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Chapter 7: A Tour of the Cell OBJECTIVES After reading this chapter and attending lecture, the student should be able to: 1. Distinguish between prokaryotic and eukaryotic cells. Prokaryotic - no nucleus, organelles; lots of ribosomes and DNA. Eukaryotic - (the opposite) 2. Describe the structure and function of the nucleus, and briefly explain how the nucleus controls protein synthesis in the cytoplasm. Contains DNA for the cell. Nuclear envenlope, chromatin, nucleolus. Sends mRNA and it is synthesized according to DNA instructions. Goes with information into cytoplasm and attaches to a ribosome, transferring the data. 3. Describe the structure and function of a eukaryotic ribosome. The sites where cell proteins are assembled. (mRNA ribosome - DNA) 4. List the components of the endomembrane system, describe their structures and functions and summarize the relationships among them. Nuclear envelope - encloses nucleus; separates from cytoplasm. Double membrane. ER - Smooth (lipids, carbs., system detox.), Rough (making secretory proteins, grows in place by budding proteins and phospholipids.) Golgi apparatus - products of ER modified, stored, released to destinations. Lysosomes - digests micromolecules (intracellular). Vacuoles - Central (store organic compounds; repository of organic ions, enrich color in pigments; protect plant.) Plasma membrane - a selective barrier that allows sufficient passage of oxygen, nutrients, and waste - in and out. 5. Describe the vacuole and list types of vacuoles. (Refer to last question.) 6. Explain the role of peroxisomes in eukaryotic cells. Contain enzymes that transfer hydrogen from various substrates to oxygen; makes hydrogen peroxide. Some break down fatty acids, liver - detox. alcohol, etc.; in fat-storing tissues of plants fatty acids to sugar. 7. Identify the three functional compartments of a chloroplast. Thylakoids - membranous system. Grana- thylakoids stacked like poker chips. Stroma - fluid outside the thylakoids. 8. Describe probable functions of the cytoskeleton. Give mechanical support to cell; help maintain its shape. Enables cell to change shape. Functions in cell motility - movement of cell and what’s inside of it. 9. Describe the structure, monomers and functions of microtubules, microfilaments and intermediate filaments. Tubules - made from tubulins x and B; shape and support cell; track on which organelles move. Filaments - made of actin; part of contractile apparatus of the cell, work with myosin to contract cells. Inter-keratins - more permanent fixtures of the cell; more support to shape. 10. Explain how the ultrastructure of cilia and flagella relates to their function. Cilia - occur in large numbers’ moves like boat oars; microtubules - nine doublets in a ring, two in center. Flagella - longer than cilia, but fewer. Cycle of movements causes beatings. 11. Describe the structure of intercellular junctions found in plant and animal cells, and relate their structure to function. Plasmodesmata in cell wall - allows strands of cytoplasm to pass though to another and connect with living cells. Unifies plant cell. Animal: 1) tight junctions - form continuous belts around the cell. Membranes of other cells, fused here. Seal prevents extracellular fluid leaks, 2) desmosomes - function like rivets; fastening cells to epithelial sheets. 3) gap junctions - provide cytoplasmic channels between adjacent cells. Special membranes surround each pore, wide enough for salts, sugars, amino acids. Chapter 8: Membrane Structure and Function OBJECTIVES After reading this chapter and attending lecture, the student should be able to: 1. Describe the function of the plasma membrane. It controls the passage of substances into and out of the cell. It is selectively permeable which means that it allows certain molecules to cross it more easily than others. 2. Describe the fluid properties of the cell membrane and explain how membrane fluidity is influenced by membrane composition. A membrane remains fluid until the temperature cools so much that it solidifies. It remains fluid to a lower temperature only if there are phospholipids (many) with unsaturated hydrocarbon tails. They do not pack as closely together as saturated hydrocarbons. 3. Explain how hydrophobic interactions determine membrane structure and function. A membrane is selectively permeable. It allows for the passage of hydrophobic molecules and small hydrophilic molecules, but does not allow for the passage of large hydrophilic molecules unless the movement is facilitated. 4. Describe how proteins are spatially arranged in the cell membrane and how they contribute to membrane function. Integral proteins penetrate far enough into the membrane for their hydrophobic regions to be surrounded by the hydrocarbon tails of lipids. Some reach only part way across the membrane, while others span the entire thing. Peripheral proteins are not embedded in the lipid bilayer. They are attached to the surface of the membrane (inside) and are exposed to parts of the integral protein. 5. Describe factors that affect selective permeability of membranes. While hydrophobic molecules can pass easily through the plasma membrane, those that are hydrophilic cannot do so. However, specific molecules that need to get into the cell, pass through transport proteins and therefore avoid passage through the hydrophobic layer of the plasma membrane. 6. Define diffusion; explain what causes it and why it is a spontaneous process. Diffusion is a natural passing of molecules from an area of higher concentration to an area of lower concentration. It is one result of thermal energy or, the energy of motion. It is spontaneous because it decreases free energy. 7. Explain what regulates the rate of passive transport. The rates of passive transport in diffusion are affected by the selectively permeable plasma membrane. 8. Define osmosis and predict the direction of water movement based upon differences in solute concentration. Osmosis is the passive transport of water across a cell membrane. If a cell is in a hypertonic solution, water molecules will diffuse across the membrane and into that solution because in the hypertonic solution water molecules are bound to the solutes and not able to move as freely. 