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The Cell Cycle Cell Division in Prokaryotes Binary Fission: the division of a prokaryotic cell into two identical offspring cells Happens in single celled organisms bacteria reproduction Asexual Reproduction Asexual Reproduction: the production of new offspring from one parent only Examples: budding, binary fission, Parthenogenesis How does Sheldon Reproduce? advantages of asexual reproduction Stages of the Cell Cycle 1. G₁(GAP) phase: growth phase, cell grows to a healthy size 2. S (synthesis) phase: DNA is replicated (copied) 3. G₂ phase: cell grows and prepares for cell division by making new organelles 4. Mitosis: nucleus divides and each new cell is identical G₀ phase: happens when the cell is matures and needs to exit the cell cycle Examples: nerve cells cell checkpoints Stages of Mitosis hank mitosis 1. Interphase: •Cell is in a resting phase, performing cell functions •DNA replicates (copies itself) •Organelles double in number to prepare for cell division Stages of Mitosis 2. Prophase: •DNA condenses into chromosomes •Centrioles migrate to the poles of the cell •The nuclear membrane and nucleolus disappears •The Mitotic spindles form Stages of Mitosis 3. Metaphase (longest Phase) •Chromosomes line up along the equator of the cell Stages of Mitosis 4. Anaphase •Chromatids separate and move to opposite poles of the cell Stages of Mitosis 5. Telophase •Chromosomes unwind and become chromatin •The nuclear membrane and the nucleolus are reformed •The Mitotic spindle disappears Stages of Mitosis 6. Cytokinesis •Cytoplasm divides into 2 new cells evenly •The Organelles are divided equally •The 2 Daughter cells are genetically identical •The Cells return to interphase •cell division •cell division2 •cell division 3 Control of the Cell Cycle Checkpoints in the cell cycle: 1. Cell Growth Checkpoint (G₁): if the cell is a healthy size, proteins stimulate DNA replication 2. DNA synthesis Checkpoint (G₂): enzymes check the DNA, if it passes inspection it can start mitosis 3. Mitosis Checkpoint: if the cell passes, proteins trigger mitosis to stop and cytokinesis to begin cell checkpoints What happens when control is lost? Cancer: because of a mutation checkpoints are skipped and the cell replicates uncontrollably Causes: viruses, genetics, environmental factors Stem Cells Stem cells: unspecialized cells that have the potential to become any type of cell Found: in human embryos, some adult cells, umbilical cord blood Potential uses: • Repair injuries of the brain and spinal cord • Cure diseases (diabetes, cancer) • Replace organs (liver, heart, kidneys)