| Online Tests C. Massengale |
| AP BIOLOGY | PRE-AP BIOLOGY |
| Unit IA Chapters 1-3 Biochemistry | Chapters 1, 2, and Nature of Science |
| Unit IB Chapters 4 – 5 Biochemistry | Chapter 3 Biochemistry |
| Cells and Cell Membranes | Evolution |
| EACH CLASS HAS ITS OWN TEST POSTED WHEN YOU ARRIVE IN CLASS! | |
Crime Scene Investigation
| Scenario: The Case of the Illegal Dumpsite John Smith had worked for the same company in the shipping and receiving department for 15 years. John was proud of his attendance record, and even though he wasn’t always giving his job 100%, he believed he was doing a good job. Everyone goofs off at work part of the time, don’t they? One morning when John arrived at work, he stopped at the bulletin board where new job listings were posted. One of the postings was for a supervisor position in a department in which he had always wanted to work. The pay was a nice increase too, and with the extra money, he could have his truck with the new tires and rims customized. That night John filled out the necessary papers for the job and hurriedly turned them in the next day. Weeks later, he and all the other employees that had applied, were called in for an interview. John just knew that he would land the job. However, when the person to fill the position was announced a few weeks later, another employee that had worked less time than John got the job. John was furious at being overlooked! That night when John clocked out and was getting into his car in the parking lot, he said, “I’ll get even with them for this.” Tony Harris loved the outdoors and he loved photography, so many years ago when he relocated his family to a wetland area near a major river, he put his two “loves” together and started doing outdoor photography. Some of Tony’s photographs had even been published in several naturalist journals. Tony was very familiar with the wetland area and the wildlife because he spent most of his free time photographing there. Tony had set out very early on a cool, crisp morning to spend the weekend camping and taking pictures at his favorite wetland area. Tony was excited about his trip and the great pictures he expected to get so when he came across the cove with its terrible stench, Tony was unprepared for what he found. In a tree-surrounded cove of the river, Tony found several dead waterfowl and turtles that had washed ashore. When he examined them, there weren’t any markings to show injuries, and the animals appeared to have been healthy when they died. Tony took several pictures of the area and the dead animals and decided to call the Game and Fish Commission when he returned home. A new hunting season had opened and with it came lots of calls about poaching problems and hunting accidents. Chelsea Brown had worked for the Game and Fish for several years since her graduation from college. She had been raised to love animals and the environment so this job was great for her. Today she was spending time in the office to catch up on some reports and to answer the hotline. She was in a very relaxed mood when the phone hotline rang, and she took a call from a Mr. Tony Harris. She remembered Mr. Harris from an awards banquet when the Game and Fish Commission gave Tony an award for some of his outstanding waterfowl photographs that they had published in their G & F magazine. Tony reported the incident with the dead waterfowl and turtles he had witnessed in the cove and said he would send the photographs of the area and the dead animals to the Game and Fish. Chelsea thanked Mr. Harris and told him she would make a report. The call didn’t seem to be too serious to Chelsea at the time. However, when Chelsea went to the G & F logbook to register the incident, she found numerous other reports called in from other hunters and campers stating that they had noticed a lot of unexplained deaths in the waterfowl and turtle populations in this area of the wetlands. This couldn’t be ignored. Chelsea said, “Guess we better get some people out there to check on this.” When the Game and Fish officers traveled to the wetlands, they found more than just dead wildlife. The scene they discovered might be the cause of the reported deaths of wildlife in this aquatic habitat. Near the area of several of the reported hotline sightings, the officers found a large amount of industrial waste that had been dumped. The waste included large piles of discarded plastics, metals, and wood. A first inspection of the wastes didn’t give the officers a clue where the trash came from or who had left it there. However, there were several deep tire tracks and shoe prints from a man’s athletic shoe in places where the ground had been extremely wet at one time. Like many areas of the wetlands with clay-based soils, when the water had receded from this area, the tracks and the ground dried hard like cement. There was a possibility that the waste could have a negative effect on the environment and the animals in the area. The EPA, Environmental Protection Agency, would have to be called to help identify the unknown plastics, metals, etc. and to determine if they were or were not hazardous. The officers closed off the area and the investigation began! STUDENT ROLE As a student, you will be a scientist on the team that the EPA sent to the wetland area to study the dump site and its effect. You will work along with the people from the Game and Fish to solve three problems — 1. What type of plastics and metal are dumped at the site? 2. Could any of the plastics or metals cause death like the waterfowl and turtles? 3. Who is responsible for the illegal dumping and subsequent clean-up and damages? EXTENSION: Devise a plan for a safe method of disposal for the trash found at the dump site? and an estimated cost for removal and damages. Evidence: Plastics, metals, tire tracks, shoe prints Teacher Preparation:
ACTIVITY # 1 – Identifying Plastics Handout – Industrial Park References: Types of Plastics PowerPoint Toxic Plastics — Fact or Myth? PowerPoint ACTIVITY # 2 – Identifying Metals References: ACTIVITY # 3 – Shoe Print & Tire Tread Patterns If the Shoe Fits PowerPoint Handout – Shoe Imprint from Dumpsite Handout – Tire Tread Pattern from Dumpsite Lab Investigations: ACTIVITY #1 – Plastics Identification ACTIVITY #2 – Metals Identification ACTIVITY #3 – Shoe Pattern & Tire Track Identification
All Materials © Cmassengale |
Copyright Owens Foundation
Introduction
American zoologists Mark and Delia Owens work as conservationists . Delia Owens, Ph.D., B.S., and Mark Owens M.Ed., B.S., have conducted research and conservation projects on endangered species in Africa for 23 years. They met in the early 70s as graduate students at the University of Georgia, and soon discovered that they shared the dream of saving part of Africa’s vanishing wilderness. Shortly after they married, they auctioned everything they owned, and with $6,000, one-way tickets and back-packs, they headed to “the Dark Continent.” Beginning in 1974, Delia and Mark worked for seven years in the Central Kalahari Game Reserve of Botswana studying brown hyenas and black maned lions where they made landmark discoveries regarding both species. For the first seven years they lived in tents in Botswana’s Central Kalahari Desert. There they studied black-maned lions and elusive brown hyenas in an area so remote that the animals had never before seen humans. Cry of the Kalahari, their best-selling book, is a gripping and vivid account of their research and adventures.
