Chapter 6Microscopes / Tools for Studying Cells Transmission electron microscopes: usually used to study the interior of cells. Images taken with the T.E.M appear flat and two-dimensional. Question: "If a modern electron microscope (TEM) can resolve biological images to the nanometer level, as opposed to the best light microscope, this is due to which of the following? " A: Electron beams have much shorter wavelengths than visible light. Question: When biologists wish to study the internal ultrastructure of cells, they most likely would use " A: A Transmission Electron Microscope Question: : If a modern electron microscope (TEM) can resolve biological images to the nanometer level, as opoosed to the best light microscope, this is due to which of the following? A: Electron beams have much shorter wavelengths than visible light. Light microscopes: use light, passes through living or dead specimen, to form an image. Cells and tissue can be stained to make the organelles easier to see. (most stain kills cells) Question: The advantage of light microscopy over electron microscopy is that A: Light microscopy allows one to view dynamic processes in living cells. Scanning Electron Microscopes- are used for studying the surface of cells, and the images have a 3D appearance. Question: A biologist is studying kidney tubules in small mammals. She wants specifically to examine the juxtapostion of different types of cells in these structures. The cells in question can be distingued by external shape, size, and 3D characteristics. Which would be the optimum method for her study? A: Scanning Electrion Microscopy Question: "A biologist is studying kidney tubules in small mammals. She wants specifically to examine the juxtaposition of different types of cells in these structures. The cells in question can be distinguished by external shape, size, and 3-dimensional characteristics. Which would be the optimum method for her study? " A: The toy microscope magnifies a good deal, but has low resolution and therefore poor quality images. Question:Why is it important to know what microscopy method was used to prepare the images you wish to study? A: So that you can make a judgment about the likelihood of artifacts having been introduced in the preparation

Cell fractionation: uses an ultra centrifuge to spin liquid samples at high speed, separating them into layers based on differences of density. (Nuclei are forced down to the bottom first, followed by mitochondria and ribosomes.) Question: A primary objective of cell fractionation is to A: Separate the major organelles so that their particular function can be determined. Question: In the fractionation of homogenized cells using centrifugation, the primary factor that determines wether a specific cellular component ends up in the supernatant or the pellet is A: the size and weight of the component. Question: Which of the following correctly lists the order in which cellular components will be found in the pellet when homogenized cells are treated with increasingly rapid sins in a centrifuge? A: Nucleus, Mitochondria, Ribosomes Question: Quantom dots are small (15-30 nm diameter), bright particles visible using light microscopy. If the dots can be specifically bound to individual proteins on a plasma membrane of a cell, which of the following correctly describes the advantage of using quantom in examining proteins? A: The dots permit the motion of the proteins to be determined more precisely.

Structure & Function of the Cell Prokaryotes No internal membranes: no nuclear membrane, E.R, Mitochondria, Vacuoles, or other organelles. Circular, naked DNA Ribosomes are very small Metabolism is anaerobic or aerobic No Cytoskeleton Unicellular Cells are very small Eukaryotes Contains distinct organelles

DNA wrapped with histone proteins into chromosomes Ribosomes are larger Metabolism is aerobic Cytoskeleton Present Multicellular with differentiation of cell types Cells are larger

Question: All of the following are part of a prokaryotic cell except A: An endoplasmic reticulum. Question: A mycoplasma is an organism with a diameter between 0.1 and 1.0 m. What does its size tell you about how it might be classified? A: It Could be a very small bacterium Question: Which of the following is a major cause of the size limits for certain types of cells? A: The need for a surface area of sufficient area to allow the cell's function Question: Which of the following statements correctly describes some aspect of protein disposal from prokaryotic cells? A: Proteins that are excreted by prokaryotes are synthesized on ribosomes that are bound to the cytoplasmic surface of the plasma membrane. Question: "The chemical reactions involved in respiration are virtually identical between prokaryotic and eukaryotic cells. In eukaryotic cells, ATP is synthesized primarily on the inner membrane of the mitochondria. Where are the

