MODULE 1.3 Flashcards
surrounds the cytoplasm within cells, which in eukaryotes is filled with membrane-bound organelles.
cell or plasma membrane
all cellular membranes are _________ allowing only certain substances to cross the membrane.
selectively permeable
All cellular membranes are composed of two layers of __________ embedded with ______ and _______.
phospholipids;
proteins and glycoproteins
A bilayer membrane structure was predicted by_____ and _______ as early as ______.
Gorter and Grendel (1925)
Gorter and Grendel knew that red blood cells (____________) have no nucleus or other organelles, and thus have only a plasma membrane.
erythrocytes
also knew that a major chemical component of these membranes were lipids, specifically phospholipids.
Gorter and Grendel
Phospholipid structure (2)
hydrophilic head
hydrophobic tail
had experimentally measured the surface area of red blood cells, disrupted them and calculated the amount of phospholipid in the membranes that remained.
Their estimate that that there were enough lipid molecules per cell to wrap around each cell twice was ‘correct’.
Gorter and Grendel
what part of the phospholipid bilayer is polar
polar hydrophilic heads
In 1935, __________ suggested that proteins might be more or less fortuitously bound to the polar heads of the phospholipids.
In 1935, Davson and Danielli
first observed membranes in the transmission electron microscope at high power some decades later, revealing them to have a trilamellar structure.
J.D Robertson
Trilamellar Membrane Structure in the Electron Microscope:
electron-dense layer: _________
electron-transparent layer:_____
electron-dense layer: proteins bound to phospholipids
electron-transparent layer:
fatty acid layer
Robertson offered his ________in which only proteins with specific functions associated with a membrane were actually bound to the phospholipid heads.
Unit Membrane theory
proposed the Fluid Mosaic model of membrane structure
Singer and Nicolson (1972)
They suggested that in addition to peripheral proteins that do bind to the surfaces of membranes, many integral membrane proteins actually span the membrane.
Singer and Nicolson (1972)
were imagined as a mosaic of protein ‘tiles’ embedded in a phospholipid medium. (the protein ‘tiles’ were predicted to be mobile (fluid) in a phospholipid sea)
integral membrane proteins
The key to the fluid mosaic is that embedded proteins are held in membranes by a __________, while they expose their ________ to the external aqueous and cytosolic environments. Thus, like phospholipids themselves, membrane proteins are _________.
hydrophobic domain
hydrophilic domains
amphipathic (have both hydrophilic and hydrophobic part)
Because the hydrophilic domains of each integral membrane protein are different from each other, we say that cellular membranes are _______. In other words, cells expose different surface structural (and functional) features to opposite sides of the membranes.
asymmetric
peripheral proteins are also known as
surface protein
are a natural barrier to the free passage of charged molecules across the membrane because of their own aqueous hydrophilic domains
membrane proteins
are responsible for the selective permeability of membranes, facilitating the movement of specific molecule in and out of cells.
membrane proteins
also account for specific and selective interactions
with their extracellular environment, including the adhesion of cells to other cells, their attachment to
surfaces, communication between cells (both direct and via hormones and neurons).
membrane proteins
The extracellular surface of plasma membranes is ‘sugar-coated’ with _________ covalently linked to membrane proteins (as _______) or to phospholipids (as _______).
oligosaccharides;
glycoproteins;
glycolipids
The __________ components of glycosylated membrane proteins inform their function.
carbohydrate
