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Transcript
Biology 1 Mr. Greene Unit 3 After viewing the list of items on the board, work with a partner and make two new lists: those items on the list comprised of cells and those items not comprised of cells. Give a rationale for each answer. How were cells discovered? Why does cell shape vary? What enables eukaryotes to perform more specialized functions than prokaryotes? 1665 used a crude compound microscope to examine a slice of cork from the bark of an oak tree observed tiny, hollow boxes called them cells did not know that cells are the basic unit of living things cell - the smallest unit that can carry out all of the activities necessary for life 1 • All organisms are composed of 1 or more cells. 2 • The cell is the basic unit of organization of organisms. 3 • All cells come from preexisting cells. Some organisms are made up of many cells and some are made up of only one • unicellular - one celled organisms • multicellular - many celled organisms do everything living organisms do both prokaryote and eukaryote (some algae and yeast) Colonial • unicellular’s that live in groups of individuals • ex. Volvox interdependent each has its own function Cell specialization • separate roles for each type of cell Visual Concept: Cell Theory Cells vary greatly in their size and shape. A cell’s shape reflects its function. Cell size is limited by a cell’s surface area-to-volume ratio. Cells can be branched, flat, round, or rectangular. All substances that enter or leave a cell must cross the surface of the cell. A cell’s ability to move substances across its surface can be estimated by finding its surface area-to-volume ratio. Cells with greater surface area-to-volume ratios can exchange substances more efficiently. When comparing cells of the same shape, small cells have greater surface area-to-volume ratios than large cells. So, small cells function more efficiently than large cells. All cells share common structural features, including a cell membrane, cytoplasm, ribosomes, and DNA. The cell membrane is the outer layer that covers a cell’s surface and acts as a barrier between the outside environment and the inside of the cell. The cytoplasm is the region of the cell within the cell membrane. The cytoplasm includes the fluid inside the cell called the cytosol. cell membrane inside cell outside cell Cell membranes are composed of two phospholipid layers. • The cell membrane has two major functions. forms a boundary between inside and outside of the cell A ribosome is a cellular structure that makes proteins. The DNA of a cell provides instructions for making proteins, regulates cellular activities, and enables cells to reproduce. Features of Prokaryotic Cells A prokaryote is an organism made of a single prokaryotic cell. Prokaryotic cells do not have a nucleus or other internal compartments. The genetic material of a prokaryotic cell is a single loop of DNA. For millions of years, prokaryotes were the only organisms on Earth. Features of Eukaryotic Cells A eukaryote is an organism made up of one or more eukaryotic cells. All multicellular organisms are made of eukaryotic cells. The DNA of a eukaryotic cell is found in an internal compartment of the cell called the nucleus. All eukaryotic cells have membrane-bound organelles. An organelle is a small structure found in the cytoplasm that carries out specific activities inside the cell. Each organelle in a eukaryotic cell performs distinct functions. The complex organization of eukaryotic cells enables them to carry out more specialized functions than prokaryotic cells. Prokaryotic and Eukaryotic Cells Cell membrane Cytoplasm Prokaryotic Cell Cell membrane Cytoplasm Nucleus Eukaryotic Cell Organelles 1 - Prokaryote - primitive - lacks an internal structure – single-celled (bacteria) 2 - Eukaryote – advanced – some unicellular/ some multicellular Visual Concept: Comparing Prokaryotes and Eukaryotes Microscope observations of organisms led to the discovery of the basic characteristics common to all living things. A cell’s shape reflects its function. Cell size is limited by a cell’s surface area-to-volume ratio. The complex organization of eukaryotic cells enable them to carry out more specialized functions than prokaryotic cells. Use a light microscope to view a slide of a eukaryotic cell. Try to find the nucleus of the cell and give your reason why you identified the structure as the nucleus. What How does the cytoskeleton do? does DNA direct activity in the cytoplasm? What organelles are involved in protein production? What How are vesicles and vacuoles? does the cell get energy? Eukaryotic cells have an intricate network of protein fibers called the cytoskeleton which provides the interior framework of the cell. The cytoskeleton helps the cell move, keep its shape, and organize its parts. There are three different kinds of cytoskeleton fibers: microfilaments, microtubules, and intermediate fibers. There are little structures called organelles that carry out specific functions. Click to animate the image. A B C D DNA contains instructions for making proteins which control most of the activity of the cell. The DNA of eukaryotic cells is stored in the nucleus. DNA instructions are copied as RNA messages, which leave the nucleus. In the cytoplasm, ribosomes use the RNA messages to assemble proteins. Nucleus A double membrane called the nuclear envelope surrounds the nucleus. Nuclear pores located on the nuclear envelope act as channels to allow certain molecules to move in and out of the nucleus. The nucleolus is a structure within the nucleus where ribosome parts are made. These ribosome parts are