Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Cell Division & Cell Cycle Control Cell Division Cell types in eukaryotic organisms: Somatic cells = body cells Humans – 46 chromosomes; diploid; 2N - Two sets of chromosomes Gametes = sex cells Humans – 23 chromosomes; haploid; N - One set of chromosomes Chromosome Anatomy Sister chromatid (each ½); each has identical DNA Only called this when Attached by Centromere Kinetochore: Area where spindle fibers (microtubules) will attach and pull the chromatids apart in M & M. Cell Division (two types) - Mitosis = process produces to somatic daughter cells identical to original cell. (Review on own) Asexual reproduction 1 One 2N (diploid) cell produces two identical 2N cells. Purpose = growth, repair, maintenance - Meiosis = produces gametes with half the genetic information as the parent cell. Associated with sexual reproduction 2N (diploid) cell produce N (haploid) cell(s). Purpose = making cells with ½ the parental genetic information increases variation in a population These cell division processes are important parts to the Cell Cycle - Has a series of checkpoints that are highly regulated by their internal and external chemical environments and size. 2 Stages of the Cell Cycle: INTERPHASE – most of cell’s life is spent here consist of (G1, S & G2). • DNA relaxed (Chromatin) G0 = after a split = cell arrest Some cells permanently stuck here Ex. Nerve cell of CNS Some cells will enter cycle via signal… Ex. skin cell, muscle cell - G1 (1st gap) = first growth phase; organelles duplicate G1 check point – controlled by: • Cell size • Growth factors • Environment - S (synthesis) = Synthesis phase ~ DNA replication (more to come…) - G2 (2nd gap) = second growth phase ~ more growth and prepare for cell division G2 check point – controlled by: • DNA replication • DNA damage/mutations • Cell Size 3 MITOSIS or MEIOSIS = division of chromosomes (PMAT) M check point (meta/ana) - controlled by Spindle fibers (microtubules) attachment to chromosomes • DNA condensed (Chromosome) CYTOKINESIS = division of cytoplasm 1. Cleavage = animal cells form cleavage furrow o Microfilaments form a contractile ring around center of cell and pinch. 2. Cell plate formation = plant cells o Golgi body forms vesicles - cell wall material = move to cell plate area…continues until o Membrane of plate is full; two plasma membranes formed from vesicle’s membrane. o At that point, two daughter cells 4 In Prokaryotes: Cell division = Binary Fission - Genes located on a singular circular chromosome. - As DNA of chromosome replicates at specific locations (origin of replication…) - Origins move to opposite ends of cell, stretching cell - Cell grows to twice the size… - Replication done, plasma membrane grows inward - Cell divides - 2 identical daughter cells results. 5 Evolutionary relationships: - The DNA sequences & protein structures that control Binary fission in prokaryotes are the same in mitosis for eukaryotic cells. Molecules of the Cell Cycle Control System: 1. Protein Kinases – activate/inactivate proteins via phosphorylation - Present in constant concentration in an inactive form - Activated (controlled) by presence of… 2. Cyclins - Fluctuating concentrations So, the kinases that help control the cell cycle are called Cdks (cyclin-dependent kinases) 6 External control of Cell Cycle: Growth factors (GF) = proteins released by certain cells that stimulate other cells to divide. • Triggers signal transduction pathway that allows a cell to pass G1 Ex. ~ injury… stimulates platelets in blood to release specific GF in area; causing fibroblast cells to divide healing the wound. Environment Ex. ~ When the associated cyclin accumulates during G2… • Cdk = MPF (M-phase promoting factor/maturation promoting factor) triggers cell to pass G2 checkpoint into the M phase. 7 • MPF involved in a phosphorylation cascade within the nuclear lamina that leads to the degradation of the nuclear envelope. • When in M phase (during anaphase) leads to destruction of its own cyclin. • Remains inactive until enough cyclin is built up again to continue past G2 checkpoint,…again. Cell density & size • Density-dependent inhibition = crowded cells stop dividing. • Due to not enough supply of GF and nutrients to supply numbers of cells for division. And… • If a cell gets too big, not enough nutrients/molecules/ ions can cross plasma membrane to run cell efficiently (SA/V). • Recalls cell from G0…. Internal control of Cell Cycle: Ex. • During M phase checkpoint… • All chromosomes must be attached at kinetochores before separation of sister chromatids 8 Cancer Cancer cells don’t respond to cell cycle control mechanisms. Cells keep dividing and can invade other tissues. - Do not respond to depletion of GF (they may make the required growth factor on their own) - Do not respond to density dependency - If they do stop at any point in the cell cycle = random points vs. normal checkpoints. Transformation = normal cells turn into cancer cells. Results in a tumor • If a tumor remains in the original tissue from where it started = benign • If tumor invades another tissue = malignant - Can impair function of the said other tissues and the organ(s) they are part of. Metastasis – physical spreading of tumor - Cancer cells may destroy attachments to neighboring cells (protein = gap junctions) - Extracellular matrix between cancer cells can spread into neighboring tissues. 9 - May secrete signal molecules that cause blood vessels to grow toward tumor. - Nearby cancer cells may separate from original tumor and enter blood stream/lymph system and travel to other locations and proliferate there. Treatment: Chemotherapy = drug given through IV (blood) that interferes with the cell cycle. Ex. stops production of protein microtubules of spindle complex. Radiation = localized radiation waves damage cancer cell DNA (more than normal cells) - Cancer cells don’t have the DNA repair mechanisms that normal cells have. 10