Foundations-Cells-7

From CellBiology

Membrane Specialisations


This lecture is also an introduction to cell compartments and describes the structure of membranes forming these compartments.


Draft - this online lecture is currently in 2018 draft status. This notice removed when completed.
Cells and Membranes: 1 Cells and sizes | 2 Prokaryotes | 3 Viruses and prions | 4 Plasma membrane | 5 Compartments | 6 Membrane structure | 7 Membrane specialisations | Foundations - Moodle

This is the last online lecture content page. You can now test your knowledge by attempting the Moodle quiz.

Terms

  • adhesion junction - a term used to describe a specialised membrane protein complex that allows cell attachment to another surface (cell, extracellular matrix).

Specialisation Types

  • plasma membrane cytoskeleton
    • not within the membrane but directly under the membranes
  • adhesion complexes
    • span the membrane and manoskeletony connect to cyt
  • receptors
    • membrane receptors bind ligands
    • concept is covered in detail elsewhere in your course
  • absorbtive and secretory
  • synaptic junctions
    • neural and immune
    • covered in detail elsewhere in your course

Adhesion Specializations

A series of different types of proteins and cytoskeleton associations forming different classes of adhesion junctions
  • Desmosomes ( = macula adherens)
  • Adherens Junctions ( = zonula adherens)
  • Septate Junctions (mainly invertebrates)
  • Tight Junctions (barrier function)
  • Gap Junctions (rapid signaling function)


For example - epithelial cells form different junctions with their direct neighbour cell (cell-cell) and with the extracellular matrix (cell - ECM) under them.

These different junctions will be described in more detail within histology.

Cell adhesion summary.png

Examples of epithelial cell adhesion junctions.


Note the above video recording does not currently include a description of the following sub-headings.

Transport

Cell potassium channels

Three major forms of transport across the membrane

  • Passive - Simple diffusion
  • Facilitated - transport proteins
  • Active - transport proteins for nutrient uptake, secretion, ion balance


This concept will be covered in detail in physiology.

Ion Channels

  • the membrane phospholipid is impermeable to ions in aqueous solution
  • protein channels permit rapid ion flux
    • 1960’s structure and function, ionophores (simple ion channels)
  • 75 + different ion channels, opening/closing, “gating” of ions



"Sometimes you eat the bacteria and sometimes... well, he eats you"

Additional Information

The material below is not part of the actual lecture and is provided for background information and student self-directed learning purposes.

Cell Apoptosis

The cell membrane is also finally used when a cell dies. The cell plasma membrane is used like a "garbage bin liner", to enclose the components of the dying cell.

  • apoptosis - programmed cell death
  • membrane "blebbing" encloses cellular component fragments
  • do not stimulate inflammatory response, easy removal by macrophages.


Link: PMID 16129889 | PMID 18073771

Cystic Fibrosis

  • membrane transport disease
  • Chloride channel - protein mutation point mutant, folded improperly, trapped and degraded in ER
  • 1989 Collins (US), Tsui and Riordan (Canada)

Ion Channel Types

3 rapid + 1 slow gate (gap junction)

  • Voltage-gated - propogation of electrical signals along nerve, muscle
  • Ligand-gated - opened by non-covalent, reversible binding of ligand between nerve cells, nerve-muscle, gland cells
  • Mechanical-gated - regulated by mechanical deformation
  • Gap junction - allow ions to flow between adjacent cells open/close in response to Ca2+ and protons

Textbook References

Here are some Cell Biology online textbooks for further general reading on these topics.


Search Online Textbooks

Historic Papers

Below are some example historical research finding related to cell membranes from the JCB Archive and other sources.


Draft - this online lecture is currently in 2018 draft status. This notice removed when completed.
Cells and Membranes: 1 Cells and sizes | 2 Prokaryotes | 3 Viruses and prions | 4 Plasma membrane | 5 Compartments | 6 Membrane structure | 7 Membrane specialisations | Foundations - Moodle