|
|
|
AP BIOLOGY: Chapter Eleven Review Answers 
1. Several enzymes in prokaryotic DNA initiate duplication at the replication origin, whereupon replication proceeds around the entire loop of DNA until two full copies are made. These copies of DNA remain attached to the cell membrane, and when the cell undergoes binary fission, new cell membrane and cell wall materials are laid down between the replicated genomes, ensuring that each daughter cell has one copy of DNA. 2. A nucleosome is a group of eight arginine/lysine histone polypeptides. DNA duplex wraps around the histone core of the nucleosome. Supercoiling is further coiling of the DNA/nucleosome string. 3. Heterochromatin is the portion of the chromosome that is always condensed, thus the genes are never expressed. Euchromatin is the chromosomal material condensed only during cell division; at other times the genes are expressible. 4. A karyotype is the particular array of chromosomes in an organism. Differentiation is accomplished by comparing length of arms, size, staining properties, and location of arm constrictions. 5. The mitotic, or M, phase of the cell cycle is associated with microtubular assembly for cell division. The C phase is cytokinesis, when the cell is actually physically pulling apart. Embryonic tissue cells spend most of their time in the S and M phases, while most mature tissues remain in G0 most of the time. 6. Chromosomes in the S phase are dispersed, and DNA is replicating. In the G2 phase, chromosomes start to condense in preparation for mitosis. During G2, cellular organelles are also duplicated, including assembly of the microtubular apparatus necessary for cell division. 7. At the beginning of prophase rRNA synthesis stops. At this point the nucleolus disappears. 8. Metaphase begins when chromosome pairs align along a central plane of the cell, the metaphase plane. It ends with the splitting of the chromosomes into sister chromatids. 9. Anaphase is characterized by movement of the chromatids to opposite poles. The two microtubular movements are (1) sliding of adjacent pole to pole microtubules, which pushes poles apart as the cell elongates and (2) microtubules attached to centrioles shorten by actual loss of tubulin subunits pulling centromeres toward the organizing center at each pole. 10. The spindle disassembles, the nuclear envelope reforms around a group of chromatids at each pole, chromatids begin to uncoil to permit gene expression, and rRNA begins to be synthesized, making the nucleolus reappear. 11. In animals the cell pinches in two via a constricting belt of microfilaments around the cleavage furrow. In plants the cell wall prevents constriction, membrane components are assembled perpendicular to the orientation of the spindle apparatus, the cell plate grows outward to the edge of the cell, and cellulose is then laid down. 12. Cell growth is controlled at the G1 check point, DNA replication is controlled at the G2 check point, and mitosis is controlled at the M check point. Cdk's and cyclins interact to trigger subsequent steps in the cell cycle if the conditions are right. 13. Proto-oncogenes are normal genes that code for frequent cell division and as such, if mutated, could become overexpressed and code unchecked for cellular duplication leading to cancer. Tumor-suppressor genes are also normal genes that code for suppression of cell division. Should a tumor-supressor gene become mutated, unchecked cellular division may result. | ||||||||||||
The information contained on the chapter guide pages has been obtained from the publisher's website. They are merely reproduced here for easier access. Please contact Asim Ali if you have any questions or comments.