9. Describe how living cells with and without walls regulate water balance. The problem of water regulation in cells without walls is solved by keep cells in an isotonic solution. That way, there is no net movement of water across the cell membrane. In cells with walls, the water balance is kept because only so much water is allowed into a cell before it exerts a back pressure to keep more from entering it. 10. Describe one model for facilitated diffusion. The transport proteins alternate between two different conformations, moving a solute across the membrane as the shape of the protein changes. The protein can transport the solute in either direction, with the net movement being down the concentration gradient of the solute. 11. Explain how active transport differs from diffusion. In diffusion, molecules naturally drift into and out of the cell. In active transport, the energy of ATP is needed to force molecules to go against their concentration gradient. 12. Explain how large molecules are transported across the cell membrane. They are transported across through exocytosis. The membrane-bounded vesicle comes in contact with the membrane and fuses, thus releasing the molecules. 13. Give an example of receptor-mediated endocytosis. It allows the cell to acquire bulk quantities of specific substances, even though those substances may not be very concentrated in the extracellular fluid. Human cells use this process to take in cholesterol for use in the synthesis of membranes and as a precursor for the synthesis of other steroids. Chapter 11: The Reproduction of Cells OBJECTIVES After reading this chapter and attending lecture, the student should be able to: 1. Overview the major events of cell division that enable the genome of one cell to be passed on to two daughter cells. Cell division involves the distribution of identical genetic material - DNA - to two daughter cells. In eukaryotes, the compact, coiled structure of DNA molecules form chomosomes. A cell preparing for duplication first duplicates all its genes and puts them equally at opposite ends of the cell. 2. Describe how chromosome number changes throughout the human life cycle. When a human life is conceived, each parents’ 23 chromosomes join to give the life 46. Then, meiosis again reduces that number down to 23 until new fertilization occurs. 3. List the phases of the cell cycle and describe the sequence of events that occurs during each phase. Interphase - divided into three: the G1 phase (a cell grows), S phase (where the chromosomes replicate), and G2 phase (nucleus well- defined. Chromosomes already duplicated, but indistinguishable because they are still in the form of loosely packed chromatin fibers. Two centrosomes outside the nucleus and in animal cells, each has a pair of centrioles.) 4. List the phases of mitosis and describe the events characteristic of each phase. Prophase - nucleus and nucleolus disappear. Chromatin fibers become tightly coiled. Each duplicated chromosome appears as two sister chromatids, joined at the centromere. The spindle fibers begin to form and chromosomes are propelled away from each other by bundles of microtubules that come between them. Prometaphase - nuclear envelope fragments. The microtubules of the spindle are now free to interact with the chromosomes. These form a row, extending the length of the cell equator. Each of the attached chromatids has a kinetochore at the centromere region. Metaphase - the centromeres of the chromosomes are all aligned with one another along the spindle, and form the metaphase plate. The identical ends of each chromatid are attached to kinetochore microtubules that are located at opposite ends of the parent cell. Anaphase - The paired centromeres separate and free the two sister chromatids. Each is now a full chromosome. They begin to move toward their kinetochores at opposite ends of the cell. By the end, each poles of the cell has an equivalent and complete set of chromosomes. Telophase and Cytokinesis - the nonkinetochore microtubules that are part of the spindle fibers, begins to elongate. Two new nuclear envelopes are formed from the fragments of the parent cell’s envelope and the nucleoli reappears and chromosomes become less tightly coiled. Now mitosis is complete and cytokiesis (division of cytoplasm) is under way. 5. Recognize the phases of mitosis from diagrams or micrographs. Prophase Telophase Metaphase Anaphase 6. Describe what characteristic changes occur in the spindle apparatus during each phase of mitosis. Prophase - in the cytoplasm, the spindle begins to form. Prometaphase - they can now enter the nucleus and interact with the chromosomes. Metaphase - becomes comprised of chromosome lined along the equator, with the respective kinetochores of the chromatids facing opposite kinetochore microtubules. Anaphase - provide a track for the new chromosomes to separate and travel to opposite poles. Telephase and Cytokinesis - the nonkinetochore microtubules elongate across the cell and the two daughter cells begin to form at opposite poles where the chromosomes have gathered. 7. Compare cytokinesis in animals and plants. Animal - occurs through a process called cleavage. The cell becomes pinched in the middle, just as microfilaments inside the plasma membrane (actin) begin to form a ring. Eventually this causes the cell to pinch in two and separate into two daughter cells. Plant - a cell plate is formed down the middle of the original plant cell. These two separate membranes remain connected (no cleavage), but each develop their own separate plasma membrane. 8. Describe the process of binary fission in bacteria and how this process may have evolved to mitosis in eukaryotes. The words literally mean, “to divide in half.” The bacteria’s genes are carried on a singular chromosome made of a DNA molecule and other proteins. The chromosome replicates and the bacterium enlarges to twice its size. Then, the plasma membrane pinches inward and the parent cell divides, leaving two new bacteria, each with a complete genome. Mitosis in eukaryotes is similar, but more advanced in that there are many more thousands of gene that need replication. 9. Explain how abnormal cell division of cancerous cells differs from normal cell division. Cancer cells are immune to the control mechanisms of the body. They divide excessively and invade other tissues. It is possible for them to kill the whole organism. As they multiply they form tumors. Benign tumors are those where cells stay in one place and cancerous tumors are those where the cells have spread to other places besides their origin.