Organic Molecules: Lipids

1. Organic Molecules: Lipids • Hydrophobic organic molecules • More calories per gram than carbohydrates. • Four primary types: • fatty acids • triglycerides • phospholipids • steroids

2. 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.

3. 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

4. Fatty Acids • Saturated fatty acid - carbon atoms saturated with hydrogen • Unsaturated fatty acid - contains C=C bonds that could bond more hydrogen

5. Triglyceride Synthesis (1) • Three fatty acids bonded to glycerol by dehydration synthesis

6. Triglyceride Synthesis (2) • Triglycerides are called neutral fats • fatty acids bond with their carboxyl ends, therefore no longer acidic

8. 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

9. 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.

10. A Phospholipid - Lecithin

11. Phospholipids • Cluster in water as their hydrophobic tails turn away from water (micelle formation). • Major constituents of cell membranes.

12. 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

13. Cholesterol • All steroids have this 4 ringed structure with variations in the functional groups and location of double bonds

14. Cholesterol – LDL vs. HDL • LDL: “Bad” cholesterol • Low-densityLipoprotein • 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

16. Organic Molecules: Proteins • 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 • Polymer of amino acids

17. 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

18. 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

19. Dipeptide Synthesis

20. 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

21. Primary Structure of Insulin • Composed of two polypeptide chains joined by disulfide bridges • Frederick Sanger determined amino acid sequence (early 1950s).

23. 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

24. Hemoglobin

25. Caused by one different amino acid in hemoglobin Genetic Pain in joints No cure at present Strangely Sickle Cell raises resistance to Malaria Sickle Cell Anemia

26. 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

27. 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

28. Enzymes and Activation Energy

29. 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

30. Enzymatic Reaction Steps

31. Metabolic Pathways • Chain of reactions, each catalyzed by an enzyme •    A  B  C  D • 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

32. 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

33. 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

34. 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.

35. 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

36. Nucleic acids are made from nucleotides Each nucleotide consists of: • A five carbon sugar;

37. 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

38. 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 sugar- phosphate backbone.

39. 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.

40. Model of DNA

41. DNA and RNA