L10-L13 notes(2).pdf - L10 Biological membrane Terms lipid...

This preview shows page 1 - 3 out of 11 pages.

L10. Biological membrane Terms: lipid bilayer saturated fatty acid ahelix phospholipid unsaturated fatty acid hydropathy analysis amphipathic cholesterol b-barrel hydrophilic head group integral membrane protein glycoprotein hydrophobic fatty acid tails peripheral membrane protein glycolipid hydrophobic effect micelle liposome transmembrane protein Topics: (1)Functions of biological membrane (2)Structure and properties of biological membrane (3)Membrane proteins Reading:Chapter 11, skipthe sections from pg. 366 last paragraph to pg. 368, and from pg. 373, second paragraph to pg. 377, first paragraph. Lecture Summary: 1.Functions of biological membranes Boundary Transport of proteins and lipids via membrane vesicles Transport of ions and small molecules in and out of the cell and organelles via transport proteins spanning the membrane Receiving and transferring information from environment and neighboring cells via proteins spanning the plasma membrane Expansion of plasma membrane drives cell motility 2.Structure and properties of biological membranes A biological membrane is a lipid bilayer. The backbone of a lipid bilayer is composed of phospholipids. -Phospholipids are amphipathic, with a hydrophilic (polar) head group and two hydrophobic (non-polar) tails. -Hydrophobic effect: aggregation of hydrophobic fatty acid tails is energetically favorable, promotes the assembly of a lipid bilayer -Hydrophilic head group allows the lipid bilayer to interact with its aqueous environment -Biological membrane spontaneously forms self-sealed, closed compartment in an aqueous environment. It is energetically unfavorable to expose free edges of a lipid bilayer. When free edges are created by rupturing the membrane, the membrane self-seals due to hydrophobic effect from the fatty acid tails of phospholipids. -Liposomes are double-layered closed vesicles that are formed when purified phospholipids are added to water.
A biological membrane is a flexible two-dimensional fluid: phospholipids can move in the plane of the bilayer. The fluidity depends on the composition of the membrane -The presence of unsaturated fatty acids: kinks allow free lateral movement and rotation of lipids, but movement between the two monolayers is not spontaneous and the two leaflets rarely flip -Cholesterol: acts as a buffer to maintain proper membrane fluidity in different temperature. §Increases membrane fluidity at cold temperature by disrupting ordered packing of phospholipids §decreases membrane fluidity at warm temperature by filling in free spaces created by unsaturated fatty acid tails, thus limiting lateral movement of phospholipids Biological membranes are asymmetrical: -Inner and outer leaflets have different phospholipids -The two leaflets do not flip spontaneously 3.Membrane proteins Membrane proteins are associated with the lipid bilayer in different ways-Integral membrane protein:embedded in the lipid bilayer or covalently associated with the lipid bilayer.

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture