biol131 hw7 kyle han

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Feb 20, 2024

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Homework 7 | Chapter 42 | 20 Points Question 1: Which of the following would occur in the sea urchin egg if there was an increase in Ca2+ without the presence of sperm? (2 points) a. Fertilization would occur but a normal embryo would never be allowed to form b. Fertilization would not occur because sperm is required to fertilize the egg c. Fertilization would occur and a normal embryo may form d. Fertilization would not occur and the egg would be terminated Question 2: What would happen if the G-actin within a sperm molecule was inactive and therefore unable to perform its major role? (2 points) a. Cortical Granule Exocytosis would occur allowing the membrane to harden and not allowing any other sperm to enter b. The sperm would live on as it would continue to work its way into the egg for fertilization c. Cortical Granule Exocytosis would not occur because the G-actin would not bind the sperm cell to the membrane of the egg d. Cortical Granule Exocytosis would not occur because the G-actin would harden up in the sperm which would not allow for binding of the sperm to the membrane of the egg Question 3: What is the primary difference between the slow block and fast block of polyspermy in sea urchins? (2 points) a. The slow block to polyspermy is the process of depolarization within the cell and the fast block is the process of cortical reaction b. The slow block is the process of cortical reaction and fast block is the process of depolarization c. The only difference is that the slow block takes a longer period of time then the fast block d. There is no difference between the two as they both occur at the same time and are the same process Question 4: A drug called lidocaine is introduced into the sea urchin egg bath solution. What is the direct consequence of this in the fertilization process? (2 points) a. Sperms in the bath solution undergo necrosis and die. b. The jelly coat on the sea urchin egg degrades allowing polyspermy. c. Cortical granules cannot fuse when the plasma membrane is disrupted. d. Sodium ions cannot enter the egg and the sea urchin egg cannot depolarize. Question 5: What is the main difference between spermatogenesis and oogenesis? (2 points) a. Spermatogenesis results in 2 sperms while oogenesis results in only 1 egg. b. Spermatogenesis results in 4 sperms while oogenesis results in only 1 egg. c. Spermatogenesis results in only 1 sperm while oogenesis results in 4 eggs. d. Spermatogenesis results in only 8 sperm while oogenesis results in 1 eggs.
Question 6: What is the function of cortical granules? (2 points) a. Cortical granule fusion with the plasma membrane raises the fertilization envelope and provides a slow block to polyspermy. b. Cortical granules fusion with the plasma membrane releases necessary nutrients for the fertilization process. c. Cortical granules fusion with the plasma membrane releases acrosomal enzymes that allows the acrosomal process. d. Cortical granules fusion with the plasma membrane enables depolarization of the cell membrane by allowing Na+ ion to flow in. Free Response: Draw a diagram of the process of sea urchin fertilization. Draw each of the 5 steps of fertilization in a panel-format, with one step in one box. Label the steps and highlight the following players in your response: Ca 2+ Enzymes released from acrosomal vesicle Microfilaments G-actin Fertilization Cone Jelly coat Bindin Step 1: Step 2: Step 3: Step 4 : Step 5 : You must also answer the following questions: 1. When does cytosolic calcium increase in the egg and what is the voltage-defined event that follows it? 2. If cytosolic calcium increased without the addition of sperm, which of the 5 steps in the acrosome reaction would not have occurred? 1. Cytosolic calcium increases in the egg following the binding of sperm to the egg membrane. This increase in calcium concentration triggers the cortical reaction, which is the voltage-defined event that follows. The cortical reaction leads to the release of cortical granules, which results in the formation of the fertilization envelope that helps to prevent polyspermy. 2. If cytosolic calcium increased without the addition of sperm, the acrosome reaction would not have occurred, as the acrosome reaction is triggered by the binding of sperm to the egg membrane. The acrosome reaction is the process in which the contents of the acrosome are released, including enzymes that help the sperm to penetrate the egg. Without the acrosome reaction, fertilization would not occur. Step 1: Binding: The sperm binds to the jelly coat surrounding the egg through the interaction between binding on the sperm's surface and the receptors on the jelly coat. Microfilaments and G-actin within the cytoplasm of the sperm cell play a crucial role in this step, providing the necessary structure for the sperm to penetrate the jelly coat. Step 2: Acrosomal Reaction: Upon binding to the jelly coat, the sperm undergoes the acrosomal reaction. This involves the release of hydrolytic enzymes, such as acrosin, from the acrosome, which help to digest the jelly coat and create a path for the sperm to reach the egg. G-actin plays a crucial role in the extension of the acrosomal process, which is used by the sperm to penetrate the jelly coat. Step 3: Fusion: The sperm cell fuses with the egg's plasma membrane, and the contents of the sperm, including the nucleus and centriole, enter the egg cytoplasm. This process is facilitated by the microfilaments present in the cytoplasm of the egg. Step 4: Calcium Release: The fusion of the sperm and egg triggers the release of calcium ions (Ca2+) from intracellular stores within the egg. This increase in Ca2+ concentration leads to the cortical reaction, which involves the release of cortical granules from the egg to prevent polyspermy. Step 5: Fertilization Cone Formation: As a result of the cortical reaction, the egg's cortex changes, forming the fertilization cone. This structure helps to move the sperm's nucleus towards the center of the egg and completes the process of fertilization. 7 : : FEI
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