ESSENTIAL CELL BIOLOGY, FOURTH EDITION

ESSENTIAL CELL BIOLOGY, FOURTH EDITION CHAPTER 1: CELLS: THE FUNDAMENTAL UNITS OF LIFE Unity and Diversity of Cells Living systems are incredibly diverse in size, shape, environment, and behavior. It is estimated that there are between 10 million and 100 million different species. Despite thiswide variety of organisms, it remains difficult to define what it means to say something isalive. Which of the following can be described as the smallest living unit? (a) DNA (b) cell (c) organelle (d) protein Indicate whether the following statements are true or false. If the statement is false, explain why it is false. A. The Paramecium is a multicellular microorganism covered with hairlike cilia. B. Cells of different types can have different chemical requirements. C. The branchlike extensions that sprout from a single nerve cell in a mammalian brain can extend over several hundred micrometers. For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; each word or phraseshould be used only once. Cells can be very diverse: superficially, they come in various sizes, ranging from bacterial cells such as Lactobacillus, which is a few in length, to larger cells such as a frog’s egg, which has a diameter of about one . Despite the diversity, cells resemble each other to an astonishing degree in their chemistry. For example, the same 20 are used to make proteins. Similarly, the genetic information of all cells is stored in their . Although contain the same types of molecules as cells, their inability to reproduce themselves by their own efforts means that they are not considered living matter. amino acids micrometer(s) viruses DNA millimeter(s) yeast fatty acids meter plants plasma membranes How does cellular specialization serve multicellular organisms and how might a high degree of specialization be detrimental? The flow of genetic information is controlled by a series of biochemical reactions that result in the production of proteins, each with its own specific order of amino acids. Choose the correct series of biochemical reactions from the options presented here. (a) replication, transcription, translation (b) replication, translation, transcription (c) translation, transcription, replication (d) translation, replication, transcription Proteins are important architectural and catalytic components within the cell, helping to determine its chemistry, its shape, and its ability to respond to changes in the environment. Remarkably, all of the different proteins in a cell are made from the same20 . By linking them in different sequences, the cell can make protein molecules with different conformations and surface chemistries, and therefore differentfunctions. (a) nucleotides. (b) sugars. (c) amino acids. (d) fatty acids. Which statement is NOT true about mutations? (a) A mutation is a change in the DNA that can generate offspring less fit for survival than their parents. (b) A mutation can be a result of imperfect DNA duplication. (c) A mutation is a result of sexual reproduction. (d) A mutation is a change in the DNA that can generate offspring that are as fit for survival as their parents are. Changes in DNA sequence from one generation to the next may result in offspring that are altered in fitness compared with their parents. The process of change and selection over the course of many generations is the basis of . (a) mutation. (b) evolution. (c) heredity. (d) reproduction. Select the option that best finishes the following statement: ―Evolution is a process .‖ (a) that can be understood based on the principles of mutation and selection. (b) that results from repeated cycles of adaptation over billions of years. (c) by which all present-day cells arose from 4–5 different ancestral cells. (d) that requires hundreds of thousands of years. Select the option that correctly finishes the following statement: ―A cell’s genome .‖ (a) is defined as all the genes being used to make protein. (b) contains all of a cell’s DNA. (c) constantly changes, depending upon the cell’s environment. (d) is altered during embryonic development. Cells Under the Microscope Which statement is NOT true about the events/conclusions from studies during the mid- 1800s surrounding the discovery of cells? (a) Cells came to be known as the smallest universal building block of living organisms. (b) Scientists came to the conclusion that new cells can form spontaneously from the remnants of ruptured cells. (c) Light microscopy was essential in demonstrating the commonalities between plant and animal tissues. (d) New cells arise from the growth and division of previously existing cells. What unit of length would you generally use to measure a typical plant or animal cell? (a) centimeters (b) nanometers (c) millimeters (d) micrometers Match the type of microscopy on