bio exam

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bio exam
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  1. What does it take to make life
    • 1. information
    • 2. chem
    • 3. compartments
  2. cell theory
    • -cell = structural unit of life
    • -all organisms are composed of one or more cell types
    • -cells can arise only by the division of a preexisting cell
  3. basic properties of cells
    • -highly complex and organized
    • -activity is controlled by a genetic program
    • -can reproduce and make copies of themselves
    • -assimilate and utilize energy
    • -carry out many chemical reactions
    • -engage in mechanical activities
    • -respond to stimuli
    • -capable of self regulation
    • -they evolve
  4. 2 classes of cells
    • prokaryotic
    • eukaryotic
  5. prokaryotic
    • bacteria 
    • structurally simpler
  6. eukaryotic
    • protists, fungi, plants, animals
    • structurally more complex
    • large number of parts
    • compartments- membrane bound structures dedicated to a particular function and components
  7. basic properties of cells
    • highly complex and organized
    • large number of parts
    • organized with respect to time and space
    • parts interact with little tolerance of error
    • fidelity of interactions is mantained through control of regulation of parts 
    • cellular organization is very consistent
    • conserved throughout evolution
  8. nuclear pore complex
    enables movement of molecules into and out of the nucleus
  9. cytoskeletal elements
    • actin filaments
    • microtubules
    • intermediate filaments
  10. cytosekeletal elements function
    • contribute to cell shape and movement
    • provide structural support
    • support transport of materials
  11. virus
    • non cellular macromolecular packages that can function and reproduce only within living cells
    • outside of cells a virus exists as an inanimate object called viron
  12. virons are composed of
    • dna 
    • rna
    • protein capule (capsid)
  13. viruses bind to
    a cell surface via proteins
  14. wide host range
    rabies can infect cells in dogs bats humans
  15. narrow host range
    human cold infects epithelial cells of human resp system
  16. once inside the cell the virus
    • hijacks cellular machinery to synthesize nucleic acids/proteins
    • assembles new virus particles
  17. 2 types of viral infection
    • lytic
    • nonlytic/ integrative
  18. lytic viral infection
    production of viral particles ruptures/kills cell ex influenza
  19. nonlytic/integrative
    • viral dna is inserted in host genome=provirus
    • viral progeny bud at cell surface
    • cell can survive but impared function
  20. function of biological membranes
    • cell boundary
    • enclose compartments
    • control movement in and out of cell
    • allow response to external stimuli 
    • enables interactions between cells
    • provides scaffold/ support for biochemical activities
  21. fluid
    individual lipid molecules can move
  22. mosaic
    different particles penetrate the lipid layer
  23. fluid mosaic model
    • bilayer of amphipathic lipids
    • amphipathic= both hydrophobic and hydrophilic regions
  24. hydrophobic
    non polar
  25. hydrophilic
    polar
  26. proteins 3 types
    • integral 
    • peripheral 
    • lipid anchored
  27. integral protein
    span lipid bilayer
  28. peripheral
    associate with surfaces of lipid bilayer
  29. lipid anchored
    attach to a lipid in the bilayer
  30. fluid mosaic model -- components can
    • interact and are mobile 
    • contain hydrated lipid bilayer
  31. common properties of plasma membranes
    • 6 nm thick
    • stable
    • flexible
    • capable of self assembly
  32. different membranes contain different types of
    • lipids and proteins
    • have different function in different cells and within the same cell

    • ex inner membrane of mitochondria contains high conc of protein
    • myelin sheath of a neuron contains low protein
  33. biological membranes are
    asymmetrical
  34. biological membranes structure
    • 2 leaflets have distinct lipid composition 
    • outer leaflet has glycolipids and glyco proteins

    glyco means they have carbohydrates
  35. fluidity in membrane determined by
    • nature of lipids in membrane 
    • unsaturated lipids increase fluidity 
    • saturated lipids decrease fluidity
    • temperature 
    • warming =inc fluidity = liquid crystal
    • cooling = dec fluidity = crystalline gel
  36. balance between ordered (rigid) structure and disordered structure allows:
    • mechanical support and flexibility 
    • dynamic interactions between membrane components
    • membrane assembly and modification
  37. fluidity =
    crucial to cell function
  38. fluididty must be maintained and can be changed by
