1. The Macromolecules of the Cell Proteins Nucleic Acids Polysaccharides Lipids 

2. Proteins The monomers are amino acids The polymers are polypeptides and proteins Several kinds of bonds and interactions are important in protein folding and stability Protein structure depends on amino acid sequence and interaction

3. Several kinds of bonds and interactions are important in protein folding and stability Disulfide bond Hydrogen bond Ionic bonds Van der Waals interactions (force) Hydrophobic interaction

4. Primary (1°) structure Specific linear sequence of amino acids in chain; all levels of structure are ultimately determined by the primary level –Amino acid sequence contains mostinformation needed to specify protein 3D shape & thus its function; changes in sequence resulting from mutation may not be readily tolerated –first was protein hormone insulin determined by Sanger & coworkers, Cambridge, early 1950s

5. Secondary (2°) structure Form hydrogen bond between imino group (-NH- ： 亞硝酸胺 ) and carbonyl group (-CO-) α-helix - backbone assumes form of cylindrical, twisting spiral; backbone inside helix, R groups project outwards –Seen in X-ray diffraction patterns of actual proteins in 1950s β-pleated sheet- consists of several polypeptide segments lying side-by-side; the backbone of each segment of polypeptide adopts a folded or pleated conformation

6. Tertiary Structure Tertiary (3°) structure is the conformation of entire protein; results from (intramolecular) noncovalent interactions between R groups –X-ray crystallography –NMR spectroscopy– 3D structure of small proteins (<30 kDa) –Most proteins have both α-helix & β-pleated sheet; triosephosphate isomerase mostly β -sheet Fibrous proteins –Collagens & elastins of connective tissue, keratins (hair, skin, fingernails), silk Globular proteins– most proteins in cell –Myoglobin - storage site for O2 in muscle tissue

7. Quaternary Structure Quaternary (4°) structure is the linking of polypeptide chains to form multisubunit functional protein via intermolecular R group interactions May be linked by disulfide bonds, but more often noncovalent bonds (hydrophobic, H bonds, etc.) like hydrophobic patches on complementary surfaces of neighboring polypeptides Chains may be identical or nonidentical –Protein composed of 2 identical subunits - homodimer –Protein composed of 2 nonidentical subunits - heterodimer

8. The Macromolecules of the Cell Proteins Nucleic Acids Polysaccharides Lipids 

9. The Macromolecules of the Cell Proteins Nucleic Acids Polysaccharides (Carbohydrates) Lipids 

10. Carbohydrates Carbohydrates comprise a group of substances, including simple sugars (monosaccharides) & larger molecules made from them –Serve primarily as chemical energy storehouse & durable building material for biological construction –Most have general formula (CH 2 O)n Important ones in cell metabolism have from 3 to 7 carbons (n = 3 - 7) Trioses, tetroses, pentoses, hexoses, & heptoses - 3, 4, 5, 6, & 7 carbons, respectively

11. The Macromolecules of the Cell Proteins Nucleic Acids Polysaccharides Lipids 

12. Composed principally of C, H & O - not macromolecules, but aggregate to form large complexes Triglyceride (neutral lipid, fats, triacylglycerol) - serves as lipid storage form for fuel (stored in adipocytes) Fatty acids - long, unbranched hydrocarbon chains with single carboxyl group at one end Sterols and steroids – complex & characteristic 4 ringed hydrocarbon structures (4 joined rings differ in numbers & positions of double bonds & functional groups) Phospholipids (phosphoglyceride, diacylglycerol) - glycerol + 2 fatty acids + phosphate group on third hydroxyl (often an amino group as well); highly charged at physiological pH; amphipathic

13. Lipids Fatty acids are the building blocks of several classes of lipids –Saturated and unsaturated fatty acids Triacylglycerols are storage lipids Phospholipids are important in membrane structure Glycolipids are specialized membrane components Steroids are lipids with variety of functions