corresponding reactions likely to occur in prokaryotic respiration? " A: On the inner plasma membrane Question: "A cell has the following molecules and structures: enzymes, DNA, ribosomes, plasma membrane, and mitochondria. It could be a cell from " A: Animal or Plant Cell Question: "The cell walls of bacteria, fungi, and plant cells and the extracellular matrix of animal cells are all external to the plasma membrane. Which of the following is a characteristic of all of these extracellular structures? " A: They are constructed of materials that are largely synthesized in the cytoplasm and then transported out of the cell Nucleus: Contains chromosomes, which are wrapped with histone proteins into a chromatin network. It is surrounded by a selectively permeable nuclear membrane or envelope that contains pores to allow for the transport of molecules, like messenger RNA (mRNA), which are too large to diffuse directly through the envelope. Contains most of the genes in the eukaryotic cell (some genes are located in mitochondria and chloroplasts). Question: "Recent evidence shows that individual chromosomes occupy fairly defined territories within the nucleus. Given the structure and location of the following parts of the nucleus, which would be more probably involved in chromosome location? " A: The nuclear matrix Question: Organelles other than the nucleus that contain DNA include A: Chloroplasts & Mitochondria Nucleolus: Ribosomal RNA (rRNA) is synthesized from instructions in the DNA. Ribosomes: The site of protein synthesis. They can be found free in the cytoplasm or attached to rough endoplasmic reticulum. Cells that high rates of protein synthesis have large numbers of ribosomes. Cells active in protein synthesis also have prominent nucleoli. Question: Large numbers of ribosomes are present in cells that specialize in producing which of the following molecules? A: Proteins Question: Under which of the following conditions would you expect to find a cell with a predominance of free ribosomes? A: a cell that is producing cytoplasmic enzymes

Endoplasmic Reticulum: Rough ER- the site of protein synthesis (resulting from the attached ribosomes). Smooth ER- has three functions: 1. Assists in the synthesis of steroid hormones and other lipids. 2. Connects Rough E.R to the Golgi apparatus. 3. Carries out various detoxification processes. Question: Which type of organelle is primarily involved in the synthesis of oils, phospholipids, and steroids? " A: Smooth endoplasmic reticulum Question: Which structure is the site of the synthesis of proteins that may be exported from the cell? A: Rough ER Question: The fact that the outer membrane of the nuclear envelope has bound ribosomes allows one to most reliably conclude that A: at least some of the proteins that function in the nuclear envelope are made by the ribosomes on the nuclear envelope. Question: The liver is involved in detoxification of many poisons and drugs. Which of the following structures is primarily involved in this process and therefore abundant in liver cells? A: Smooth ER Golgi Apparatus: lies near the nucleus and consist of flattened membranous sacs stacked next to one another surrounded by vesicles. They package substances produced in the rough endoplasmic reticulum and secret them to other cell parts or to the cell surface for export. Question: The difference in lipid and protein composition between the membranes of the endomembrane system is largely determined by A: The function of the Golgi apparatus in sorting membrane components. Question: Which of the following produces and modifies polysaccharides that will

be secreted? A:Golgi apparatus

Lysosomes: Sacs of digestive (hydrolytic) enzymes surrounded by a single membrane. They are the principal site of intracellular digestion. With the help of the lysosome, the cell continually renews itself by breaking down and recycling cell parts. Programmed destruction of cells (apoptosis) by their own digestive enzymes is a critical part of the development of multicellular organisms. They are generally not found in plant cells. Question: "In animal cells, hydrolytic enzymes are packaged to prevent general destruction of cellular components. Which of the following organelles functions in this compartmentalization? " A: Lysosome Question: Tay-Sachs disease is a human genetic abnormality that results in cells accumulating and becoming clogged with very large and complex lipids. Which cellular organelle must be involved in this condition? A: Lysosome Question: Which of the following contains hydrolytic enzymes? A: Lysosomes Peroxisomes: are found in both plant and animal cells. They contain catalase, which converts hydrogen peroxide (H2O2) , a waste product of respiration in the cell, into water with the release of oxygen atoms. They also detoxify alcohol in liver cells. Question: Which of the following contains enzymes that transfer hydrogen from various substratesto oxygen?