    • temp
    • desaturation of lipids
    • exchange of lipid chains
  39. cholesterol
    regulates membrane fluidity
  40. lipids move easily
    laterally within leaflet
  41. lipids movement to toher leaflet is
    slow
  42. membrane proteins can diffuse within bilayer
    • proteins movement is restricted
    • some dont move
    • rapid movement is spatially limited
    • long range diffusion is slow
    • biochemical modification can dramatically alter protein mobility in the membrane (signal transduction)
  43. lipid rafts
    • small area of plasma membrane that are enriched in certain types of lipids eg cholesterol
    • relatively rigid
    • membrane proteins accumulate in rafts
    • may form functional compartment
  44. movement of substances across cell membranes
    • lipid bilayers do not allow many compounds to pass through them freely 
    • small uncharged molecules cross membranes relatively easily (02 c02 no h20)
    • large polar charged compounds cannot easily cross lipid bilayers
    • specific mechanisms exist for the controlled transport of many substances across membranes
  45. 4 mechanisms to move molecules across
    • simple diffusion
    • diffusion through channel 
    • facilitated diffusion 
    • active transport
  46. simple diffusion
    • passive, nonmediated
    • small molecules uncharged move down concentration gradient
  47. diffusion through channel
    • passive non mediated 
    • small charged molecules 
    • move down concentration gradient
  48. ion channels formed by
    • integral membrane proteins that are aqueus 
    • selective allow one kind to pass
    • move down 
    • channels gated can open and close
  49. ON channels are formed by
    INTEGRAL MEMBRANE proteins that
    line an aqueous pore
    • channels are selective, allowing
    • only one type of ion to pass
    • • ions move down concentration
    • gradient
    • • often channels are ‘gated’ (can be
    • open or closed)
  50. 3 Types of Gated Channels
    • Voltage-gated channels (e.g. K+ channel)
    • Ligand-gated channels (e.g. acetylcholine)
    • Mechano-gated channels
  51. 1) Voltage-gated channels (e.g. K+ channel)
    • ➡ Channel responds to changes in charge across
    • membrane
  52. Ligand-gated channels (e.g. acetylcholine)
    • Channel responds to binding of specific molecule
    • (a ‘ligand’)
  53. Mechano-gated channels
    • Channel responds to physical force on
    • membrane (e.g. stretch)
  54. facilitated diffusion
    • • Compound binds specifically to
    • integral membrane protein called a
    • ‘FACILITATIVE TRANSPORTER’
    • • Change in transporter conformation
    • allows compound to be released on
    • other side of membrane
    • • Compound moves down a
    • concentration gradient
  55. d) active transport
    • • Compound binds specifically to
    • integral membrane protein called
    • an ‘ACTIVE TRANSPORTER’
    • • Change in transporter
    • conformation allows compound
    • to be released on other side of
    • membrane
    • • Compound moves against a
    • concentration gradient
    • • Requires input of ENERGY
  56. Active transport:
    The Na+/K+ ATPase maintains cellular [Na+] and [K+] using ATP
  57. Most cells have
    a glycocalyx
    • Glycocalyx = assembly of carbohydrate groups attached to
    • proteins and lipids on the outside of the plasma membrane
    • - mediates cell-cell and cell-ECM interactions
    • - provides mechanical protection
    • - serves as a barrier to some particles
    • - binds regulatory factors
  58. The Extracellular Matrix (ECM
    • organized network of material
    • produced and secreted by cells
  59. ECM function
    • sites for cell attachment
    • - physical support for cells
    • - substrate through which cells can move
    • - contains regulatory factors (signals)
    • - separate/define tissues
  60. Proteoglycans
    proteins with chains of polysaccharides
  61. Plant cell walls:
    • • composed of cellulose, hemicellulose, pectin and
    • proteins
    • • provide structural support to cell and to organism
    • as a whole (~ ‘skeleton’)
    • • protect cell from mechanical damage and pathogen
    • attack
    • • contain biochemical signals for cell
  62. Cell Walls are composed of
    • cellulose microfibrils
    • embedded in a polysaccharide matrix
  63. cytosol
    • protein synthesis, many metabolic
    • pathways
  64. nucleus
    • contains genome, DNA, RNA synthesis,
    • ribosome assembly
  65. endoplasmic reticulum (ER)
    synthesis of lipids, synthesis of proteins
  66. Golgi apparatus
    • protein modification, packaging of
    • proteins and lipids
  67. lysosomes
    degradation of cellular material
  68. endosomes
    sorting and recyclingq
  69. mitochondria
    • atp synthesis 
    • apoptosis
  70. chloroplasts
    • photosynthesis
    • atp synthesis
  71. peroxisomes
