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Answered Review Questions Cell Structure and Function Cell Structure Cell membrane (Plasma membrane) Location-Structure Forms outer boundary of cell; Forms membrane-bound organelles Function Semi-permeable (restricts the access of certain compounds and ions) Prokaryote/ Eukaryote Both Aids in maintaining the complex internal organization of a cell Cytoplasm Everything between the nuclear envelope (nucleoid region in prokaryotes) and the cell boundary Cytosol The semi-fluid portion of the cytoplasm Nucleus 10% of the volume of the cell Mission control—manages protein synthesis Eukaryotes only Nucleolus Small dense spheres within the nucleus (often 2-3 visible)—tightly coiled regions of the DNA Genes for ribosomal RNA (building block of ribosomes) Eukaryotes only Nuclear envelope Porous double-membrane organelle; Protects the DNA Eukaryotes only Forms outer boundary of nucleus Bound ribosomes Small dense granules (each has a large and a small subunit) made of proteins and rRNA; Site of most chemical reactions of life Both Both mRNA exits the nucleus through pores after transcription Site of protein synthesis Eukaryotes only Ribosomes build proteins Attached to endoplasmic reticulum; Can become free; Part of the endomembrane system Free ribosomes Small dense granules (each has a large and a small subunit) made of proteins and rRNA; Suspended in cytosol; Can become bound Site of protein synthesis Ribosomes build proteins Both Rough endoplasmic reticulum Network of membranous tubes dotted with bound ribosomes; Loosely surrounds the nucleus; Part of the endomembrane system Smooth endoplasmic reticulum Network of membranous tubes; Loosely surrounds the nucleus; Modify proteins Eukaryotes only Many proteins are modified here by cleaving the polypeptide, forming quaternary structures, removing amino acids or adding non-protein substances (e.g. enzymes often require a metallic ion to work) Makes carbohydrates and lipids Eukaryotes only (e.g. the SER of liver cells convert glucose to glycogen, and make triglycerides and cholesterol) Part of the endomembrane system Transport vesicle Membrane-bound bubble; Buds off both RER and SER; Moves modified proteins, lipids, and carbohydrates to cis face of Golgi apparatus Eukaryotes only Receives compounds from ER; Eukaryotes only Part of endomembrane system Golgi apparatus Network of membranous tubes; Located closer to cell boundary than ER; Attaches a chemical “address label” for compounds destined for export Cis face toward nucleus; Trans face toward cell membrane; Part of the endomembrane system Secretory vesicle Membrane-bound bubble; Buds off trans face of Golgi apparatus; Part of endomembrane system Moves finished compounds to cell membrane for export Eukaryotes only Lysosome Membrane-bound bubble containing hydrolytic enzymes; Cell’s stomach; Eukaryotes only Merges with food vacuole and digests organic compounds; Buds off Golgi apparatus Autophagy (recycles old and damaged organelles and cytosol); Apoptosis (programmed cell death/self-destruction) Food vacuole Membrane-bound bubble; Buds off cell membrane Transports food particles and captured microbes from outside the cell into cytoplasm; N/A Fuses with lysosome Mitochondrion Double membrane bound organelle; Inner membrane called cristae; Aerobic cellular respiration; Eukaryotes only Harvests chemical energy from organic monomers and stores the energy in ATP Semi-fluid interior called matrix; Has own DNA and proteinmaking machinery Descendent of free-living prokaryote Chloroplast Double membrane bound organelle; Inner membrane discs called thylakoids; semi-fluid space surrounding thylakoids called stroma; Has own DNA and proteinmaking machinery Descendent of free-living prokaryote Photosynthesis; Harnesses light energy and uses it to build sugar Eukaryotes only (Plants and Photosynthes izing Protists) Cytoskeleton All through cytoplasm Three filament types (Listed below) Gives shape to cell; Supports organelles; Aids in motion and cell division; Moves material (organelles) through cytoplasm Actin Filaments One kind of cytoskeletal element; Most often located just below cell membrane; Movement (e.g. Amoeba pseudopods, cytoplasmic streaming, formation of cleavage furrow, microvilli extension and retraction) Eukaryotes only Internal monorail system for moving organelles through cytoplasm; Eukaryotes only Twisting strand