transported out of the nucleus into the cytoplasm where they are assembled to form a complete ribosome. Click to animate the image. B C D A Ribosomes Each ribosome in a cell is made of RNA and many different proteins. Ribosomes that are suspended in the cytosol are called “free” ribosomes. Free ribosomes make proteins that remain inside the cell. Ribosomes Ribosomes that are attached to the membrane of another organelle are called “bound” ribosomes. Bound ribosomes make proteins that are exported from the cell. Ribosomes can switch between being bound or free, depending on what proteins the cell needs to make. Some proteins that a cell manufactures are needed outside the cell that makes them. Proteins that are sent outside the cell are packaged in vesicles. Vesicles are small, membrane-bound sacs that enclose the proteins and keep them separate from the rest of the cytoplasm. The endoplasmic reticulum and Golgi apparatus are organelles involved in preparing proteins for extracellular export. Endoplasmic Reticulum The endoplasmic reticulum, or ER, is an extensive system of internal membranes that moves proteins and other substances through the cell. The membranes of the ER are connected to the outer membrane of the nuclear envelope. The endoplasmic reticulum is divided into two portions: rough ER and smooth ER. Endoplasmic Reticulum The portion of the ER with attached ribosomes is called rough ER because it has a rough appearance when viewed with an electron microscope. The portion of the ER with no attached ribosomes is smooth ER because it has a smooth appearance when viewed with a microscope. The ribosomes on the rough ER make proteins that are packaged into vesicles. Enzymes of the smooth ER make lipids and break down toxic substances. Visual Concept: ER and Ribosomes Golgi Apparatus The Golgi apparatus is a set of flattened, membrane-bound sacs. The Golgi apparatus helps modify, sort, and package cell products for distribution. Making and Exporting Proteins The ribosomes located on the rough ER make proteins which then cross into the membranes of the ER. The ER membrane then pinches off and forms a vesicle around the proteins. Vesicles transport the proteins from the rough ER to the Golgi apparatus, where they are modified by enzymes and repackaged in new vesicles. These new vesicles transport the modified proteins to the cell membrane to be released outside the cell. Lysosomes Vesicles help maintain homeostasis by storing and releasing a variety of substances as the cell needs them. A lysosome is a vesicle produced by the Golgi apparatus that contains enzymes that break down large molecules. Lysosomes recycle old or damaged organelles and digest food particles to provide nutrients for the cell. Visual Concept: Lysosomes Vacuoles A vacuole is a fluid-filled vesicle found in the cytoplasm of many plant cells. Plant cells contain a large compartment called the central vacuole, which stores water, ions, nutrients, and wastes. When water fills the central vacuole, the cell becomes rigid, allowing the plant to stand up. When the vacuole loses water, the cell shrinks, and the plant wilts. Visual Concept: Vacuoles Other Vacuoles Some protists have contractile vacuoles which pump excess water out of the cell in order to control the concentration of salts and other substances. A food vacuole is another type of vacuole. It is formed when the cell membrane surrounds food particles outside the cell and pinches off to form a vesicle inside the cell. Cells need a constant source of energy. The energy for cellular functions is produced by chemical reactions that occur in the mitochondria and chloroplasts. In both organelles, chemical reactions produce adenosine triphosphate (ATP), the form of energy that fuels almost all cell processes. Chloroplasts A chloroplast is an organelle found in plant and algae cells that uses light energy to make carbohydrates from carbon dioxide and water. Chloroplasts are surrounded by two membranes and have several stacks of flattened sacs where energy production takes place. Plant cells may have several chloroplasts. Mitochondria Mitochondria are cell organelles that use energy from organic compounds to make ATP. Most of the ATP needed by a cell is produced inside mitochondria. Both animal and plant cells contain mitochondria. A smooth outer membrane and a folded inner membrane surround a mitochondrion. ATP is produced by enzymes on the folds of the inner membrane. a relatively inflexible structure that surrounds the plasma membrane • provides support and • • • • protection much thicker found in plants, fungi, bacteria have cell walls composed of cellulose in plants composed of chitin in fungi animals have no cell walls cilia short hairlike projections from the plasma membrane organized in tightly packed rows move like a "wave" in a football stadium flagella long, threadlike cable projections move in a whiplike motion one or two per cell that have them consists of a circle of 9 microtubules around 2 central microtubules major means of locomotion for unicellular The cytoskeleton helps the cell move, keep its shape, and organize its parts DNA instructions are copied as RNA messages, which leave the nucleus. In the cytoplasm, ribosomes use the RNA messages to assemble proteins. The endoplasmic reticulum and Golgi apparatus are organelles involved in preparing proteins for extracellular export. Vesicles help maintain homeostasis by storing and releasing a variety of substances as the cell needs them. The energy for cellular functions is produced by chemical reactions that occur in the mitochondria and chloroplasts. What type of society would you prefer to live in: one in which you must