Cell Org III

Question 1

name 3 major components of the cytoskeleton

Answer 1

1. Actin filaments
2. Intermediate filaments
3. Microtubules

Question 2

describe the structure of microtubules (MT)

Answer 2

• Structure
  
  • non-branching, rigid, hollow tubes
    
    • Alpha and beta tubulin protein subunits
  • Polar
    
    • (-) end
    • (+) end

Question 3

describe the function of MT

Answer 3

• Intracellular transport
  
  • Movement of vesicles and organelles
• Cell motility
  
  • Movement of cilia and flagella
  • Cell elongation and movement
• Mitotic spindle
  
  • attachment of chromosomes and their movement during cell divison
• Rigid intracellular skeleton
  
  • Maintenance of cell shape and polarity
• Assemble and disassemble as the needs of cell change

Question 4

describe structure of centrioles

Answer 4

• 9 triplets of MTs arranged around a central axis
  
  • Each triplet consists of 1 complete and 2 incomplete MTs fused

Question 5

describe the function of centrioles

Answer 5

• Organize the centrosome
• Basal body formation
  
  • Provide basal bodies necessary for assembly of cilia and flagella
• Mitotic spindle formation
  
  • Formation of centrosome and alignment of the mitotic spindle during cell division

Question 6

what is the centrosome and describe the structure

Answer 6

• Centrosome is the microtubule organizing center (MTOC)
• Structure
  
  • Contains a pair of centrioles at perpendicular angles
  • Amorphous protein matrix
    
    • >200 proteins
  • Gamma-tubulin ring complexes
    
    • Nucleating sites for MTs

Question 7

describe the function of centrosomes

Answer 7

• Organize MTs
• Initiate MT formation
  
  • MTs are nucleated at the centrosome at their (+) end
  • (+) ends point out and grow toward cell periphery

Question 8

describe mitotic spindle poisons (the first one)

Answer 8

• Colchicine
  
  • anticancer compound
    
    • Prevents polymerization
      
      • Binds to unpolymerize tubulin molecules
    • If given to dividing cells, mitotic spindle breaks down
      
      • Programmed cell death
  • Related compounds
    
    • Vinca alkoids
      
      • Vinblastine
      • Vincristine

Question 9

describe the 2nd mitotic spindle poison

Answer 9

• Taxol
  
  • Anticancer drug
    
    • Stabilizes and prevents MT disassembly
      
      • Preferentially binds tubulin within assembled MTs
    • Arrests dividing cells in mitosis
      
      • Unable to acheive metaphase sindle conformation
      • Programmed cell death

Question 10

Name the first MT motor famil

Answer 10

• Dynein family
  
  • Move along MTs toward the (-) end
  • 2 members
    
    • Cytoplasmic dynein
    • Axonemal dynein
      
      • Cilia and flagella
  • Binding sites for vesicles, organelles or another MT
  • Largest anf fastest of the molecular motors
    
    • 14 um/sec

Question 11

Name the 2nd motor family

Answer 11

• Kinesin Family
  
  • Move along MT toward the (+) end
    
    • 3 um/sec
  • Binding sites for vesicles, organelles, MTs
  • ~40 distinct kinesins in humans

Question 12

describe the structure and function of cilia

Answer 12

• MT-based, hair-like structure
  
  • Motile
    
    • Beat in synchronous pattern
  • 9 + 2 MT arragement
  • Pair of Dynein arms
    
    • Motor protein
    • Binds adjacent MT
  • Move fluid and particles along epithelial surfaces
  • Anchored to cell via the basal body
    
    • Thin, dark-staining band at base of cilia

Question 13

describe the structure and function of primary cilia

Answer 13

• MT-based, antennae-like structure
  
  • 9 + 0 arrangement
• Emanates from almost all cells
• Anchored to cell via the basal body
• Develops from one centriole following cell division

Question 14

where are primary cilia located?

