Lecture20.ppt

* Lipids: Fats Flipped structure Fats are esters of carboxylic acids & glycerine CH2(OH)CH2(OH)CH2(OH) * Cis- & trans- fatty acids Metabolic studies have shown that trans fats have adverse effects on blood lipid levels--increasing LDL ("bad") cholesterol while decreasing HDL ("good") cholesterol. This combined effect on the ratio of LDL to HDL cholesterol is double that of saturated fatty acids.3 Stearic acid (saturated) * Zero calorie fat: Olestra Glycerine Stearic acid Sucrose * Other Lipids: Cellular Membranes Cellular membranes are made of phospholipids. Like soaps, these molecules have an ionic/polar end and a long non-polar region. Hydrophobic: nonpolar Hydrophillic: polar * Cellular Membrane Cellular membranes are composed of a phospholipid bilayer ? with the polar side facing the aqueous environments inside and outside the cell, and the nonpolar ends comprising the inside of the bilayer. * Cellular Membrane Movement into and out of the membrane will depend on the polar/non-polar characteristics of proteins and other molecules (such as pharmaceutical drugs). Antibiotic ?Gramicidin A? is nonpolar on the outside, and polar on the inside. Disrupts ion balance to kill the bacteria. * Potassium ion channel protein * Science, December 2005, V. 310, pp 1461-1465. Cell membrane proteins Genetic Material: DNA and RNA Just as proteins can be considered polymers of amino acids, DNA and RNA are polymers of nucleotides. Nucleotide = phosphate + sugar + base phosphate sugar base phosphate sugar base phosphate sugar base DNA Nucleotide Components In DNA, the ?sugar? is deoxyribose. There are four possible bases in DNA. (A, C, G, T) DNA Polynucleotide RNA RNA has uracil base instead of thymine. RNA ?sugar? is ribose. Double Helix Complementary base pairs exist There is enough room for exactly an A-T pair or a C-G pair inside the double helix Like puzzle pieces: A-T pair can make two hydrogen bonds, C-G pair can make three. Double Helix DNA exists as a ?double helix? shape, with the two helices held together through hydrogen bonding. Due to the complementary pairing, DNA can replicated itself by separating its strands during cell division. Complementary Base Pairs (DNA) The DNA Structure Replication Replication Translation A sequence of three bases indicates specific amino acids. Example: AAA = lysine, AAC = asparagine 3-base sequences called ?codons? Converting information from nucleotide sequence to amino acid sequence in a protein is ?translation.? portion of DNA unwinds mRNA reads and codes (?transcription?) tRNA links amino acids in correct order Translation DNA base sequence ? protein amino acid sequence DNA base sequence ? protein amino acid sequence The Big Picture An important consequence of 3-D shape is specificity This is how enzymes work. We can take advantage of this idea for drug therapies. DNA and RNA are ?polymers? of nucleotides DNA and RNA make use of complementary base pairings to store and reproduce genetic information Base pairings work via intermolecular forces Viruses can invade a host cell (through protein/membrane interactions ? which are based on intermolecular forces and shape recognition) and make it reproduce the viral genetic information instead.