BIO 101 1st EditionLecture 16Outline of Last LectureI. Calvin CycleII. Light Reactionsa. Photosystem Ib. Photosystem IIIII. The Circle of LifeOutline of Current LectureI. Cell divisiona. Genetic materialII. Cell Cyclea. Interphaseb. Mitosisi. Prophaseii. Prometaphaseiii. Metaphaseiv. Anaphasev. Telophasec. CytokinesisIII. Cell Division Controlsa. CheckpointsChapter 12- The Cell Cycle- All cells come from other cells have the ability to reproduce- Parent cell divides to produce 2 identical daughter cells- Not a simple “pinching apart” of one cell to make 2- Complex process which passes an identical copy of the genetic material (DNA) to each new daughter cell- Occurs in 2 stages:1. Accurate replication of DNA to make 2 identical copies2. Allocation of one of the identical copies to each new daughter cell- Cell reproduction= cell division= produces 2 genetically identical daughter cellso In single-celled organisms, cell division reproduces the whole organism (ex. Bacteria, eukaryotes like amoeba or euglena_o In multicellular organisms, cell division is often used for growth and tissue repairCellular organization of the Genetic materialGenetic material= DNAGenome= a cell’s total genetic information- One or more long DNA molecules - Genes are arranged along the DNA, 100s to 1000s of genes per DNA molecule- Each gene has the code for how to make a proteinBIO 101 1st Edition- Proteins determine what an organism is and what it can doDNA is arranged as CHROMOSOMES- DNA molecule with associated proteins to help maintain structure and control the activity of the geneChromosomes take different forms- these are given different names1. Chromatin- mass of dispersed DNA plus proteins found in between periods ofcell division2. Replicated chromosome- when the DNA molecules replicate (an exact copy is made)- the 2 copies remain held together along the length by proteins called cohesins and take on a condensed form (become shorter and thicker and can be seen more easily)- In replicated chromosome each DNA molecules is called a SISTER CHROMATID and the 2 sister chromatids of a replicated chromosome are more tightly held together at a region called the centromereCell Cycle- In eukaryotic cells, cell division is complex and usually there are multiple chromosomes- Cell division occurs in 2 MAJOR PHASES1. Interphase- a period of growth2. Mitosis and cytokinesis- division of the nucleus and cytoplasmInterphase- approx. 90% of cell cycle is spent in interphase- 3 substages1. G1- cell grows and gets bigger2. S- DNA replicates, cell continues to grow3. G2- cell gets ready for mitosis and cytokinesis- makes special proteins needed for thatMitosis- division of the nucleus (5 phases)1. Prophase- Replicated chromosomes condense- Nuclei: break down- Spindle apparatus is formed= serves to more chromosome aroundBIO 101 1st Edition2. Prometaphase- Nuclear envelope breaks down- Spindle apparatus attaches to replicated chromosomes at the KINETOCHORE= protein complexes located at the centromere where sister chromatids are connected3. Metaphase- Replicated chromosomes line up single file in the center of the cell4. Anaphase- Sister chromatids separate and are pulled to opposite poles of the cell-once the sister chromatids separate, they are bone fide chromosomes5. Telophase- Chromosomes decondense chromatid- Spindle apparatus disappears- Nuclear envelope reformsBIO 101 1st EditionCytokinesis- division of the cytoplasm- Animal cellso Cells are pinched aparto First a “cleavage furrow” forms between 2 newly formed nucleio Microfilaments form a ring at cleavage furrow and tighten to pinch 2 cells apart- Plant cells- vesicles from golgi meet and fuse in center of cello Forms 2 new membranes within single cell wallo New cell wall forms between 2 new membranesControl of Cell Division- Important for a cell to know when to divide and when to stop dividing- Varies with cell typeEx: skin cells (epidermis)- divide frequently throughout life (always sluffing off and being replaced)Liver cells- only divide for repair purposesBIO 101 1st EditionNerve and muscle (specialized cells)- do not divide in the adult- Mechanisms that control CELL CYCLE are of intense interesto Understand how normal cells regulate growtho Understand how cancer cells escape the usual controlsWhat are the signals that tell cells to divide?- This is often studied using tissue culture-grow cells in flasks using artificial growth media- Normal Cells in tissue culture grow and divide and compete with each other for growth factors in media o Exhibit density dependent inhibition= CONTACT INHIBITION= grow until they touch one another and then STOPo Limited number of cell divisions normal cells divide 20-50 times, then STOP, AGE, and DIE- Cancer Cells in tissue culture behave differently from normal cellso Don’t show CONTACT INHIBITION- pile up on top of each othero IMMORTAL they divide indefinitelyWhat are the important CELL CYCLE CONTROL POINTS?There are cell cycle control points called CHECKPOINTS- points in cycle where STOP and GO AHEAD signals are givenMolecular sensors at checkpoint- check to see if all the right things have happenedMolecular brakes at checkpoint- slow things down if something is wrongApoptosis- cell suicide- if cell cycle controls don’t result in correction of a problem, the cell may kill itselfThere are 3 major CHECKPOINTS in cell cycle- in G1, G2, and MITOSIS- G1/S checkpoint is most important in many cellso The cell determines if it is going to divide or NOT at this checkpointo Based on signals from environment and also on internal signals (is cellBIG enough to divide)o If cell passes the G1/S checkpoint, then it is COMMITTED to divide- it will go STEPWISE G1SG2M always completing each step before starting the nextBIO 101 1st Editiono If it decides NOT to divide, it will exit the cell cycle and enter a NON-DIVIDING STATE= G0Most of the cells of the body at in G0- G2 and M checkpoints are understood to some extent at the molecular levelCancer Cells and cell cycle controlso Mostly ignore (or don’t perceive) cell cycle controls to stop dividingo If they DO STOP dividing they often don’t STOP at the right place- STOP randomly NOT at G1/S checkpointo Results (sometimes) in cancer cell having wrong amount of DNA (if they STOP in middle of S