Transcript the Cell
Membrane Structure & Function Spring 2013 - Althoff Reference: Mader & Windelspecht Ch. 5) Lec 05 • ____________________– “the boundary” between the cell’s inside workings and the world outside it. Keys to consider: 1) ____________ for exchange between inside and outside the cell 2) _________________ are exchanged A Little History… • Beginning of 20th century researchers noted lipid soluble molecules entered cells more rapidly than water soluble molecules In ______________________________ determined phospholipid content of a cell “just enough” to form a bilayer around the cells In ______________________________ proposed proteins also part of membrane. Model they proposed was “sandwich-like”, further enhanced by Robertson in late 1950s. A Little History… • Robinson’s ______ _________ model. late1950s BILAYER PHOSPHOLIPID “SANDWICH”, • Singer & Nicolson __________ model, 1972. EMBEDDED PROTEIN MOLECULES PHOSPHOLIPID OUTSIDE THE CELL INSIDE THE CELL (similar to Mader p86 Fig. 5.1) Components of the PLASMA MEMBRANE Lipids • Phospholipids “bilayer” (meaning 2 layers) • “Exterior” portions are hydrophilic (2 places) • “Interior” portion of the bilayer is hydrophobic • Provides essential “structure” to this portion of the cell Proteins • Protein molecules are embedded in the plasma membrane • Serve to stabilize and shape the plasma membrane • Various (many) proteins perform specific functions: 1) channel 2) transport 3) cell recognition 4) receptors 5) enzymes 6) form “junctions” PLASMA MEMBRANE: A matrix of proteins Proteins • Some proteins span the entire bilayer distance (__________________ proteins) • Some proteins reach the inside surface only OUTSIDE INSIDE Fluidity of the Plasma Membrane • At room temperature, the __________________ of the plasma membrane has the consistency of olive oil • Result: ___________________ • _____________________ —those not attached to the cytoskeleton—can move within the fluid lipid bilayer • This “fluidity” is critical to the _________ of proteins, particularly enzymes which speed up chemical reactions Lipid Movement Plasma Membrane PROTEINS • CHANNEL proteins – “_________________”, control passage of molecules • CARRIER proteins – “____________” combine with a substance and move it across the membrane • CELL RECOGNITION proteins – “_________” looking for pathogens, alert immune system • RECEPTOR proteins – “__________”, bind with other molecules resulting in shape change that brings about cellular response • ENZYMATIC proteins– “________”, facilitate/speed up metabolic reactions directly • JUNCTION proteins – “___________________” form junctions between cells CHANNEL CARRIER RECOGNITION RECEPTOR ENZYMATIC JUNCTION When Function Goes _____ • CHANNEL proteins – faulty chloride (Cl-) channel results in cystic fibrosis (thick mucus collects in airways, pancreatic ducts, liver ducts) • CARRIER proteins – inability to use energy transport for sodium potassium (Na+K-)transport may cause obesity for some • CELL RECOGNITION proteins – can explain rejection of organ transplants, liked to MHC (major histocompatibility complex) glycoprotein • RECEPTOR proteins – why some are pygmies. Membrane receptors faulty and cannot interact with growth hormone • ENZYMATIC proteins– diarrhea: impact of cholera bacteria toxin released on enzyme adenylate cyclase, which reduces water & Na retention in large intestine Plasma Membrane: Permeability • _______________________________ – the plasma membrane is ‘choosy” about the passage of molecules into and out of the cell. Energy Not Required DIFFUSION FACILITIATED TRANSPORT Energy Required ACTIVE TRANSPORT EXOCYTOSIS ENDOCYTOSIS 3 Some sugars, amino acids & ions Lipid-soluble molecules, H20, & gases 1 2 Some sugars & amino acids 4 macromolecules 5 (Mader p89 Fig. 5.4) macromolecules Key process Direction of molecule passage DIFFUSION Toward _______ concentration FACILITATED TRANSPORT Toward _______ concentration ACTIVE TRANSPORT Toward _______ concentration EXOCYTOSIS Toward _______ of cell ENDOCYTOSIS Toward _______ of cell REQUIRES ENERGY Key process Requirement DIFFUSION Concentration gradient FACILITATED TRANSPORT Channels or carrier AND concentration gradient ACTIVE TRANSPORT Carrier plus energy EXOCYTOSIS Vesicle fuses with plasma membrane Vesicle formation ENDOCYTOSIS REQUIRES ENERGY PROCESS OF DIFFUSION (Mader p91 Fig. 5.5) DIFFUSION is spontaneous and ___ chemical energy is required PROCESS OF OSMOSIS (Mader p93 Fig. 5.8) _______ the Cell: EUKARYOTIC CELLS MULTICELLUAR ORGANISMS • • • • Must make the “____________” between cells Permits ________________ between cells Permits _________________ between cells Components and construction ______ between plants and animals • We consider these “_________________” structures examples for plants: __________ & plasmodesmata examples for animals: __________________ PLANTS -- Outside CELL #1 CELL #2 CYTOPLASMA PLASMODESMATA CELL WALL -- PRIMARY ANIMAL: Extracellular Matrix • “MESHWORK” OF _______________________ • Examples: “structural proteins” ________________ – matrix strength ________________ – resilience • Examples: “rigid packing gel” permits ________________ of nutrients, metabolites, and hormones between blood and tissue cells ANIMAL: Extracellular Matrix INSIDE OUTSIDE (Mader p99 Fig. 5.13) Extracellular Matrix: Rigid or Flexible? • RIGID: ______ is rock solid because the extracellular matrix includes mineral salts (i.e., calcium salts) deposited outside the cell • FLEXIBLE: _________ Animal Cell JUNCTIONS ADHESION JUNCTIONS • _________ sheet of cells results • Attach to ____________, within the cell via cytoplasmic plaques, intercellular filaments • Common in heart, stomach, and bladder where ___________ must stretch CELL #1 CELL #2 Animal Cell JUNCTIONS TIGHT JUNCTIONS • ____________ fastening • Plasma membrane proteins _______ to each other • Common in kidney where urine passes through; intestines have this type of lining to __________ ______________ from entering lining CELL #1 CELL #2 Animal Cell JUNCTIONS GAP JUNCTIONS • Permits ______________ • __________ plasma membrane channels join • Common in the ________ muscle & _____________ (stomach) • Permit _____________ to facilitate synchronous contraction CELL #1 CELL #2 Know Where You Are Inside or Outside the Eukaryotic Cell RELATIVE TO THE _____________________ COMPONENTS INSIDE looking out OUTSIDE looking in Cell wall (plants) Nucleus Ribosomes Yes No No Yes Plasmodesmata (plants) Golgi apparatus Extracellular matrix (animals) Adhesion junctions (aniamls) Gap junctions (animals) Know What Requires Energy & What Doesn’t Relative to _________________ of the Plasma Membrane Energy Required Direction of passage* Passage type Diffusion No Endocytosis Yes Exocytosis Toward outside Active Transport Facilitated Transport *Toward lower concentration *Toward outside *Toward higher concentration *Toward inside