The Different Types of Cells free essay sample

There are three major parts of a cell the nucleus, cytoplasm, and cell membrane, if these are stained appropriately, they can be easily seen under a light microscope. The nucleus (in many cell types) is the innermost and is enclosed by a thin membrane. The nucleus contains the genetic material which directs the cells function. The cytoplasm includes specialized structures called cytoplasmic organelles that are suspended in a liquid called cytosol. The organelles divide the labor in a cell by partitioning off certain areas or providing specific functions (dismantling debris, extracting energy from nutrients, or packaging secretions). They are not still, some move within the cell and others that stay in one place are the sites of ongoing biochemical activity. The cell membrane (also called a plasma membrane) contains the cytoplasm that surrounds the nucleus. This is the outermost limits of a cell, it is an actively functioning part of the cell. We will write a custom essay sample on The Different Types of Cells or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page Many important metabolic reactions take place on the surface, and it harbors molecules that enable cells to communicate and interact. 4. What does selectively permeable membrane mean? Selectively permeable membrane is a membrane that controls the entrance and exit of substances, allowing some in while preventing others from entering. 5. What are some functions of cell membrane proteins? Many trans membrane proteins bind to specific incoming molecules, such as hormones, triggering responses from within the cell. Certain compact and granular proteins span the cell membrane and provide routes for small molecules and ions to cross the otherwise impermeable phosphobilipid bilayer. Some of these form â€Å"pores† that admit water. In nerve cells, selective channels control the movement of sodium and potassium ions. Peripherial proteins may be enzymes and many are part of signal transduction pathways. Some function as cellular adhesion molecules that enable certain cells to touch or bind. Peripherial proteins that have carbohydrates attached form glycoproteins that help recognize and bind from the cells surface. 6. Fill in the following table (LOOK AT PAGE 99 AND REDO? ) OrganelleStructureFunction Cell membrane Membrane mainly composed of protein and lipid molecules Maintains integrity of the cell, controls the passage of materials in and out of the cell, and provides signal transduction Smooth Endoplasmic reticulum Complex organelle composed of membrane-bound flattened sacs, elongated canals, and fluid-filled vesicles. As the ER nears the cell membrane, it widens and lacks the ribosomes, and becomes the Smooth ER. Smooth ER contains enzymes that are important in synthesizing lipids, absorbing fats from the digestive tract, and breaking down drugs. Rough Endoplasmic reticulum Complex organelle composed of membrane-bound flattened sacs, elongated canals, and fluid-filled vesicles. The outer membranous surface of some Endoplasmic reticulum is studded with many ribosomes that give it a studded view. This is the Rough ER. The ribosomes of the rough ER are sites of protein synthesis. Ribosome Particles composed of connected, membrane-mound sacs, canals, and vesicles. Synthesize proteins Golgi Apparatus A stack of about a six or so flattened, membranous sacs called cisternae. Packages and modifies protein molecules for transport and secretion Mitochondria Elongated, fluid-filled sacs. Two layers, an outer and inner layer. A typical cell has about 1,700 mitochondria. It physically resembles that of bacteria Release energy from food molecules and convert the energy into a useable form. Lysosome Can be difficult to identify because their shapes vary, but they often appear as tiny, membranous sacs. Contains enzymes capable of digesting worn cellular parts or substances that enter cells. Peroxisome Membranous sacs that resemble lysomes in size and shape. Located in all human cells but are most abundant in cells of the liver and kidneys. Contain enzymes called peroxidases, Contains enzymes called peroxidases, important in the breakdown of many organic molecules. Microfilaments and microtubules Microfilaments are tiny rods of protein actin that form mesh works or bundles and provide certain cellular movements. Microtubles are long, slender tubes with diameters two or three times greater than those of microfilaments. They are composed of globular protein tibulim, are usually rigid, which helps maintain the shape of the cell. In muscle cells microfilaments constitute myofibrils, which shorten or contract these cells. In other cells, microfilaments associated with the inner surface of the cell membrane aid cell motility. In cilia and flagella, microtuble interactions provide movement. They also move organelles and other cellular structures. Centrosome Located in the cytoplasm near the nucleus. It is nonmembranous and consists of two cylinders (centrioles), built of tubelike structures called microtubles organized as nine groups of three. They also form parts of hairlike cellular projections called cilia and flagella. During cell division, the centrioles migrate to either side of the nucleus, where they form spindle fibers that pull on and and distribute chromosomes, which carry DNA information to the newly forming cells. Cilia Is a hairlike structure that attaches just beneath the cell membrane. Cilia dot cells in precise patterns. Beat rythmatically to propel fluids across the cellular surface. Flagella Much longer then a cilium and a cell usually only has one. The tail of a sperm cell is the only known flagellum in humans and generates swimming movements. Vesicles Membranous sacs, they vary in size and contents. Contains substances that recently entered the cell, provides attachment for ribosomes, and sythnesizes lipids. Nuclear envelope Has an inner and outer lipid bilayer membrane that encloses the nucleus. The two membranes have a small space between them, but are joined at places that surround openings called nuclear pores. The nuclear pores allow certain dissolved substances to move between the nucleus and the cytoplasm. Nucleolus Small dense body largely composed of RNA and protein. It has no surrounding membrane and is formed in specialized regions of certain chromosomes. A cell may have more than one nucleolus. This is the only site of ribosome production. Once they are formed, they migrate through the nuclear pores to the cytoplasm. Chromatin Consists of the cells 46 chromosomes each of which contains DNA wound around many proteins (like a very long thread wound around multiple spools. The position of the chromatin in the nucleus is not random, but reflects which genes are active. When cell division begins, chromatin fibers coil so tightly, this varies along the chromosomes, depending upon which genes are being accessed for their information. 