AP Biology Chapters 12 and 16
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Describe how the three sub-phases of interphase are alike and how they are different.
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- They are alike in that many of the cell's metabolic processes occur in all three. - They are different because either the DNA has not replicated (G1), is replicating (S) or has already replicated (G2). The checkpoints are also different in each of phase.
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Is binary fission the same as mitosis? Explain.
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- Binary fission is the division of a prokaryotic cell, which lacks a nucleus. - Mitosis is the division of the nucleus of a eukaryotic cell. They are not the same thing.
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During prometaphase, the nuclear envelope disappears. Where does it go?
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- The components of the nuclear envelope are in the cytoplasm.
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Imagine a cell that mutates and loses the function of its kinetochore proteins. Explain what this might do to the cell the next time it divides.
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- The kinetochores could not pull the replicated chromatids apart after the centromere breaks. The chromosomes would stay together and the chromosome number would likely double with each replication.
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Is mitosis the same thing as Cytokinesis? Explain.
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- No. Mitosis is the division of the nucleus while cytokinesis is the division of the cytoplasm.
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Imagine another cell mutation that allows the cell to ignore anchorage dependency. Discuss what might be the results of this mutation.
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The cells might divide and travel off. This is what happens when cancer undergoes metastasis and spreads through the body.
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Identify where in the cell cycle the three main checkpoints are located. What determines if the cell moves past each checkpoint?
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G1 checkpoint - cell must receive a go-ahead signal or exit into Go G2 checkpoint - requires MPF activity to go-ahead to mitosis M checkpoint - controls the onset of anaphase.
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Chemicals, such as colchicine from the Autumn Crocus plant, are known to disrupt spindle fibers. Speculate on what affect this will have on a cell undergoing mitosis. Identify what ploidy level (N=?) of the cell resulting from this treatment.
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- The spindle fibers will not form during mitosis and the chromatids cannot be pulled apart. - This tends to double the chromosome number (tetraploid).
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Imagine that the enzyme that breaks down cyclin is on strike and refuses to work. Explain what might be result from this situation.
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- Cyclin would remain and active MPF would be constantly present. This would signal the cell to continually divide.
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Small cuts that open blood vessels and bleed often heal faster than cuts that don't bleed (e.g. paper cuts). Using your knowledge of factors that affect cell division, speculate on a possible mechanism for why this occurs.
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- Bleeding brings platelets to the area to form blood clots. The presence of platelets places the cell division stimulate PDGF in the cut. PDGF would stimulate cell division and close the wound faster.
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What key event happens during the S phase?
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- The genetic material is duplicated
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Can plants (such as African violets) complete cytokinesis by using a cleavage furrow? Explain.
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- No. In a plant cell you have the cell wall so there's a cell plate that forms between the two cells, eventually growing all the way across to cut the cell into two daughters.
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Contrast and compare a benign tumor and a malignant tumor.
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What is a function of nonkinetochore microtubules?
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They elongate the cell during anaphase.
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Griffith
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discovered a \"transforming agent\" after he observed a non-virulent bacteria become virulent
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Avery, McCarty and MacLeod
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tested both protein and DNA, eventually proving that DNA was the \"transforming agent\"
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Hershey and Chase
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used the \"blender experiment,\" in which they tagged protein and DNA and used radioactive bacteriophages to prove that DNA was the transforming agent
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Chargaff
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came up with the rules for base pairing: %A = %T %C = %G
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Franklin
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used x-ray crystallography to determine the spacing per turn of DNA, the sugar backbone, the double-helix, and the inside location of the bases. Photo 51
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Meselson and Stahl
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let bacteria grow in different isotopes of Nitrogen (heavy and light), eventually proving the semiconservative replication of DNA
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Imagine that the bacteria in the experiment of Meselson and Stahl were grown originally on 15N media then and switched to 14N media. What should the results of the density bands look like after the 1st generation of DNA replication? After two generations of replication?
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- 1st generation. cells subjected to density-gradient centrifugation will produce a single band of DNA with medium density. - 2 generations. 50% 15N 14N DNA and 50% 14N 14N DNA
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Why is DNA replication described as semi conservative and not conservative?
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- In this case of DNA replication, the term \"semi-conservative\" means that after DNA replication, half of the DNA molecules in the daughter DNA is original DNA. This means that during DNA replication, the original double stranded DNA is separated into two DNA strands and each strand serves as a template for replication. The semi-conservative model for DNA replication was confirmed by the Meselson-Stahl experiment. In this experiment, the scientists used labeling and centrifugation to support semi-conservative DNA replication.
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What are the key points or features of DNA molecular structure as worked out by Watson and Crick?
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DNA was a double helix. Adenine and thymine form two bonds, cytosine and guanine form three bonds.
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Compare and contrast DNA replication on the leading and lagging strands.
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The leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction. DNA Replication of both strands proceeds rapidly from specific start sites
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Describe the structure of a nucleosome, the basic unit of DNA packing in eukaryotic cells.
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Consists of DNA wound around a protein core composed of two molecules each of 4 types of histones: H2A, H2B, H3, H4
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Imagine that human DNA repair mechanism No. 128 has mutated and no longer works. Speculate on the effect this might have on human cells.
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Active genes would probably experience mutations that would not get fixed. Things that could happen: 1. The cell stops doing what it's supposed to do (cells in multicellular organisms are differentiated, and many types perform jobs for the organism as a whole). 2. A mutation occurs at a gene that the cell needs for its own metabolism, and the cell dies. 3. The cell may start doing something it's not supposed to do. 4. A mutation may occur in a gene that inhibits reproduction and the cell may reproduce and its descendants form a tumor.
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What is a telomere and what is its function?
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- A telomere is a compound structure at the end of a chromosome. Telomere's protects the end of chromosomes from deterioration.
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Why is telomerase a potential target for cancer therapy? Explain.
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One of the hallmarks of advanced malignancies is continuous cell growth and this almost universally correlates with the reactivation of telomerase. Telomerase is a cellular reverse transcriptase (molecular motor) that adds new DNA onto the telomeres that are located at the ends of chromosomes. We believe that due to chromosome end fusions, there are rearrangements of chromosomes and eventually activation of telomerase. Unchecked, telomerase allows for unlimited lifespan, a hallmark of cancer cells. Telomerase is detected in about 90% of tumors. This is why telomerase is a potential target for cancer therapy
