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Organic Molecules: Lipids • Hydrophobic organic molecules • More calories per gram than carbohydrates. • Four primary types: – fatty acids – triglycerides – phospholipids – steroids Fats are macromolecules constructed from: • Glycerol, a three-carbon alcohol. • Fatty acids *Composed of a carboxyl group at one end and an attached hydrocarbon chain (“tail”). * Carboxyl group (“head”) has properties of an acid. * Hydrocarbon chain – long carbon skeleton. Non-polar C-H bonds make the chain hydrophobic and not water soluble. Fatty Acids • Chain of usually 4 to 24 carbon atoms • Carboxyl (acid) group on one end and a methyl group on the other • Polymers of two-carbon acetyl groups Fatty Acids • Saturated fatty acid - carbon atoms saturated with hydrogen • Unsaturated fatty acid - contains C=C bonds that could bond more hydrogen Triglyceride Synthesis (1) • Three fatty acids bonded to glycerol by dehydration synthesis Triglyceride Synthesis (2) • Triglycerides are called neutral fats – fatty acids bond with their carboxyl ends, therefore no longer acidic Triglycerides • Hydrolysis of fats occurs by lipase enzyme • Triglycerides at room temperature – liquids called oils, often polyunsaturated fats from plants – solids called fats, saturated fats from animals • Function - energy storage – also insulation and shock absorption for organs Phospholipids • Composed of a hydrophilic “head” attached to two fatty acids. • Third fatty acid is replaced with a negatively charged phosphate group. • Can have small variable molecules (usually polar or charged) attached to phosphate. A Phospholipid - Lecithin Phospholipids • Cluster in water as their hydrophobic tails turn away from water (micelle formation). • Major constituents of cell membranes. Steroids • Cholesterol – other steroids derive from cholesterol • cortisol, progesterone, estrogens, testosterone and bile acids – is an important component of cell membranes – produced only by animals • 85% naturally produced by our body • only 15% derived from our diet Cholesterol • All steroids have this 4 ringed structure with variations in the functional groups and location of double bonds Cholesterol – LDL vs. HDL • LDL: “Bad” cholesterol – Low-density Lipoprotein – Builds up as plaques in arteries causing heart attacks – Hydrogenated oils & trans fatty acids are sources • HDL: “Good” cholesterol – High-density Lipoprotein – Removes LDL cholesterol back to the liver Organic Molecules: Proteins • Polymer of amino acids • 20 amino acids – identical except for -R group attached to central carbon – amino acid properties determined by -R group • The amino acids in a protein determine its structure and function Amino Acids • Nonpolar -R groups are hydrophobic • Polar -R groups are hydrophilic • Proteins contain many amino acids and are often amphiphilic • -R groups determine shape of protein Peptides • A polymer of 2 or more amino acids • Named for the number of amino acids they contain – dipeptides have 2, tripeptides have 3 – oligopeptides have fewer than 10 to 15 – polypeptides have more than 15 – proteins have more than 100 • Dehydration synthesis creates a peptide bond that joins amino acids Dipeptide Synthesis Protein Structure • Primary structure – determined by amino acid sequence • Secondary structure – α helix (coiled), β-pleated sheet (folded) shapes held together by hydrogen bonds between nearby groups • Tertiary structure – interaction of large segments to each other and surrounding water • Quaternary structure – two or more separate polypeptide chains interacting Primary Structure of Insulin • Composed of two polypeptide chains joined by disulfide bridges • Frederick Sanger determined amino acid sequence (early 1950s). Conjugated Proteins • Contain a non-amino acid moiety called a prosthetic group • Hemoglobin has 4 polypeptide chains, each chain has a complex iron containing ring called a heme moiety Hemoglobin Sickle Cell Anemia • Caused by one different amino acid in hemoglobin • Genetic • Pain in joints • No cure at present • Strangely Sickle Cell raises resistance to Malaria Protein Conformation and Denaturation • Conformation - overall 3-D shape is crucial to function – important property of proteins is the ability to change their conformation • opening and closing of cell membrane pores • Denaturation – drastic conformational change that destroys protein function • occurs with extreme heat or pH • often permanent Enzymes • Function as catalysts – promote rapid reaction rates • Substrate - the substance an enzyme acts upon • Naming convention – enzymes now named for their substrate with -ase as the suffix • amylase enzyme digests starch (amylose) • Lower activation energy – energy needed to get reaction started is lowered • enzymes facilitate molecular interaction Enzymes and Activation Energy Enzyme Structure and Action • Active sites – area on enzyme that attracts and binds a substrate • Enzyme-substrate complex – temporarily changes a substrate’s conformation, promoting reactions to occur • Reusability of enzymes – enzymes are unchanged by reactions and repeat process • Enzyme-substrate specificity – active site is specific for a particular substrate • Effects of temperature and pH – change reaction rate by altering enzyme shape – optimum: temp = body temp, pH = location of enzyme Enzymatic Reaction Steps Metabolic Pathways • Chain of reactions, each catalyzed by an enzyme • ABCD – A is initial reactant, B+C are intermediates and D is the end product – , , represent enzymes • Regulation of metabolic pathways – activation or deactivation of the enzymes in a pathway regulates that pathway • end product D may inhibit or enzymes Protein Functions • Structure – collagen, keratin • Communication – some hormones, cell receptors • ligand - molecule that reversibly binds to a protein • Membrane Transport – form channels, carriers (for solute across membranes) • Catalysis – enzymes are proteins Protein Functions 2 • Recognition and protection – glycoprotein antigens, antibodies and clotting proteins • Movement – muscle contraction – cilia and flagella – spindle fibers • Cell adhesion – proteins bind cells together Nucleic Acids • The primary structure of proteins is determined by genes – hereditary units that consist of DNA, a type of nucleic acid. • There are two types of nucleic acid: 1. Deoxyribonucleic acid (DNA) *Contains coded info that programs all cell activity. *Contains directions for its own replication. *Copied and passed on from one generation to another. *In eukaryotic cells, it is found primarily in the nucleus. Nucleic Acids The second type of nucleic acid is: 2. Ribonucleic acid (RNA) *Functions in the actual synthesis of proteins coded for by DNA. *Ribosomes – sites of protein synthesis. *Messenger RNA (mRNA) – carries encoded genetic message from nucleus to cytoplasm. *Flow of genetic info: DNA →RNA →Protein Nucleic acids are made from nucleotides Each nucleotide consists of: 1. A five carbon sugar; 2. A phosphate group attached to the number 5 carbon of the sugar; and 3. A nitrogenous base at C1 *There are two families of nitrogenous bases: 1. Pyrimidines 2. Purines DNA DNA is a polymer of nucleotides joined by linkages between the phosphate of one nucleotide and the sugar of the next. Variable nitrogenous bases are added to this sugarphosphate backbone. Watson and Crick – 3D Structure of DNA (1953) • Two nucleotide chains wound as a double helix. • S-P backbones on outside of helix. • N bases paired in the interior of the helix and are held together by H-bonds. • Base-pairing rules: guanine (G)-cytosine (C) and thymine (T)-adenine (A). • Two strands of DNA are complementary – serve as templates. • Most DNA molecules are long – thousands to millions of base pairs each. Model of DNA DNA and RNA