BIOL 0800 Reading- Chapter 3 Flashcards
List four functions of the plasma membrane.
To regulate the passage of substances into and out of cells and between cell organelles and cytosol; Detect chemical messengers arriving at the cell surface; Link adjacent cells together by membrane junctions; Anchor cells to the extracellular matrix
What is one of the advantages of restricting the movements of molecules across membranes?
Confining the products of chemical reactions to specific cell organelles
What are the major membrane lipids?
Phospholipids
What is a phospholipid?
Has one end that’s charged/polar, and the other end that’s two long fatty acid chains that is nonpolar
What are the polar heads of phospholipids oriented toward the surface of the membrane?
Because they are attracted to the polar water molecules in the ECF and cytosol
Do chemical bonds usually link the phospholipids together?
Usually not.
Which membrane type contains cholesterol, intracellular or plasma membrane?
The plasma membrane: increases fluidity
Is cholesterol amphipathic?
Yup: single polar hydroxyl group on its nonpolar ring structure
What role does cholesterol play in the plasma membrane?
Associates with certain classes of plasma membrane phospholipids and proteins to form organized clusters that work together to pinch off portions of the plasma membrane to form vesicles that deliver their contents to various intracellular organelles
What are the two classes of membrane proteins?
Integral and peripheral
What are integral membrane proteins?
Associated with membrane lipids and can’t be extracted; amphipathic (polar amino acid side chains on one side, and nonpolar side chains clustered together in a separate region); not all can move freely in the membrane, some are anchored to peripheral proteins
What are most integral proteins referred to as, if they span the entire membrane?
Transmembrane proteins: often cross the lipid bilayer several times
What is a peripheral membrane protein?
Not amphipathic, don’t associated with the nonpolar regions of the lipids in the interior of the membrane; located at membrane surface, bound to polar regions of the integral membrane proteins; mostly on cytosolic surface of the plasma membrane, associated with cytoskeletal elements that influence cells shape and motility
Why is glycocalyx?
The layer of short, branched chains of monosaccharides that extend from the cell surface into the ECF; carbohydrates covalently linked to some membrane lipids and proteins
What is the glycocalyx for?
Enabling cells to identify and interact with each other
What are two examples of a region in the plasma membrane that doesn’t conform to the fluid-mosaic model?
Lipid rafts (cholesterol-rich regions of reduced membrane fluidity that serve as organizing centers for the generation of complex intracellular signals); also membrane junctions (proteins linked in special patches)
What are lipid rafts?
Cholesterol-rich regions of reduced membrane fluidity that serve as organizing centers for the generation of complex intracellular signals
What are integrins?
Certain transmembrane proteins in the plasma membrane that bind to specific proteins in the extracellular matric and link the to membrane proteins on adjacent cells
What are desmosomes?
Firmly attaches two cells together; regions between two adjacent cells where the apposed plasma membranes are separated by about 20 nm; characterized be accumulations of protein known as “dense plaques” along the cytoplasmic surface that serve as anchoring point for cadherins (proteins that extend from the cell into the extracellular space to link up and bind with cadherins in an adjacent cell)
What are dense plaques?
Proteins that accumulate along the cytoplasmic surface along desmosomes that are anchor points for cadherins
What are cadherins?
Proteins that extend from the cell into extracellular space and bind to cadherins from the next cell; anchored to dense plaques for desmosomes
What are tight junctions?
When the extracellular surfaces of two adjacent plasma membranes join together so that no extracellular space remains between them; occurs in a band around the entire circumference of the cell
What kind of cell type is most often joined by tight junction?
Epithelial cells, usually on the apical surfaces