Lecture 4 Cytoplasmic Membrane PDF

Lecture 4: Cytoplasmic Membrane and transport (Chapter 2 pgs 38-42) Learning Objective: Compare and contrast bacterial and archaeal cytoplasmic membrane structures and function Cytoplasmic membrane Vital barrier surrounding the cells and separating the...

Lecture 4: Cytoplasmic Membrane and transport (Chapter 2 pgs 38-42) Learning Objective: Compare and contrast bacterial and archaeal cytoplasmic membrane structures and function Cytoplasmic membrane Vital barrier surrounding the cells and separating the cytoplasm from the environment If broken, the integrity of the cell is lost, resulting in cell death Offers little protection from osmotic lysis but functions as a selective permeability barrier allowing nutrients to enter and wastes to be excreted © 2018 Pearson Education, Inc.  The Bacterial Cytoplasmic Membrane General structure: phospholipid bilayer containing embedded proteins 8-10 nm thick Consistency is somewhat fluid Contains both hydrophobic (water-repelling) and hydrophilic (water-attracting) components hydrophobic = fatty acids hydrophilic = glycerol + phosphate and another functional group (e.g., sugars, ethanolamine, choline) Fatty acids point inward to form a hydrophobic environment; hydrophilic portions remain exposed to the external environment or the cytoplasm © 2018 Pearson Education, Inc.  The Bacterial Cytoplasmic Membrane © 2018 Pearson Education, Inc.  The Bacterial Cytoplasmic Membrane Cytoplasmic membranes of some bacterial species are strengthened by hopanoids (rigid, sterol-like molecules, but different ring structure than sterols) Embedded proteins often arranged in clusters to allow proteins that interact to be in close proximity Associated proteins include: Integral membrane proteins: significantly embedded, typically span the membrane Peripheral membrane proteins: loosely associated with membrane surfaces; often have a lipid tale that anchors the protein to the membrane © 2018 Pearson Education, Inc.  The Bacterial Cytoplasmic Membrane © 2018 Pearson Education, Inc.  The Archaeal Cytoplasmic Membrane Structure similar to bacterial membranes, but chemistry is different: Bacteria and Eukarya: ester linkages between the fatty acids and the glycerol Archaea: ether bonds between the glycerol and their hydrophobic side chains, which are NOT true fatty acids Archaeal lipid side chains are repeating units of isoprene, a 5-carbon hydrocarbon glycerol = R group (side chain) © 2018 Pearson Education, Inc.  The Archaeal Cytoplasmic Membrane Major lipids are either: Phosphoglycerol diethers with 20-carbon side chains called phytanyl groups Diphosphoglycerol tetraethers with 40-carbon side chains called biphytanyl groups, which can form lipid monolayers (phytanyl groups covalently linked to form a biphytanyl group) © 2018 Pearson Education, Inc.  The Archaeal Cytoplasmic Membrane Some Archaeal lipids contain rings structures within the hydrocarbon chains Common membrane lipid in Crenarchaeota (major phylum of Archaea) contains four C5 rings and one C6 ring Rings affect the chemical properties of the membrane  affect membrane function © 2018 Pearson Education, Inc.  The Archaeal Cytoplasmic Membrane As in other organisms, polar head groups in archaeal lipids can be sugars, ethanolamine, or other molecules Hopanoids (rigid, sterol-like molecules) have not been found in archaeal membranes Despite differences in chemistry, the fundamental construction of the cytoplasmic membrane is the same: Inner and outer hydrophilic surfaces Hydrophobic interior © 2018 Pearson Education, Inc.  Cytoplasmic Membrane Functions Permeability barrier (“gatekeeper”) Polar and charged molecules must be transported Transport proteins accumulate solutes against the concentration gradient Protein anchor Holds transport proteins in place Energy conservation and consumption Generation of proton motive force © 2018 Pearson Education, Inc.  Cytoplasmic Membrane Functions Cytoplasm contains salts, sugars, amino acids, nucleotides, etc. The hydrophobic portion of the cytoplasmic membrane prevents diffusion of these solutes out of the cell Some small hydrophobic molecules can diffuse through the membrane but large polar and charged molecules and ions must be transported Water can pass freely in both directions, polar but small, but its movement is accelerated by the presence of aquaporins Most substances must be carried in or out by transport proteins © 2018 Pearson Education, Inc.  Cytoplasmic Membrane Transport Proteins Accumulate solutes against a concentration gradient; require energy; highly specific for single molecule or class of molecules Necessary to carry out biochemical reactions Transport systems exhibit saturation effects and a high specificity for the target molecule(s) Biosynthesis of transport proteins/systems is highly regulated by the cell (i.e., the transport proteins present in the membrane are a function of available resources and their concentrations) © 2018 Pearson Education, Inc.