    oxidation of toxic molecules
  72. endosymbiont theory
    • ancestral prokaryote
    • infolding of plasma membrane 
    • endosymbiosis 
    • ancestral eukaryote
  73. mitochondria undergo
    fusion and fission
  74. mitochondria have two membranes
    • outer mitochondrial membrane
    • inner mitochondrial membrane
  75. outer mitochondrial membrane
    • contains many enzymes with diverse metabolic functions 
    • porins 
    • - large channels 
    • -when open membrane is feely permeable
  76. inner mitochondrial membrane
    • high protein lipid ratio 3:1
    • double layered folds = cristae
    • rich in phopholipid called cardio lipin
  77. cristae
    • increase membrane surface area 
    • contain machenery for aerobic respiration and atp formation
  78. aqueous compartments of mitochondria
    • intermembrane space 
    • matrix
  79. mitochondria matrix
    • high protein - gel like 
    • mitochondrial ribosomes
    • mitochondrial dna
  80. oxidative phosphorylation (atp synthesis in mitochondria) step 1
    • electron transport and proton pumping 
    • generates and electrochemical gradient 
    • hihg energy electrons pass from coenzymes (NADH an FADH2 ) in the matrix to electron carriers in IMM
    • series of e carriers = electron transport chain 
    • energy transfer at each complex used to pump protons from matric into intermembrane space 
    • low energy e is transferred to terminal e acceptro O2
    • water is produced
  81. oxidative phosphorylation step 2 (atp synthesis)
    controlled movement of protons back across IMM

    via atp synthase 

    potential energy in electrochemical gradient across inner mitochondrial membrane converteed to atp in the matrix
  82. apoptosis
    normal occurrence in which a coordinated sequence of events leads to death of a cell
  83. apoptosis s characterized by
    • shrinkage of cell 
    • blebbing of the plasma membrane
    • framentation of DNA and nucleus
    • loss of attachment to other cells
    • engulfment by phagocytosis
  84. the intrinsic pathway of apoptosis
    • initiated by intracellular stimuli
    • proapoptotic proteins stimulate mictochondria to leak proteins
    • release of apoptotic mitochondrial proteins commits the cell to apoptosis
  85. release of cytochrome c and culear fragmentation during apoptosis = caspases
    • disrupts cell adhesion
    • destroys lamins
    • breaks down cytoskeleton 
    • activates DNase
  86. cytoplasmic endomembrane system
    • within the cytoplasm contains membrane boudn organelles and vesivles 
    • extensive network of membranous canals and stack of sacs = cisternae
  87. cisternae
    stacks of sacs
  88. in the cytoplasm there is
    • endoplasmic reticulum 
    • golgi complex
    • lysosomes
    • vacuoles
    • endosomal transport vesicles
  89. secreted protein
    • synthesized in the rough er
    • processed in the er
    • further processed in golgi 
    • concentrated in vesicles
    • delivered to plasma membrane
  90. technique to track cell components
    use green fluorescent protein t
  91. vesicular transport (trafficking)
    • transport of material between ompartments 
    • uses transport vesicles
    • targeted movement --directed and uses cyto seleton and motor proteins and sorting signals are recognized by receptors
  92. transport vesicles
    small spherical membrane enclosed organelles that bud off donor compartment and fuse with acceptor compartment
  93. vesicular transport -- tethering vesicle to target compartment
    via Rabs
  94. Docking of vesicle to target compartment
    proteins called snares
  95. orientation of protein wrt cytoplasm is
    maintained
  96. exocytosis
    organelle to plasma membrane
  97. endocytosis
    plasma membrane to organelle
  98. endoplasmic reticulum
    • inter connected network of membrane encoled tubules and flattened sacs
    • inerior = lumen and separate from cytosol
    • er membrane is continuous with the outher membrane of the nucleus
  99. smooth er
    • production of steroid hormones
    • detoxification -- contains enzymes that modify foreign compounds 
    • sequestration/ storage of Ca 2+
  100. rough er
    • protein synthesis modification and transport 
    • synthesis of membrane phospholipids
    • gycosylation of proteins -- add carbohydrate
    • protein folding - quality control
  101. Protein Synthesis
    • In the cytoplasm,
    • ribosomes synthesize
    • polypeptides from mRNA
    • (= translation)
  102. Protein Translation
    • All protein translation begins on free ribosomes
    • 1) Translation completed on free ribosomes
    • - cytosolic proteins
    • - peripheral membrane proteins
    • - these proteins will be targeted to nucleus,
    • mitochondria, peroxisomes, chloroplasts
    • 2) Translation completed by ribosomes attached to ER
    • membrane (rough ER)