Answer 14

• Photoreceptors
  
  • Outer segment of rods
• chemoreceptors
  
  • odor detection by receptors on primary cilia of olfactory neurons
• Mechanoreceptors
  
  • primary cilia of epithelial cells monitors the flow of fluid through the kidney tubules
  • Defects underlie a variety of disorders
    
    • Polycystic Kidney Disease

Question 15

describe the structure and function of intermediate filaments

Answer 15

• Formed from non-polar and highly variable subunits
• Functions:
  
  • Stabilize cell structure
    
    • Mechanical strength
    • Maintain the position of the nucleus and other organelles
  • Resist shearing forces
    
    • extend across cytoplasm
    • connecting with desmosomes and hemidesmosomes
• Essential for integrity of cell-cell and cell-ECM junction

Question 16

name the 6 classes of IF

Answer 16

1. 1 & 2: Keratins
   
   1. Acid and base cytokeratins
   2. Found in all epithelial cells
2. Vimentin and vimentin-like
   
   1. Diverse family
      
      1. Most widely distributed in the body
   2. Vimentin
      
      1. Most abundant in mesoderm-derived cells
   3. Vimentin-like found in a variety of cells
      
      1. Desmin: muscle cells
      2. Glial fibrillary acid protein (GFAP): glial cells and astrocytes
3. Neurofilaments
   
   1. Extend from cell body into the ends of axons and dendrites
4. 5: Lamins
   
   1. Found in nucleus of all nucleated cells
      
      1. Nuclear lamina
5. Beaded filaments
   
   1. Eye lens-specific group

Question 17

describe the structure and function of actin filaments (microfilaments)

Answer 17

• Polarzied structures
  
  • Fast growing (+) end
  • slow growing (–) end
• Function
  
  • Anchorage
  • Structural core of microvilli and stereocilia
  • Cell motility
    
    • locomotion
  • Extension of cell processes

Question 18

name the 2 types of actin protein

Answer 18

• G-actin: free actin molecules in the cytoplasm
• F-actin: polyermized actin in a filament; ATP dependent

Question 19

which fungal products affect actin? (phalloidin)

Answer 19

• Phalloidin
  
  • Toxin found in Amanita phalloides
  • Disrupts normal function of actin
    
    • Binds F-actin more tightly than G-actin
    • Promotes excessive polymerization and inhibits depolymerization
    • Inhibits cell movement
  • Other toxins (amatoxins) are responsible for toxic effects following oral ingestion
    
    • Liver and kidney failure and death 4-8 days after eating

Question 20

what does the fungus cytochalasins do to actin?

Answer 20

• Block polymerization of actin
  
  • ​Opposite of phalloidin, which promotes polymerization
• Can be used to inhibit cell movement, division and induce programmed cell death

Question 21

what are the actin motors?

Answer 21

• Myosin family
  
  • Myosin II
    
    • generates the force for skeletal muscle contraction
    • Formed from 2 heavy chains and 4 light chains
    • Tail-tail interactions result in formation of bipolar thick filaments
    • Each head binds and hydrolyzes ATP

Question 22

list the structural changes to myosin

Answer 22

• Stage 1: Attachment
  
  • Rigor conformation
• Stage 2: Release
  
  • ATP binds
  • Reduces myosin affinity for actin
• Stage 3: Bending
  
  • ATP hydrolysis
  • Conformational change
• Stage 4: Force generation
  
  • Weak binding of myosin to actin causes release of inorganic phosphate
  • Release triggers binding and power stroke
    
    • Force-generating conformational change
• Stage 5: Reattachment
  
  • Rigor conformation

Question 23

describe the process of cell movment

Answer 23

1. Protrusion
   
   1. actin polymerization at (+) end protrude lamellipodium
2. Attachment
   
   1. focal adhesions anchor the actin cytoskeleton to the extracellular matrix via integrin proteins
3. Contraction
   
   1. Bulk of the trailing cell and cytoplasm is drawn forward