Download 1. There are some terms that you should be familiar with before

October 24, 2013
1. There are some terms that you should be familiar with before diving into cellular division and mitosis. De:ine/explain the following terms: > Genome: Cell’s endowment of DNA or its genetic information. Before the cell can divide, the cells genome must be copied. > Somatic cells: All body cells except gametes. > Gametes: Sperm and egg cells. These are haploid, and have half the number of chromosomes as a diploid cell. Meiosis results in gametes. > Chromosome: A eukaryotic DNA molecule with proteins attached to it. Before a cell enters nuclear division, it duplicates every one of its chromosomes. > Sister Chromatid: Each chromosome and its copy stay attached to each other until late in mitosis, as sister chromatids. > Centromere: This is where sister chromatids are attached. It’s a constricted region along the length of the sister chromatid. > Diploid: Chromosome number is diploid, when a cell has two of each type of chromosome characteristic. October 24, 2013
2. What is the signi:icance of chromosome replication and cell division?
Chromosomes are duplicated before nuclear division. Each chromosome and its copy stay attached to each other until late it mitosis.
October 24, 2013
3. When we say that cells go through the cell cycle, what does that mean? The cell cycle is the life of a cell from the time it is :irst formed from a dividing parent cell until its own division into two cells. Starts every time a new daughter cell forms by mitosis and cytoplasmic division and ends when that cell :inished its own division. Mitosis, cytokinesis, and interphase constitute one turn of the cell cycle. October 24, 2013
October 24, 2013
4. What is interphase and what are the three stages of interphase? Interphase is the portion of the cell cycle when a cell increases in mass, roughly doubles the number of its cytoplasmic components and duplicates its DNA. Makes up 90% of the cell cycle. October 24, 2013
5. Give a brief description of each of the phases of interphase. G1 Phase-­‐ “Gap” Cell grows while carrying out cell functions unique to its cell type. Chromosomes are unduplicated and this is before DNA replication. Most of our cells remain in G1, when they build nearly all of the proteins, carbohydrates, and lipids they use or export. S Phase-­‐ “Synthesis” The cell continues to carry out its unique functions but does one other important process-­‐it duplicates its chromosomes. It faithfully makes a copy of the DNA that makes up the cell’s chromosomes. DNA replication is completed. G2 Phase-­‐ Second interval “Gap” This is the gap after the chromosomes have been duplicated and just before mitosis. The cell is preparing for division. October 24, 2013
6. The cell cycle is directed by internal controls or checkpoints. Internal and external signals provide stop and go signs at checkpoints. What are the major cell cycle checkpoints? G1 checkpoint-­‐ Seems to be the most important. If the cell gets the go-­‐
ahead signal at this checkpoint, it usually completes the whole cell cycle and divides. If it does not receive the go-­‐ahead signal, it enters a nondividing phase called the G0 phase. Cells are stimulated by the appropriate external growth factors here. G2 checkpoint-­‐ checks for damage after DNA is replicated, and if there is damage, it prevents the cell from going into mitosis.
M phase checkpoint-­‐ checkpoint assures that the mitotic spindles or microtubules are properly attached to the kinetochores (anchor sites on the chromosomes). If the spindles are not anchored properly, the cell does not continue on through mitosis.
October 24, 2013
7. Explain the signi:icance of the following complexes and proteins that control cell division. CDK’s (cyclin dependent kinases): Kinases are protein enzymes that control the cell cycle. They exist in cells at all times but are only active when they are connected to cyclin proteins. Thus, they are called cyclin-­‐dependent kinases. Speci:ic kinases give the go-­‐
ahead signals at the G1 and G2 checkpoints. MPF (mitosis promoting factor): When a CDK partners with a cyclin, a complex such as a MPF is formed. When enough molecules of MPF are produced, the cells pass the G2 checkpoint, and initiate the events of mitosis. October 24, 2013
8. When does mitosis occur? What does mitosis produce? Mitosis occurs after DNA replication, is followed by cytokinesis, and produces two genetically identical daughter cells. October 24, 2013
Prophase-­‐ 1.
The chromatin becomes more tightly coiled into discrete chromosomes. 2.
The nucleoli disappear. 3.
The mitotic spindle (consisting of microtubules extending from the two centrosomes) begins to form in the cytoplasm. October 24, 2013
Prometaphase (Transition to Metaphase) 1.
The nuclear envelope begins to fragment, allowing the microtubules to attach to the chromosomes. 2.
The two chromatids of each chromosome are held together by protein kinetochores in the centromere region. 3.
The microtubules will attach to the kinetochores. October 24, 2013
Metaphase 1.
The microtubules move the chromosomes to the metaphase plate at the equator of the cell. The microtubule complex is referred to as the spindle. 2.
The centrioles have migrated to opposite poles in the cell, riding along on the developing spindle. October 24, 2013
Anaphase
1.
Sister chromatids begin to separate, pulled apart by motor molecules interaction with kinetochore microtubules. 2.
The cell elongates, as the nonkinetochore microtubules ratchet apart, again with the help of motor molecules. 3.
By the end of anaphase, the opposite ends of the cell both contain complete and equal sets of chromosomes. October 24, 2013
Telophase
1.
The nuclear envelopes re-­‐form around the sets of chromosomes located at the opposite ends of the cell. 2.
The chromatin :iner of the chromosomes becomes less condensed. 3.
Cytokinesis October 24, 2013
10. Describe the process of cytokinesis. This begins during telophase in mitosis. The cytoplasm of the cell is divided. In animal cells, a cleavage furrow forms that eventually divides the cytoplasm. In plant cells, a cell plate forms that divides the cytoplasm.
October 24, 2013
11. How are the cell cycle and cancer related? Cancer cells do not exhibit density-­‐dependent inhibition (where crowded cells stop dividing) or anchorage dependency, in which normal cells are attached to a substratum, like tissue, to divide.