Chapter 1 COPY
By definition, procaryotic cells do not possess __________. (a) a nucleus (b) replication machinery (c) ribosomes (d) membrane bilayers
(a) a nucleus
Drosophila melanogaster is a/an __________. This type of animal is the most abundant of all animal species, making it an appropriate choice as an experimental model. (a) insect (b) bird (c) amphibian (d) mammal
(a) insect
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 biochemical reactions from the options presented here. (a) replication, transcription, translation (b) replication, translation, transcription (c) translation, transcription, replication (d) translation, replication, transcription
(a) replication, transcription, translation
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 are useful 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
(d) all of the above
What unit of length would you generally use to measure a typical human cell? (a) centimeters (b) nanometers (c) millimeters (d) micrometers
(d) micrometers
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 of a microscope is limited by the __________ of light. (a) absorption (b) intensity (c) filtering (d) wavelength
(d) wavelength
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
(a) oxygen
The __________ __________ is made up of two concentric membranes and is continuous with the membrane of the endoplasmic reticulum. (a) plasma membrane (b) Golgi network (c) mitochondrial membrane (d) nuclear envelope
(d) nuclear envelope
Which of the following characteristics would not support the idea that the ancestral eucaryote was a predator cell that captured and consumed other cells? (a) dynamic cytoskeleton (b) large cell size (c) ability to move (d) rigid membrane
(d) rigid membrane
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 procaryotic organisms.
True
Indicate whether the following statements are true or false. If the statement is false, explain why it is false. B. Cells of different types can have different chemical requirements.
True
Indicate whether the following statements are true or false. If the statement is false, explain why it is false. B. The Golgi apparatus is made up of a series of membrane-enclosed compartments through which materials destined for secretion must pass.
True
Indicate whether the following statements are true or false. If the statement is false, explain why it is false. B. Protozoans are single-celled eucaryotes with cell morphologies and behaviors that can be as complex as those of some multicellular organisms.
True.
Although there are many distinct procaryotic species, most have a small range of shapes, sizes, and growth rates. Which of the following characteristics are not observed in procaryotes? (a) a highly structured cytoplasm (b) endoplasmic reticulum (c) the ability to divide rapidly (d) a cell wall
(a) a highly structured cytoplasm (b) endoplasmic reticulum
Chloroplasts are found only in eucaryotic cells that carry out photosynthesis: plants and algae. Plants and algae appear green as a result of the presence of chlorophyll. Where is chlorophyll 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
(d) in the third, innermost membrane
Given what you know about the differences between procaryotic cells and eucaryotic 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
A) bad B) good C) bad D) good E) bad
Circle the simplest model organism best used to study the following processes: A) programmed cell death - e. coli, yeast, c elegans B) chloroplast function - c. elegans, arabidopsis, drosophila C) immunology - Mouse, yeast, arabidopsis D) development of a multicellular tissue - Drosophila, e. coli, yeast
A) c. elegans B) arabidopsis C) mouse D) drosophila
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. A) DNA B) nucleus C) plasma membrane D) choroplast E) cell wall F) lysosome G) mitochondrion H) golgi apparatus
A- a,p,b B- a,p C- a,p,b D- p,b E- p,b F- a,p G- a,p H- a,p
Use the list of structures below to label the schematic drawing of an animal cell in Figure Q1-13. A. plasma membrane B. nuclear envelope C. cytosol D. Golgi apparatus E. endoplasmic reticulum F. mitochondrion G. transport vesicles
A-3 B-5 C-1 D-2 E-4 F-7 G-6
Genes that have homologues in a variety of species have been discovered through the analysis of genome sequences. In fact, it is not uncommon to find a family of homologous genes encoding proteins that are unmistakably similar in amino acid sequence in organisms as diverse as budding yeast, archaea, plants, and humans. Even more remarkably, many of these proteins can substitute functionally for their homologues in other organisms. Explain what it is about the origins of cells that makes it possible for proteins expressed by homologous genes to be functionally interchangeable in different organisms.
