Binary FissionThe Cell Cycle Control SystemLoss of Cell Cycle Controls in Cancer CellsProphase IMetaphase IAnaphase ITelophase I and CytokinesisProphase IIMetaphase IIAnaphase IITelophase II and CytokinesisLocal and Long-Distance Signaling1. ReceptionIntracellular Reception2. Signaling Transduction3. Nuclear and Cytoplasmic ResponsesChapter 12: The Cell Cycle- Multicellular organisms depend on cell division for:o Development from a zygoteo Growtho Repair- Cell division is an integral part of the cell cycle, the life of a cell from formation to itsown division.- Most cell division (mitosis) results in daughter cells with identical DNA. The daughter cells are identical to each other and the parent cells they came from.- Meiosis produces non-identical daughter cells (gametes: sperm and egg cells). - All of the DNA in a cell constitutes the cell’s genome. Genome refers to all of the DNA in a cell.- DNA molecules in a cell are packaged into chromosomes.- Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus.- Stomatic cells (non-reproductive cells) have two sets of chromosomes (1 from eachparent)- Gametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells. Gametes only have one copy of each chromosome because they combine and join with another cell—sperms and eggs combine their DNA.- Eukaryotic chromosomes consist of chromatin, a complex of DNA and protein that condenses during cell division.- In preparation for cell division, DNA is replicated and the chromosomes condense.- Each replicated chromosome has two sister chromatids, which separate during celldivision.o The term sister chromatid refers to replicated chromosomes, so they are identical.- The centromere of the replicated chromosome is where the two chromatids are most closely attached.- Figure 12.4- Eukaryotic cell division consists of:o Mitosis, the division of the nucleuso Cytokinesis, the division of the cytoplasm- The cell cycle (lifespan of the cell) consists of:o Mitotic (M) phase—the dividing phase (mitosis and cytokinesis)o Interphase—the non-dividing phase (cell growth and copying of chromosomes in preparation for cell division)- Interphase (about 90% of the cell cycle) can be divided into subphases:o G1 Phase—first gap: the cell is getting bigger in sizeo S Phase—synthesis: when the cell is getting replicatedo G2 Phase—second gap- The cell grows during all three phases, but chromosomes are replicated only during the S phase.- Figure 12.5o Most of the cell’s lifespan is spent in interphase. Very little time is actually spent dividing- Mitosis is conventionally divided into five phases:o Prophaseo Prometaphaseo Metaphaseo Anaphaseo Telophase Cytokinesis is well underway by late telophase- Homologous chromosomes have the same genes that control the same characteristics, but they are not identical. They’re a homologous pair because they have the same genes; they just have different versions of the genes. Before mitosis can occur, each chromosome must be copied and produce identical sister chromatids. Sister chromatids are identical to each other, but homologous chromosomes are not.- What process produces sister chromatids? S phase- Figure 12.6bo Kinetochores—where the kinetochore microtubules attach to the chromosomes o During prophase and prometaphase, kinetochore microtubules are attachingto the chromosomes- Figure 12.6do During metaphase, chromosomes line up at the metaphase plate with sister chromatids facing opposite ends of the cell.o During anaphase, the microtubules from the spindle that attached the to kinetochore pull the sister chromatids aparto During telophase, the cleavage furrow forms and the cell begins to divide. The nuclear envelope forms and the cells begin to split apart.- The mitotic spindle is an apparatus of microtubules that controls chromosome movement during mitosis.- During prophase, assembly of spindle microtubules begins in the centrosome, the microtubule-organizing center.- The centrosome replicates, forming two centrosomes that migrate to opposite ends of the cell, as spindle microtubules grow out from them.- During prometaphase, some spindle microtubules attach to the kinetochores of chromosomes and begin to move the chromosomes.- At metaphase, the chromosomes are all lined up at the metaphase plate, the midway point between the spindle’s two poles.- Figure 12.7- In anaphase, sister chromatids separate and move along the kinetochore microtubules toward opposite ends of the cell.- Non-kinetochore microtubules from opposite poles overlap and push against each other, elongating the cell.- In telophase, genetically identical daughter nuclei form at opposite ends of the cell.- In animal cells, cytokinesis occurs by a process known as cleavage, forming a cleavage furrow.- In plant cells, a cell plate forms during cytokinesis, which will form the cell walls of the daughter cells.Binary Fission- Prokaryotes (bacteria and archaea) reproduce by a type of cell division called binary fission.- In binary fission, the chromosome replicates, and the two daughter chromosomes actively move apart.- Binary fission is asexual reproduction. The bacteria and archaea reproduce themselves, so the only way for DNA to change is if a mutation occurs.The Cell Cycle Control System- The sequential events of the cell cycle are directed by a distinct cell cycle control system, which is similar to a clock.- The clock has specific checkpoints where the cell cycle stops until a go-ahead signalis received.- If cells get damaged, the DNA is mutated, etc., the best case scenario is that the checkpoint will notice the difference and send the cell to cell arrest where it is not allowed to divide, thus preventing the replication of the mutation.- Figure 12.14o There is a checkpoint in the G1 Phase. This is an important checkpoint, because DNA is copied in the S phase, so the mistakes need to be noticed by the S Phase.o Following the S phase is the G2 checkpoint that makes sure the S phase did not miscopy any DNA. If there is a mutation, the cell is not allowed for division.o Before mitosis is a checkpoint that makes sure the replications are okay and that the cell should be allowed to divide.- For many cells, the G1 checkpoint seems to be the most important one.- If a cell receives a go-ahead signal at the G1 checkpoint, it will usually complete the S,G2, or M phases and divide.- If a cell does not receive the go-ahead signal, it will
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