of globular actin subunits Microtubules One kind of cytoskeletal element; Spread through out cytoplasm; Small hollow tube built of tubulin dimers Intermediate filaments components of centrosome, centrioles, cilia, and flagella; Microtubules are the spindle fibers that move the chromosomes in cell division One kind of cytoskeletal element; Scaffolding that supports organelles; Spread through out cytoplasm; Gives shape to cells Eukaryotes only Anchored to cell membrane and organelles Centrosome (Microtubule Organizing Center [MTOC]) Within cytoplasm; Centriole Small pair of hollow tubes; In animal cells the location is covered by a pair of centrioles Built of microtubules Organized into a 9+0 arrangement Covers centrosome in animal cells Region of the cytoplasm that makes spindle fibers for cell division Associated with cell division but not necessary Eukaryotes Eukaryotes (Animal cells) Cilia Small oar-like structure projecting outside the cell membrane; Built of microtubules (9+2 arrangement); Synchronized rhythmic rowing; Eukaryotes Movement for single-celled microbes; Ciliary escalator in trachea Basal body has 9+0 arrangement like centriole Flagella Long whip-like tail projecting outside the cell membrane; Wiggles back and forth moving cell through liquid; Sperm cells have a flagellum Both (prokaryotic flagella are different in structure and motion [rotary]) Large membranous sac in plant cells; Maintains structural integrity of plant cells (turgidity); Eukaryotes (Plants only) Takes up most of the space in cytoplasm Water storage; Built of microtubules (9+2 arrangement); Basal body has 9+0 arrangement like centriole Central Vacuole Alkaloid storage; Pigment storage Perioxisome Small membrane bound organelle in aerobic eukaryotes PLASMA MEMBRANE Catalase enzymes in organelle convert hydrogen peroxide (slightly toxic intermediate metabolite of superoxide free radical breakdown) to water and oxygen gas Eukaryotes NUCLEUS, NUCLEAR ENVELOPE, NUCLEAR PORES GENERALIZED ANIMAL CELL GENERALIZED PLANT CELL BOUND AND FREE RIBOSOMES RER AND SER GOLGI APPARATUS LYSOSOME MITOCHONDRION CHLOROPLAST PEROXISOME CENTRIOLES FLAGELLA AND CILIA MICROTUBULES ACTIN FILAMENT INTERMEDIATE FILAMENT Trace the path of the production of a protein from the DNA in the nucleus to its secretion outside the cell. (endomembrane system). Explain the function of each member. Proteins are synthesized by the bound ribosome. The resulting protein is modified (glycoprotein is attached, plus any other modifications) by the rough endoplasmic reticulum. A small section of the RER containing the protein pinches off the end enclosing the protein inside a transport vesicle. The transport vesicle moves to the Golgi apparatus where it fuses with the cis face of the Golgi apparatus. The protein receives a chemical address label (glycoprotein is modified) as it is moved through the layers of membranous sacs of the Golgi apparatus. On the trans face of the Golgi apparatus the finished protein is enclosed inside a secretory vesicle that moves to the cell membrane and dumps the protein out of the cell. Secretory vesicle Lipids or carbohydrates are synthesized by the smooth endoplasmic reticulum. A small section of the SER containing the compound pinches off the end enclosing the protein inside a transport vesicle. The transport vesicle moves to the Golgi apparatus where it fuses with the cis face of the Golgi apparatus. The compound receives a chemical address label (glycoprotein is modified) as it is moved through the layers of membranous sacs of the Golgi apparatus. On the trans face of the Golgi apparatus the finished compound is enclosed inside a secretory vesicle that moves to the cell membrane and dumps the compound out of the cell. Explain the endosymbiosis theory. Mitochondria and chloroplasts have many characteristics that make them look like prokaryotic cells (see table below). Lynn Margulis hypothesized that these two energy-producing organelles were once free-living prokaryotes with a special talent that were engulfed but not digested by a larger prokaryote. A mutalistic relationship developed. The smaller aerobic cellular respiring bacterium was protected and in return the larger symbiont was supplied with energy. In plants and photosynthesizing protists, symbiotic cyanobacteria were added to the mix making the larger symbionts autotrophic. Contrast plant and animal cells. See comparison below.