All living beings on Earth (and thus, all cells) are thought to be derived from a common ancestor. Solutions to many of the essential challenges that face a cell (such as the synthesis of proteins, lipids, and DNA) seem to have been achieved in this ancient common ancestor. The ancestral cell therefore possessed sets of proteins to carry out these essential functions. Many of the essential challenges facing modern-day cells are the same as those facing the ancestral cell, and the ancient solutions are often still effective. Thus, it is not uncommon for organisms to use proteins and biochemical pathways inherited from their ancestors. Although these proteins usually show some species-specific diversification, they still retain the basic biochemical characteristics of the ancestral protein. For example, homologous proteins often retain their ability to interact with a specific protein target, even in cells of diverse species. Because the basic biochemical characteristics are retained, homologous proteins are often capable of functionally substituting for one another.
Evolutionary biologists have always used a broad range of modern organisms to infer the characteristics that ancestral organisms may have possessed. Genomic sequences are now available for an increasing number of species, and scientists studying evolutionary processes can take advantage of this enormous amount of data to bring evolution into the arena of molecular studies. By aligning the sequences of homologous genes and looking for regions of similarity and where changes have occurred, it is possible to infer the sequence of the ancestral gene. B. It is possible to express an ancestral gene sequence in modern organisms and subsequently compare its function with that of the modern protein. Why might this approach give misleading conclusions?
Although an inferred ancestral sequence can be reconstructed and the protein expressed, you would be placing an inferred, ancient protein in the context of a modern cell. If there are important interacting partners for the modern protein, there is a chance they may not recognize the ancestral protein, and therefore any information about its function may be inaccurate.
Match each biological process with the model organism that is best suited or most specifically useful for its study, based on information provided in your textbook. You may list individual processes more than once. A. cell division B. development (multicellular) C. programmed cell death D. photosynthesis E. immunology _____ A. thaliana (Arabidopsis) _____ M. musculus (mouse) _____ S. pombe _____ C. elegans _____ S. cerevisiae _____ D. rerio (zebrafish) _____ D. melanogaster
B, D - A. thaliana (Arabidopsis) B, E - M. musculus (mouse) A - S. pombe C - C. elegans A - S. cerevisiae B - D. rerio (zebrafish) B - D. melanogaster
The protozoan Didinium feeds on other organisms by engulfing them. Why are bacteria, in general, unable to feed on other cells in this way?
Didinium engulfs prey by changing its shape, and for this it uses its cytoskeleton. Bacteria have no cytoskeleton and cannot easily change their shape because they are generally surrounded by a tough cell wall.
The antibiotic streptomycin inhibits protein synthesis in bacteria. If this antibiotic is added to a culture of animal cells, protein synthesis in the cytosol continues normally. However, over time the population of mitochondria in the cell becomes depleted. Specifically, it is observed that the protein synthesis machinery inside the mitochondria is inhibited. A. Explain this observation based on what you know about the origins of the modern eucaryote.
If the mitochondria originated from an ancient aerobic bacterium that was engulfed by an ancient eucaryote, as postulated, it is possible that an antibiotic that inhibits protein synthesis in bacteria could also block that process in mitochondria.
The antibiotic streptomycin inhibits protein synthesis in bacteria. If this antibiotic is added to a culture of animal cells, protein synthesis in the cytosol continues normally. However, over time the population of mitochondria in the cell becomes depleted. Specifically, it is observed that the protein synthesis machinery inside the mitochondria is inhibited. B. What do you expect to observe if, in a new experiment, animal cells are treated with diphtheria toxin, a compound that is known to block cytosolic protein synthesis but does not have any impact on bacterial growth?
We would expect that although cytosolic protein synthesis would stop, mitochondrial protein synthesis should still occur normally (at least for a little while). This result would lend further support to the idea that mitochondria are derived from a non-eucaryotic organism. If this were not the case, these compounds would be expected to affect protein synthesis at both locations.
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.
