Day 2, Lecture 1: Fundamentals of Cell Biology, Part 1

Question 1

Plasma Membrane

Answer 1

• Barrier between cytoplasm and extracellular environment
• Composed of Lipids, proteins and carbohydrates
• Lipid Bilayer
  
  • continuous double layer of lipids approximately 5nm thick. The lipid composition provides an impermeable barrier to the passage of water-soluble molecules

Question 2

Cytoskeleton

Answer 2

• Network of protein filaments that that extends throughout the cytoplasm of eukaryotic cells and has roles in:
  
  • Cell movement
  • Support an strength for cell
  • Phagocytosis and cytokinesis
  • Cell-Cell and Cell-matrix attachment
  • Changes in cell shape
• Composed of three major types of protein filaments
  
  • Microfilaments (actin filaments)
  • Microtubules
  • Intermediate filaments

Question 3

Cytoplasm

Answer 3

• Cytosol
  
  • site of protein synthesis
• Cytoskeleton
• Cytoplasmic organelles suspended in cytosol

Question 4

membrane proteins

Answer 4

• Proteins can act as sensors (receptors) of external signals, or can serve as structural links that connect the plasma membrane ot the cytoskeleton or to the extracellular matrix
• Carry out specific funcitons of plasma membrane
• Integral membrane proteins
  
  1. Transmembrane proteins
     
     • hydrophobic portions of the protein pass through the lipid bilayer (while hydrophilic regions are located on either surface of the membrane). These proteins may be covalently anchored to the plasma membrane via insertion of a lipid bilayer
  2. Membrane surface proteins
     
     • Proteins are associated only with the internal or external surface of the plasma membrane, and are anchored to the plasma membrane via insertion of a lipid side chain into the lipid bilayer
• Peripheral memebrane proteins
  
  • are bound by noncovalent interactions with other membrane proteins

Question 5

Connexon

Answer 5

A hexigonal array of connexins that form a pore with a diameter of 1nm for intercellular-communication

Question 6

Microtubules

Answer 6

• Long, rigid, Hollow cylinders made of the protein tubulin
• Polymerization and depolymerization of tubulin controls the movement of transport vesicle and other organelles
• originate at the centrosome (microtuble organizing center)
• outer diameter of 25nm

Question 7

Microfilaments (actin filaments)

Answer 7

• flexible, Double-stranded helical polymers of actin
• Involved in cell movements , especially near the cell surface
• Diameter 5-9 nm

Question 8

Tubulin

Answer 8

is a protein that polymerizes into microtubules

Question 9

Intermediate filaments

Answer 9

• Intermediate in size between microfiaments and microtubules
• Ropelike fibers that provide structural support and cell attachment sites
• Ex
  
  • keratin
  • vimentin
  • desmin
  • GFAP
  • Nuclear lamins

Question 10

cell junctions

Answer 10

• Specialized proteins that provide
  
  • cell-to-cell adhesion
  • communication
  • cell-to-matrix adhesion
  • Cellular polarity
  • Barrier capabilities
• Juncitonal complex
  
  • Zonula occludens (tight junction)
  • Zonula adherens (belt desmosome)
  • Macula adherens (desmosomes)
  • Gap junctions
  • Hemidesmosome

Question 11

microvilli

Answer 11

• non-motile, about 1 micron long
• comprised of core of actin
• Increase absorptive surface area
• composed of a core of actin filaments
• Major Locations:
  
  • Intestinal Tract and Kidney Tubules

Question 12

cilia

Answer 12

• Motile processes on apical surface
• about 10 microns long
• Coordinated movement aids luminal transport of materials
• 9+2 arrangement of microtubules forms core complex of axoneme
  
  • Radial spokes and connecting structures stabilize the axoneme
• lines the apical surface fo respiratory and reproductive epithelium

Question 13

stereocillia

Answer 13

• Ultrastructurally identical to microvilli
• Approximately 20-50 microns in length
• Absorptive function (e.g. Epididymis of male reproductive tract)

Question 14

gap junction

Answer 14

• intercellular communication
  
  • allows the passage of small water-soluble ions and molecules
  • Results in electrical and metabolic coupling
  • Cooridinates activities
    
    • Ex.
      