  103. Proteins Synthesized in the Rough ER
    • secreted proteins
    • ✤ integral membrane proteins
    • ✤ soluble proteins associated with inside
    • (lumen) of endomembrane system
    • ‣ e.g. proteins that function within the
    • ER, Golgi, lysosomes
  104. How is the site of translation determined?
    • protein contains ‘signal sequence’
    • - located at its amino-terminus (N-terminus)
    • - contains several consecutive hydrophobic
    • amino acids
    • ‘signal sequence’ directs synthesis to ER
    • • protein moves through channel into ER
    • = COTRANSLATIONAL IMPORT
  105. Cotranslational protein import
    • 1) Signal Recognition Particle (SRP) binds
    • to signal sequence – translation STOPS

    • 2) Targeting of translation complex to ER
    • [SRP/ribosome/new polypeptide]
    • - SRP binds to SRP receptor
    • 3) SRP is released and ribosome binds
    • TRANSLOCON
    • - protein synthesis resumes
    • 4) Polypeptide enters the ER (through the
    • translocon) as it is translated
  106. Once a protein is fully synthesized and
    properly folded it has 1 of 2 options:
    • 1. It is retained in the ER if that is where the
    • protein functions.
    • 2. It is transported from the ER to the Golgi
    • complex for further modification and delivery
    • to distal parts of the biosynthetic/secretory
    • pathway.
  107. ✴ ER Golgi
    ✴ organelle PM
    exocytosis
  108. PM organelle

    ✴ organelle organelle
    endocytosis
  109. Exit sites:
    • membrane and ER
    • lumen bud off to form
    • TRANSPORT VESICLES
  110. ER golgi intermediate compartment
    • - region between ER & Golgi complex
    • - transport vesicles fuse to form larger vesicles &
    • interconnected tubules
    • = Vesicular-Tubular Clusters (VTCs)
    • - these then form the ‘cis-Golgi network’
  111. material moves from
    ER to GOLGI
  112. golgi order
    cis medial trans
  113. golgi complex structure
    • -smooth, flattened, disk-like cisternae
    • (~ 0.5 - 1 micron in diameter)
    • ~ 8 (or fewer) cisternae/stack
    • (range from a few to several 1000 stacks per cell)
    • - curved like a shallow bowl
    • - shows polarity:
    • ‣ cis - medial - trans cisternae
    • ‣ cisternae are biochemically unique
    • - membrane supported by protein “skeleton” (actin, spectrin)
    • - scaffold linked to motor proteins that direct movement of
    • vesicles into and out of the Golgi
  114. CGN
    • acts as a “sorting station”
    • i.e., sorts whether proteins
    • should continue on to the next
    • Golgi station or be shipped back
    • to the ER
  115. TGN
    • sorts protein into different types
    • of vesicles
    • - Vesicles go to Plasma membrane
    • or other intracellular destinations
    • (e.g. lysosomes)
  116. proteins are modified _________ as they traverse the golgi
    step wise
  117. functions of golgi complex
    • • synthesis of complex polysaccharides
    • • modification of proteins and lipids
    • - glycosylation (glycoproteins & glycolipids)
    • - proteolytic modification
    • • TRANSPORT and sorting of proteinsprocessing plant’ of the cell
  118. Fully processed proteins are
    exported from the
    • trans
    • cisterna, enter the trans-Golgi
    • network (TGN) and are then
    • sorted and delivered to their
    • final destinations
    • ➡ endosomes
    • ➡ secretory granules
    • ➡ lysosomes
    • ➡ plasma membrane
  119. coat
    • coat has 2 functions
    • (i) helps form the vesicle
    • (ii) helps select ‘cargo’
  120. How do COPI and COPII proteins
    carry out functions
    • COPI and COPII proteins assemble on the cytosolic surface
    • of donor membranes at sites where budding takes place.
