AP Biology - Reading Guide QuestionsCh. 12: The Cell Cycle

Instructions: You are to complete every question, regardless of the quality of your answer. Each question must also be answered using complete sentences and thoughts. Grammar and the accuracy of your statements count, so think through your answer. Incorrect information can cancel a correct thought. If you choose to include a diagram, it must be properly and completely labeled, but cannot be the only response provided. Finally, you are not permitted to copy/plagiarize any source including your text book and websites. You are to produce your own original work and while paraphrasing may sometimes seem like the only way to answer a question, you need to prove to me that you have processed the information for your own understanding.

1. Link the terms gametes, chromosomes, chromatin, somatic cells and genome together.

Chromosomes are genetic material in the nucleus of the cell that are made up of the DNA, which contains the genes. This gives the cell its unique characteristics. What is also unique to the cell is the number of chromosomes it contains; each cell contains a specific amount. Somatic cells, which are the body cells of humans excluding sperm and eggs cells, have 46 chromosomes, 23 from one parent and the other 23 from the other parent. On the other hand sperm and egg cells, gametes, have only 23 chromosomes. All of these chromosomes, including all other eukaryotic cells’ chromosomes, consist of the DNA material along with proteins to help the chromosome function and remain secure. This is known as chromatin. Together, all of this genetic material is known as the cell’s genome. In order for all cells to have a proper genome, when a cell divides to form a new cell, the DNA first has to be doubled.

2. Produce a simple compare and contrast of mitosis and meiosis.

During mitosis, somatic cells are produced. This happens when the starting cell’s (parent cell) DNA, and therefore chromosomes, are copied and then doubled. This results in the formation of two sister chromatids that make up the chromosome. Identical genetic information is found amongst the sister chromatids. Then, these two sister chromatids begin to break apart from each other and form two, single chromosomes. As the nucleus begins to separate, these chromosomes are brought to the two daughter cells once cytokinesis occurs. These chromosomes have the exact genetic information as each other ultimately 46 chromosomes will make

up one (body/somatic) cell. This process is similar to meiosis in that chromosomes are distributed to from new cells. However, meiosis is different because it creates new daughter cells in the gonads that do not have the exact genetic information as each other. Additionally, the daughter cells that are produced are gametes, not somatic cells. These daughter cells that form also only have 23 chromosomes rather than 46.

3. Name and describe what occurs and either limits or permits each stage of the cell cycle.

The first stage is Interphase, which is made up of G1 phase, S phase, and G2 phase. During the G2 phase, the nucleus, with a nucleoli, is surrounded by nuclear envelope. A centrosome doubles to form another centrosome. Chromosomes have been doubled from the S phase but have not taken their shape yet. Next is prophase. During this stage, chromosomes begin to take shape because chromatin fibers begin to coil. Two sister chromatids form from the chromosomes. Centrosomes move apart and release microtubules, forming an aster of microtubules that make up the mitotic spindle. The nucleoli also disappear. Then there is prometaphase. During this phase, the nuclear envelope begins to deteriorate which causes microtubules to move towards chromosomes to pass through the middle of cell. Chromatids of chromosomes contain kinetochore (proteins), which is the attachment site to the spindle. There are also microtubules connected to the kinetochore to move the chromosomes. Next is metaphase. This is the longest stage. Centrosomes are at completely different ends by this point. Chromosomes with their centromeres align themselves on metaphase plate (center). Kinetochores are connected to microtubules, again creating keeping the spindle. After this comes anaphase, which is the shortest. During anaphase, sister chromatids separate to form individual chromosomes, which move to different sides of the cell (starting with centromere) and causes kinetochore microtubules to shrink. The cell stretches out when other microtubules stretch. At the end of this stage, chromosomes are equally distributed to both sides of cell so that it can soon divide. The last two phases are telophase and cytokinesis. During telophase, 2 daughter nuclei begin to take shape as well as a nuclear envelope from the parent cell’s envelope. Chromosomes loosen and lose their compactness. During cytokinesis, the cytoplasm doubles and splits. Cleavage furrow forms (indent) in animal to separate the cells apart. This production of 2 daughter cells is the M phase. After, the newly formed cells can then go through interphase and G1 phase so that the cells can grow and duplicate within to prepare for more divisions.

4. What role does the centrosome play in both plants and animal cell division?

Centrosomes are important in both plant and animal cell division because they help create the mitotic spindle (microtubules and proteins), which is necessary in mitosis in order for the chromosomes to separate and then to move apart so that the cell can divide. The centrosome helps to build this spindle because it helps bring all the microtubule fibers together. In order for this to happen, the centrosome must first double to form another centrosome. Then the two centrosomes must relocate (during prophase and prometaphase) to different ends of the cell. As they do so, microtubules are released out from the centrosomes. By the time the two centrosomes reach different sides of the cell and move to the pole of the spindle, the microtubules form an aster, multiple microtubule fibers that are connected to each centrosome. The apparatus forms. The centrosome plays almost the same role in both animal and plant cells. The only difference is that in animal cells, centrioles are found in the centrosomes. However, they have little importance when it comes to forming the mitotic spindle.

