Exam 3 Review General Cell Division 03 26 2014 Varying life spans can be very short o Taste Cells 10 days vs Muscle Cells 15 years o Most cells in body are NOT dividing Highly regulated by signals which prevent over growth o Unregulated growth leads to tumors cancer o The Cell Cycle Series of events checkpoints that must occur before a cell divides Regulated by proteins Mutations deficiencies lead to uncontrolled growth G0 Non dividing cells exit the cycle and enter G0 o G1 Growth Preparation for DNA Synthesis Non DNA contents replicate cell size increases Production of proteins enzymes needed for replication Checkpoint at the end of the phase before S Phase checks for DNA damage proper growth nutrients and energy o S DNA Replication Synthesis In eukaryotic cells DNA is organized to chromosomes Number length varies by species Each chromosome is made of one double stranded DNA piece After duplication there are two pieces sister chromatids Attached at the centromere Still mostly uncondensed during S Phase Intra S Phase checkpoint Proofreading of DNA Errors are identified and corrected o G2 Preparation for Mitosis Growth G1 G2 Checkpoint Completes growth chromosomes start to condense checks that all organelles are ready for division Cycle is halted if there is any minor DNA damage Apoptosis occurs if there is major damage o Collectively G0 G1 and G2 are the Interphase o M Prophase Metaphase Anaphase Telophase Duplicated chromosomes are separated into two genetically identical sets of chromosomes Cell has not divided into two cells at the end of mitosis o Cytokinesis Division of cellular content o Proto Oncogenes Gas Pedal Proteins that send signals to stimulate cell division Mutations can cause continual signal problem o Tumor Suppressors Brakes Proteins that send signals to stop cell division Mutations can allow cells to divide when they shouldn t o In proto oncogenes and tumor suppressors two copies 1 mom and 1 dad a mutation in a one dominant trait is sufficient enough to supercede normal protein In a recessive trait both copies need mutation for supercession Human Chromosomes Come in pairs diploid o 1 from mom 1 from dad material Stages of Mitosis o 23 unique chromosomes of unique chromosomes designated by n n 23 but diploid so 2n 46 Paired chromosomes homologous chromosomes Centrioles Star shaped cylindrical microtubule structure o Only in animal cells Pericentriolar Material Shapeless dense mass of proteins o Anchor microtubules that radiate out from centrosome o Helps form mitotic spindle Centrosomes Pair of perpendicular centrioles and pericentriolar Prophase Chromosomes super coil condense o Become visible to microscope DNA wraps around histone proteins supercoil Nucleosome Histone with DNA wrapped around it o Nucleolus nucleoli disappear o Centrosomes move to opposite ends of cell animals Microtubules radiate out from centrosomes Start to extend form mitotic spindle Prometaphase Nuclear envelope breaks apart o Mitotic spindle microtubules enter nuclear space o Each chromosome forms two kinetochores at the centromere 1 on each chromatid Kinetochore microtubules hook onto each kinetochore of each sister chromatid Metaphase Kinetochore microtubules move chromosomes to metaphase plate equator of the cell o Metaphase Spindle Checkpoint Prevents separation until properly attached aligned Ensures each daughter cell gets full correct set Anaphase Proteins that bind sister chromatids together at centromere are cleaved and sister chromatids are pulled towards poles by shortening microtubules o Each side of the cell gets all 46 chromosomes 23 pairs Telophase Nuclear envelope reforms around each set o Nucleoli reappear and chromosomes decondense o Cell continues to elongate still only one cell Cytokinesis Separation into two daughter cells o Includes division of cell membrane cytoplasm and organelles o NOT a stage of mitosis this is its own stage of the cell cycle and often begins at the same time as telophase o Contractile Ring animals Actin microfilaments form where metaphase plate was o Cleavage Furrow Microfilaments contract until membrane pinches and separates into 2 cells o In plant cells Vesicles from Golgi carrying lipids proteins and carbohydrates move along microtubules to center Vesicles fuse to form cell plate Growing cell plate fuses with existing cell membrane to form two daughter cells New wall forms between the two membranes of the cell plate Errors in Mitosis o Aneuploidy Fewer extra chromosomes in daughter cells Results in altered cell function apoptosis Common feature in many cancers Downs Syndrome 3 copies of chromosomes 21 Nondisjunction is when chromatids fail to separate during anaphase 1 cell gets 3 copies triploidy and other cell will only have 1 copy monosomy Partial Aneuploidy Partial chromosomes float around randomly and end up in one of the daughter cells should not pass checkpoints but sometimes do o Since cancer results form uncontrolled division many treatments work by preventing cell division target microtubules to prevent spindle formation Others target checkpoints to prevent entry into mitosis Impacts ALL dividing cells even healthy Clicker Questions 20 Chromatids 10 Centromeres DNA is too thin to be seen unless super coiled Centrosomes start to move to the poles as the mitotic spindle starts to form in Prophase Sexual Reproduction and Meiosis Asexual Reproduction Offspring are genetically identical to parent o Advantages Speed low energy requires only one parent o Disadvantages Lack of variation if environment changes Sexual Reproduction Genetic information from 2 parents combo o Advantages Variation survival advantages o Disadvantages Times energy risk harmful combos need 2 parents o Sex does NOT require reproduction is merely the exchange of genetic information can occur without reproduction Horizontal Gene Transfer exchange without new cells Genes Sequences of DNA coding for protein Alleles Variation in the DNA sequence for that gene variation Chromosomes One long piece of DNA that contains several genes o Gene location on chromosomes locus plural loci o Homologous Chromosomes Chromosomes that contain same genes at the same locus Homologs Alleles of genes may be same different Reproduction of Diploid Organisms o Must be a way to reduce ploidy in combination o Gametes Cells specialized for reproduction Fuse with another gamete to produce new individual o Gametes are produced through Meiosis 2n germ cells divide to produce 4 haploid gametes