A: Peroxisome Question: "The peroxisome gets its name from its interaction with hydrogen peroxide. If a liver cell is detoxifying alcohol and some other poisons, it does so by removal of hydrogen from the molecules. What, then, do the enzymes of the

peroxisome do? " A: Transfer the hydrogens to oxygen molecules Question: How does the cell multiply its peroxisomes? A: They split in two after they are too large.

Mitochondria: The mitochondria are the site of cellular respiration. All cells have many mitochondria; a very active cell could have 2,500 of them. Mitochondria have an outer double membrane and an inner series of membranes called cristae. They also contain their own DNA. Question: Which is one of the main energy transformers of cells? A: Mitochondrion Question: Which of the following contains its own DNA and ribosomes? A: Mitochondrion Question: "The mitochondrion, like the nucleus, has two or more membrane layers. How is the innermost of these layers different from that of the nucleus? " A: The inner mitochondrial membrane is highly folded Question:Why isn't the mitochondrion classified as part of the endomembrane system? A: Its structure is not derived from the ER Question: Question: "Of the following, which cell structure would most likely be visible with a light microscope that has been manufactured to the maximum resolving power possible? " A: Mitochondrian Vacuoles: Vaculoes are single, membrane-bound structures for storage. Question: The volume enclosed by the plasma membrane of plant cells is often much larger than the corresponding volume in animal cells. The most reasonable explanation for this observation is that

A: Plant cells contain a large vacuole that reduces the volume of the cytoplasm Question: Which of the following is a compartment that often takes up much of the volume of a plant cell? A: Vacuole Chlorplasat: Have a double membrane and are the site of photosynthesis. In addition to the double outer membrane, they have an inner one that forms a series of structures called grana (consisting of thylakoids). The grana lies in the stroma. They contain their own DNA. Question: "Grana, thylakoids, and stroma are all components found in " A: Chloroplasts Question: "A biologist ground up some plant leaf cells and then centrifuged the mixture to fractionate the organelles. Organelles in one of the heavier fractions could produce ATP in the light, while organelles in the lighter fraction could produce ATP in the dark. The heavier and lighter fractions are most likely to contain, respectively, " A: Chloroplasts and mitochondria. Question: Which of the following are capable of converting light energy to chemical energy? A: Chloroplasts

Cytoskeleton: a complex network of protein filaments that extends throughout the cytoplasm and gives the cell its shape, enables it to move, and anchors the organelles to the plasma membrane. The cytoskeleton includes microtubules and microfilaments. 1. Microtubules: are hollow tubes made of the protein tubulin that make up the cilia, flagella, and spindle fibers. Cilia and flagella, which move cells from one place to another consists of 9 pares of microtubules organized around 2 singlet microtubules. Spindle fibers help separate chromosomes during mitosis and meiosis and consist of microtubules organized into 9 triplets with no microtubules in the center. Flagella, when present in prokaryotes, are not made of microtubules. 2. Microfilimanets: help support the shape of the cell. They enable ameoba to move by sending out pseudopods. Question: "The nuclear lamina is an array of filaments on the inner side of the nuclear membrane. If a method were found that could cause the lamina to fall into disarray, what would you expect to be the most likely consequence? " A: A change in the shape of the nucleus Question: Motor proteins provide for molecular motion in cells by interacting with what types of cellular structures? A: Cytoskeletons Question: "Cells can be described as having a cytoskeleton of internal structures

that contribute to the shape, organization, and movement of the cell. Which of the following are part of the cytoskeleton? " A: Microfilaments Question: Which of the following contain the 9 + 2 arrangement of microtubules? A: Cilia & Flagella Question: "Tubulin is a dimer, made up of 2 slightly different polypeptides, alpha and beta. Given the structure above, what is the most likely consequence to the structure of the microtubule? " A: One end of a microtubule can grow or release dimers at a faster rate than the other. Question: "Centrioles, cilia, flagella, and basal bodies have remarkably similar structural elements and arrangements. This leads us to which of the following as a probable hypothesis? A: Natural selection for motility must select for microtubular arrays in circular patterns. Question: "If an individual has abnormal microtubules, due to a hereditary condition, in which organs or tissues would you expect dysfunction? " A: Sperm, larynx, and trachea Question: Which of the following possesses a microtubular structure similar to a basal body? A: Centriole Question: Which of the following statements about the cytoskeleton is true? A: Movement of cilia and flagella is the result of motor proteins causing microtubules to move relative to each other.

