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Lecture 4

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Biology 1001A
Tom Haffie

September 20/2011 Biology Chapter 9- Cell Cycles (LECTURE 4) 9.1- The Cycle of Cell Growth and Division: An Overview • In mitotic cell division, DNA replication is followed by the equal separation (segregation) of the replicated DNA molecules and their delivery to daughter cells. The process ensures that the two cell products of a division have the same genetic information as the parent cell entering division • MITOSIS- the basis for growth and maintenance of body mass in multi-celled eukaryotes and for the reproduction of many single-celled eukaryotes • Chromosomes of eukaryotic cells are individual, linear DNA molecules with associated proteins • DNA replication and the duplication of chromosomal proteins convert each chromosome into a structure composed of two exact copies known as sister chromatids • When a chromosome is replicated, the amount of DNA increases but the number of chromosomes does NOT change! 9.2- The Mitotic Cell Cycle • Mitosis and interphase constitute the mitotic cell cycle. Mitosis occurs in five stages. 1. PROPHASE- The chromosomes condense into short rods and the spindle forms in the cytoplasm 2. PROMETAPHASE- The nuclear envelope breaks down, the spindle enters the former nuclear area, and the sister chromatids of each chromosome make connections to opposite spindle poles. Each chromatid has a kinetochore that attaches to spindle microtubules 3. **Kinetochore-A METAPHASE- specialized structure Spindle is fully formed and the chromosomes, moved consisting of proteins attached to by the a centromere that spindle microtubules, become mediates the aligned at the attachment and metaphase movement of plate chromosomes along 4. ANAPHASE- Spindle separates the mitotic spindle the sister chromatids and moves them to opposite spindle poles. At this point, chromosome segregation is complete. 5. TELOPHASE- The chromosomes decondense and return to the extended state typical of interphase. A new nuclear envelope forms around the chromosomes 6. CYTOKINESIS- the division of the cytoplasm, completes cell division by producing two daughter cells, each containing a daughter nucleus produced by mitosis a. Cytokinesis in animal cells proceeds by furrowing, in which a band of microfilaments just under the plasma membrane contracts, gradually separating the cytoplasm into two parts b. In Plant Cytokinesis, cell wall material is deposited along the plane of the former spindle midpoint; the deposition continues until a continuous new wall, the cell plate, separates the daughter cells Q-DURING WHICH STAGE(S) OF THE CELL CYCLE IS A CHROMOSOME COMPOSED OF TWO CHROMATIDS? A-AFTER REPLICATION DURING THE S-PHASE OF THE CELL CYCLE, EACH CHROMOSOME IS DOUBLE AT ALL POINTS AND CONSISTS OF TWO SISTER CHROMATIDS UNTIL THE SISTER CHROMATIDS ARE SEPARATED IN ANAPHASE Prophase: chromatin condenses into Interphase visible chromosomes centrosome chromosomes chromatin Intermediate filaments Prometaphase: microtubules invade Metaphase: chromosomes align at central fragmented nucleus plate Microtubule Region Are all chromosomes hooked up to spindles? Are all kinetochores attached? Anaphase: chromatids separate Telophase and Cytokinesis microfilaments ONE CHROMOSOME STILL ONE CHROMOSOME 9.3- Formation and Action of the Mitotic Spindle • IN ANIMAL CELLS the centrosome divides and the two parts move apart. As they do so, microtubules of the spindle form between them • IN PLANT CELLS with no centrosome, the spindle microtubules assemble around the n
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