the left with the corresponding description provided below. There is one best match for each. A. confocal B. transmission electron C. fluorescence D. phase-contrast E. scanning electron F. bright-field uses a light microscope with an optical component to take advantage of the different refractive indices of light passing through different regions of the cell. employs a light microscope and requires that samples be fixed and stained in order to reveal cellular details. requires the use of two sets of filters. The first filter narrows the wavelength range that reaches the specimen and the second blocks out all wavelengths that pass back up to the eyepiece except for those emitted by the dye in the sample. scans the specimen with a focused laser beam to obtain a series of two-dimensional optical sections, which can be used to reconstruct an image of the specimen in three dimensions. The laser excites a fluorescent dye molecule, and the emitted light from each illuminated point is captured through a pinhole and recorded by a detector. has the ability to resolve cellular components as small as 2 nm. requires coating the sample with a thin layer of a heavy metal to produce three- dimensional images of the surface of a sample. Indicate whether the following statements are true or false. If the statement is false, explain why it is false. A. The nucleus of an animal cell is round, small, and difficult to distinguish using light microscopy. B. The presence of the plasma membrane can be inferred by the well-defined boundary of the cell. C. The cytosol is fairly empty, containing a limited number of organelles, which allows room for rapid movement via diffusion. Cell biologists employ targeted fluorescent dyes or modified fluorescent proteins in both standard fluorescence microscopy and confocal microscopy to observe specific details in the cell. Even though fluorescence permits better visualization, the resolving power is essentially the same as that of a standard light microscope because the resolving power ofa microscope is limited by the of light. (a) absorption (b) intensity (c) filtering (d) wavelength What is the smallest distance two points can be separated and still resolved using light microscopy? (a) 20 nm (b) 0.2 µm (c) 2 µm (d) 200 µm The Prokaryotic Cell By definition, prokaryotic cells do not possess . (a) a nucleus. (b) replication machinery. (c) ribosomes. (d) membrane bilayers. Although there are many distinct prokaryotic species, most have a small range of shapes, sizes, and growth rates. Which of the following characteristics are not observed in prokaryotes? (a) a highly structured cytoplasm (b) endoplasmic reticulum (c) the ability to divide rapidly (d) a cell wall Indicate whether the following statements are true or false. If the statement is false, explain why it is false. A. The terms ―prokaryote‖ and ―bacterium‖ are synonyms. B. Prokaryotes can adopt several different basic shapes, including spherical, rod- shaped, and spiral. C. Some prokaryotes have cell walls surrounding the plasma membrane. Prokaryotic cells are able to evolve very fast, which helps them to rapidly adapt to new food sources and develop resistance to antibiotics. Which of the options below lists the three main characteristics that support the rapid evolution of prokaryotic populations? (a) microscopic, motile, anaerobic (b) aerobic, motile, rapid growth (c) no organelles, cell wall, can exchange DNA (d) large population, rapid growth, can exchange DNA Indicate whether the following statements are true or false. If the statement is false, explain why it is false. A. Oxygen is toxic to certain prokaryotic organisms. B. Mitochondria are thought to have evolved from anaerobic bacteria. C. Photosynthetic bacteria contain chloroplasts. Some prokaryotes can live by utilizing entirely inorganic materials. Which of the following inorganic molecules would you predict to be the predominant building blockfor fats, sugars, and proteins? (a) O2 (b) N2 (c) CO2 (d) H2 The Eukaryotic Cell Use the list of structures below to label the schematic drawing of an animal cell in FigureQ1- 23. Figure Q1-23 A. plasma membrane B. nuclear envelope C. cytosol D. Golgi apparatus E. endoplasmic reticulum F. mitochondrion G. transport vesicles For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; each word or phraseshould be used only once. Eukaryotic cells are bigger and more elaborate than prokaryotic cells. By definition, all eukaryotic cells have a , usually the most prominent organelle. Another organelle found in essentially all eukaryotic cells is the , which generates the chemical energy for the cell. In contrast, the is a type of organelle found only in the cells of plants and algae, and performs photosynthesis. If we were to strip away the plasma membrane from a eukaryotic cell and remove