Membrane Structure and Function PDF
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Isabela State University, College of Medicine
Eugene John F. Balmores Jr., MD
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Summary
These notes provide an overview of membrane structure and function, covering topics such as lipid bilayers, membrane proteins, and transport mechanisms. The document emphasizes the importance of membrane structure in various cellular processes, along with the impact of mutations on membrane proteins. It also explains different types of transport and the molecules involved.
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Isabela State University College of Medicine _________________________________________________________ BIOCHEMISTRY NOTES By: Eugene John F. Balmores Jr., MD References (T...
Isabela State University College of Medicine _________________________________________________________ BIOCHEMISTRY NOTES By: Eugene John F. Balmores Jr., MD References (Text, Tables, Figures): Harper’s Illustrated Biochemistry; Kaplan Biochemistry and Medical Genetics MEMBRANE STRUCTURE AND FUNCTION Function of cell membrane: contains/protects the cell; regulates the traffic of molecules and substances in and out of the cell o Semi-permeable membrane: maintains the difference in composition between the inside and outside of the cell through several mechanisms (e.g. transporters, ion channels, gap junctions, exocytosis, endocytosis) Structure of cell membrane: composed of lipids, proteins, and carbohydrate-containing molecules The basic structure of all membranes is the lipid bilayer. Membrane proteins may be integral (firmly embedded in the bilayer) or peripheral (attached to the outer or inner membrane surface), and this depends on the primary and secondary structure of the proteins; o proteins allow for transport to be ▪ Selective o This bilayer is formed by two sheets of phospholipids in which the hydrophilic polar ▪ bi-directional head groups are directed away from each other and are exposed to the aqueous environment on the outer and inner surfaces of the membrane. o The hydrophobic nonpolar tails of these molecules are oriented toward each other, in the direction of the center of the membrane. o Note that one of the tails of the phospholipid is in “trans” configuration, making the membrane fluid; cholesterol, meanwhile, intercalates among the phospholipids of the membrane, which makes the membrane less fluid ▪ concentration dependent o proteins in the membrane can also act as surface receptors for signal transduction occur Transport of small substances across the membrane can be through the following: o Certain solutes, for example, glucose, enter cells by facilitated diffusion along a downhill gradient o Certain hydrophobic molecules freely diffuse from high to low concentration using specific across membranes. carrier proteins (transporters). o The major ATP-driven pumps are classified as P (phosphorylated), F (energy factors), V (vacuolar), and ABC transporters. o Ligand- or voltage-gated ion channels are often employed to move charged molecules (Na+, K+, Ca2+, etc) across membranes down their electrochemical gradients. Large molecules are transported through endocytosis or exocytosis Mutations that affect the structure of membrane proteins may cause diseases. -END-