From 1985 through 1997 the Owenses worked to rehabilitate a 5,000 square mile area in north Zambia by eliminating elephant and meat poaching for the benefit of the people and the wildlife living there. From 1986 to 1997 the Owenses developed the North Luangwa Conservation Project (NLCP) in Zambia, a multidimensional approach to wildlife conservation and resource development. When Mark and Delia arrived in North Luangwa, more than 100,000 elephants and several thousand black rhinos had already been slaughtered by poachers in the Luangwa Valley; each year 1,000 elephants were still being killed in the “North Park” alone. By 1997, elephant poaching was controlled in North Luangwa. The Eye of the Elephant, the second book by Mark and Delia, published in 1992 by Houghton Mifflin, details their efforts to reclaim the North Luangwa wilderness from commercial ivory and meat poachers.
In 1997, Delia and Mark returned to the US and began assisting grizzly bear conservation in North Idaho, which is one of the five remnant grizzly bear populations in the lower 48 states. Today, Delia and Mark continue their support for the people and wildlife of Zambia as well as working for grizzly bear conservation in the northwestern US.
Project
Read Cry of the Kalahari by Mark and Delia Owens and view the two National Geographic videos, Eternal Enemies and Lions of the African Night. You will take three tests over the book and then write a paper on the book and videos.
Tests
Cry Quiz #1 – Read pages 1-118 ____________________
Cry Quiz #2 – Read pages119-214 ____________________
Cry Quiz #3 – Read 214 to the end of the book ____________________
Format of the Paper
I. Biography of Mark and Delia Owens
II. Republic of Botswana
III. Lion Prides
IV. Brown Hyena Packs
V. Ungulates of the Kalahari
VI. Interactions of Predators and Prey
VII. Fencing and Disease Control
VIII. Bibliography (all 3 sources – book and 2 videos)
IX. Appendix (Must include 2 drawings from book – Map of Africa showing Kalahari location and Map of Deception Valley)
* The paper should be 6 – 8 pages typed (9-10 pages handwritten) NOT counting the bibliography or appendix.
* You must use font size 12, Times New Roman, Double spaced, 1″ margins.
* Include a cover sheet with the title, and your name and period.
Due ___________ Counts as a Unit Test Grade (200 points)
Delia and Mark Owens near Marula Puku Research camp in North Luangwa National Park of Zambia.
Copyright Owens Foundation
Description: The purpose of this experiment is to determine the types of pigments found in various vegetation. The students will gather plants, soak them in acetone and use coffee filter strips to separate the pigments. Then the students will determine the pigments found in each type of leaf. The pigments found in spinach leaves, lettuce leaves and marigold leaves are all different. Paper Chromatography is a technique that enables us to separate plant pigments. The pigments found in plants vary and the process of chromatography is important in the detection of the types of pigments found in each.
Needed Materials: Acetone fingernail polish remover, test tubes or other empty containers (enough for 5 containers per group), felt tip markers, coffee filters, pigment guide, masking tape, scissors, spinach leaves, mum leaves, iceberg lettuce and leaves of various plants found in your schoolyard.
Safety Rule: Avoid inhaling the vapors from the acetone and spilling it on your clothing.
Student Information: The following information will provide you with the steps for conducting your plant chromatography experiment. It is important to hold all of the variables constant except for those that are being manipulated. Constant (or controlled variables) would be such things as: the length of the filter paper strip, the amount of time the paper is left in the solution, the amount of acetone in the container, the size of the container being used, etc. Manipulated (or independent) variables would be those things that we change to see if the response will be different, such as: type of plant being studied. The responding (or dependent) variable for this experiment will be the different pigments found in each of the different types of vegetation.
