Chapter 7: Membranes Flashcards
The purpose plasma membranes serve for living cells
- A living cell must be able to contain molecules within it and exclude molecules from it.
- Respond to the environment: Membranes are studded with sensor receptors that receive info.
- Obtain nutrients and dispel waste: Membranes are studded with channel proteins that allow things in and out of the cell.
Components of the plasma membrane including the structure and function of each component
1.) Lipids (phospholipid bilayer)
2.) Proteins – ability to attach the outside of membrane or extend into/through the membrane
A. Peripheral membrane proteins – found on the inner membrane surface
B. Integral membrane proteins – partially or wholly embedded in the membrane (covalently attached stuck to membrane)
3.) Cholesterol – Affects the fluidity of the membrane
• Structure of different types of phospholipids
Phosphoglycerides have a glycerol backbone containing 3 carbons
•Two carbons have attached nonpolar fatty acid tails,
third carbon is attached to a polar phosphate group
• Phosphoglycerides can be differentiated based on the
fatty acid tails and various groups attached to the phosphate
- amphipathic.
The nature of phospholipids in an aqueous environment & how they move within the membrane
- Water forms a cage around hydrophobic molecules, water would rather form bonds and be stable than form none. this cage is more ordered than rest of water -> requires energy to maintain.
- When hpho molecules group together energy is minimized.
- The forces that cause bilayer formation, cause it to be self-sealing: interior of the bilayer can avoid contact with water.
- Because free edges expose hpho tails to water, the amphipathic sheets needs to bend to minimize water contact.
• Mechanisms of changing membrane fluidity
- ) Change the length of the fatty acid tail
- ) Change the shape of the fatty acid tail
- ) Change the amount of cholesterol molecules present.
Distinguishing features of saturated & unsaturated fatty acids
Saturated Fats
• No double bonds
• High density
• High melting temp
Unsaturated Fats: more fluid
• Double bonds- cause kink
• Low density
• Low melting temp
• Differentiate between various membrane proteins & how they are folded in order to interact with
phospholipids (for both channel proteins and single-pass proteins)
Integral: embedded or covalently attached
Peripheral: protein attached (loose attachment to 1 side of mem. non covalently) need to be activated to leave the attachment.
Transmembrane: integral proteins extending through membrane to other side. (alpha helices & amphipathic)
- beta barrel: beta sheets rolled into cylindrical structure. r groups of pore are polar and fatty acid tail interacting r groups are non polar.
How new phospholipids are made and how they’re moved around in the membrane to create
symmetry/asymmetry
- produced by enzymes on cytosolic side of ER. enzymes specifically + new phospholipids to cytosolic side of bilayer creating asymmetry.
- transporter protein scramblase randomly takes phospholipids from one side of membrane to other to hasten process.
• These TP recognize & move specific phospholipids 1 side to another: overarching group
• Flippase = transporter moving specific phospholipids from exterior to interior
• Floppase = transporter moving specific phospholipids from interior to exterior - Based on number of phospholipids and type
- to grow symmetrically, lipids can sometimes flip-flop from side to side, but that is rare.
The nature of detergents and micelles
- disrupt the membrane using amphipathic detergents like SDS or Triton X-100
- small molecules have single np tail making them cone shaped and prone to form micelles
- detergents shield hpho portions of transmembrane proteins once membrane disrupted. Without the detergent, the hydrophobic portions of the membrane proteins would cluster causing the proteins to leave solution
• Once the membrane proteins are included in protein-lipid-detergent group, their structure & function can be
studied. - Micelle: an cluster of amphipathic molecules.
Structure and function of the cell cortex and cytoskeleton
- Cell cortex: network of filamentous proteins, this attaches to tmp on inner cytosolic face of membrane, differs from cytoskeleton, found on inner surface and provides support to membrane. spectrin is main comp. of rbc cortex. attached to mem. via attachment anchor proteins. deficits in spectrin can cause anemia.
- Cytoskeleton: found throughout cell and maintains overall cell shape.
Types of membrane domains and the purpose of tight junctions
Membrane Domains: functionally specialized regions on the cell (or organelle) surface. cell can physically restrain certain phospholipids or proteins to certain sides.
- tethered inside
- tethered outside
- tethered by proteins on surface of adjacent cell
- membrane barrier that restricts movement
Tight junctions: produce a barrier that restricts proteins to apical or basal sides of cell. seals gaps between cells to prevent linkage.
The structure and function of sugar-bound proteins
Glycoproteins: proteins w/ short sugar chain called oligosaccharides
Proteoglycans: proteins w/ 1 or more long polysaccharide chains
- on cell membranes and lipids is called glycocalyx, provides protections, helps absorb water, helps some cells squeeze through tight spaces w/o sticking. allows for cell to cell recognition (lectins recognize sugar groups to recognize certain cell types)
Single pass and multi pass transmembrane proteins
- Single pass: pp of a transmembrane protein crosses membrane once, often receptors for extracellular signals
- multi pass: pp of a transmembrane protein crosses membrane multiple times using series of helices, often channels that allow water soluble molecules through.