  121. Clathrin
    • coated vesicles move
    • from TGN to other vesicles
    • (e.g. lysosomes, endosomes,
    • plant vacuoles)
  122. COPI-
    retrograde direction
  123. COP II
    • COPII-coated vesicles move
    • in anterograde direction
  124. exocytosis is
    • constitutive 
    • regulated
  125. lysosomes
    digestive organelles
  126. lysosome function
    • AUTOPHAGY = organelle turnover
    • - lysosome fuse with autophagic vacuole forms autolysosome 
    • - contents enzymatically digested
    • ➡ forms residual body
    • 2. Degradation of internalized material
    • e.g. - plasma membrane components
    • - bacteria (in phagocytic cells)
    • released (exocytosis)
  127. tonoplast
    • tonoplast
    • = vacuolar membrane
    • - contains active transport
    • systems that generate
    • high interior [ion]
  128. function of plant vacuoles
    • ✤ intracellular digestion
    • - low pH, acid hydrolases
    • ✤ mechanical support; turgor pressure
    • - gives rigidity to plant - supports soft tissues
    • - stretches cell wall during growth
    • ✤ storage
    • - solutes and macromolecules
    • - chemical storage (no excretory system)
    • ‣ isolate toxic compounds
    • ‣ sequesters pigments (e.g. anthocyanin)
  129. CYTOSKELETON:
    • Dynamic network of interconnected filaments
    • and tubules that extends throughout the cytosol
    • (and some organelles) of eukaryotes
  130. cytoskeleton function
    • 1) structural support
    • 2) spatial organization within cell
    • 3) intracellular transport
    • 4) contractility and motility
  131. Microtubules (MT)
    • ‣ largest cytoskeletal element (25 nm diameter)
    • ‣ polymer of proteins α-tubulin and β-tubulin
    • ‣ 2 major types:
    • (i) axonemal MT
    • - highly organized, stable
    • - part of structures (axoneme) involved in cell
    • movement (e.g cilia, flagella)
    • (ii) cytoplasmic MT
    • - loosely organized, very dynamic
    • - located in cytosol
  132. Microtubules (MT) Structure
    • - α/β heterodimers form long protofilaments
    • - 13 protofilaments form longitudinal array
    • ‣ hollow cylinder
    • - heterodimers aligned in same direction (head to tail)
    • ‣ STRUCTURAL polarity
    • - MTs have fast-growing ‘plus’ end
    • and slow-growing ‘minus’ end
  133. Microtubules Undergo
    • Dynamic
    • Assembly and Disassembly

    • - in vivo, this leads to rapid turnover of most MTs
    • within cell (half-life is minutes)
    • ‣ ‘dynamic instability’
    • - shrinkage can occur very rapidly at the ‘plus’ end
    • (termed ‘catastrophe’)
    • - formation of MTs is regulated/controlled
    • - Microtubule-Organizing Center (MTOC)
    • = central site of MT assembly
  134. Microtubule-associated Proteins (MAPs)
    • - several different proteins that bind MTs
    • ‣ modulate assembly, function
    • ‣ mediate interactions with other cellular
    • structures (e.g vesicles/organelles)
    • 21
    • Microtubule-associated Proteins (MAPs)
    • - often stabilize MTs or stimulate assembly
  135. 2 Classes of MAPs:
    • 1. Motor MAPs:
    • - 2 main types: kinesin and dynein
    • - use ATP to generate force
    • - can move material along MT ‘track’
    • - can generate sliding force between MTs
    • 2. Non-Motor MAPs:
    • - control MT organization in cytosol
    • (e.g. Tau in neurons)
  136. Dynein:
    minus end directed
  137. kinesin
    plus end
  138. Intermediate Filaments (IF)
    • • intermediate size (10-12 nm diameter)
    • • exclusive to multicellular animals
    • • provide structural support, mechanical strength
    • • stable (relative to MTs or microfilaments)
    • • fibrous proteins, contain central α-helical domain
  139. 5 classes of intermediate filaments
    • - keratins: epithelial cells
    • - neurofilaments: neurons
    • - lamins: nucleus of all cells
  140. Structure of Intermediate Filaments
    • • α-helical domains wrap
    • around each other
    • forming rope-like dimer
    • (coiled-coil = )
    • Structure of Intermediate Filaments
    • Fig. 9.42 22
    • 2
    • • 2 dimers associate antiparallel
    • to make tetramer
    • Therefore assembled
    • filaments are NOT polar
    • 3
    • • monomers are aligned in
    • parallel; IF dimers are polar
