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BDS 1: Cell Biology > Cell Junctions > Flashcards

Cell Junctions Flashcards

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1
Q

What are the 3 types of cell junction?

A
  • Impermeable junctions
  • Anchoring junctions
  • Communicating junctions (gap junctions)
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2
Q

Which 2 types of electron microscopy are used to visualise cell junctions?

A
  • Conventional transmission electron microscopy

- Freeze fracture microscopy

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3
Q

Describe the steps involved in conventional transmission electron microscopy

A
  1. Tissue specimen is fixed using a preservative and embedded
  2. Thin slice cut (approx. 50nm)
  3. Specimen placeed on copper grid
  4. Grid and specimen placed in transmission electron microscope
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4
Q

Describe the steps involved in freeze fracture microscopy

A
  1. Tissue specimen frozen in liquid nitrogen (-196 degrees centigrade)
  2. Specimen transferred to small cyrogenic chamber where it is fractured using something like a razor blade
  3. Transferred to another part of the machine where electrical filament sits above specimen
  4. Electric current runs though the filament causing gold to splatter over fractured surface
  5. Layer of gold approx. 20-30nm thick
  6. Specimen placed in potassium hydroxide to dissolve tissue specimen and leave gold coating
  7. The gold replicate is collected and viewed through a transmission electron microscope
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5
Q

Briefly describe impermeable junctions

A
  • Tight

- Seal space between cells so nothing can leak

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6
Q

Where are impermeable junctions found?

A

Between epithelial cells

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7
Q

Describe the structure of impermeable junctions

A
  • Membranes of 2 adjacent cells push closely against each other
  • Tight junction proteins are embedded in the membranes, these proteins connect to each other bringing the membranes close
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8
Q

What is the secondary function of impermeable junctions?

A
  • Creates cell surface domains:
    Different parts of the membrane contain different sets of membrane proteins (ie. top proteins are different to the bottom and sides).
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9
Q

Briefly describe anchoring junctions

A

Link the cytoskeleton between adjacent cells, or attach cells to something else in the extracellular matrix.
NB: the cytoskeletal filaments do not directly interact

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10
Q

Describe how the cytoskeletons of 2 cells become linked

A
  • Attachment protein binds to the cytoskeletal filament
  • Attachment protein binds to a transmembrane linker protein
  • Same process occurs in adjacetn cell, the 2 transmembrane linker proteins attach to eachother
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11
Q

Describe how the cytoskeleton of a cell can attach to the extracellular matrix

A
  • Attachment protein binds to cytoskeletal filament
  • Transmembrane linker protein attaches to the attachment protein
  • Transmembrane linker protein attaches directly to extracellular matrix
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12
Q

What are the 2 types of anchoring junction?

A
  1. Adherens junctions

2. Desmosomes junctiosn

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13
Q

Describe adherens junctions

A
  • Connects actin between cells
  • Attachment protein = vinculin
  • Transmembrane linker protein = cadherin
  • Connecting to ECM = focal contact
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14
Q

Describe desmosomes junctions

A
  • Connects intermediate filaments between cells
  • Attachment protein = desmoplakin
  • Transmembrane linker protein = desmoglein
  • Connecting to ECM = hemidesmosome
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15
Q

Name a pathology caused by a defect in desmoglein

A

Desnoglein = transmembrane linker protein in desmosomes

Disease: Pemphigus vulgaris

  • Autoimmune disease which attacks desmoglein
  • Internal structures of the skin disintegrate and the skin structure is compromised
  • Results in large blisters, dehydration and infection
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16
Q

Briefly describe communicating junctions (gap junctions)

A
  • Allow adjacent cells to communicate and coordinate their activities
  • Aqueous channels between cells
17
Q

Describe the structure of communicating junctions

A
  • Proteins called connexins form hexametric structures called connexons
  • Connexons have an aqueous channel connecting the cytosol of adjacent cells
  • Ions and small molecules can move through these channels
18
Q

Give 5 examples of communicating junctions in the body

A
  1. Spreads contractile signals in the heart, allows myocytes to coordinate behaviour
  2. Contraction of smooth muscle e.g. in the gut, blood vessels, pupil
  3. Respiratory system; coordination of cilia to beat mucous out
  4. Nervous system; electrical synapses are made of gap junctions
  5. Coordination in developing embryos

BDS 1: Cell Biology (2 decks)

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