AP Biology Chapter 6: A tour of the cell

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  1. Light Microscope (LM):
    • visible light is passed through a specimen and than through glass lenses. lenses refract (bend) the light, so that the image is magnified
    • -can magnify effectively to about 1,000 times the size of the actual specimen
    • -most subcellular structures, including organelles are too small to be resolved by an LM
  2. Magnification:
    the ratio of an objects image size to its real size
  3. Resolution:
    the measure of the clarity of the image, or the minimum distance of 2 distinguishable points
  4. Contrast:
    visible differences in parts of the sample
  5. Organelles:
    membrane-enclosed compartments in a cell
  6. Scanning electron microscopes (SEMs):
    focus a beam of electrons onto the surface of a specimen, providing images that look 3-D
  7. transmission electron microscopes (TEMs):
    • focus a beam of electrons through a specimen
    • -used mainly to study the internal structure of cells
  8. cell fractionation:
    takes cells apart & separates the major organelles from one another
  9. Basic features of all cells:
    • 1. plasma membrane
    • 2. semifluid substance called cytosol
    • 3. chromosomes (carry genes)
    • 4. ribosomes (make proteins)
  10. Prokaryotic cells are characterized by having:
    • 1. no nucleus
    • 2. DNA in an unbound region called nucleoid
    • 3. no membrane-bound organelles
    • 4. cytoplasm bound by the plasma membrane
  11. Eukaryotic cells are characterized by having:
    • 1. DNA in a nucleus that is bounded by a membranous nuclear envelope
    • 2. membrane-bound organelles
    • 3. cytoplasm in the region between the plasma membrane and nucleus
  12. Eukaryotic cells are generally much larger than prokaryotic cells
  13. Plasma Membrane:
    a selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell
  14. the general structure of a biological membrane:
    a double layer of phospholipids
  15. metabolic requirements set upper limits on the size of cells
    -the surface area to volume ratio of a cell is critical
  16. as the surface area increase by a factor of n2 the volume increases by a factor of n3
  17. small cells have a greater surface area relative to volume
  18. a eukaryotic cell has internal membranes that partition the cell into organelles
    -plant and animal cells have most of the same organelles
  19. the nucleus contains most of the DNA in a eukaryotic cell
    -ribosomes use the information from the DNA to make proteins
  20. Nucleus:
    contains most of the cell's genes and is usually the most conspicuous organelle
  21. Nuclear enevolpe:
    encloses the nucleus, separating it from the cytoplasm
  22. the nuclear membrane is a double membrane; each membrane consists of a lipid bilayer
  23. pores regulate the entry and exit of molecules from the nucleus
  24. the shape of the nucleus is maintained by:
    the nuclear lamina, which is composed of protein
  25. in the nucleus, DNA is organized into discrete units called:
    • chromosomes
    • ¬† - each chromosome is composed of a single DNA molecule associated with proteins
  26. the DNA & proteins of chromosomes are together called:
    • chromatin
    • ¬† -chromatin condenses to form discrete chromosomes as a cell prepares to divide
  27. nucleolus:
    located within the nucleus and is the site of ribosomal RNA (rRNA) synthesis
  28. Ribosomes:
    particles made of ribosomal RNA and protein
  29. Ribosomes carry out protein synthesis in 2 locations:
    • 1. in the cytosol (free ribosomes)
    • 2. on the outside of the endoplasmic reticulum or the nuclear envelope (bound ribosomes)
  30. components of the endomembrane system:
    • 1. nuclear envelope
    • 2.endoplasmic reticulum
    • 3. Golgi apparatus
    • 4. lysosomes
    • 5. vacuoles
    • 6. plasma membrane
  31. the componenets of the endomembrane systems are either continuous or connected via transfer by vesicles
  32. Endoplasmic reticulum (ER):
    accounts for more than half the total membrane in many eukaryotic cells
  33. the ER membrane is continuous with the nuclear envelope
  34. 2 distinct regions of ER:
    • 1. smooth ER (lacks ribosomes)