True
Many of the mechanisms that cells use for maintenance and reproduction were first studied at the molecular detail in bacteria. Which bacterial species had a central role in advancing the field of molecular biology? (a) E. coli (b) D. melanogaster (c) S. pombe (d) C. elegans
(a) E. coli
Brewer's yeast, apart from being an irreplaceable asset in the brewery and in the bakery, is an experimental organism used to study eucaryotic cells. However, it does face some limitations. Which of the processes below cannot be studied with yeast? (a) DNA replication (b) cell motility (c) exocytosis (d) cell division
(b) cell motility
The nucleus, an organelle found in eucaryotic cells, confines the __________, keeping them separated from other components of the cell. (a) lysosomes (b) chromosomes (c) peroxisomes (d) ribosomes
(b) chromosomes
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
(b) evolution
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 organism because __________________. (a) it can withstand extremely cold climates (b) it can reproduce in 8-10 weeks (c) it produces thousands of offspring per plant (d) Both (b) and (c) are true.
(b) it can reproduce in 8-10 weeks
You wish to explore how mutations in specific genes affecting sugar metabolism might alter tooth development. Which organism is likely to provide the best model system for your studies and why? (a) horses (b) mice (c) E. coli (d) Arabidopsis
(b) mice
Which of the following organelles has both an outer and an inner membrane? (a) endoplasmic reticulum (b) mitochondrion (c) lysosome (d) peroxisome
(b) mitochondrion
B. Which principal organelle does a plant cell contain that a fungal cell does not?
Chloroplasts
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 indexes 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 a 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.
D, F, C, A, B, E
Your friend has just returned from a deep sea mission and claims to have found a new single-celled life form. He believes this new life form may not have descended from the common ancestor that all types of life on Earth share. You are convinced that he must be wrong, and you manage to extract DNA from the cells he has discovered. He says that the mere presence of DNA is not enough to prove the point: his cells might have adopted DNA as a useful molecule quite independently of all other known life forms. What would you do to persuade him that he was wrong?
You could use modern technology to discover the sequence of the DNA. If you are right, and he is wrong, you would expect to find parts of this sequence that are unmistakably similar to corresponding sequences in other, familiar, living organisms; it would be highly improbable that such similar sequences would have evolved independently. You could, of course, also analyze other features of the chemistry of his cells — for example, do they contain proteins made of the same set of 20 amino acids? But he would probably not find such general chemical similarities as persuasive as detailed similarities of DNA sequence.
The cytoskeleton provides support, structure, motility, and organization, and it forms tracks to direct organelle and vesicle transport. Which of the cytoskeletal elements listed below is the thickest? (a) actin filaments (b) microtubules (c) intermediate filaments (d) none of the above (all the same thickness)
(b) microtubules
C. elegans is a nematode. During its development, it produces more than 1000 cells However, the adult worm only has 959 somatic cells. The process by which 131 cells are specifically targeted for destruction is called (a) directed cell pruning. (b) programmed cell death. (c) autophagy. (d) necrosis.
(b) programmed cell death.
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
(b) sugar
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 same 20 __________. By linking them in different sequences, the cell can make protein molecules with different conformations and surface chemistries, and therefore different functions. (a) nucleotides (b) sugars (c) amino acids (d) fatty acids
(c) amino acids
Zebrafish (Danio rerio) are especially useful in the study of early development because their embryos ______________. (a) are exceptionally large (b) develop slowly (c) are transparent (d) are naturally fluorescent
(c) are transparent
Mitochondria contain their own genome, are able to duplicate, and actually divide on a different timeline from the rest of the cell. Nevertheless, mitochondria cannot function for long when isolated from the cell because they are (a) viruses. (b) parasites. (c) endosymbionts. (d) anaerobes.
(c) endosymbionts
__________ 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
(c) peroxisomes
Despite the differences between eucaryotic and procaryotic cells, procaryotes have proteins that are distantly related to eucaryotic actin filaments and microtubules. What is likely to be the most ancient function of the cytoskeleton? (a) cell motility (b) vesicle transport (c) membrane support (d) cell division
(d) cell division
The cell constantly exchanges materials by bringing nutrients in from the external environment and shuttling unwanted by-products back out. Which term describes the process of by which external materials are captured inside vesicles and brought into the cell? (a) degradation (b) exocytosis (c) phagocytosis (d) endocytosis
(d) endocytosis
A. In what way does a fungal cell structurally resemble a plant cell, rather than an animal cell?
Both have cell walls
Evolutionary biologists have always used a broad range of modern organisms to infer the characteristics that ancestral organisms may have possessed. Genomic sequences are now available for an increasing number of species, and scientists studying evolutionary processes can take advantage of this enormous amount of data to bring evolution into the arena of molecular studies. By aligning the sequences of homologous genes and looking for regions of similarity and where changes have occurred, it is possible to infer the sequence of the ancestral gene. A. What term is used to describe the changes in gene sequence that have occurred? How can we use what we know about this process to construct a timeline showing when various sequence changes occurred and when they lead to the modern sequences that we know today?
