Unformatted text preview: BIO 201 The Plasma Membrane and Membrane Transport Cell surface structure Cell surface functions Membrane transport Membrane sensitivity Plasma Membrane Defines cell boundary Controls passage of materials in and out of cell (semi-permeable (semi-permeable, selectively permeable) permeable) intracellular face - side faces cytoplasm extracellular face side faces outwards Controls interactions with other cells (sensitivity) (sensitivity) identification protection adhesion Plasma Membrane and Transport 1 BIO 201 Membrane Lipids
Lipids constitute 90 to 99% of the plasma membrane Phospholipid bilayer h h l d bl 75% of the lipids hydrophilic heads (phosphate) on each side hydrophobic tails in the center Membrane Lipids
Lipids constitute 90 to 99% of the plasma membrane Cholesterol Glycolipids 20% of the lipids, affects membrane fluidity (low conc. more rigid, high conc. more fluid) 5% of the lipids, found only on extracellular face, contribute to glycocalyx (carbohydrate coating on cell surface) Plasma Membrane and Transport 2 BIO 201 Membrane Proteins
Proteins constitute about 2% of the molecules found in plasma membrane Transmembrane proteins pass completely through membrane most are glycoproteins adhere to intracellular surface of membrane anchors to cytoskeleton Peripheral proteins Membrane Protein Functions Pores, channels, carriers, pumps (semi-permeable) (semi-permeable) Receptors, identity (sensitivity) (sensitivity) Adhesion, second messenger systems, enzymes Plasma Membrane and Transport 3 BIO 201 Overview of Membrane Transport Plasma membrane is selectively permeable controls which things enter or leave the cell movement of particles is down their concentration gradient transports particles against their concentration gradient Simple diffusion and f l l d ff d facilitated diffusion require no ATP d d ff Active transport requires ATP Simple Diffusion Simple diffusion is the movement of particles across a membrane from an area of high concentration to an area of low concentration (down or with the co ce t at o gradient concentration g ad e t) gradient) t) Small, uncharged solutes most gases, lipids Plasma Membrane and Transport 4 BIO 201 Proteins allow small solutes across cell membrane (like a door) Solutes still move down concentration gradient Facilitated Diffusion Charged particles (ions, amino acids, nucleotides)
Ligand Receptor Pores Channels Carriers Osmosis Movement of water through a selectively permeable membrane from an area of more water to an area of less water from an area of less solutes to an area of more solutes Aquaporins are channel proteins in cell membrane that allow water to move freely in or out of the cell (determined by tonicity of solution) ( y y ) Plasma Membrane and Transport 5 BIO 201 Active Transport Protein-mediated, Protein-mediated, active transport of solute across membrane against its concentration gradient t ti di t Energy (usually ATP) required Prominent example is the sodiumsodium-potassium pump 3 Na+ out/2 K+ in/1 ATP used Primary vs. Secondary Active Transport Primary aka ATP-dependent ATPDirectly uses energy from ATP Secondary aka ATP-independent ATPuses energy from ion gradients (usually Na+) the gradient dependent upon ATP Plasma Membrane and Transport 6 BIO 201 Bulk (Vesicular) Transport Transport of large particles or fluid droplets through membrane in bubblebubble-like vesicles of plasma membrane, uses ATP Exocytosis vesicular transport out of cell Endocytosis vesicular transport into cell phagocytosis engulfing large particles f Receptor Proteins Receive information about the environment Change shape when bound to "ligand" ligand Initiate a cellular response The cellular response 1st messengers direct response 2nd messengers indirect response Metabolic Mitotic Apoptotic (suicide) Growth Synthesis Development Plasma Membrane and Transport 7 ...
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- Spring '08