The reporting form for this experiment is set up so that you can determine how many different kinds of vegetation you would like to use, the kind of container you would like to use and how long your strips of filter paper will be. Also remember that a good scientific experiment is repeated a minimum of three times. Therefore, your data will be more accurate if you conduct several experiments that are exactly the same and then compile an average of your data before submitting it.
Discussion Questions
| Charity Day October 11- 30 |
Guidelines:
Rewards:
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Chapter 6 A Tour of the Cell Lecture Outline
Overview: The Importance of Cells
· All organisms are made of cells.
° Many organisms are single-celled.
° Even in multicellular organisms, the cell is the basic unit of structure and function.
· The cell is the simplest collection of matter that can live.
· All cells are related by their descent from earlier cells.
A. How We Study Cells
1. Microscopes provide windows to the world of the cell.
· The discovery and early study of cells progressed with the invention of microscopes in 1590 and their improvement in the 17th century.
· In a light microscope (LM), visible light passes through the specimen and then through glass lenses.
° The lenses refract light such that the image is magnified into the eye or onto a video screen.
· Microscopes vary in magnification and resolving power.
° Magnification is the ratio of an object’s image to its real size.
° Resolving power is a measure of image clarity.
§ It is the minimum distance two points can be separated and still be distinguished as two separate points.
§ Resolution is limited by the shortest wavelength of the radiation used for imaging.
· The minimum resolution of a light microscope is about 200 nanometers (nm), the size of a small bacterium.
· Light microscopes can magnify effectively to about 1,000 times the size of the actual specimen.
° At higher magnifications, the image blurs.
· Techniques developed in the 20th century have enhanced contrast and enabled particular cell components to be stained or labeled so they stand out.
· While a light microscope can resolve individual cells, it cannot resolve much of the internal anatomy, especially the organelles.
· To resolve smaller structures, we use an electron microscope (EM), which focuses a beam of electrons through the specimen or onto its surface.
° Because resolution is inversely related to wavelength used, electron microscopes (whose electron beams have shorter wavelengths than visible light) have finer resolution.
° Theoretically, the resolution of a modern EM could reach 0.002 nanometer (nm), but the practical limit is closer to about 2 nm.
· Transmission electron microscopes (TEMs) are used mainly to study the internal ultrastructure of cells.
° A TEM aims an electron beam through a thin section of the specimen.
° The image is focused and magnified by electromagnets.
° To enhance contrast, the thin sections are stained with atoms of heavy metals.
· Scanning electron microscopes (SEMs) are useful for studying surface structures.
° The sample surface is covered with a thin film of gold.
° The beam excites electrons on the surface of the sample.
° These secondary electrons are collected and focused on a screen.
° The result is an image of the topography of the specimen.
° The SEM has great depth of field, resulting in an image that seems three-dimensional.
· Electron microscopes reveal organelles that are impossible to resolve with the light microscope.
° However, electron microscopes can only be used on dead cells.
· Light microscopes do not have as high a resolution, but they can be used to study live cells.
· Microscopes are major tools in cytology, the study of cell structures.
· Cytology combined with biochemistry, the study of molecules and chemical processes in metabolism, to produce modern cell biology.
2. Cell biologists can isolate organelles to study their functions.
· The goal of cell fractionation is to separate the major organelles of the cells so their individual functions can be studied.
· This process is driven by an ultracentrifuge, a machine that can spin at up to 130,000 revolutions per minute and apply forces of more than 1 million times gravity (1,000,000 g).
· Fractionation begins with homogenization, gently disrupting the cell.
· The homogenate is spun in a centrifuge to separate heavier pieces into the pellet while lighter particles remain in the supernatant.
° As the process is repeated at higher speeds and for longer durations, smaller and smaller organelles can be collected in subsequent pellets.
· Cell fractionation prepares isolates of specific cell components.
· This enables the functions of these organelles to be determined, especially by the reactions or processes catalyzed by their proteins.
° For example, one cellular fraction was enriched in enzymes that function in cellular respiration.
° Electron microscopy revealed that this fraction is rich in mitochondria.
° This evidence helped cell biologists determine that mitochondria are the site of cellular respiration.
· Cytology and biochemistry complement each other in correlating cellular structure and function.
B. A Panoramic View of the Cell
1. Prokaryotic and eukaryotic cells differ in size and complexity.
· All cells are surrounded by a plasma membrane.
· The semifluid substance within the membrane is the cytosol, containing the organelles.
· All cells contain chromosomes that have genes in the form of DNA.
· All cells also have ribosomes, tiny organelles that make proteins using the instructions contained in genes.
· A major difference between prokaryotic and eukaryotic cells is the location of chromosomes.
· In a eukaryotic cell, chromosomes are contained in a membrane-enclosed organelle, the nucleus.
