1 / 21

Biomembrane Structure and Function

Biomembrane Structure and Function. Paul D. Brown, PhD BC21D: Bioenergetics & Metabolism. Learning Objectives. Describe the structural relationship among the components of the membrane and general functional roles served by each of them

tyrell
Download Presentation

Biomembrane Structure and Function

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Biomembrane Structure and Function Paul D. Brown, PhD BC21D: Bioenergetics & Metabolism

  2. Learning Objectives • Describe the structural relationship among the components of the membrane and general functional roles served by each of them • Describe the processes by which small solutes, ions and macromolecules cross biomembranes • Describe various membrane transport pumps including their energy source, stoichiometry and functional significance

  3. Biomembrane structure • Cell (plasma) membrane: defines cell boundaries • Internal membranes define a variety of cell organelles • Nucleus • Mitochondria • Endoplasmic reticulum (rough and smooth) • Golgi apparatus • Lysosomes • Peroxisomes • Chloroplasts • Other

  4. Membrane functions • Form selectively permeable barriers • Transport phenomena • Passive diffusion • Mediated transport • Facilitated diffusion • Carrier proteins • Channel proteins • Gated or non-gated channels • Active transport • Cell communication and signalling • Cell-cell adhesion and cellular attachment • Cell identity and antigenicity • Conductivity

  5. Fluid mosaic model • Mosaic • Membrane lipids: supporting structure • Phospholipids • Glycolipids • Cholesterol • Membrane proteins: bits and pieces • Integral (integral) proteins • Peripheral (extrinsic) proteins

  6. Biomembrane composition • Phospholipid bilayer (basic structure) • Various membrane proteins, depending on membrane function • Glycolipids and glycoproteins (lipids and proteins with attached carbohydrates) • Cholesterol (in animal cells)

  7. Membrane lipids • Phospholipids • Major lipid component of most biomembranes • Amphipathic: hydrophobic and hydrophilic • Examples • Phosphatidylcholine • Sphingomyelin • P-serine • P-ethanolamine • P-inositol

  8. Phospholipid bilayer

  9. Membrane lipids • Glycolipids • Least common of the membrane lipids (ca. 2%) • Always found on outer leaflet of membrane • Carbohydrates covalently attached • Involved in cell identity (blood group antigens)

  10. Membrane lipids • Cholesterol • Steroid; lipid-soluble • Found in both leaflets of bilayer • Amphipathic • Found in animal cells • Membrane fluidity “buffer” • Synthesized in membranes of ER

  11. Membrane proteins • Integral (intrinsic) proteins • Penetrate bilayer or span membrane • Can only be removed by disrupting bilayer • Types • Transmembrane proteins • Single-pass or Multiple-pass • Covalently tethered integral proteins • Many are glycoproteins • Covalently-linked via asparagine, serine, or threonine to sugars • Synthesized in rough ER • Function: enzymatic, receptors, transport, communication, adhesion

  12. Membrane proteins • Five types of associations

  13. Membrane proteins • Peripheral (extrinsic) proteins • Do not penetrate bilayer • Not covalently linked to other membrane components • Form ionic links to membrane structures • Can be dissociated from membranes • Dissociation does not disrupt membrane integrity • Located on both extracellular and intracellular sides of membrane • Synthesis • Cytoplasmic (inner) side – cytoplasm • Extracellular (outer) side – made in ER and exocytosed

  14. Membrane dynamics • Asymmetry • Lateral mobility • Fluidity

  15. Membrane asymmetry • The inner and outer leaflets of the membrane have different compositions of lipids and proteins

  16. Fluid mosaic model • Biomembranes are a two-dimensional “mosaic” of lipids and proteins • Most membrane lipids and protein can freely move through the membrane plane

  17. Membrane fluidity • Movement of hydrophobic tails • Depends on temperature and lipid composition How does lipid composition affect fluidity?

  18. Lipids and membrane fluidity • Interactions between hydrophobic tails decrease fluidity (movement): • Shorter tails have fewer interactions • Unsaturated fatty acids are kinked and decrease interactions • Cholesterol “buffers” fluidity • Prevents interactions • Restricts tail movement

  19. Biomembranes • Surrounds cell • Separates cell from environment • Allows cellular specialization • Separate some of the cellular organelles • Allows specialization within the cell • Continuity of membranes between adjoining cells (tight junctions) can separate two extracellular compartments • Important in organ function

  20. “Accessory” structures • Extracellular matrix (ECM) • Outside animal cells • Composed of proteins and carbohydrates • Attached to plasma membrane • Cell wall • Surrounds plant cells • Composed of cellulose (carbohydrate) • Adds rigidity

  21. Transport across membranes • Nutrients in and waste out • Specific ion gradients • Signals relayed • Mediated by membrane proteins

More Related