Cell Cycle and Mitosis AP Biology Unit 3

Cell Cycle Cell Cycle = the entire cycle of a cell from one division to the next –Interphase (G1, S, G2) = between cell divisions –M Phase (Mitosis and Cytokinesis) = cell division –Continuous process of replication  alignment  separation (of DNA)

Interphase Most of the time, a cell is in Interphase G1 (Gap1) –Cell grows, copies organelles –Protein synthesis and all normal activities of cell (like cellular respiration) are carried out

Interphase S (Synthesis) –DNA is copied –Protein synthesis, cellular respiration occur –Cell continues to grow, copy organelles G2 (Gap2) –Cell growth continues –Protein synthesis and cellular respiration occur –Cell prepares to divide

M Phase Mitosis = division of the nucleus Cytokinesis = division of the rest of cytoplasm and its contents Results in 2 identical daughter cells Important for growth, repair, asexual reproduction

Duplicating Chromosomes Before cell division can occur, all of the DNA must be copied in S phase After duplication, you have 2 sister chromatids per chromosome

Sister Chromatids Sister Chromatids = identical copies of a chromosome Centromere = where sister chromatids are attached to one another Chromosome BEFORE duplication Chromosome AFTER duplication Chromosome after mitosis

Question… Why do chromosomes duplicate? –To have a copy of DNA for each new daughter cell

Haploid vs. Diploid Diploid (2n) –2 copies of each chromosome –All somatic cells are diploid (non-gametes) Haploid (n) –1 copy of each chromosome –Sperm and egg are haploid

Mitosis vs. Meiosis Mitosis –Results in 2 identical diploid daughter cells from the original diploid cell Meiosis –Results in 4 nonidentical haploid cells from one original diploid cell

Phases of Mitosis Prophase Prometaphase Metaphase Anaphase Telophase “ P P M A T ”

Phases of Mitosis Prophase (P) –Chromosomes begin to condense into chromatids –Mitotic spindle forming Prometaphase –Chromosomes condensed & attached to spindle fibers, nuclear envelope in fragments

Phases of Mitosis Metaphase (M) –Chromosomes line up in the middle of the cell Anaphase (A) –The spindle fibers pull the sister chromatids apart Telophase (T) –Nuclear Envelope reforms

Overview: Phases of Mitosis

Cytokinesis Cytokinesis differs between Animal and Plant cells Animal Cells – forms a cleavage furrow –Cells narrow and pinch off from each other Plant Cells- forms a cell plate Cleavage Furrow Cell Plate

Control of the Cell Cycle Checkpoints –determine if the cell is able to continue to the next phase –Regulated by external and internal signals (trigger signal transduction pathways) –ability proceed usually depends on whether certain processes have been completed Ex. Cell cannot start G2 until DNA has been replicated

Control of Cell Cycle Ex. PDGF –Platelet Derived Growth Factor –Released by platelet cells in response to an injury –Allows fibroblast cells in the damaged area to pass the G1 checkpoint  divide –Cell division helps to repair the damaged area

Control of Cell Cycle: G 0 G 0 –A nondividing state that cells go into if they don’t get the signal to proceed in the cell cycle –Most cells in the human body are in this state –Cells can also be triggered to come out of G 0 and re-enter the cell cycle by external signals

Control of Cell Cycle Cyclins and Cyclin-dependent kinases (Cdks) –Regulatory proteins that determine if the cell can pass checkpoints –Cyclins vary in concentration throughout the cell cycle –presence of specific cyclin/Cdks bound together (MPF) determines if cell can continue through cell cycle

Binary Fission Bacteria don ’ t go through mitosis Why not? –No nucleus, just free floating DNA Steps of Binary Fission –Cell grows in size –Copy DNA –Split cell into 2 new cells

Cancer Cancer is uncontrolled cell growth Cancer cells do not respond to checkpoint signals  keep on dividing Cancer cells no longer perform their normal functions, steal nutrients from other cells, crowd out other cells.