do everything for yourself, including growing and gathering food, building shelter, etc., or one in which each person does the job that they do best? What are some advantages to having each person do a specialized job? What are some advantages to doing everything yourself? What makes cells and organisms different? How are cells organized in a complex multicellular organism? What makes an organism truly multicellular? Both prokaryotic and eukaryotic cells can have a variety of shapes and structures. The function of a cell is determined by its shape and the organelles found in the cell. The different organelles and features of cells enable organisms to function in unique ways in different environments. Diversity in Prokaryotes Prokaryotes can vary in shape, the way they obtain and use energy, and their ability to move. Many prokaryotes have a flagellum, a long, hair-like structure that grows out of the cell and enables the cell to move through its environment. Prokaryotes may also have pili, short outgrowths that allow the cell to attach to surfaces or other cells. B C D A E F Click to animate the image. Eukaryotic Cell Specialization Eukaryotic cells can vary in shape and external features. Depending on their function, eukaryotic cells can also vary in their internal organelles. For example, muscle cells, which use large amounts of energy, contain many mitochondria. Animal and plant cells are two types of eukaryotic cells. Plant cells also have chloroplasts, a large vacuole, and a cell wall. I J C D K H A B E A M L J F I H G G D C B E F Click to animate the image. Plants and animals have many highly specialized cells that are arranged into tissues, organs, and organ systems. A tissue is a distinct group of similar cells that perform a common function. An organ is a collection of tissues that work together to form a structure which performs a specific function. An organ system is composed of a group of organs that work together to perform major body functions. Click to animate the image. Unicellular organisms can thrive independently or live together in groups. Cells that are permanently associated but do not work together or integrate cell activities are called colonial organisms. A multicellular organism is composed of many individual, permanently associated cells that coordinate their activities with each other. True multicellularity occurs only in eukaryotes. Visual Concept: Comparing Unicellular and Multicellular In a multicellular body, cells are interdependent. Distinct types of cells have specialized functions to help the organism survive. The individual cells in a multicellular organism cannot survive alone and are dependent on the other cells of the organism. Must multicellular organisms begin as a single cell, which divides to form more cells. These cells then grow and become specialized in a process called differentiation. Visual Concept: Differentiation The different organelles and features of cells enable organisms to function in unique ways in different environments. Plants and animals have many highly specialized cells that are arranged into tissues, organs, and organ systems. A multicellular organism is composed of many individual, permanently associated cells that coordinate their activities with each other. Humans must have their body temperature at a constant temperature. Make a list of ways the body responds when it gets cold. How does the cell membrane help a cell maintain homeostasis? How does the cell membrane restrict the exchange of substances? What are some functions of membrane proteins? All living things respond to their environments. These reactions help our bodies maintain homeostasis. Homeostasis is the maintenance of stable internal conditions in a changing environment. Individual cells, as well as organisms, must maintain homeostasis in order to live. One way that a cell maintains homeostasis is by controlling the movement of substances across the cell membrane. Cells are suspended in a fluid environment. Even the cell membrane is fluid. It is made up of a “sea” of lipids in which proteins float. By allowing some materials but not others to enter the cell, the cell membrane acts as a gatekeeper. The cell membrane also provides structural support to the cytoplasm, recognizes foreign material, and communicates with other cells, all of which contribute to maintaining homeostasis. The cell membrane is made of phospholipids. A phospholipid is a specialized lipid made of a phosphate “head” and two fatty acid “tails.” The phosphate head is polar and is attracted to water. The fatty acid tails are nonpolar and are repelled by water. Click above to play the video Structure Because there is water inside and outside the cell, the phospholipids form a double layer called the lipid bilayer. The nonpolar tails, repelled by water, make up the interior of the lipid bilayer. The polar heads are attracted to the water, so they point toward the surfaces of the lipid bilayer. One layer of polar heads faces the cytoplasm, while the other layer is in contact with the cell’s immediate surroundings. Click above to play the video Click above to play the video Barrier Only certain substances can pass through the lipid bilayer. The phospholipids form a barrier through which only small, nonpolar substances can pass. Ions and most polar molecules are repelled by the nonpolar interior of the lipid bilayer. Various proteins can be found in the cell membrane. Some proteins face inside the cell, and some face outside. Other proteins may stretch across the lipid bilayer and face both inside and outside. Proteins are made of amino acids. Some amino acids are polar, and others are nonpolar. The