Biology_Unit_5 (1110837), страница 11
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The chemical energyis used inside the chloroplasts to assemble carbohydrates and otherorganic molecules from simple inorganic raw materials (Figure5.27).• The large central vacuole, which consists of a tonoplast enclosingan inner space, develops pressure that supports plant cells,accounts for much of cellular growth by enlarging as cells mature,and serves as a storage site for substances including waste materials(Figure 5.10).• A cellulose cell wall surrounds plant cells, providing support andprotection. Plant cell walls are perforated by plasmodesmata, channels that provide direct pathways of communication between thecytoplasm of adjacent cells (Figure 5.28).Practice: Structure of a chloroplastAnimation: Plant cell walls5.5 The Animal Cell SurfaceCHAPTER 5THE CELL: AN OVERVIEW113• Animal cells have specialized surface molecules and structures thatfunction in cell adhesion, communication, and support.• Cell adhesion molecules bind to specific molecules on other cells.The adhesions organize and hold together cells of the same type inbody tissues.• Cell adhesions are reinforced by various junctions.
Anchoringjunctions hold cells together. Tight junctions seal together theplasma membranes of adjacent cells, preventing ions and mol-ecules from moving between the cells. Gap junctions open directchannels between the cytoplasm of adjacent cells (Figure 5.29).• The extracellular matrix, formed from collagen proteins embeddedin a matrix of branched glycoproteins, functions primarily in celland body protection and support but also affects cell division,motility, embryonic development, and wound healing (Figure 5.30).Animation: Animal cell junctionsunderstand and applyTest Your Knowledge1. You are examining a cell from a crime scene using an electron microscope.
It contains ribosomes, DNA, a plasma membrane, a cellwall, and mitochondria. What type of cell is it?a. lung celld. cell from the surface ofb. plant cella human fingernailc. prokaryotic celle. sperm cell2. A prokaryote converts food energy into the chemical energy ofATP on/in its:a. chromosome.d. cell wall.b. flagella.e. plasma membrane.c. ribosomes.3. Eukaryotic and prokaryotic ribosomes are similar in that:a. both contain a small subunit, but only eukaryotes contain alarge subunit.b. both contain the same number of proteins.c. both use mRNA to assemble amino acids into proteins.d.
both contain the same number of types of rRNA.e. both produce proteins that can pass through pores into thenucleus.4. Which of the following structures does not require an immediatesource of energy to function?a. central vacuolesd. microfilamentsb. ciliae. microbodiesc. microtubules5. Which of the following structures is not used in eukaryotic protein manufacture and secretion?a. ribosomed.
secretory vesicleb. lysosomee. Golgi complexc. rough ER6. Which of the following are glycoproteins whose function is affected by the common cold virus?a. plasmodesmatad. flagellab. desmosomese. ciliac. cell adhesion molecules7. An electron micrograph shows that a cell has extensive amounts ofrough ER throughout.
One can deduce from this that the cell is:a. synthesizing and metabolizing carbohydrates.b. synthesizing and secreting proteins.c. synthesizing ATP.d. contracting.e. resting metabolically.8. Which of the following contributes to the sealed lining of the digestive tract to keep food inside it?a. a central vacuole that stores proteinsb.
tight junctions formed by direct fusion of proteinsc. gap junctions that communicate between cells of the stomach lining and its muscular walld. desmosomes forming buttonlike spots or a belt to keep cellsjoined togethere. plasmodesmata that help cells communicate their activities114UNIT ONEMOLECULES AND CELLS9. Which of the following statements about proteins is correct?a. Proteins are transported to the rough ER for use within thecell.b. Lipids and carbohydrates are added to proteins by the Golgicomplex.c.
Proteins are transported directly into the cytosol for secretion from the cell.d. Proteins that are to be stored by the cell are moved to therough ER.e. Proteins are synthesized in vesicles.10. Which of the following is not a component of the cytoskeleton?a. microtubulesb. actinsc. microfilamentsd.
ciliae. cytokeratinsDiscuss the Concepts1. Many compound microscopes have a filter that eliminates allwavelengths except that of blue light, thereby allowing only bluelight to pass through the microscope. Use the spectrum of visiblelight (see Figure 9.4) to explain why the filter improves the resolution of light microscopes.2. Explain why aliens invading Earth are not likely to be giant cellsthe size of humans.3. An electron micrograph of a cell shows the cytoplasm packedwith rough ER membranes, a Golgi complex, and mitochondria.What activities might this cell concentrate on? Why would largenumbers of mitochondria be required for these activities?4.
Assuming that mitochondria evolved from bacteria that enteredcells by endocytosis, what are the likely origins of the outer andinner mitochondrial membranes?5. Researchers have noticed that some men who were sterile becausetheir sperm cells were unable to move also had chronic infectionsof the respiratory tract.
What might be the connection betweenthese two symptoms?Design an ExperimentThe unicellular alga Chlamydomonas reinhardtii has two flagellaassembled from tubulin proteins. If a researcher changes the pH fromapproximately neutral (their normal growing condition) to pH .,Chlamydomonas cells spontaneously lose their flagella.
After the cellsare returned to neutral pH, they regrow the flagella—a process calledreflagellation. Assuming that you have deflagellated Chlamydomonascells, devise experiments to answer the following questions:1. Do new tubulin proteins need to be made for reflagellation to occur, or is there a reservoir of proteins in the cell?2. Is the production of new mRNA for the tubulin proteins necessary for reflagellation?3. What is the optimal pH for reflagellation?Apply Evolutionary ThinkingInvestigators studying protein changes during aging examinedenzyme activity in cells extracted from the nematode worm Caenorhabditis elegans. The cell extracts were treated to conserveenzyme activity, although the investigators noted that some proteinswere broken down by the extraction procedure.
Th e extracts werecentrifuged, and seven fractions were collected in sequence to isolatethe location of activity by protease enzymes called cathepsins.Examine the activity profiles in the figure below. In which fractionand, hence, in which eukaryotic cellular structure are these enzymesmost active?What aspects of cell structure suggest that prokaryotes and eukaryotesshare a common ancestor in their evolutionary history?Percent total activity recoveredInterpret the DataExpress Your OpinionResearchers are modifying prokaryotes to identify what it takes to “bealive.” They are creating “new” organisms by removing genes fromliving cells, one at a time.
What are the potential advantages or bioethical pitfalls of this kind of research? Go to academic.cengage.com/login to investigate both sides of the issue and then vote.1008060402001234567Fraction numberKEYAcid phosphatase (lysosomal marker enzyme)β-Hexosaminidase (lysosomal marker enzyme)Cathepsin Ce1 + Ce2Cathepsin DDistribution of enzyme activity in fractions from centrifugation of an organelle pellet.
The fractions arenumbered 1–7 from the top to the bottom of the centrifuge tube. Fraction 1 contains cytosolic contents and is the supernatant, and fraction 7 contains cellular debris and membrane fragments.Source: G. J. Sarkis et al. 1988. Decline in protease activities with age in the nematodeCaenorhabiditis elegans.
Mechanisms of Ageing and Development 45:191–201.CHAPTER 5THE CELL: AN OVERVIEW115.
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