MCB 450 1st EditionExam # 2 Study Guide Lectures: 8 - 14Lecture 8 (February 17)I. Know structure, nomenclature & properties of saturated & unsaturated FAa. Melting temperatures and what impacts themi. 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 linkagesc. Triacylglycerols as a food reservei. Fatty acids store more energy than carbohydratesii. a gram of nearly anhydrous fat stores more than six times as muchenergy as a gram of hydrated glycogeniii. glycogen and glucose provide enough energy to sustain biological function for about 18 to 24 hoursiv. triacylglycerol stores allow survival for several weeksd. 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 tailii. Fatty acids attached to a platform, a phosphate group is also attached to this platform, an alcohol group is attached to the phosphate groupe. Be able to recognize phospholipid headgroupsf. Difference between phosphoglycerides and sphingolipids?i. Phosphoglycerides - phospholipids with a glycerol backbone to which are attached two fatty acid chains and a phosphorylated alcoholii. Sphingolipids – phospholipids built on a sphingosine backbone g. Amphipathic nature of membrane lipidsi. Have a hydrophilic head and a hydrophobic tailii. This allows them to form membranesh. How does cholesterol differ from phosphoglycerides and sphingolipids?i. Cholesterol:1. The most common steroid2. A precursor to many biochemically active steroids3. 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 endII. How are lipids extracted and analyzed?a. Tissue homogenized in chloroform/methanol/waterb. Methanol/Water will separate out – polar lipids will be present in this layerc. Chloroform layer – neutral lipids will be present hered. Then phase partitioning used: against H2O to remove polar moleculese. Next use silica gel chromatography or thin-layer chromatographyIII. How and why do amphipathic lipids self-assemble in water?a. Membrane formation is due to their amphipathic nature of the moleculesb. Compose a lipid bilayer due to the hydrophobic effectc. The hydrocarbon tails are hydrophobic and thus release their water molecules to form the core of the lipid bilayer away from waterIV. Bilayer fluidity and transition temperatures & what influences thema. Shorter chains and double bonds allow bilayers to be more fluid and also is what determines the transition temperaturesb. Longer chains have more van der Waals forces and thus are more rigidc. Double bounds interfere with the highly ordered packing of fatty acid chains and thus the transition temperature is lowerV. Lateral mobility of lipids and how to measure ita. Lipids and many membrane proteins are constantly in motion – lateral diffusionb. Visualized with fluorescence microscopy and the technique of fluorescence recovery after photobleachingVI. 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-flopii. asymmetry influences membrane functionb. in membranes from different organellesi. nuclear membrane – 49% phosphatidylcholineii. golgi apparatus – 42% phosphatidylcholineiii. mitochondria – 38% phosphatidylcholine, 34% phosphatidylethanolamineiv. lsyosomes – 27% phosphatidylcholine, 33% cholesterolv. plasma membrane – 28% phosphatidylcholine, 28% cholesterolLecture 9 (February 19)I. Know the ways in which proteins can be associated with membranesa. a-helical transmembrane segments and their featuresi. integral membrane proteinsii. hydrophobiciii. can be released only when the membrane is physically disruptediv.helix of 20-25 amino acids would span the bilayerb. Types of lipid anchors & their membrane sidednessi. Cytoplasmic face of membranes1. Thioester-linked 16:0 palmitate2. Amide-linked 14:0 myristate (at N-terminus)3. Thioether-linked 15 or 20 carbon isoprenoid on C-terminal Cysii. Extracytoplasmic face1. Glycosylphosphatidylinositol (GPI) or glycolipid-anchored proteiniii. Palmitoylation is reversibleII. What are hydropathy plots and can you interpret them?a. Give each amino acid side chain a score according to its relative hydrophobicityb. Sum the hydrophobicity score for successive segments of peptidec. Plot hydropathy index vs amino acid residue numberd. Plots with high hydropathy indexes indicates transmembrane proteins due to their hydrophobicityIII. 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 proteinsa. Why are membranes impermeable to most substances?i. Due to the hydrophobic environment in the middle of the membraneii. The need to remove a coordination shell of water molecules creates the barrierb. What determines rates of passage of ions and molecules across a membrane?i. The concentration gradient of the molecule across the membraneii. The molecule’s solubility in the hydrophobic environment of the membraneIV. 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 bilayerb. 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 systemc. 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 gradientd. 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 fasterii. If no energy – facilitated