all of its membrane- enclosed organelles, we would be left with the , which contains many long, fine filaments of protein that are responsible for cell shape and structure and thereby form the cell’s . chloroplast cytosol nucleus chromosome cytoskeleton endoplasmic reticulum mitochondrion ribosomes The is made up of two concentric membranes and is continuouswith the membrane of the endoplasmic reticulum. (a) plasma membrane (b) Golgi network (c) mitochondrial membrane (d) nuclear envelope The nucleus, an organelle found in eukaryotic cells, confines the , keeping them separated from other components of the cell. (a) lysosomes (b) chromosomes (c) peroxisomes (d) ribosomes Which of the following organelles has both an outer and an inner membrane? (a) endoplasmic reticulum (b) mitochondrion (c) lysosome (d) peroxisome Mitochondria perform cellular respiration, a process that uses oxygen, generates carbon dioxide, and produces chemical energy for the cell. Which answer below indicates a correct pairing of material ―burned‖ and the form of energy produced during cellular respiration? (a) fat, ADP (b) sugar, fat (c) sugar, ATP (d) fat, protein You fertilize egg cells from a healthy plant with pollen (which contains the male germ cells) that has been treated with DNA-damaging agents. You find that some of the offspring have defective chloroplasts, and that this characteristic can be passed on to future generations. This surprises you at first because you happen to know that the male germ cell in the pollen grain contributes no chloroplasts to the fertilized egg cell and thusto the offspring. What can you deduce from these results? Mitochondria contain their own genome, are able to duplicate, and actually divide on a different time line from the rest of the cell. Nevertheless, mitochondria cannot functionfor long when isolated from the cell because they are . (a) viruses. (b) parasites. (c) endosymbionts. (d) anaerobes. The mitochondrial proteins found in the inner membrane are involved in the conversion of ADP to ATP, a source of energy for the cell. This process consumes which of the following substances? (a) oxygen (b) nitrogen (c) sulfur (d) carbon dioxide Indicate whether the following statements are true or false. If the statement is false, explain why it is false. A. With respect to cellular respiration, the only organelles used by animal cells are mitochondria, while plant cells use both mitochondria and chloroplasts. B. The number of mitochondria inside a cell remains constant over the life of the cell. Chloroplasts are found only in eukaryotic cells that carry out photosynthesis: plants and algae. Plants and algae appear green as a result of the presence of chlorophyll. Where ischlorophyll located in the chloroplast? (a) in the first, outer membrane (b) in the space between the first and second membranes (c) in the second, inner membrane (d) in the third, innermost membrane Photosynthesis enables plants to capture the energy from sunlight. In this essential process, plants incorporate the carbon from CO2 into high-energy molecules, which the plant cell mitochondria use to produce ATP. (a) fat (b) sugar (c) protein (d) fiber Indicate whether the following statements are true or false. If the statement is false, explain why it is false. A. Membrane components in the cell are made in the endoplasmic reticulum. B. The Golgi apparatus is made up of a series of membrane-enclosed compartments through which materials destined for secretion must pass. C. Lysosomes are small organelles where fatty acid synthesis occurs. Circle the appropriate cell type in which the listed structure or molecule can be found. Note that the structure or molecule can be found in more than one type of cell. Which of the following choices best describes the role of the lysosome? (a) transport of material to the Golgi (b) clean-up, recycling, and disposal of macromolecules (c) sorting of transport vesicles (d) the storage of excess macromolecules The protozoan Didinium feeds on other organisms by engulfing them. Why are bacteria, in general, unable to feed on other cells in this way? The cell constantly exchanges materials by bringing nutrients in from the external environment and shuttling unwanted by-products back out. Which term describes theprocess by which external materials are captured inside vesicles and brought into thecell? (a) degradation (b) exocytosis (c) phagocytosis (d) endocytosis Eukaryotic cells are able to trigger the release of material from secretory vesicles to the extracellular space using a process called exocytosis. An example of materials commonly released this way is . (a) hormones. (b) nucleic acids. (c) sugars. (d) cytosolic proteins. are fairly small organelles that provide a safe place within the cell to carry out certain biochemical reactions that generate