MCB 450 1st Edition Exam 2 Study Guide Lectures 8 14 Lecture 8 February 17 I Know structure nomenclature properties of saturated unsaturated FA a Melting temperatures and what impacts them i Shorter chain lengths and the presence of double bonds lowers the melting temperature b What are triacylglycerols i Storage form of fatty acids three fatty acid chains attached to a glycerol molecule through ester linkages c Triacylglycerols as a food reserve i Fatty acids store more energy than carbohydrates ii a gram of nearly anhydrous fat stores more than six times as much energy as a gram of hydrated glycogen iii glycogen and glucose provide enough energy to sustain biological function for about 18 to 24 hours iv triacylglycerol stores allow survival for several weeks d What are phospholipids i Membrane lipids that consist of fatty acids attached to a scaffold that also bears a charged phosphoryl group creating a macromolecule with a polar head and nonpolar tail ii Fatty acids attached to a platform a phosphate group is also attached to this platform an alcohol group is attached to the phosphate group e Be able to recognize phospholipid headgroups f Difference between phosphoglycerides and sphingolipids i Phosphoglycerides phospholipids with a glycerol backbone to which are attached two fatty acid chains and a phosphorylated alcohol ii Sphingolipids phospholipids built on a sphingosine backbone g Amphipathic nature of membrane lipids i Have a hydrophilic head and a hydrophobic tail ii This allows them to form membranes h How does cholesterol differ from phosphoglycerides and sphingolipids i Cholesterol 1 The most common steroid 2 A precursor to many biochemically active steroids 3 Attached to the steroid nucleus three cyclohexane rings and cyclopentane ring joined together is a hydrocarbon tail on one end and a hydroxyl group to the other end II How are lipids extracted and analyzed a Tissue homogenized in chloroform methanol water b Methanol Water will separate out polar lipids will be present in this layer c Chloroform layer neutral lipids will be present here d Then phase partitioning used against H2O to remove polar molecules e Next use silica gel chromatography or thin layer chromatography III How and why do amphipathic lipids self assemble in water a Membrane formation is due to their amphipathic nature of the molecules b Compose a lipid bilayer due to the hydrophobic effect c The hydrocarbon tails are hydrophobic and thus release their water molecules to form the core of the lipid bilayer away from water IV Bilayer fluidity and transition temperatures what influences them a Shorter chains and double bonds allow bilayers to be more fluid and also is what determines the transition temperatures b Longer chains have more van der Waals forces and thus are more rigid c Double bounds interfere with the highly ordered packing of fatty acid chains and thus the transition temperature is lower V Lateral mobility of lipids and how to measure it a Lipids and many membrane proteins are constantly in motion lateral diffusion b Visualized with fluorescence microscopy and the technique of fluorescence recovery after photobleaching VI Lipid distributions a between leaflets of bilayers how is membrane asymmetry established i membrane is established due to the length of time very slow that it takes a phospholipid molecule to flip flop ii asymmetry influences membrane function b in membranes from different organelles i nuclear membrane 49 phosphatidylcholine ii golgi apparatus 42 phosphatidylcholine iii mitochondria 38 phosphatidylcholine 34 phosphatidylethanolamine iv lsyosomes 27 phosphatidylcholine 33 cholesterol v plasma membrane 28 phosphatidylcholine 28 cholesterol Lecture 9 February 19 I Know the ways in which proteins can be associated with membranes a a helical transmembrane segments and their features i integral membrane proteins ii hydrophobic iii can be released only when the membrane is physically disrupted iv helix of 20 25 amino acids would span the bilayer b Types of lipid anchors their membrane sidedness i Cytoplasmic face of membranes 1 Thioester linked 16 0 palmitate 2 Amide linked 14 0 myristate at N terminus 3 Thioether linked 15 or 20 carbon isoprenoid on C terminal Cys ii Extracytoplasmic face 1 Glycosylphosphatidylinositol GPI or glycolipid anchored protein iii Palmitoylation is reversible II What are hydropathy plots and can you interpret them a Give each amino acid side chain a score according to its relative hydrophobicity b Sum the hydrophobicity score for successive segments of peptide c Plot hydropathy index vs amino acid residue number d Plots with high hydropathy indexes indicates transmembrane proteins due to their hydrophobicity III What are amphipathic helices and what kinds of protein have them amphipathic helices polar amino acid residues are spaced in the 1 sequence such that they end up distributed on one face of the a helix with non polar aa on the other side often form bundles and seen in transport proteins a Why are membranes impermeable to most substances i Due to the hydrophobic environment in the middle of the membrane ii The need to remove a coordination shell of water molecules creates the barrier b What determines rates of passage of ions and molecules across a membrane i The concentration gradient of the molecule across the membrane ii The molecule s solubility in the hydrophobic environment of the membrane IV What is meant by simple diffusion facilitated diffusion active transport a Simple diffusion easily pass through a membrane because they move from an area of high concentration to an area with low concentration also not phased by the hydrophobicity of the lipid bilayer b Facilitated diffusion passive transport diffusion across the membrane is facilitated by the channel that is formed by membrane proteins the energy driving the ion movement originates in the ion gradient itself without any contribution by the transport system c Active transport protein pumps embedded in the membrane are capable of using an energy source to move the molecule up a concentration gradient and therefore will create a gradient d How can you tell a transport process is carrier mediated i Saturable once all transport proteins are working and saturated with solute transport rate won t go any faster ii If no energy facilitated diffusion iii If energy required active transport V What are the general features of a membrane transport protein a Multispanning with amphipathic