1. Cell Growth Review Size limitations—most cells are small, but size varies –Red Blood Cells less than 1mm diameter –Nerve cells up to a meter or more in length Need to be small enough for diffusion to occur efficiently –Wastes out –Nutrients in

2. THE CELL CYCLE AND DNA STRUCTURE KEY CONCEPT: CELLS HAVE DISTINCT PHASES OF GROWTH, REPRODUCTION, AND NORMAL FUNCTIONS

3. Cell Cycle Cell grows, prepares for division, and divides to form two new genetically identical daughter cells. Form of asexual reproduction Needed for growth and development, wound healing Cells have different life spans –Hours to NEVER (for humans) –Minutes (bacteria)

4. Stages of Cell Cycle Interphase –Longest G1 phase G2 phase G3 phase Cell Division –Shortest M phase

5. CELL CYCLE STAGES GAP 1 ( G1 ) –CELLS GROW –CARRY OUT NORMAL FUNCTIONS –REPLICATE THEIR ORGANELLES –LONGEST PART OF CELL CYCLE

6. CELL CYCLE STAGES SYNTHESIS ( S ) –DNA IN NUCLEUS COPIED DNA REPLICATION/DUPLICATION –TWO COMPLETE SETS OF DNA –Each chromosome consists of two identical “sister” chromatids attached at a centromere

8. CELL CYCLE STAGES GAP 2 ( G 2 ) –CONTINUE NORMAL FUNCTIONS –ADDITIONAL GROWTH –CHECK POINT CELL SIZE UNDAMAGED DNA READY FOR MITOSIS & DIVISION

9. CELL CYCLE STAGES MITOSIS ( M ) –TWO PROCESSES: MITOSIS – DIVISION OF CELL NUCLEUS AND ITS CONTENTS –NUCLEAR MEMBRANE DISSOLVES –DUPLICATED DNA CONDENSES –THEN SEPARATES INTO 2 NUCLEI CYTOKINESIS – DIVISION OF THE CELL CYTOPLASM RESULTING IN 2 DAUGHTER CELLS

10. What would happen if… The cell divided without replicating its DNA first? The cell continued through the cell cycle without growing? The cell kept growing without dividing? Kept replicating its DNA without dividing?

11. CELL CYCLE STAGES MITOSIS CYTOKINESIS

12. INTERPHASE MITOSIS NUCLEUSCHROMOSOMES NUCLEOLUS GRAINY

14. CELLS DIVIDE AT DIFFERENT RATES PROKARYOTES FASTER THAN EUKARYOTES IN HUMANS – S, G 2, M : ABOUT 12 HOURS G 1 DIFFERS MOST AMONG CELL TYPES RATE VARIES WITH : AGE, TYPE OF TISSUE, WEAR AND TEAR LIFE SPAN : FEW DAYS TO MANY YEARS G 0 – CELLS UNLIKEY TO DIVIDE - NEURONS Infer Do you think a skin cell would have a long or short G 1 stage? Explain why.

15. CHROMOSOME STRUCTURE CHROMOSOME: A LONG CONTINUOUS THREAD OF DNA WITH MANY GENES HUMAN BODY CELLS CONTAIN 46 EACH DNA IN ONE CELL ABOUT 3 METERS (10’) WRAPS AROUND HISTONE PROTEINS –LIKE THREAD ON SPOOLS, AT REGULAR INTERVALS; SIMILAR TO BEADS ON A STRING CHROMATIN: LOOSE COMBINATION OF DNA AND PROTEINS

16. FIGURE 5.5 CHROMOSOME STRUCTURE DNA double helix DNA and histones Chromatin Supercoiled DNA

17. CHROMOSOME STRUCTURE DURING MITOSIS OF CELL DIVISION, CHROMATIN CONDENSES AROUND ORGANIZING PROTEINS FORMS SMALL THICK RODS LOOK LIKE “X” DNA COPIED IN S STAGE DNA loose and hard to see in interphase

18. CHROMOSOME STRUCTURE CHROMATID : ONE HALF OF A DUPLICATED CHROMOSOME; SISTER CHROMATIDS HELD TOGETHER AT: CENTROMERE ENDS OF DNA MADE OF REPEATING UNITS CALLED: TELOMERES