01 - Plasma Membranes

lidocaine

exists in ionized or unionized forms

• given pKa of 7.9, about 25% of lidocaine is present in non-ionized form at physiological pH of 7.4

cell membrane

bilayer sheet that functions to separate extracellular and intracellular environments and create internal compartments that allow specific tasks to be achieved separately

• selectively permeable and contains receptors that allow for communication

• does not live in isolation → interacts with extracellular matrices, neighboring cells, cytoskeletal structures

  • interactions can change gene expression and influence things on inside

• can have different properties depending on location → apical domain vs basolateral domain

• polar heads bind electron-dense metals to allow for staining

• communication vis receptors and signaling pathways

• maintains homeostasis through ion gradients and compartmentalization

lipid composition in cell membrane

• phospholipid: can be neutral or anionic (negatively charged)

  • nomenclature of glycerophospholipid → phosphatidyl [head group]

  • amphiphatic, asymmetrically distributed, flipping limited to use of enzyme

    • can have different types of phospholipids intermingled among each other

  • cis double bond prevents close packing of fatty acids

• sphingolipids: important for signaling and structural stability

• cholesterol: amphiphatic sterol with polar head group and nonpolar hydrocarbon body

  • membrane constituent that participates in membrane fluidity and integrity

  • low temperature → cholesterol maintains fluidity; high temperature → cholesterol decreases fluidity

protein composition in cell membrane

proteins function for transport, signal reception, adhesion, enzymatic activity, and cytoskeletal linkage

• integral: amphiphatic proteins that are embedded in membrane

  • removed using detergents

  • asymmetrically distributed in membrane

• peripheral: interacts with some part of membrane

  • removed by removing its ionic interactions

• lipid-anchored: bound and anchored to one leaflet

  • fatty acyl group → anchors protein to inner leaflet

  • GPI-linkage → anchors protein to outer leaflet

• glycoprotein: integral proteins that are asymmetrically distributed

  • N-linked sugars face extracellular environment

  • intrachain disulfide bonds face extracellular environment

  • sulfhydryl groups face cytosol

membrane asymmetry patterns

• inner leaflet → phosphatidylserine and phosphatidylinositol give negative charge and responsible for signaling

  • PS flips to outer leaflet during apoptosis for signaling to immune cells

• outer leaflet → glycolipids and sugars for recognition and protection

glycocalyx

carbohydrate-rich layer on cell exterior

• made from sugars attached to proteins or lipids

• function for cell-cell recognition, protection from mechanical or chemical damage, prevents unwanted protein adhesion, and selective absorption (in GI tract)

epithelial polarity

• apical surface: faces lumen, specialized for absorption and secretion

• basolateral surface: faces neighboring cells and extracellular matrix, contains pumps and transporters

• tight junctions: act as “fences” to keep domains separate and maintain function

• loss of polarity causes loss of directional transport and tissue dysfunction