog = 78 gorilla, chimp = 48

2. all cells (except the sex cells) in an organism have the 2. all cells (except the sex cells) in an organism have the same number of chromosomes example: human = 46 human skin cells = 46 human muscle cells = 46 human heart cells = 46

a. cyclins initiate the various stages of cell cycle G. Regulating the Cell Cycle – not all cells move through cell cycle at the same rate 1. in eukaryotic cells, timing of the cell cycle is regulated by – proteins called cyclins a. cyclins initiate the various stages of cell cycle

2. cell cycle checkpoints -- regulate progress of cell cycle a. ensure that damaged DNA not passed on to daughter cells b. G1 checkpoint at end of G1 phase -- determines whether cell is ready to divide or not c. G2 checkpoint at end of G2 phase – check if DNA replication finished d. M checkpoint at Metaphase – check for whether chromosomes properly attached to spindle fibers

3. injuries affect rate of cell division a. cells at edge of injury stimulated to divide rapidly -- producing new cells b. when healing is completed, rate of cell division -- slows down and returns to normal

4. when cells come into contact with each other 4. when cells come into contact with each other in culture, they stop dividing

G. Uncontrolled Cell Growth 1. control over cell cycle can break down resulting in – cancer 2. cancer cells do not respond normally to – signals that regulate cell division 3. cells divide uncontrollably forming – tumors and can invade other tissues

4. mutations in DNA leading to tumors can be caused by: a. chemicals – smoking or asbestos (lung cancer) b. radiation – sun -- UV rays (skin cancer) c. viruses – HPV (cervical cancer) or hepatitis (liver cancer) d. immune system disorders – HIV (many different cancers) e. heredity – genetics

3. p53 – “ guardian of the genome” a. plays role in triggering control mechanisms at checkpoints -- suppresses tumors to prevent cancer b. p53 can either – repair faulty DNA or – kill off cell if it can’t be repaired (apoptosis) c. problems with gene p53 -- related to more than 50% of all cancers

Chromosome Appearance & Location Phase Chromosome Appearance & Location Important Events Interphase Prophase Metaphase Anaphase Telophase Cytokinesis DNA replication, cell grows and replicates organelles DNA/chromatin copies itself Nuclear envelope disappears, spindle fibers form Chromosomes coil up Chromosomes line up in the middle Spindle fibers connect to chromosomes Spindle fibers pull chromosome copies apart to opposite poles Chromosome copies divide and move apart Nuclear envelopes reform, 2 new nuclei are formed, spindle fibers disappear Chromosomes uncoil back into chromatin Division of the rest of the cell: cytoplasm and organelles Chromatin