· In a prokaryotic cell, the DNA is concentrated in the nucleoid without a membrane separating it from the rest of the cell.
· In eukaryote cells, the chromosomes are contained within a membranous nuclear envelope.
· The region between the nucleus and the plasma membrane is the cytoplasm.
° All the material within the plasma membrane of a prokaryotic cell is cytoplasm.
· Within the cytoplasm of a eukaryotic cell are a variety of membrane-bound organelles of specialized form and function.
° These membrane-bound organelles are absent in prokaryotes.
· Eukaryotic cells are generally much bigger than prokaryotic cells.
· The logistics of carrying out metabolism set limits on cell size.
° At the lower limit, the smallest bacteria, mycoplasmas, are between 0.1 to 1.0 micron.
° Most bacteria are 1–10 microns in diameter.
° Eukaryotic cells are typically 10–100 microns in diameter.
· Metabolic requirements also set an upper limit to the size of a single cell.
· As a cell increases in size, its volume increases faster than its surface area.
° Smaller objects have a greater ratio of surface area to volume.
· The plasma membrane functions as a selective barrier that allows the passage of oxygen, nutrients, and wastes for the whole volume of the cell.
· The volume of cytoplasm determines the need for this exchange.
· Rates of chemical exchange across the plasma membrane may be inadequate to maintain a cell with a very large cytoplasm.
· The need for a surface sufficiently large to accommodate the volume explains the microscopic size of most cells.
· Larger organisms do not generally have larger cells than smaller organisms—simply more cells.
· Cells that exchange a lot of material with their surroundings, such as intestinal cells, may have long, thin projections from the cell surface called microvilli. Microvilli increase surface area without significantly increasing cell volume.
2. Internal membranes compartmentalize the functions of a eukaryotic cell.
· A eukaryotic cell has extensive and elaborate internal membranes, which partition the cell into compartments.
· These membranes also participate directly in metabolism, as many enzymes are built into membranes.
· The compartments created by membranes provide different local environments that facilitate specific metabolic functions, allowing several incompatible processes to go on simultaneously in a cell.
· The general structure of a biological membrane is a double layer of phospholipids.
· Other lipids and diverse proteins are embedded in the lipid bilayer or attached to its surface.
· Each type of membrane has a unique combination of lipids and proteins for its specific functions.
° For example, enzymes embedded in the membranes of mitochondria function in cellular respiration.
C. The Nucleus and Ribosomes
1. The nucleus contains a eukaryotic cell’s genetic library.
· The nucleus contains most of the genes in a eukaryotic cell.
° Additional genes are located in mitochondria and chloroplasts.
· The nucleus averages about 5 microns in diameter.
· The nucleus is separated from the cytoplasm by a double membrane called the nuclear envelope.
° The two membranes of the nuclear envelope are separated by 20–40 nm.
° The envelope is perforated by pores that are about 100 nm in diameter.
° At the lip of each pore, the inner and outer membranes of the nuclear envelope are fused to form a continuous membrane.
° A protein structure called a pore complex lines each pore, regulating the passage of certain large macromolecules and particles.
· The nuclear side of the envelope is lined by the nuclear lamina, a network of protein filaments that maintains the shape of the nucleus.
· There is evidence that a framework of fibers called the nuclear matrix extends through the nuclear interior.
· Within the nucleus, the DNA and associated proteins are organized into discrete units called chromosomes, structures that carry the genetic information.
· Each chromosome is made up of fibrous material called chromatin, a complex of proteins and DNA.
° Stained chromatin appears through light microscopes and electron microscopes as a diffuse mass.
· As the cell prepares to divide, the chromatin fibers coil up and condense, becoming thick enough to be recognized as the familiar chromosomes.
· Each eukaryotic species has a characteristic number of chromosomes.
° A typical human cell has 46 chromosomes.
° A human sex cell (egg or sperm) has only 23 chromosomes.
· In the nucleus is a region of densely stained fibers and granules adjoining chromatin, the nucleolus.
° In the nucleolus, ribosomal RNA (rRNA) is synthesized and assembled with proteins from the cytoplasm to form ribosomal subunits.
° The subunits pass through the nuclear pores to the cytoplasm, where they combine to form ribosomes.
· The nucleus directs protein synthesis by synthesizing messenger RNA (mRNA).
° The mRNA travels to the cytoplasm through the nuclear pores and combines with ribosomes to translate its genetic message into the primary structure of a specific polypeptide.
2. Ribosomes build a cell’s proteins.
· Ribosomes, containing rRNA and protein, are the organelles that carry out protein synthesis.
° Cell types that synthesize large quantities of proteins (e.g., pancreas cells) have large numbers of ribosomes and prominent nucleoli.
· Some ribosomes, free ribosomes, are suspended in the cytosol and synthesize proteins that function within the cytosol.
· Other ribosomes, bound ribosomes, are attached to the outside of the endoplasmic reticulum or nuclear envelope.