    • 2.rough ER (surface is studded with ribosomes)
  35. functions of smooth ER:
    • 1. synthesizes lipids
    • 2. metabolizes carbohydrates
    • 3. detoxifies drugs & poisons
    • 4. stores calcium ions
  36. functions of rough ER:
    • 1. has bound ribosomes which secrete glycoproteins (proteins covalently bounded¬† to carbs)
    • 2. distributes transport vesicles (proteins surrounded by membranes)
    • 3. is a membrane factory for the cell
  37. Golgi apparatus:
    consists of flattened membranous sacs called cisternae
  38. functions of the Golgi apparatus:
    • 1. modifies products of the ER
    • 2. manufactures certain macromolecules
    • 3. sorts & packages materials into transport vesicles
  39. lysosome:
    a membranous sac of hydrolytic enzymes that can digest macromolecules
  40. lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and nucleic acids
  41. lysosomal enzymes work best in the acidic environment inside the lysosome
  42. some types of cell can engulf another cell by phagocytosis; this forms a food vacuole
  43. a lysosome fuses with the food vacuole and digests the molecules
  44. lysosomes also use enzymes to recycle the cell's own organelles and macromolecules, a process called:
  45. a plant cell or fungal cell may have one or several vacuoles, derived from endoplasmic reticulum and Golgi apparatus
  46. food vacuoles:
    formed by phagocytosis
  47. contractile vacuoles:
    found in many freshwater protists, pump excess water out of cells
  48. central vacuoles:
    found in many mature plant cells, hold organic compounds and water
  49. the endomembrane system is a complex and dynamic player in the cell's compartmental organization
  50. Mitochondria:
    the sites of cellular respiration, a metabolic process that uses oxygen to generate ATP
  51. Chloroplasts:
    (found in plants and algae) are the sites of photosnythesis
  52. peroxisomes are oxidative organelles
  53. mitochondria and chloroplasts have similarities with bacteria
    • 1. enveloped by a double membrane
    • 2.contain free ribosomes & circular DNA molecules
    • 3. grow and reproduce somewhat independently in cells
  54. the endosymbiont theory:
    • 1. an early ancestor of eukaryotic cells engulfed a nonphotosynthetic prokaryotic cell, which formed an endosymbiont relationship with its host
    • 2. the host cell and endosymbiont merged into a single organism, a eukaryotic cell with a mitochondrion
    • 3. at least one of these cells may have taken up a photosynthetic prokaryote, becoming the ancestor of cells that contain chloroplasts
  55. mitochondria are in nearly all eukaryotic cells
    -they have a smooth outer membrane and an inner membrane folded into cristae
  56. the inner membrane of mitochondria creates 2 compartments:
    • 1. intermembrane space
    • 2. mitochondrial matrix
  57. some metabolic steps of cellular respiration are catalyzed in the mitochondrial matrix
  58. cristae present a large surface area for enzymes that synthesize ATP
  59. chloroplasts contain the green pigment chlorophyll, as well as enzymes and other molecules that function in photosynthesis
  60. chloroplast structure includes:
    • thylakoids, membranous sacs, stacked to form a granum
    • stroma, the internal fluid
  61. plastids:
    a group of plant organelles, of which, chloroplasts are one
  62. Peroxisomes:
    • specialized metabolic compartments bounded by a single membrane
    • produce hydrogen peroxide and convert it to water
    • perform reactions with many different functions
  63. cytoskeleton:
    • a network of fibers extending throughout the cytoplasm
    • organizes the cell's structure and activities, anchoring many organelles
    • helps to support the cell and maintain its shape
  64. The cytoskeleton is composed of 3 types of molecular structures:
    • 1. microtubules (thickest of the 3)
    • 2. microfilaments (also called actin filaments, thinnest of the 3)
    • 3. intermediate filaments (diameters in a middle range)
  65. the cytoskeleton interacts with motor proteins to produce motility
  66. inside the cell, vesicles can travel along "monorails" provided by the cytoskeleton
  67. Microtubules:
    hollow rods about 25nm in diameter and about 200nm to 25 microns long
