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Cell Cycle and Cellular Reproduction Mader-Chapter 9… and some extra stuff Essential knowledge 3.A.2: In eukaryotes, heritable information is passed to the next generation via processes that include the cell cycle and mitosis or meiosis plus fertilization. a. The cell cycle is a complex set of stages that is highly regulated with checkpoints, which determine the ultimate fate of the cell. Evidence of student learning is a demonstrated understanding of each of the following: 1. Interphase consists of three phases: growth, synthesis of DNA, preparation for mitosis. 2. The cell cycle is directed by internal controls or checkpoints. Internal and external signals provide stop-and-go signs at the checkpoints. To foster student understanding of this concept, instructors can choose an illustrative example such as: • Mitosis-promoting factor (MPF) • Action of platelet-derived growth factor (PDGF) • Cancer results from disruptions in cell cycle control 3. Cyclins and cyclin-dependent kinases control the cell cycle. ✘✘ Knowledge of any one cyclin-CdK pair or growth factor is beyond the scope of the course and the AP Exam. 4. Mitosis alternates with interphase in the cell cycle. 5. When a cell specializes, it often enters into a stage where it no longer divides, but it can reenter the cell cycle when given appropriate cues. Nondividing cells may exit the cell cycle; or hold at a particular stage in the cell cycle. b. Mitosis passes a complete genome from the parent cell to daughter cells. Evidence of student learning is a demonstrated understanding of each of the following: 1. Mitosis occurs after DNA replication. 2. Mitosis followed by cytokinesis produces two genetically identical daughter cells. 3. Mitosis plays a role in growth, repair, and asexual reproduction 4. Mitosis is a continuous process with observable structural features along the mitotic process. Evidence of student learning is demonstrated by knowing the order of the processes (replication, alignment, separation). ✘✘Memorization of the names of the phases of mitosis is beyond the scope of the course and the AP Exam. Where it all began… You started as a cell smaller than a period at the end of a sentence… Getting from there to here… • Going from egg to baby…. the original fertilized egg has to divide… and divide… and divide… and divide… Why do cells divide? • For reproduction – asexual reproduction • one-celled organisms • For growth – from fertilized egg to multi-celled organism • For repair & renewal – replace cells that die from normal wear & tear or from injury amoeba Size vs. Surface Area A cell that is actively metabolizing must stay small by continuously dividing so that it can efficiently move metabolites into and out of the cell Also, remember that there is only one copy of DNA! The Life Cycle of the Cell Do all mammalian cells, through the adult stages of life, continuously move through the cell cycle? Cell Cycle G2 Gap 2 • Cell has a “life cycle” S Synthesis cell is formed from a mitotic division cell grows & matures to divide again G1, S, G2, M epithelial cells, blood cells, stem cells M Mitosis cell grows & matures to never divide again liver cells G1G0 brain / nerve cells muscle cells G1 Gap 1 G0 Resting Interphase • 90% of cell life cycle – cell doing its “everyday job” • produce RNA, synthesize proteins/enzymes – prepares for duplication if triggered I’m working here! Time to divide & multiply! Interphase • Divided into 3 phases: – G1 = 1st Gap (Growth) • cell doing its “everyday job” • cell grows – S = DNA Synthesis • copies chromosomes – G2 = 2nd Gap (Growth) • prepares for division • cell grows (more) • produces organelles, proteins, membranes G0 green = key features Interphase • Nucleus well-defined – DNA loosely packed in long chromatin fibers • Prepares for mitosis – replicates chromosome • DNA & proteins – produces proteins & organelles S phase: Copying / Replicating DNA • Synthesis phase of Interphase – dividing cell replicates DNA – must separate DNA copies correctly to 2 daughter cells • human cell duplicates ~3 meters DNA • each daughter cell gets complete identical copy • error rate = ~1 per 100 million bases – 3 billion base pairs in mammalian genome – ~30 errors per cell cycle » mutations (to somatic (body) cells) ACTGGTCAGGCAATGTC Organizing DNA • DNA is organized in chromosomes – double helix DNA molecule – wrapped around histone proteins DNA histones • like thread on spools – DNA-protein complex = chromatin chromatin • organized into long thin fiber – condensed further during mitosis double stranded chromosome duplicated mitotic chromosome Copying DNA & packaging it… • After DNA duplication, chromatin condenses – coiling & folding to make a smaller package mitotic chromosome DNA chromatin double-stranded mitotic human chromosomes Mitotic Chromosome Duplicated chromosome 2 sister chromatids narrow at centromeres contain identical copies of original DNA homologous chromosomes homologous chromosomes single-stranded sister chromatids double-stranded homologous = “same information” Mitosis • Dividing cell’s DNA between 2 daughter nuclei – “dance of the chromosomes” • 4 phases – prophase – metaphase – anaphase – telophase Overview of mitosis interphase prophase I.P.M.A.T. (pro-metaphase) cytokinesis metaphase anaphase telophase Cytokinesis • Animals – constriction belt of actin microfilaments around equator of cell • cleavage furrow forms • splits cell in two • like tightening a draw string Cytokinesis in Animals (play Cells Alive movies here) (play Thinkwell movies here) Mitosis in whitefish blastula Cytokinesis in Plants • Plants – cell plate forms • vesicles line up at equator – derived from Golgi • vesicles fuse to form 2 cell membranes – new cell wall laid down between membranes • new cell wall fuses with existing cell wall Cytokinesis in plant cell Mitosis in plant cell onion root tip Getting the right stuff • What is passed on to daughter cells? – exact copy of genetic material = DNA • mitosis – organelles, cytoplasm, cell membrane, enzymes • cytokinesis chromosomes (stained orange) in kangaroo rat epithelial cell notice cytoskeleton fibers Cell Cycle Checkpoints… Control of the Cell Cycle •Regulated by internal and external signals •Check points are built in stop points that must be overridden by go-ahead signals •G1 Checkpoint- If cell receives goahead, cell usually continues through cycle. Keep in mind, most cells of a human remain in the G0 phase •G2 Checkpoint- production of MPF pushes cell into mitosis •M Checkpoint- Before anaphase occurs, all chromosomes must be attached to spindle fibers Control of the Cell Cycle • Protein kinases (enzymes that activate other proteins by phosphorylation), Cdks in this case, remain at a constant level • Cyclins build up • The two combine to form MPF, maturation promoting factor, which pushes the cell into the M phase Stop and Go-Internal and External Signals • Nutrient factors in medium • Growth factors- local regulators, proteins, that initiate the cell communication that results in cyclins being produced. Cell communication from nearby cells is termed paracrine signaling • Density dependent inhibition • Anchorage dependence Cancer- the loss of cell cycle control • Do not heed normal cell signals • Normal cell undergoes “transformation” through one or more gene mutations • Loss of density dependent inhibition and anchorage dependence • Benign tumors stay in local tissue but malignant tumors can spread to other tissue