° These synthesize proteins that are either included in membranes or exported from the cell.
· Ribosomes can shift between roles depending on the polypeptides they are synthesizing.
D. The Endomembrane System
· Many of the internal membranes in a eukaryotic cell are part of the endomembrane system.
· These membranes are either directly continuous or connected via transfer of vesicles, sacs of membrane.
° In spite of these connections, these membranes are diverse in function and structure.
° The thickness, molecular composition and types of chemical reactions carried out by proteins in a given membrane may be modified several times during a membrane’s life.
· The endomembrane system includes the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, and the plasma membrane.
1. The endoplasmic reticulum manufactures membranes and performs many other biosynthetic functions.
· The endoplasmic reticulum (ER) accounts for half the membranes in a eukaryotic cell.
· The ER includes membranous tubules and internal, fluid-filled spaces called cisternae.
· The ER membrane is continuous with the nuclear envelope, and the cisternal space of the ER is continuous with the space between the two membranes of the nuclear envelope.
· There are two connected regions of ER that differ in structure and function.
° Smooth ER looks smooth because it lacks ribosomes.
° Rough ER looks rough because ribosomes (bound ribosomes) are attached to the outside, including the outside of the nuclear envelope.
· The smooth ER is rich in enzymes and plays a role in a variety of metabolic processes.
° Enzymes of smooth ER synthesize lipids, including oils, phospholipids, and steroids.
° These include the sex hormones of vertebrates and adrenal steroids.
° In the smooth ER of the liver, enzymes help detoxify poisons and drugs such as alcohol and barbiturates.
§ Frequent use of these drugs leads to the proliferation of smooth ER in liver cells, increasing the rate of detoxification.
§ This increases tolerance to the target and other drugs, so higher doses are required to achieve the same effect.
° Smooth ER stores calcium ions.
§ Muscle cells have a specialized smooth ER that pumps calcium ions from the cytosol and stores them in its cisternal space.
§ When a nerve impulse stimulates a muscle cell, calcium ions rush from the ER into the cytosol, triggering contraction.
§ Enzymes then pump the calcium back, readying the cell for the next stimulation.
· Rough ER is especially abundant in cells that secrete proteins.
° As a polypeptide is synthesized on a ribosome attached to rough ER, it is threaded into the cisternal space through a pore formed by a protein complex in the ER membrane.
° As it enters the cisternal space, the new protein folds into its native conformation.
° Most secretory polypeptides are glycoproteins, proteins to which a carbohydrate is attached.
° Secretory proteins are packaged in transport vesicles that carry them to their next stage.
· Rough ER is also a membrane factory.
° Membrane-bound proteins are synthesized directly into the membrane.
° Enzymes in the rough ER also synthesize phospholipids from precursors in the cytosol.
° As the ER membrane expands, membrane can be transferred as transport vesicles to other components of the endomembrane system.
2. The Golgi apparatus is the shipping and receiving center for cell products.
· Many transport vesicles from the ER travel to the Golgi apparatus for modification of their contents.
· The Golgi is a center of manufacturing, warehousing, sorting, and shipping.
· The Golgi apparatus is especially extensive in cells specialized for secretion.
· The Golgi apparatus consists of flattened membranous sacs—cisternae—looking like a stack of pita bread.
° The membrane of each cisterna separates its internal space from the cytosol.
° One side of the Golgi, the cis side, is located near the ER. The cis face receives material by fusing with transport vesicles from the ER.
° The other side, the trans side, buds off vesicles that travel to other sites.
· During their transit from the cis to the trans side, products from the ER are usually modified.
· The Golgi can also manufacture its own macromolecules, including pectin and other noncellulose polysaccharides.
· The Golgi apparatus is a very dynamic structure.
° According to the cisternal maturation model, the cisternae of the Golgi progress from the cis to the trans face, carrying and modifying their protein cargo as they move.
· Finally, the Golgi sorts and packages materials into transport vesicles.
° Molecular identification tags are added to products to aid in sorting.
° Products are tagged with identifiers such as phosphate groups. These act like ZIP codes on mailing labels to identify the product’s final destination.
3. Lysosomes are digestive compartments.
· A lysosome is a membrane-bound sac of hydrolytic enzymes that an animal cell uses to digest macromolecules.
· Lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and nucleic acids.
· These enzymes work best at pH 5.
° Proteins in the lysosomal membrane pump hydrogen ions from the cytosol into the lumen of the lysosomes.
° Rupture of one or a few lysosomes has little impact on a cell because the lysosomal enzymes are not very active at the neutral pH of the cytosol.
° However, massive rupture of many lysosomes can destroy a cell by autodigestion.
· Lysosomal enzymes and membrane are synthesized by rough ER and then transferred to the Golgi apparatus for further modification.
· Proteins on the inner surface of the lysosomal membrane are spared by digestion by their three-dimensional conformations, which protect vulnerable bonds from hydrolysis.
