AP Biology Cell Cycle

Cell Cycle ● Anything with a centromere is a chromosome ● In eukaryotes, cells divide & transmit genetic information via Mitosis & Meiosis ● Cells divide for growth & maintenance ● Cells know when to divide through chemical signals ● Interphase ○ Phase of cell growth (cells spend a majority of their life in this stage) ● Checkpoints: Ligand signals that allow/regulate a cell to continue its process ○ G1= growth ■ G1 checkpoint (before the cell begins the S phase): Checks for cell size, growth factor, & environment ○ S= Chromosomes duplicate (DNA synthesis) ○ G2 = growth/preparation for mitosis ■ G2 checkpoint (before the cell begins the Mitosis): Checks for MPF (CDK + cyclin) ● MPF: Controls the cell’s transition of G2 into Mitosis by phosphorylating & activating proteins that involves with chromosomes condensation, nuclear envelope breakdown, spindle assembly, & an enzyme that will breakdown the MPF itself ● Cyclin/CDKs: Cyclin binds to the CDK (Cyclin Dependent Kinases) enzyme (they phosphorylate) & they produce MPF (this bumps the cell into mitosis) ○ Cyclins are created during the S & G2 phases ○ CDKs are inactive until they bind with cyclin ○ When cyclin is created & is present in high amounts, it allows for MPF production & will allow for Mitosis to begin ○ MPF & cyclin activity peak during mitosis ○ During mitosis, cyclins get degraded and the CDKs become inactive again ○ The amount of CDK always remains constant ● Mitosis: The division of genetic material in the nucleus (used in tissue repair) ○ Prophase ○ Metaphase ■ M checkpoint: If the kinetochores remain unattached to spindles microtubules, anaphase will not begin ○ Anaphase ○ Telophase ● Cytokinesis: The division of the cytoplasm and produces 2 genetically identical daughter cells (in Mitosis) ● G0: A stage where the cell no longer divides/doesn’t divide as often (but it can reenter the cell cycle at some point). ○ Ex. Heart/nervous system cells ○ A cell exits the cycle & enters this stage if it doesn’t pass the G1 checkpoint ● Disruptions to the cell cycle may result in cancer or apoptosis (programmed cell death) ○ Cancer is the failure of cell-division-control (uncontrolled cell growth) ■ Control is lost when checkpoints stop functioning or if the p53 gene is shut off ■ P53 prevents cell growth by inhibiting the cell cycle (damaged DNA is not replicated & the CDK inhibitor is stimulated so cell division can’t take place) ■ Mutations that cause Cancer: ● UV radiation ● Chemical exposure -Carcinogens ● Radiation exposure - X-rays ● Pollution ● Gender ● Age (the older you are the longer you have been in contact with radiation) ● Genetics ● Gametes: Produced by Meiosis ● Meiosis (Diploid to Haploid): Produces 4 non-identical daughter cells that each have only one set of chromosomes & ½ as many chromosomes as the parent cell. ○ Involves 2 rounds (meiosis 1 & meiosis 2) ○ Meiosis 1 ■ Single stranded chromosomes replicate, creating two sister chromatids connected by a centromere ■ Prophase 1: Homologous chromosomes (1 maternal set & 1 paternal set) perform synapsis ● Synapsis/crossing over/recombination: Homologous chromosomes exchange DNA segments to increase genetic diversity among the produced gametes ● Parental: Daughter cells that look like the maternal/paternal ● Recombinant: Daughter cells that have different pieces of DNA7 ■ Anaphase 1: The homologous maternal & paternal pairs separate ■ Meiosis 2 ■ Prophase 2: No synapses ■ Anaphase 2: The chromatids are separated ■ It produces gametes (sperms/eggs) ■ Evolved from mitosis because its process is similar ■ Diversity/Variation through Meiosis: ● Crossing over (homologous chromosomes swap over pieces of chromosomes) ● Independent/ Random Assortment of chromosomes ● Random fertilization ■ Synapsis is the pairing of two homologous chromosomes that occurs during meiosis ■ Humans: Diploid cell (2n) = 46 chromosomes & Haploid cell (n) = 23 chromosomes (# of chromosomes in a gamete) Mitosis Meiosis Chromosomes # of Diploid (2n) Diploid (2n) # of DNA Replications 1 1 # of Divisions 1 2 # of Daughter Cells 2 4 Diploid (2n) Haploid (n) To produces genetically To produce GENETIC IDENTICAL cells VARIATION in Growth; repair, & cell GAMETES parent cells produced Chromosome # of Daughter Cells Purpose reproduction