harmful, highly reactive oxygen species. These chemicals are both generated and broken down in the same location. (a) Nucleosomes (b) Lysosomes (c) Peroxisomes (d) Endosomes The cytoskeleton provides support, structure, motility, and organization, and it forms tracks to direct organelle and vesicle transport. Which of the cytoskeletal elements listedbelow is the thickest? (a) actin filaments (b) microtubules (c) intermediate filaments (d) none of the above (all the same thickness) Despite the differences between eukaryotic and prokaryotic cells, prokaryotes have proteins that are distantly related to eukaryotic actin filaments and microtubules. What islikely to be the most ancient function of the cytoskeleton? (a) cell motility (b) vesicle transport (c) membrane support (d) cell division Which of the following characteristics would not support the idea that the ancestral eukaryote was a predator cell that captured and consumed other cells? (a) dynamic cytoskeleton (b) large cell size (c) ability to move (d) rigid membrane Choose the phrase that best completes this sentence: Microtubules and are required to pull duplicated chromosomes to opposite poles of dividing cells. (a) generate contractile forces (b) are intermediate in thickness (c) can rapidly reorganize (d) are found in especially large numbers in muscle cells Indicate whether the following statements are true or false. If the statement is false, explain why it is false. A. Plants do not require a cytoskeleton because they have a cell wall that lends structure and support to the cell. B. The cytoskeleton is used as a transportation grid for the efficient, directional movement of cytosolic components. C. Thermal energy promotes random movement of proteins, vesicles, and small molecules in the cytosol. Which pair of values best fills in the blanks in this statement: On average, eukaryotic cells are times longer and have times more volume than prokaryotic cells. (a) 5, 100 (b) 10, 200 (c) 10, 100 (d) 10, 1000 Indicate whether the following statements are true or false. If the statement is false, explain why it is false. A. Primitive plant, animal, and fungal cells probably acquired mitochondria after they diverged from a common ancestor. B. Protozoans are single-celled eukaryotes with cell morphologies and behaviors that can be as complex as those of some multicellular organisms. C. The first eukaryotic cells on Earth must have been aerobic; otherwise, they would not have been able to survive when the planet’s atmosphere became oxygen-rich. Model Organisms Given what you know about the differences between prokaryotic cells and eukaryotic cells, rate the following things as ―good‖ or ―bad‖ processes to study in the model organism E. coli. A. formation of the endoplasmic reticulum B. DNA replication C. how the actin cytoskeleton contributes to cell shape D. how cells decode their genetic instructions to make proteins E. how mitochondria get distributed to cells during cell division Scientists learned that cell death is a normal and even important part of life by studying the development of the nematode worm C. elegans. What was the most important featureof C. elegans for the study of programmed cell death? (a) The nematode is smaller and simpler than the fruit fly. (b) 70% of C. elegans genes have homologs in humans. (c) The developmental pathway of each cell in the adult worm was known. (d) Its genome was partially sequenced. Biologists cannot possibly study all living species. Instead, they try to understand cell behavior by studying a select subset of them. Which of the following characteristics areuseful in an organism chosen for use as a model in laboratory studies? (a) amenability to genetic manipulation (b) ability to grow under controlled conditions (c) rapid rate of reproduction (d) all of the above Many of the mechanisms that cells use for maintenance and reproduction were first studied at the molecular level in bacteria. Which bacterial species had a central role inadvancing the field of molecular biology? (a) E. coli (b) D. melanogaster (c) S. pombe (d) C. elegans Brewer’s yeast, apart from being an irreplaceable asset in the brewery and in the bakery, is an experimental organism used to study eukaryotic cells. However, it does have somelimitations. Which of the processes below cannot be studied in yeast? (a) DNA replication (b) cell motility (c) exocytosis (d) cell division For each process (A–D), circle the simplest model organism from the list of three that would be best used for investigation: A. thaliana, or Arabidopsis, is a common weed. Biologists have selected it over hundreds of thousands of other flowering plant species to serve as an experimental model organismbecause . (a) it can withstand extremely cold climates. (b) it can reproduce in 8–10 weeks. (c) it produces thousands of of