· Lysosomes carry out intracellular digestion in a variety of circumstances.
· Amoebas eat by engulfing smaller organisms by phagocytosis.
° The food vacuole formed by phagocytosis fuses with a lysosome, whose enzymes digest the food.
° As the polymers are digested, monomers pass to the cytosol to become nutrients for the cell.
· Lysosomes can play a role in recycling of the cell’s organelles and macromolecules.
° This recycling, or autophagy, renews the cell.
° During autophagy, a damaged organelle or region of cytosol becomes surrounded by membrane.
° A lysosome fuses with the resulting vesicle, digesting the macromolecules and returning the organic monomers to the cytosol for reuse.
· The lysosomes play a critical role in the programmed destruction of cells in multicellular organisms.
° This process plays an important role in development.
° The hands of human embryos are webbed until lysosomes digest the cells in the tissue between the fingers.
° This important process is called programmed cell death, or apoptosis.
4. Vacuoles have diverse functions in cell maintenance.
· Vesicles and vacuoles (larger versions) are membrane-bound sacs with varied functions.
° Food vacuoles are formed by phagocytosis and fuse with lysosomes.
° Contractile vacuoles, found in freshwater protists, pump excess water out of the cell to maintain the appropriate concentration of salts.
° A large central vacuole is found in many mature plant cells.
§ The membrane surrounding the central vacuole, the tonoplast, is selective in its transport of solutes into the central vacuole.
§ The functions of the central vacuole include stockpiling proteins or inorganic ions, disposing of metabolic byproducts, holding pigments, and storing defensive compounds that defend the plant against herbivores.
§ Because of the large vacuole, the cytosol occupies only a thin layer between the plasma membrane and the tonoplast. The presence of a large vacuole increases surface area to volume ratio for the cell.
E. Other Membranous Organelles
1. Mitochondria and chloroplasts are the main energy transformers of cells.
· Mitochondria and chloroplasts are the organelles that convert energy to forms that cells can use for work.
· Mitochondria are the sites of cellular respiration, generating ATP from the catabolism of sugars, fats, and other fuels in the presence of oxygen.
· Chloroplasts, found in plants and algae, are the sites of photosynthesis.
° They convert solar energy to chemical energy and synthesize new organic compounds such as sugars from CO2 and H2O.
· Mitochondria and chloroplasts are not part of the endomembrane system.
° In contrast to organelles of the endomembrane system, each mitochondrion or chloroplast has two membranes separating the innermost space from the cytosol.
° Their membrane proteins are not made by the ER, but rather by free ribosomes in the cytosol and by ribosomes within the organelles themselves.
· Both organelles have small quantities of DNA that direct the synthesis of the polypeptides produced by these internal ribosomes.
· Mitochondria and chloroplasts grow and reproduce as semiautonomous organelles.
· Almost all eukaryotic cells have mitochondria.
° There may be one very large mitochondrion or hundreds to thousands of individual mitochondria.
° The number of mitochondria is correlated with aerobic metabolic activity.
° A typical mitochondrion is 1–10 microns long.
° Mitochondria are quite dynamic: moving, changing shape, and dividing.
· Mitochondria have a smooth outer membrane and a convoluted inner membrane with infoldings called cristae.
° The inner membrane divides the mitochondrion into two internal compartments.
° The first is the intermembrane space, a narrow region between the inner and outer membranes.
° The inner membrane encloses the mitochondrial matrix, a fluid-filled space with DNA, ribosomes, and enzymes.
° Some of the metabolic steps of cellular respiration are catalyzed by enzymes in the matrix.
° The cristae present a large surface area for the enzymes that synthesize ATP.
· The chloroplast is one of several members of a generalized class of plant structures called plastids.
° Amyloplasts are colorless plastids that store starch in roots and tubers.
° Chromoplasts store pigments for fruits and flowers.
° Chloroplasts contain the green pigment chlorophyll as well as enzymes and other molecules that function in the photosynthetic production of sugar.
· Chloroplasts measure about 2 microns × 5 microns and are found in leaves and other green organs of plants and algae.
· The contents of the chloroplast are separated from the cytosol by an envelope consisting of two membranes separated by a narrow intermembrane space.
· Inside the innermost membrane is a fluid-filled space, the stroma, in which float membranous sacs, the thylakoids.
° The stroma contains DNA, ribosomes, and enzymes.
° The thylakoids are flattened sacs that play a critical role in converting light to chemical energy. In some regions, thylakoids are stacked like poker chips into grana.
° The membranes of the chloroplast divide the chloroplast into three compartments: the intermembrane space, the stroma, and the thylakoid space.
· Like mitochondria, chloroplasts are dynamic structures.
° Their shape is plastic, and they can reproduce themselves by pinching in two.
· Mitochondria and chloroplasts are mobile and move around the cell along tracks of the cytoskeleton.
2. Peroxisomes generate and degrade H2O2 in performing various metabolic functions.
· Peroxisomes contain enzymes that transfer hydrogen from various substrates to oxygen.