7. What kinds of substances most readily diffuse through a cell membrane? The cell membrane is a selective barrier that controls which substances enter and leave the cell. Lipid-soluble substances, such as oxygen, carbon-dioxide, steroids, and general aesthetics, freely cross the cell membrane by simple diffusion. Explain the difference between diffusion, facilitated diffusion and osmosis. Diffusion- Also called simple diffusion is the tendency of atoms, molecules, and ions in a liquid or air solution to move from areas of higher concentration to areas of lower concentration, thus becoming more evenly distributed, or more diffuse. Diffusion can only occur if the cell membrane is permeable to that substance and a concentration gradient exists such that the substance is at a higher concentration on one side of the membrane or the other. Facilitated diffusion- Facilitated diffusion is the diffusion of small solutes that are not lipid-soluble, such as ions of sodium,potassium, and chloride, through specific protein channels in the membrane. This type of movement follows the concentration gradient and depends membrane proteins. Osmosis- Osmosis is the movement of water across a selectively permeable membrane into a compartment containing solute that cannot cross the same membrane. The mechanism of osmosis is complex, but it part involves diffusion of water. Cell membranes are generally permeable to water, so water equilibrium by osmosis throughout the body, and the concentration of water ans solutes everywhere in the intracellular and extracellular fluids is essentially the same. p102 9. Define concentration gradient and equilibrium. The net movement of particles from an area of higher concentration to an area of lower concentrations. The difference in concentrations is called a concentration gradient, and atoms, molecules, and ions are said to diffuse down a concentration gradient. With time, the concentration of a given substance becomes uniform, this is diffusional equilibrium. However, diffusional equilibrium does not normally occur in organisms. Instead, they tend to reach a physiological steady state, where concentrations of diffusing substances are unequal but stable. p100 10. What is the difference between isotonic, hypertonic and hypotonic solutions? Also describe what happens to a red blood cell in each of those solutions. Isotonic is any solution that has the same osmotic pressure as body fluids, such as . 9% NaCl. In red blood cells, in an isotonic solution, equal volumes of water enter and leave the red blood cells, so they maintain their characteristic  sizes and shapes. Hypertonic solutions are solutions that have a higher osmotic pressure than body fluids. IF cells are put into a hypertonic solution, there will be a net movement of water by osmosis out of the cells and the cells will shrink. This is the case with red blood cells, in a hypertonic solution, more water leaves than enters the red blood cells, so they in turn, shrink. Cells in a hypotonic solution, which has a lower osmotic pressure than body fluids, gain water by osmosis and swell. Red blood cells in a hypotonic solution, more water enters than leaves, so the cells swell and may burst. This is called hemolysis. p102 11. Explain how filtration occurs in the body. Filtration is the body’s way of forcing molecules through membranes. It is commonly used to separate solids from water. In the body, tissue fluid forms when water and dissolved substances are forced out through the thin, porous walls of blood capillaries, but larger particles such as blood protein molecules are left inside. 12. In active transport, molecules move from regions of ____Lower_____concentrations to regions of ____Higher_____________concentrations. 13. Compare active transport and facilitated diffusion. How are they similar and how do they differ? In active transport, molecules move from regions of lower concentrations to regions of higher concentrations (against the concentration gradient). The opposite is true of facilitated diffusion, here, the molecules move from regions of higher concentrations to regions of lower concentrations (with the concentration gradient). The two are similar in that they both use carrier molecules within cell membranes. The carrier proteins that transport substances from regions of lower concentrations to areas of higher concentrations are called â€Å"pumps. † 14. How does a cell maintain unequal concentrations of ions on opposite sides of a cell membrane? A cell maintains unequal concentrations of ions on opposite sides of a cell membrane by active transport. Sodium ions, for example can diffuse slowly through cell membranes, yet the concentration of these ions is many times greater outside the cells than inside the cells. This is because sodium ions are continually moved through the cell membrane from regions of lower concentration (inside) to regions of higher concentration (outside). 