attraction and repulsion of polar and nonpolar parts of the protein to water help hold the protein in the membrane. Types of Proteins Proteins in the cell membrane include cellsurface markers, receptor proteins, enzymes, and transport proteins. Cell-surface markers act like a name tag. A unique chain of sugars acts as a marker to identify each type of cell. Types of Proteins Receptor proteins enable a cell to sense its surroundings by binding to certain substances outside the cell. When this happens, it causes changes inside the cell. Many substances that the cell needs cannot pass through the lipid bilayer. Channel or transport proteins aid the movement of these substances into and out of the cell. One way that a cell maintains homeostasis is by controlling the movement of substances across the cell membrane. The lipid bilayer is selectively permeable to small, nonpolar substances. Proteins in the cell membrane include cellsurface markers, receptor proteins, enzymes, and transport proteins. Write three sentences using the word diffuse or one of its conjugates. Consult a dictionary if you have trouble thinking of how the word is used. What determines the direction in which passive transport occurs? Why How is osmosis important? do substances move against their concentration gradients? In a solution, randomly moving molecules tend to fill up a space. When the space is filled evenly, a state called equilibrium is reached. The amount of a particular substance in a given volume is called the concentration of the substance.When one area has a higher concentration than another area does, a concentration gradient exists. The movement of substances down a concentration gradient is called diffusion. The cell membrane separates the cytoplasm from the fluid outside the cell. Some substances enter and leave the cell by diffusing across the cell membrane. The direction of movement depends on the concentration gradient and does not require energy. In passive transport, substances cross the cell membrane down their concentration gradient. Some substances diffuse through the lipid bilayer. Other substances diffuse through transport proteins. Simple Diffusion Small, nonpolar molecules can pass directly through the lipid bilayer. This type of movement is called simple diffusion. Oxygen moves down its concentration gradient into the cell. Carbon dioxide diffuses out of the cell. Natural steroid hormones, which are nonpolar and fat soluble, can also diffuse across the lipid bilayer. Facilitated Diffusion Many ions and polar molecules that are important for cell function do not diffuse easily through the nonpolar lipid bilayer. During facilitated diffusion, transport proteins help these substances diffuse through the cell membrane. Two types of transport proteins are channel proteins and carrier proteins. Facilitated Diffusion Ions, sugars, and amino acids can diffuse through the cell membrane through channel proteins. These proteins, sometimes called pores, serve as tunnels through the lipid bilayer. Each channel allows the diffusion of specific substances that have the right size and charge. Click above to play the video. Facilitated Diffusion Carrier proteins transport substances that fit within their binding site. A carrier protein binds to a specific substance on one side of the cell membrane. This binding causes the protein to change shape. As the protein’s shape changes, the substance is moved across the membrane and is released on the other side. Click above to play the video. Water can diffuse across a selectively permeable membrane in a process called osmosis. Osmosis in cells is a form of facilitated diffusion. Polar water molecules do not diffuse directly through the bilayer. But the cell membrane contains channel proteins that only water molecules can pass through. Osmosis allows cells to maintain water balance as their environment changes. When ions and polar substances dissolve in water, they attract and bind some water molecules. The remaining water molecules are free to move around. If a concentration gradient exists across a membrane for solutes, a concentration gradient also exists across the membrane for free water molecules. Osmosis occurs as free water molecules move down their concentration gradient into the solution that has the lower concentration of free water molecules. Click above to play the video. The direction of water movement in a cell depends on the concentration of the cell’s environment. If the solution is hypertonic, or has a higher solute concentration than the cytoplasm does, water moves out of the cell. The cell loses water and shrinks. If the solution is isotonic, or has the same solute concentration that the cytoplasm does, water diffuses into and out of the cell at equal rates. The cell stays the same size. If the solution is hypotonic, or has a lower solute concentration than the cytoplasm does, water moves into the cell. The cell gains water and expands in size. If left unchecked, the swelling caused by a hypotonic solution could cause a cell to burst. The rigid cell walls of plants and fungi prevent the cells of these organisms from expanding too much. In fact, many plants are healthiest in a hypotonic environment. Some unicellular eukaryotes have contractile vacuoles, which collect excess water inside the cell and force the water out of the cell. Animal cells have neither cell walls nor contractile vacuoles. Many animal cells can avoid swelling caused by osmosis by actively removing solutes from the cytoplasm. In order to move substances against their concentration gradients, cells must use energy. Active transport requires energy to move substances against their concentration