° An intermediate product of this process is hydrogen peroxide (H2O2), a poison.
° The peroxisome contains an enzyme that converts H2O2 to water.
° Some peroxisomes break fatty acids down to smaller molecules that are transported to mitochondria as fuel for cellular respiration.
° Peroxisomes in the liver detoxify alcohol and other harmful compounds.
° Specialized peroxisomes, glyoxysomes, convert the fatty acids in seeds to sugars, which the seedling can use as a source of energy and carbon until it is capable of photosynthesis.
· Peroxisomes are bound by a single membrane.
· They form not from the endomembrane system, but by incorporation of proteins and lipids from the cytosol.
· They split in two when they reach a certain size.
F. The Cytoskeleton
· The cytoskeleton is a network of fibers extending throughout the cytoplasm.
· The cytoskeleton organizes the structures and activities of the cell.
1. The cytoskeleton provides support, motility, and regulation.
· The cytoskeleton provides mechanical support and maintains cell shape.
· The cytoskeleton provides anchorage for many organelles and cytosolic enzymes.
· The cytoskeleton is dynamic and can be dismantled in one part and reassembled in another to change the shape of the cell.
· The cytoskeleton also plays a major role in cell motility, including changes in cell location and limited movements of parts of the cell.
· The cytoskeleton interacts with motor proteins to produce motility.
° Cytoskeleton elements and motor proteins work together with plasma membrane molecules to move the whole cell along fibers outside the cell.
° Motor proteins bring about movements of cilia and flagella by gripping cytoskeletal components such as microtubules and moving them past each other.
° The same mechanism causes muscle cells to contract.
· Inside the cell, vesicles can travel along “monorails” provided by the cytoskeleton.
· The cytoskeleton manipulates the plasma membrane to form food vacuoles during phagocytosis.
· Cytoplasmic streaming in plant cells is caused by the cytoskeleton.
· Recently, evidence suggests that the cytoskeleton may play a role in the regulation of biochemical activities in the cell.
· There are three main types of fibers making up the cytoskeleton: microtubules, microfilaments, and intermediate filaments.
· Microtubules, the thickest fibers, are hollow rods about 25 microns in diameter and 200 nm to 25 microns in length.
° Microtubule fibers are constructed of the globular protein tubulin.
° Each tubulin molecule is a dimer consisting of two subunits.
° A microtubule changes in length by adding or removing tubulin dimers.
· Microtubules shape and support the cell and serve as tracks to guide motor proteins carrying organelles to their destination.
· Microtubules are also responsible for the separation of chromosomes during cell division.
· In many cells, microtubules grow out from a centrosome near the nucleus.
° These microtubules resist compression to the cell.
· In animal cells, the centrosome has a pair of centrioles, each with nine triplets of microtubules arranged in a ring.
° Before a cell divides, the centrioles replicate.
· A specialized arrangement of microtubules is responsible for the beating of cilia and flagella.
° Many unicellular eukaryotic organisms are propelled through water by cilia and flagella.
° Cilia or flagella can extend from cells within a tissue layer, beating to move fluid over the surface of the tissue.
§ For example, cilia lining the windpipe sweep mucus carrying trapped debris out of the lungs.
· Cilia usually occur in large numbers on the cell surface.
° They are about 0.25 microns in diameter and 2–20 microns long.
· There are usually just one or a few flagella per cell.
° Flagella are the same width as cilia, but 10–200 microns long.
· Cilia and flagella differ in their beating patterns.
° A flagellum has an undulatory movement that generates force in the same direction as the flagellum’s axis.
° Cilia move more like oars with alternating power and recovery strokes that generate force perpendicular to the cilium’s axis.
· In spite of their differences, both cilia and flagella have the same ultrastructure.
° Both have a core of microtubules sheathed by the plasma membrane.
° Nine doublets of microtubules are arranged in a ring around a pair at the center. This “9 + 2” pattern is found in nearly all eukaryotic cilia and flagella.
° Flexible “wheels” of proteins connect outer doublets to each other and to the two central microtubules.
° The outer doublets are also connected by motor proteins.
° The cilium or flagellum is anchored in the cell by a basal body, whose structure is identical to a centriole.
· The bending of cilia and flagella is driven by the arms of a motor protein, dynein.
° Addition and removal of a phosphate group causes conformation changes in dynein.
° Dynein arms alternately grab, move, and release the outer microtubules.
° Protein cross-links limit sliding. As a result, the forces exerted by the dynein arms cause the doublets to curve, bending the cilium or flagellum.
· Microfilaments are solid rods about 7 nm in diameter.
° Each microfilament is built as a twisted double chain of actin subunits.
° Microfilaments can form structural networks due to their ability to branch.
· The structural role of microfilaments in the cytoskeleton is to bear tension, resisting pulling forces within the cell.
· They form a three-dimensional network just inside the plasma membrane to help support the cell’s shape, giving the cell cortex the semisolid consistency of a gel.
