Cell Cycle 2022 - Foundational Sciences PHA810 PDF

Foundational Sciences PHA810 Cell Cycle Goals: To describe the phases of the cell cycle Objectives: 1. Describe the events that take place in each phase of the cell cycle 2. Apply information to real-world scenarios or patient cases Keywords: Interphase, G1 phase, S phase, DNA replication, G2 phase...

Foundational Sciences PHA810 Cell Cycle Goals: To describe the phases of the cell cycle Objectives: 1. Describe the events that take place in each phase of the cell cycle 2. Apply information to real-world scenarios or patient cases Keywords: Interphase, G1 phase, S phase, DNA replication, G2 phase, M phase, mitosis, cytokinesis, anaphase promoting complex, DNA polymerase Reading: Essential Cell Bio, Chp 18; Chp 19 (in BI Center) or any other cell biology book I. Two general phases of the cell cycle (Interphase and M phase) A. Interphase (G1, S, G2) 1. G1 phase a. Cell growth b. Some cells exit G1 into a stage called Go permanently (or for long periods of time) where they are considered quiescent (not dividing). The cell cycle genes are turned off in Go i. Examples: Differentiated nerve and muscle cells are in Go 2. S phase a. Replication of genome (DNA synthesis/replication). 46 chromosomes to replicate. b. DNA is copied by DNA polymerases (with the help of several other enzymes). DNA polymerases synthesize the complementary strands to the parent strands. i. DNA Helicases: Enzymes that unwind the helix by breaking hydrogen bonds ii. Topoisomerase: Enzyme that break and reform helix to relieve stress from supercoiling. (breaking and reforming phosphodiester bonds in DNA strands). https://www.youtube.com/watch?v=k4fbPUGKurI  c. The duplicate chromosomes remain bound together by proteins called cohesions (until M-phase when the chromosomes will be separated) 3. G2 phase a. Cell growth-cell has to get bigger so daughter cells are not smaller than the original parent cell B. M phase (includes mitosis and cytokinesis) 1. Mitosis (nuclear division; PPMAT) a. Prophase i. The replicated chromosomes condense ii. Centrosomes (which replicated during S phase) start to move to opposite sides of the cell and the mitotic spindle begins to assemble outside the nucleus a. Centrosomes shoot out microtubules to form mitotic spindle b. Prometaphase i. Nuclear envelope breaks down ii. This allows the mitotic spindles to contact the condensed chromosomes iii. The microtubules bind to kinetochores located at centromeres of sister chromatids a. Kinetochores are protein complexes which assemble on the condensed chromosomes c. Metaphase i. Mitotic spindle gathers all the chromosomes to the center (equator) of the cell d. Anaphase i. The two sister chromatids in each replicated chromosome synchronously split apart ii. Spindle draws them to opposite poles of the cell  iii. Anaphase begins abruptly with the release of the linkage that hold the sister chromatids together a. Activation of anaphase promoting complex (APC) triggers the separation of sister chromatids iv. Now chromatids are pulled to the spindle pole to which it is attached v. This segregates the sets of chromosomes to opposite ends of the spindle e. Telophase i. Nuclear envelope reassembles around each of the two sets of separated chromosomes to form two nuclei ii. Nucleus expands and chromosomes decondense to interphase state iii. Assembly of contractile ring (composed of actin and myosin) necessary for cytokinesis  2. Cytokinesis (cytoplasmic division) a. Division of the cytoplasm (including all organelles) by the contractile ring which pinches the two daughter cells apart. b. Begins in anaphase and is complete by the end of telophase Cell Cycle and Mitosis: https://www.youtube.com/watch?v=WAGjRcoolds (Note: this video discusses only PMAT, but later research led to dividing M phase into 5 phases PPMAT as I discussed in class)