    • molecules
  141. Microfilaments (MF)
    • • smallest cytoskeletal element (~ 8 nm)
    • • polymer of protein actin
    • • polypeptide = 42 kDa, binds ATP
    • - individual molecules = G-actin (globular)
    • - polymerized microfilament = F-actin
  142. F-actin
    polymerized microfilament
  143. G actin
    individual molecules
  144. microfilament function
    • - maintenance of cell shape
    • - cell movement
    • - cytokinesis
    • - muscle contraction
  145. nucleation
    • nucleation (slow)
  146. elongation
    • elongation (fast)
  147. f- actin filaments
    • Polymerization/Depolymerization
    • and
    • Structure/Organization
    • - are regulated by actin-binding proteins
    • Fig. 9.70 Fig. 9.75
    • - filaments can be loose arrays/networks or
    • tight bundles/cables
  148. actin binding proteins
    • Examples of actin-binding proteins
    • • nucleating proteins; e.g. Arp2/3
    • • monomer-polymerizing proteins; e.g. profilin
    • • filament-depolymerizing proteins; e.g. cofilin
  149. arp2/3
    • Arp2/3 nucleates
    • polymerization at
    • branch points
  150. directed cell motility
    • Coordinated activity of actin-binding proteins
    • controls microfilament formation in a lamellipodium to
    • allow directed cell movement
  151. MYOSIN:
    • an Actin-associated Motor Protein
    • - large family of proteins
    • - most move toward plus end of microfilament
    • - divided into 2 broad groups
    • 1) conventional myosins
    • - type II
    • - primary motors for muscle contraction
    • 2) unconventional myosins
    • - type I and types III-XVIII
  152. Unconventional myosins
    • generate force and
    • contribute to motility in non-muscle cells
  153. Microtubule
    • based and microfilament-based motors
    • can cooperate in intracellular transport
    • Movement of
    • pigment granules
    • via the cytoskeleton
  154. NUCLEUS function
    • ๏ storage, replication, and repair of genetic material
    • ๏ expression of genetic material
    • - transcription
    • mRNA, tRNA, rRNA
    • - splicing
    • ๏ ribosome biosynthesis
  155. nucleus structure
    • ๏ Nuclear envelope
    • - nuclear membrane
    • - nuclear pores
    • - nuclear lamina
    • • Nuclear contents
    • - chromatin
    • - nucleoplasm
    • - nucleolus
  156. Nuclear Envelope (NE)
    • 2 parallel phospholipid bilayers
    • • separated by 10-50 nm
    • • Outer membrane (ONM) binds ribosomes and is
    • continuous with rough endoplasmic reticulum
    • • Inner membrane (INM)
    • - bears integral proteins
    • - connects to nuclear lamina
  157. intermembrane space is continuous with ER
    lumen
  158. function of nuclear envelope
    • • separates nuclear content from cytoplasm
    • - separates transcription & translation
    • • selective barrier
    • - allows limited movement of molecules
    • between nucleus and cytoplasm
    • • supported by nuclear lamina
  159. Nuclear Lamina
    • • thin meshwork of filamentous proteins
    • - lamins (class V intermediate filaments)
    • • bound to inner membrane of NE by integral
    • membrane proteins
    • • provides structural support for NE
    • • attachment sites for chromatin
  160. nuclear pores
    • • gateways between cytoplasm & nucleoplasm
    • • 3,000 to 4,000 pores/nucleus
    • • pores occur where inner and outer membranes fuse
    • • pores have a complex protein structure
    • ‣ Nuclear Pore Complex (NPC)
  161. Nuclear Pore Complex
    • - composed of nucleoporins (NUPs)
    • - octagonal symmetry
    • - projects into cytoplasm and
    • nucleoplasm
  162. NPC Function
    • • passive diffusion of molecules smaller than 50 kDa
    • ‣ rapid (100/min./pore)
    • • regulated movement of larger molecules
    • ‣ slow (6/min./pore)
    • 24
    • Regulated movement of proteins into the nucleus
    • requires a Nuclear Localization Signal (NLS)
    • NLS = a short stretch of positively charged
    • amino acids within the protein sequence
  163. Function of the Nucleolus
    • Ribosome Biogenesis
    • • synthesis of rRNA
    • • rRNA processing
    • • assembly of subunits
    • (rRNA + proteins)
    • • 40S and 60S subunits are
    • exported to cytoplasm

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