6.1 Biologists use microscopes and the tools of biochemistry to study cells6.2 Eukaryotic cells have internal membranes that compartmentalize their functions6.3 The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes6.4 The endomembrane system regulates protein traffic and performs metabolic functions in the cell6.5 Mitochondria and chloroplasts change energy from one form to another6.6 The cytoskeleton is a network of fibers that organizes structures and activities in the cellChapter 6: A Tour of the Cell6.1 Biologists use microscopes and the tools of biochemistry to study cells- Light microscope (LM): visible light is passed through the specimen and then through glass lenses, the lenses refract (bend) the light in such a way that the image of the specimen is magnified as it is projected into the eye or into a camerao Magnification: the ratio of an object’s image size to its real sizeo Resolution: a measure of the clarity of the image; it is the minimum distance two points can be separated and still be distinguished as two pointso Contrast: accentuates differences in parts of the sample- Organelles: membrane-enclosed structures within eukaryotic cells- Electron microscope (EM): focuses a beam of electrons through the specimen or onto its surface; used to study subcellular structures- Scanning electron microscope (SEM): especially useful for detailed study of the topography of a specimen; the electron beam scans the surface of the sample (usually coated with a thin film of gold) and provides images that appear 3-D- Transmission electron microscope (TEM): used to study the internal structure of cells; focuses a beam of electrons through a specimen- Cytology: the study of cell structure- Biochemistry: the study of the chemical processes (metabolism) of cells- Cell fractionation: takes cells apart and separates major organelles and other subcellular structures from one another- Centrifuge: spins test tubes holding mixtures of disrupted cells at a series of increasing speeds; at each speed, the resulting force causes a fraction of the cell components to settle to the bottom of the tube, forming a pellet- Biochemistry and cytology complement each other in correlating cell function with structure- Microsomes: pieces of plasma membranes and cells’ internal membranes; found in pellets after centrifuge6.2 Eukaryotic cells have internal membranes that compartmentalize their functions- Cytosol: a semifluid, jellylike substance inside all cells in which subcellular components are suspended- Chromosomes: carry genes in the form of DNA- Ribosomes: tiny complexes that make proteins according to the instructions from the genes- Eukaryotic cell: most of the DNA is in an organelle called the nucleus, which is bounded by a double membrane; protists, fungi, animals, and plants; “true nucleus”; membrane-bound organelles; cytoplasm is in the region between the plasma membrane and nucleus- Prokaryotic cell: no nucleus, DNA is concentrated in a region that is not membrane-enclosed, called the nucleoid; no membrane-bound organelles; Bacteria and Archaea; “before nucleus” (reflecting the fact that prokaryotic cells evolved before eukaryotic cells); cytoplasm is bound by the plasma membrane- Cytoplasm: interior of either type of cell; in eukaryotic cells, this term refers only to the region between the nucleus and the plasma membrane- Size is a general feature of a cell structure that relates to cell function; eukaryotic cells are generally much larger than prokaryotic cells1- Plasma membrane: at the boundary of every cell, functions as a selective barrier that allows passage of enough oxygen, nutrients, and wastes to service the entire cell; the general structure of a biological membrane is a double layer of phospholipids- Larger organisms do not generally have larger cells than smaller organisms, they simply have more cells- Microvilli: long, thin projections from cells that exchange a lot of material with their surroundings (like intestinalcells), which increase surface area without an appreciable increase in volume- Mitochondria: function in cellular respiration- In animal cells but not plant cells: o Lysosomes: digestive organelles where macromolecules are hydrolyzedo Centrosomes with centrioles: region where the cell’s microtubules are initiated; contains a pair of centrioleso Flagella: motility structure present in some animal cells, composed of a cluster of microtubules within an extension of the plasma membrane – present in some plant sperm- In plant cells but not animal cells: o Chloroplasts: photosynthetic organelle; converts energy of sunlight to chemical energy stored in sugar moleculeso Central vacuole: prominent organelle in older plant cells; functions include storage, breakdown of wasteproducts, hydrolysis of macromolecules; enlargement of vacuole is a major mechanism of plant growtho Cell wall: outer layer that maintains cell’s shape and protects cell from mechanical damage; made of cellulose, other polysaccharides, and proteino Plasmodesmata: cytoplasmic channels through cell walls that connect the cytoplasms of adjacent cells6.3 The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes- Nucleus: contains most of the genes in the eukaryotic cell- Nuclear envelope: double membrane that encloses the nucleus separating its contents from the cytoplasm- Pore complex: intricate protein structure that lines each pore and plays an important role in the cell by regulating the entry and exit of proteins and RNAs, as well as large complexes of macromolecules- Nuclear lamina: a netlike array of protein filaments that lines the nuclear side of the envelope except at the pores and maintains the shape of the nucleus by mechanically supporting the nuclear envelope- Nuclear matrix: a framework of protein fibers extending throughout the nuclear interior- Chromosomes: structures of DNA within the nucleus that carry out the genetic information; each chromosome is composed of a single DNA molecule associated with proteins- Chromatin: the complex of DNA and proteins making up chromosomes; condenses to form discrete chromosomes as a cell prepares to divide- Nucleolus: where a type of RNA called ribosomal RNA (rRNA) is synthesized from instructions in the DNA; proteins imported from the cytoplasm are assembled with rRNA into large and small subunits of
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