  68. functions of microtubules:
    • shaping the cell
    • guiding movement of organelles
    • separating chromosomes during cell division
  69. in many cells, microtubules grow out from a centrosome near the nucleus
  70. the centrosome is a "microtubule-organizing center"
  71. in animal cells, the centrosome has a pair of centrioles, each with 9 triplets of microtubules arranged in a ring
  72. microtubules control the beating of cilia and flagella, locomotor appendages of some cells
  73. common structure between cilia and flagella:
    • a core of microtubules sheathed by the plasma membrane
    • a basal body that anchors the cilium or fladellum
    • a motor protein called dynein, which drives the bending movements of a cilium or flagellum
  74. microfilaments:
    solid rods about 7nm in diameter, built as a twisted double chain of actin subunits
  75. the structural role of microfilaments is to bear tenson, resisting pulling forces within the cell
  76. microfilaments form a 3-D network called the cortex just inside the plasma membrane to help support the cell's shape
  77. bundles of microfilaments make up the core of microvilli of intestinal cells
  78. microfilaments that function in cellular motility contain the protein myosin in addition to actin
  79. in muscle cells, thousands of actin filaments are arranged parallel to one another
  80. thicker filaments composed of myosin interdigitate with the thinner actin fibers
  81. localized contraction brought about by actin & myosin also drives amoeboid movement
  82. pseudopodia:
    (cellular extensions) extend and contract through the reversible assembly and contraction of actin subunits into filaments
  83. cytoplasmic streaming:
    a circular flow of cytoplasm within cells.this streaming speeds distribution of materials within the cell
  84. in plant cells, actin and myosin interactions and solgel transformation drive cytoplasmic streaming
  85. intermediate filaments:
    • range in diameter from 8-12n, larger than microfilaments but smaller than microtubules
    • they support cell shape and fix organelles in place
    • are more permanent cytoskeleton fixtures than the other two classes
  86. most cells synthesize and secrete materials that are external to the plasma membrane
    - these extracellular structures include:
    • cell walls of plants
    • the extracellular matrix (ECM) of animal cells
    • intercellular junctions
  87. cell wall:
    • an extracellular structure that distinguishes plant cells from animal cells
    • protects the plant cell, maintains its shape, and prevents excessive uptake of water
  88. plant cell walls are made of cellulose fibers embedded in other polysaccharides and proteins
  89. plant cell walls may have multiple layers:
    • 1. primary cell wall (relatively thin and flexible)
    • 2. middle lamella (thin layer between primary walls of adjacent cells)
    • 3. secondary cell wall (added between the plasma membrane and the primary cell wall)
  90. plasmodesmata are channels between adjacent plant cells
  91. animal cells lack cell walls but are covered by an elaborate extracellular matrix (ECM)
  92. the ECM is made up of glycoproteins such as collagen, proteoglycons, and fibronectin
  93. ECM proteins bind to receptor proteins in the plasma membrane called intedrins
  94. functions of the ECM:
    • support
    • adhesion
    • movement
    • regulation
  95. neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact
    -intercellular junctions facilitate this contact
  96. intercellular junctions:
    • plasmodesnata
    • tight junctions
    • desmosomes
    • gap junctions
  97. plasmodesmata:
    • channels that perforate plant cell walls
    • through plasmodesmata, water and small solutes can pass from cell to cell
  98. at tight junctions, membranes of neighboring cells ate pressed together, preventing leakage of extracellular fluid
  99. desmosomes:
    (anchoring junctions) fasten cells together into strong sheets
  100. gap junctions:
    (communicating junctions) provide cytoplasmic channels between adjacent cells
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AP Biology Chapter 6: A tour of the cell
2014-11-12 00:35:08

Chapter 6 notes
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