5. Label the following diagrams indicating key features in each cell stage.

The nucleus, with a nucleoli, is surrounded by nuclear envelope. Two centrosomes are present after first centrosome doubles. Chromosomes have been doubled but have not taken their shape yet.

Chromosomes begin to take shape as chromatin fibers coil. Two sister chromatids form from the chromosomes. Centrosomes move apart and release microtubules (asters form), forming mitotic spindle. Nucleoli disappears.

Nuclear envelope begins to break apart which causes microtubules to move towards chromosomes; microtubules pass through middle of cell. Chromatids of chromosomes contain kinetochore (protein) which is the attachment site. There are also microtubules connected to the kinetochore to move the chromosomes.

6. Taken from pg. 225 (7th edition), Figure 12.8: Inquiry – During anaphase, do kinetochore microtubules shorten at their spindle pole ends or their kinetochore ends?

Kinetochore microtubules shorten at their kinetochore ends, not their spindle pole ends, which explains that as chromosomes move and follow the microtubules and move to different ends of the cell, the kinetochore microtubules shorten at their kinetochore ends.

7. Who/what utilizes binary fission and what are the complications with a so-called simpler division?

Prokaryotic cells reproduce and create new cells through binary fission, which occurs when the DNA (bacterial chromosome) doubles at the origin of replication and then the two separate chromosomes move away from each other until they reach different sides of the cell. The plasma membrane must also be doubled so that the prokaryote can split to form two cells. However, there are complications that come with binary fission. However, although this process is simpler because there is only one bacterial chromosome that contains the DNA, when this chromosome

Longest stage. Centrosomes are at completely different ends. Chromosomes with their centromeres align themselves on metaphase plate. Kinetochores connected to microtubules, again keeping the spindle.

Shortest stage. Sister chromatids separate to form individual chromosomes, which move to different sides of the cell (starting with centromere) and causes kinetochore microtubules to shrink. Cell stretches out when other microtubules stretch. Chromosomes equally distributed to both sides of cell.

2 daughter nuclei take shape with nuclear envelope from parent cell. Chromosomes loosen.Cytoplasm doubles and splits. Cleavage furrow (indent) in animal cells to separate.

starts to double the chromosomes begin to take over the cell because the cell is so small. In order for the chromosomes to fit within the cell before it has the chance to expand and eventually split, the chromosomes have to be folded or coiled a lot more than they usually would have to. Because of this there can always be problems with creating new and exact genomes.

8. Your textbook provides an analogy for the cell cycle control system. This question asks that you provide a different visual anaology (i.e. – draw one) and label it properly with the correct checkpoints.

9. Translate into Freshman-level English, this phrase from your textbook, “…kinases are enzymes that activate or inactivate other proteins by phosphorylating them.” and explain in what area of cell division this applies (with AP-level detail).

Kinases are enzymes that are used to attach phosphate groups to other proteins, so that those proteins change in some way to be effective within the cell cycle. Protein kinases are involved during the G1 and G2 checkpoints, because they are the proteins that control whether or not the cell can continue its cycle or not. If a cell can pass through the G2 checkpoint it can then enter the M phase. However, in order for kinases to work and be active they are connected with cyclin to form Cdks. One type of cyclin Cdk complex is MPF, which adds phosphate groups to proteins to help begin mitosis. During anaphase, cyclin is removed from the MPF so that the Cdk remains, waiting for new cyclin made during S and G2 phases so that it can produce MPK again.

10. How do the terms density-dependent inhibition, metastasis and anchorage dependence relate to the growth of cancer cells?

Cancer cells are cells within the body that grow without limitations. Cancer cells are so dangerous because they do not have density-dependent inhibition, which is the idea that cells divide and reproduce only as much as they need to based on growth factors and nutrients. When cells run out of nutrients and growth factors (protein that encourages cell reproduction) it will no longer reproduce; it will stay at that density. Cancer cells, on the other hand, do not have this; they continue to reproduce regardless of the amount of growth factors or nutrients. This is caused by abnormalities or wrong signals as well as the idea that cancer cells can control what they want their growth factor amounts to be. If cancer cells are given enough nutrients that will continue to grow and divide. Additionally, cancer cells do not exhibit anchorage dependence, which is that cells must be anchored to some sort of other layer or siding in order to divide. Metastasis relates to cancer cells because as cancer cells reproduce and are contained in one area, they have the ability to spread to other areas of the organism via blood and lymph vessels. When tumors form, some cells from the tumor can travel through the blood vessels and spread throughout the body, which makes cancer that much more dangerous.