Centrioles, centrosomes, or microtubule organizing centers: are non membranous structures that lie outside the nuclear membranes. They organize spindle fibers, and give rise to the spindle apparatus required for cell division. Two centrioles oriented at the right angles to each other make up one centrosome and consists of 9 triplets of microtubules arranged in a circle. Plant cells lack centrosomes but have microtubule organizing centers. In animal cells the microtubule organizing centers is the same as the centrosome. Cell Wall: is one cell structure not found in animal cells. Plants and algae have cell walls made of cellulose. The cell walls of fungi are usually made of chitin. Those of prokaryotes consist of other polysaccharides and complex polymers. The primary cell wall is immediately outside the plasma membrane. Some cells produce a second cell wall underneath the primary cell wall, called the secondary cell wall. When a plant cell divides, a think gluey layer is formed between the two new cells, which becomes the middle lamella. The middle lamella glues adjacent cells together.

Question: All of the following serve an important role in determining or maintaining the structure of plant cells. Which of the following are distinct from the others in their composition? A: Plant Cell Walls Question: Which of the following relationships between cell structures and their respective functions is correct? A: Cell wall: support, protection Question: "When a potassium ion (K+) moves from the soil into the vacuole of a cell on the surface of a root, it must pass through several cellular structures. Which of the following correctly describes the order in which these structures will be encountered by the ion? " A: primary cell wall -> plasma membrane -> cytoplasm -> tonoplast

Intercellular Junctions Question: "Which of the following makes it necessary for animal cells, although they have no cell walls, to have intercellular junctions? " A: "Large molecules, especially proteins, do not readily get through one, much less two adjacent cell membranes. " Question: Recent evidence shows that the extracellular matrix can take part in regulating the expression of genes. A likely possibility for this might be which of the following? A: "Mechanical signals of the ECM can alter the cytoskeleton, which can alter

intracellular signaling. Tight Junctions: At tight junctions, the plasma membrane of the neighboring cells, are very tightly pressed against each other, bound together by specific proteins. Forming continuous seals around prevent leakage of extracellular fluid across a layer of epithelial cells. For example, tight junctions between skin cells make us watertight by preventing leakage between cells and our sweat glands. Desmosomes: (also called anchoring junctions) function like rivets, fastening cells together into strong sheets. Intermediate filaments made of sturdy keratin proteins anchor desmosomes in the cytoplasm. Desmosomes attach muscle cells to each other in a muscle. Some muscle tears involve the rupture of desmosomes. Gap Junctions: (also called communicating junctions) provide cytoplasmic channels from once cell to an adjacent cell and in this way are similar in their functions to the plasmodesmata in plants. Gap junctions consist of membrane proteins that surround a pore through which ions, sugars, amino acids, and other small molecules may pass. Gap junctions are necessary for communication between cells in many types of tissues, including heart, muscle and in animal embryos. Question: Plasmodesmata in plant cells are most similar in function to which of the following structures in animal cells? A: Gap Junctions Question: Ions can travel directly from the cytoplasm of one animal cell to the cytoplasm of an adjacent cell through A: Gap Junctions _________ Integrins: built in the plasma membrane. Integrins span the membrane and bind on their cytoplasmic side to associated proteins attached to microfilaments of the cytoskeleton. Question: The extracellular matrix is thought to participate in the regulation of animal cell behavior by communicating information from the outside to the inside of the cell via which of the following? A: Integrins Question: "Of the following molecules of the ECM, which is capable of transmitting signals between the ECM and the cytoskeleton? " A: Integrins