Lipids

1. Lipids • Hydrophobic molecules • Carbons bound to hydrogens are not polar • Most often found as fatty-acid • Carboxyl group at one end • Carbon/hydrogen chain • Chain may be saturated or unsaturated • Saturated means that each carbon (except the carboxyl carbon) is bound to the maximum number of hydrogen atoms

2. Fats • Used primarily as a long term method of energy storage • Animal fats tend to contain saturated lipids • Plant fats contain unsaturated fat • Saturated fats are linear molecules and thus able to pack in more tightly and are solid at room temp • Unsaturated fats have angles and do not pack in tightly. They are liquid at room temp. • Fats that are liquid at room temp are called oils

3. Fig. 5-12 Structural formula of a saturated fat molecule Stearic acid, a saturated fatty acid (a) Saturated fat Structural formula of an unsaturated fat molecule Oleic acid, an unsaturated fatty acid cis double bond causes bending (b) Unsaturated fat

4. Structure of fats • Three fatty acid chains bound to a glycerol backbone • Also called triaclyglycerol • Formed by dehydration reaction • Fatty acids are bound to glycerol by ester linkage

5. Phospholipids • Major component of cell membranes • Contain hydrophilic domain that contains phosphate (and other hydrophilic structure) • Contains hydrophobic domain of lipid chains

6. Amphipathic Molecules • Contain both hydrophobic and hydrophilic domains • Tend to aggregate with hydrophobic domains turned together and hydrophilic domais turned outward • Can for bilayers or micelle structures • Bilayers are essential for membrane structure

7. Fig. 5-14 Hydrophilic head WATER Hydrophobic tail WATER

8. Hormones • Derived from cholesterol molecules • Used as global regulators in biology • Send signals to distant cells to affect behavior • Are complicated ring structures • Are essential for homeostasis

9. Lipids Summary • Non-polar molecules that are hydrophobic • Typically found as fatty acids • Contain carboxyl group at end of a hydrocarbon chain • Can be saturated or unsaturated • Are used for long-term energy storage • Phospholipids are amphipathic molecules that are essential for membrane structure • Are the basis for hormone structure

10. Protein Functions • Most versatile of the macromolecules • Structural: collagen, keratin, silk, tubulin • Storage: casein, ovalbumin • Transport: hemoglobin • Hormones: insulin • Receptor: ASGPR • Contractile: actin • Defensive: antibodies • Enzymatic:lysozyme and many others

11. Monomeric subunit of polypeptides Have amino group and carboxyl group 20 natural amino acids Each has different R group Differences in R group makes amino acids react differently Amino acids

12. Functional Groups of Amino Acids • Based on the chemical properties of the R side group • Nonpolar (hydrophobic):glycine, alanine, valine, leucine, isoleucine, methionine, phenylalanine, tryptophan and proline • Polar (hydrophilic): serine, threonine, cysteine, tyrosine, asparagine and glutamine • Electrically charged: • Acidic: aspartic acid, glutamic acid • Basic: lysine, arginine and histidines

13. Synthesis of Polypeptides • Polypeptide is synthesized by dehydration reaction • Chain grows from amino terminus to carboxy terminus • Chain has a repetitive backbone with variable side groups • R groups frequently interact with others

14. Fig. 5-18 Peptide bond (a) Side chains Peptide bond Backbone Amino end (N-terminus) Carboxyl end (C-terminus) (b)

15. Four Levels of Protein Structure • Biological activity of protein is determined by these levels • Primary structure is the sequence of amino acids in a polypeptide (Usually read N-C) • Secondary structures are localized folds or helices that form within a region of a polypeptide • Tertiary structures are larger folding events that are stabilized by interactions between R groups • Quaternary structure is the interaction of multiple polypeptides within one active proteins

16. Primary Structure • Sequence of amino acids within a single polypeptide • Are often similar among proteins of similar function • Usually written from amino terminus to carboxy terminus • Can also provide some insight into additional structures by the position of particular groups of amino acids

17. Secondary Structure • Localized within regions of polypeptide • Stabilized by hydrogen bonding • a helix-stabilized by frequent polar groups • Right handed helices • b-pleated sheets are formed by consecutive polar groups on two regions of polypeptide

18. Tertiary Structure • Large folding events that are stabilized by interactions between amino acids • Hydrophobic interactions • Nonpolar regions generally internalize in structure • Disulfide bridge • Very stable bond formed between two distant cysteine residues • Ionic interactions • Strong bond between oppositely charged side groups -Hydrogen bonds form between polar groups

19. Quaternary Structure • Only seen in compound proteins • Interactions are maintained between polypeptide chains by bonds similar to tertiary structure • Function is often unique to quaternary structure • Individual components are unable to accomplish task alone

20. Protein Structure Revisited

21. Protein Conformation • The 3D structure in which the protein is biologically active is called the active conformation • Denatured protein has lost its active conformation • Shape of a protein is consistent under identical conditions • Proteins will attempt to find the lowest energy form under conditions • Conditions that affect conformation • Solvent (polar versus non-polar),pH, temperature and chemical agents (2-mercaptoethanol)

22. Protein summary • Very important biological macromolecules that perform a wide array of functions • Polymers of amino acids • 20 natural amino acids that have distinct R side groups • The side groups determines the shape and function of a polypeptide • There are four levels of structural organization of proteins