gradients. Most often, the energy needed for active transport is supplied directly or indirectly by ATP. Click above to play the video. Pumps Many active transport processes use carrier proteins to move substances. In facilitated diffusion, the carrier proteins do not require energy. In active transport, the carrier proteins do require energy to “pump” substances against their concentration gradient. The sodium-potassium pump is a carrier protein that actively transports three sodium ions out of the cell and two potassium ions into the cell. This pump is one of the most important carrier proteins in animal cells. It prevents sodium ions from building up in the cell, resulting in osmosis into the cell. The concentration gradients of sodium ions and potassium ions also help transport other substances, such as glucose, across the cell membrane. Click above to play the video. Vesicles Many substances, such as proteins and polysaccharides, are too large to be transported by carrier proteins. Instead, they cross the cell membrane in vesicles, which are membrane-bound sacs. The vesicle membrane is a lipid bilayer, like the cell membrane. Therefore, vesicles can bud off from the membrane, fuse with it, or fuse with other vesicles. Vesicles The movement of a large substance into a cell by means of a vesicle is called endocytosis. During endocytosis the cell membrane forms a pouch around the substance. The pouch then closes up and pinches off from the membrane to form a vesicle inside the cell. Vesicles that form by endocytosis may fuse with lysosomes or other organelles. Vesicles The movement of material out of a cell by means of a vesicle is called exocytosis. During exocytosis, vesicles inside the cell fuse with the cell membrane. From the cell membrane, the contents of the vesicle are released to the outside of the cell. Cells use exocytosis to export proteins modified by the Golgi apparatus. Some cells also use exocytosis to remove bacteria or other microbes. In passive transport, substances cross the cell membrane down their concentration gradient. Osmosis allows cells to maintain water balance as their environment changes. Active transport requires energy to move substances against their concentration gradients. Write several sentences that describe where hormones are produced, how they reach the cells they stimulate, and how those target cells recognize the hormones. How do cells use signal molecules? How do cells receive signals? How do cells respond to signaling? We communicate in many ways to share information. Cells in both multicellular and unicellular organisms need to communicate in order to coordinate activities. Cells use various methods of communication. These methods vary depending on whether the target is specific or general. They also depend on whether the target is nearby or far away. Cells communicate and coordinate activity by sending chemical signals that carry information to other cells. A signaling cell produces a signal, often a molecule, that is detected by the target cell. Typically, target cells have specific proteins that recognize and respond to the signal. Neighboring cells can communicate through direct contact between their membranes. Short-distance signals may act locally, a few cells away from the originating cell. Long-distance signals are carried by hormones and nerve cells. Hormones . are signal molecules that are made in one part of the body. Hormones are distributed widely in the bloodstream throughout the body, but they affect only specific cells. Nerve cells also signal information to distant locations in the body, but their signals are not widely distributed. While most signal molecules originate within the body, some signals come from outside. A target cell is bombarded by hundreds of signals. But it recognizes and responds only to the few signals that are important for its function. This response to some signals, but not to others, is made possible by receptor proteins, such as the ones in the cell’s membrane. A receptor protein binds specific substances, such as signal molecules. The outer part of the receptor protein is folded into a unique shape, called the binding site. A receptor protein binds only to signals that match the specific shape of its binding site. Only the “right” shape can fit into the receptor protein while the “wrong” shape have no effect on that particular receptor protein. A cell may also have receptor proteins that bind to molecules in its environment. Receptor proteins enable a cell to respond to its environment. Once it binds the signal molecule, the receptor protein changes its shape in the membrane. This change in shape relays information into the cytoplasm of the target cell. When a signal molecule binds to a receptor protein, the protein changes shape, which triggers changes in the cell membrane. The cell may respond to a signal by changing its membrane permeability, by activating enzymes, or by forming a second messenger. Transport proteins may open or close in response to a signal. Some receptor proteins are enzymes or they activate enzymes in the cell membrane. Enzymes trigger chemical reactions in the cell. Binding of a signal molecule outside the cell may cause a second messenger to form. The second messenger acts as a signal molecule within the cell and causes changes in the cytoplasm and nucleus. Cells communicate and coordinate activity by sending chemical signals that carry information to other cells. A receptor protein binds only to the signals that match the specific shape of its binding site. The cell may respond to a signal by changing its membrane permeability, by activating enzymes, or by forming a second messenger.