· Microfilaments are important in cell motility, especially as part of the contractile apparatus of muscle cells.
° In muscle cells, thousands of actin filaments are arranged parallel to one another.
° Thicker filaments composed of myosin interdigitate with the thinner actin fibers.
° Myosin molecules act as motor proteins, walking along the actin filaments to shorten the cell.
· In other cells, actin-myosin aggregates are less organized but still cause localized contraction.
° A contracting belt of microfilaments divides the cytoplasm of animal cells during cell division.
° Localized contraction brought about by actin and myosin also drives amoeboid movement.
§ Pseudopodia, cellular extensions, extend and contract through the reversible assembly and contraction of actin subunits into microfilaments.
à Microfilaments assemble into networks that convert sol to gel.
à According to a widely accepted model, filaments near the cell’s trailing edge interact with myosin, causing contraction.
à The contraction forces the interior fluid into the pseudopodium, where the actin network has been weakened.
à The pseudopodium extends until the actin reassembles into a network.
· In plant cells, actin-myosin interactions and sol-gel transformations drive cytoplasmic streaming.
° This creates a circular flow of cytoplasm in the cell, speeding the distribution of materials within the cell.
· Intermediate filaments range in diameter from 8–12 nanometers, larger than microfilaments but smaller than microtubules.
· Intermediate filaments are a diverse class of cytoskeletal units, built from a family of proteins called keratins.
° Intermediate filaments are specialized for bearing tension.
· Intermediate filaments are more permanent fixtures of the cytoskeleton than are the other two classes.
· They reinforce cell shape and fix organelle location.
G. Cell Surfaces and Junctions
1. Plant cells are encased by cell walls.
· The cell wall, found in prokaryotes, fungi, and some protists, has multiple functions.
· In plants, the cell wall protects the cell, maintains its shape, and prevents excessive uptake of water.
· It also supports the plant against the force of gravity.
· The thickness and chemical composition of cell walls differs from species to species and among cell types within a plant.
· The basic design consists of microfibrils of cellulose embedded in a matrix of proteins and other polysaccharides. This is the basic design of steel-reinforced concrete or fiberglass.
· A mature cell wall consists of a primary cell wall, a middle lamella with sticky polysaccharides that holds cells together, and layers of secondary cell wall.
· Plant cell walls are perforated by channels between adjacent cells called plasmodesmata.
2. The extracellular matrix (ECM) of animal cells functions in support, adhesion, movement, and regulation.
· Though lacking cell walls, animal cells do have an elaborate extracellular matrix (ECM).
· The primary constituents of the extracellular matrix are glycoproteins, especially collagen fibers, embedded in a network of glycoprotein proteoglycans.
· In many cells, fibronectins in the ECM connect to integrins, intrinsic membrane proteins that span the membrane and bind on their cytoplasmic side to proteins attached to microfilaments of the cytoskeleton.
° The interconnections from the ECM to the cytoskeleton via the fibronectin-integrin link permit the integration of changes inside and outside the cell.
· The ECM can regulate cell behavior.
° Embryonic cells migrate along specific pathways by matching the orientation of their microfilaments to the “grain” of fibers in the extracellular matrix.
° The extracellular matrix can influence the activity of genes in the nucleus via a combination of chemical and mechanical signaling pathways.
§ This may coordinate the behavior of all the cells within a tissue.
3. Intercellular junctions help integrate cells into higher levels of structure and function.
· <BL1>Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact.
· Plant cells are perforated with plasmodesmata, channels allowing cytosol to pass between cells.
° Water and small solutes can pass freely from cell to cell.
° In certain circumstances, proteins and RNA can be exchanged.
· Animals have 3 main types of intercellular links: tight junctions, desmosomes, and gap junctions.
· In tight junctions, membranes of adjacent cells are fused, forming continuous belts around cells.
° This prevents leakage of extracellular fluid.
· Desmosomes (or anchoring junctions) fasten cells together into strong sheets, much like rivets.
° Intermediate filaments of keratin reinforce desmosomes.
· Gap junctions (or communicating junctions) provide cytoplasmic channels between adjacent cells.
° Special membrane proteins surround these pores.
° Ions, sugars, amino acids, and other small molecules can pass.
° In embryos, gap junctions facilitate chemical communication during development.
4. A cell is a living unit greater than the sum of its parts.
· While the cell has many structures with specific functions, all these structures must work together.
° For example, macrophages use actin filaments to move and extend pseudopodia to capture their bacterial prey.
° Food vacuoles are digested by lysosomes, a product of the endomembrane system of ER and Golgi.
· The enzymes of the lysosomes and proteins of the cytoskeleton are synthesized on the ribosomes.
· The information for the proteins comes from genetic messages sent by DNA in the nucleus.
· All of these processes require energy in the form of ATP, most of which is supplied by the mitochondria.
· A cell is a living unit greater than the sum of its parts.
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