15. What is the difference between pinocytosis and phagocystosis? Pintocytosis is when cells take in tiny droplets of liquids from their surroundings. When this happens, a small portion of the cell membrane indents (invaginates). The open end of the tubelike part that forms, then seals of, producing a small vesicle, this tiny fluid filled sac then detaches from the surface and moves into cytoplasm. It remains separated for a short time, eventually breaking down and releasing the contents into the cytoplasm. The cell uses the pintocytosis as a way to take in things that otherwise would be too large to enter. Phagocystosis is similar to pintocytosis but it takes in solids rather than liquids. Some white blood cells are called phagocytes because they can take in solid particles such as bacteria and cellular debris. The newly formed vesicle that brings the solid into the cell, usually attaches to a lysome, the lysomal digestive enzymes decompose the contents and may then diffuse contents into the cytoplasm, where they may be used as raw materials in metabolic processes. Phagocytosis is an important line of defense against infection. p105 16. Describe receptor-mediated endocytosis. Receptor-mediated endocytosis moves very specific types of particles into the cell. This process uses protein molecules that extend through the cell membrane and are exposed on the outer surface. These proteins are receptors to which specific molecules from the surrounding fluids can bind and selectively and enter the cell (ligands). Receptor-mediated endocytosis is important because it allows cells with the appropriate receptors to remove and process specific types of substances from their surroundings, even when these substances are present in very low concentrations. p105 17. What does transcytosis accomplish? Transcytosis combines endocytosis and exocytosis to selectively and rapidly transport a substance or particle from one end of a cell to another. It moves substances across barriers formed by tightly connected cells. This process occurs in normal physiology and in disease. Transcytosis enables the healthy immune system to monitor pathogens in the small intestine, protecting against some forms of food poisoning. 107 18. Why is the precise division of the genetic material during mitosis so important? Precise division of the genetic material during mitosis is so important to ensure each new cell receives a complete copy of the genetic information. The chromosomes were duplicated in interphase, but it is in interphase that the chromosome sets are evenly distributed between the two forming cells. P109 19. Describe the events that occur during mitosis. (You can include a diagram too) Prophase- chromatin condenses into chromosomes; centrioles move to opposite sides of cytoplasm; nuclear membrane and nucleus disperse; microtubles assemble and associate with centrioles and chromatids of chromosomes. Metaphase- spindle fibers from the centrioles attach to the centromeres of each chromosome; chromosomes align midway between the centrioles. Anaphase- centromeres separate, and chromatids of the chromosomes separate spindle fibers shorten and pull these new individual chromosomes toward centrioles. Telophase- chromosomes elongate and form chromatin threads; nuclear membranes form around each chromosome set; nucleoli form; microtubles break down. 20. What factors control the number of times and the rate at which cells divide? The DNA at the tips of chromosomes, called telemeters had a mitotic clock. When this tip wears down, the signal tells the cell to cease dividing. Some factors include; severe psychological or emotional stress, inside cells; waxing and waning levels of proteins called kinases and cyclins, cell size (the ration between the surface area the cell membrane provides and the cell volume). Volume increases faster than does surface area. Some external controls include hormones and growth factors. Space availability is another external factor, healthy cells do not divide if they are surrounded by other cells. Control of cell division is crucial to health. Too infrequently and embryo could not develop, a child could not grow, and wounds would not heal. Too frequent division, produce abnormal growth, or neoplasm, which may form a disorganized mass called a tumor. p112 21. What is the difference between a benign and malignant tumor? A benign tumor remains in place like a lump, eventually interfering with the function of healthy tissue. A malignant tumor or cancerous, tumor looks different it is invasive, extending into surrounding tissue. A growing malignant tumor may resemble a crab with ourreaching claws. Cancer cells, if not stopped, eventually reach the circulation and spread, or metastasize, to other sites. p112 22. What are 2 ways that genes cause cancer? There are two ways genes cause cancer, oncogenes and tumor suppressor genes. Oncogenes are abnormal variants of genes that normally control the cell cycle, but are over expressed, increasing cell division. Tumor suppressor genes normally hold mitosis in check. When these are removed or inactivated, this lifts cell division, and uncontrolled cell division leads to cancer cells. p112 23. What is the difference between a stem cell and progenitor cell? A stem cell divides mitotically to yield either two daughter cells like itself, or one daughter cell that is a stem cell and one that is particularly specialized. It can divide into other cells and also can differentiate as many different cell types. A progenitor cell is a partly specialized cell that is the daughter of a stem cell but is intermediate between a stem cell and a fully differentiated cell. It is said to be â€Å"committed† because its daughter cells can become any of a restricted number of cell types. All of the differentiated cell types in a human body can be traced back through lineages of progenitor and stem cells. p113 24. Define totipotent , pluripotent and apotosis. (I believe this is spelled APOPTOSIS) Totipotent means that they can give rise to every cell type. Pluripotent means that their daughter cells can follow any of several pathways, but not all of them. These include stem cells that present later in development, as well as progenitor cells. Apoptosis is a form of cell death also called â€Å"programmed cell death: because it is a normal part of development. Apoptosis sculps organs from tissues that naturally overgrow, in the fetus, apoptosis carves away webbing between fingers and roes, prunes extra brain cells, and preserves only those immune system cells that recognize the body’s surface. 25. How do cells differentiate? Cells come from preexisting cells, by the process of mitosis and cytokinesis. Cell division explains how a fertilized egg develops into an individual consisting of trillions of cells, of at least 260 specialized types. This process of specialization is called differentiation. Cells specialize or differentiate along cell lineage pathways from stem cells or progenitor cells.