      • Peristalsis
      • heart contractions
      • cilia movement
• formed by integral membrane proteins connexins coming together to form a hexagonal array (called connexons). Thes register with pores in the apposing membrane
  
  • allow rapid flow of small molecules (

Question 15

desmosomes (macula adherens)

Answer 15

• Intercellular adhesion via “spot” attachements)
• Plaque-like adhesions of 500nm diameter, restricted to epithelial cells and a few others
• Apposed membranes separated by gap of 20-35 nm
• Dense cytoplasmic plaque beneath plasma membrane associated with cytoplasmic keratin intermediate filaments (tonofilaments) and various cadherin proteins)
  
  • Complementary cadherin proteins attach to each other extracellularly, and to protein plaques intracellularly

Question 16

tight junction (zonula occludens)

Answer 16

• Widely distribulted in all tissues but especially abundant in epithelium
• located just basolateral to the apical membrane
• Provides paracellular barrier
  
  • forms a tight, circumferential seal between lateral membranes of epithelial cells occluding the passage of macromolecules and electrolytes between cells
  • prevents vectorial movement of membrane proteins and lipids from apical to lateral membranes
• complementary transmembrane proteins (e.g. occludin and claudins) attach to each other extracellularly

Question 17

zonula adherens (belt desomosome)

Answer 17

• Mechanical attachment between neighboring cells
• provides mechanical adhesion between cells
• widely distributed in all cells but generally found as part of the junctional complex of polarized epithelial cells
• located basolateral relative to the tight junction
• Transmembrane Cadherin proteins attach to each other extracellularly
  
  • Attach to cytoplasmic proteins anchored to filamentous actin

Question 18

hemidesmosome

Answer 18

• Anchors intermediate filaments in a cell to the basal lamina
• (note Bullous pemphigoid , a blistering skin disease is due to production of autoantibodies to protein in plaque of hemidesmosomes

Question 19

nucleus

Answer 19

• Site of DNA and RNA synthesis

Question 20

nucleolus

Answer 20

• Site of ribosomal RNA synthesis and initial pre-ribosomal assembly
• Contains multiple loops of DNA encoding rRNA genes

Question 21

nuclear envelope

Answer 21

• Encloses the Nucleus
• Composed of two phospholipid bilayers
• Outer membrane continous with ER
• Inner and outer nuclear membrane with perinuclear space between membranes
• Nuclear lamina of intermediate filaments underlying inner membrane
• Phosphorylation and de-phosphorylation of nuclear lamins regulate disassembly of nuclear envelope during cell division

Question 22

nuclear pores

Answer 22

• Bi-directional transport of proteins and RNA occurs via gated transport through nuclear pores
• outer and inner nuclear membranes fuse in places to form nuclear pores
• Cytosolic nuclear import receptors bind to prospective nuclear protein
  
  • Requires nuclear localization signal (7a.a)

Question 23

mitochondria

Answer 23

• Generates ATP for energy

Question 24

rough endoplasmic retiulum

Answer 24

Question 25

smooth endoplasmic reticulum

Answer 25

Question 26

lysosome

Answer 26

• Formed by vesicle fusion of endosomes and transport vesicles from the Golgi Apparatus
• function:
  
  • controlled degradation of intracellular macromolecules
• Unique phospholipids and glycosylation of membrane proteins protect membrane from enzymatic degradation

Question 27

endosome

Answer 27

• Protein and membrane trafficking

Question 28

peroxisome

Answer 28

Question 29

Golgi apparatus

Answer 29

• Transport vesicles bud off from one compartment and fuse with another
• Intramembranous and soluble (cytosolic) proteins and the lipid portions of membranes are transported from the RER to the Golgi apparatus by vesicular transport
• Post-Translational modifications occur in the lumen of the Golgi Apparatus
  
  • Note that specific modifications occur in specific subcompartments, because localization of modifying enzyme is tightly controlled
  • More than 200 different proteins participate

Question 30

endocytosis

Question 31

exocytosis

Answer 31

Question 32

The centrosome is composed of

Answer 32

• Paired centrioles located near center of the cell
• Nucleates polymerization of tubulin into microtubles
• duplicates once every cell cycle

Question 33

what is the site of origin of basal bodies of cilia

Answer 33

Centrosome

Question 34

____ anchors cilia microtubules

Answer 34

Basal bodies (note that basal bodies have a triplet formation while cilia have a doublet)

Question 35

what regulates the disassembly and reassembly of nuclear envelope during cell division?

Answer 35

Phosphorylation and de-phosphorylation of nuclear lamins

Question 36

A lightly stained nucleus is an indication of what

Answer 36

Cancer cells: large, light nuclei

Question 37

Question 38

Question 39

Answer 39

Question 40

Secretory Granules

Answer 40

contents released by exocytosis upon hormonal or neuronal stimulation

Question 41

Macrophages contain numerous____ for the controlled intracellular degradation of phagocytized macromolecules

Answer 41

Lysosomes

Question 42

Question 43