Changes in gene sequence occur through mutation. Mutations accumulate over time, occurring independently and at different sites in each gene lineage. Homologous genes that diverged recently will differ only slightly; genes that diverged long ago will differ more. Knowing the average mutation rate, you can estimate the time that has elapsed since the different versions of the gene diverged. By seeing how closely the various members of the family of homologous genes resemble one another, you can draw up a family tree, showing the sequence of lineage splittings that led from the ancestral gene to its many modern descendants. Suppose this family tree shows that family members A and B diverged from one another long ago, but that C diverged from B more recently; and suppose that at a certain site in the gene A and B have the same sequence but C is different. Then it is likely that the sequence of A and B is ancestral, while that of C reflects a recent mutation that has occurred in the lineage of C alone.
Indicate whether the following statements are true or false. If the statement is false, explain why it is false. C. A human white blood cell is larger than a Paramecium cell.
False. A human white blood cell is about 10 μm in diameter. The single-celled paramecium is roughly 10 times that size.
Indicate whether the following statements are true or false. If the statement is false, explain why it is false. A. A virus is a living organism.
False. A virus lacks the full machinery required to copy itself and is therefore not considered a living organism.
Indicate whether the following statements are true or false. If the statement is false, explain why it is false. C. Lysosomes are small organelles where fatty acid synthesis occurs.
False. Lysosomes house enzymes that breakdown nutrients for use by the cell and help recycle materials that cannot be used, which will later be excreted from the cell.
Indicate whether the following statements are true or false. If the statement is false, explain why it is false. B. Mitochondria are thought to have evolved from anaerobic bacteria.
False. Mitochondria use oxygen to generate energy and are thought to have evolved from aerobic bacteria.
Indicate whether the following statements are true or false. If the statement is false, explain why it is false. C. Although bacteria use a variety of organic substances as food, bacteria are not able live on inorganic substances.
False. Some bacteria can live by consuming exclusively inorganic substances such as CO2, N2, water, and minerals.
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.
False. The mitochondria in modern plant, animal, and fungal cells are very similar, implying that these lines diverged after the mitochondrion was acquired by the ancestral eucaryote.
Indicate whether the following statements are true or false. If the statement is false, explain why it is false. C. Animal, plant, fungal, and bacterial cells all possess cell walls.
False. The outermost layer in animal cells is the plasma membrane.
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 thus to the offspring. What can you deduce from these results?
Your results show that not all of the information required for making a chloroplast is encoded in the chloroplast's own DNA; some, at least, must be encoded in the DNA carried in the nucleus. The reasoning is as follows. Genetic information is carried only in DNA, so the defect in the chloroplasts must be due to a mutation in DNA. But all of the chloroplasts in the offspring (and thus all of the chloroplast DNA) must derive from those in the female egg cell, since chloroplasts only arise from other chloroplasts. Hence, all of the chloroplasts contain undamaged DNA from the female parent's chloroplasts. In all the cells of the offspring, however, half of the nuclear DNA will have come from the male germ cell nucleus, which combined with the female egg nucleus at fertilization. Since this DNA has been treated with DNA-damaging agents, it must be the source of the heritable chloroplast defect. Thus, some of the information required for making a chloroplast is encoded by the nuclear DNA.
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 this wide variety of organisms, it remains difficult to define what it means to say something is alive. Which of the following can be described as the smallest living unit? (a) DNA (b) cell (c) organelle (d) protein
b) cell
Fill in the blanks Eucaryotic cells are bigger and more elaborate than procaryotic cells. By definition, all eucaryotic cells have a __________________, usually the most prominent organelle. Another organelle found in essentially all eucaryotic 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 eucaryotic 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 __________________.
nucleus, mitochondrion, chloroplast, cytosol, cytoskeleton