Chapter 3 Molecules of Life (Sections 3.4 - 3.6)

1. Chapter 3Molecules of Life(Sections 3.4 - 3.6)

2. 3.4 Lipids • Cells use lipids as major sources of energy and as structural materials • lipid • Fatty, oily, or waxy organic compound • All are hydrophobic (nonpolar )

3. Types of Lipids • Fats and some other lipids have fatty acid tails;triglycerideshave three • Phospholipidsare the main structural component of cell membranes • Waxesare lipids that are part of water-repellent and lubricating secretions • Steroidsoccur in cell membranes, and some are remodeled into other molecules

4. Key Terms • fat • Lipid that consists of a glycerol molecule with one, two, or three fatty acid tails • triglyceride • A fat with three fatty acid tails • fatty acid • Organic compound that consists of a chain of carbon atoms with an acidic carboxyl group at one end • Carbon chain of saturated types has single bonds only; that of unsaturated types has one or more double bonds

5. Fats and Fatty Acids • Unsaturated fatty acids have one or more double bonds that limit their flexibility • These bonds are termed cis or trans, depending on the way the hydrogens are arranged around them • A cis bond kinks the tail, and a trans bond keeps it straight

6. Saturated and Unsaturated Fats • Animal fats are saturated • Tend to remain solid at room temperature because their saturated tails pack tightly together • Most vegetable oils are unsaturated • Kinked tails do not pack tightly, so unsaturated fats are typically liquid at room temperature • Partially hydrogenated vegetable oils have a trans double bond that allows them to pack tightly, like saturated fats • Solid at room temperature

7. Fatty Acids

8. carboxyl group (head) hydro carbon tail A stearic acid B linoleic acid C linolenic acid Fig. 3.8, p. 42

9. Trans and Cis

10. Phospholipids • phospholipid • Lipid with a highly polar phosphate group in its hydrophilic head, and two nonpolar, hydrophobic fatty-acid tails • Main constituent of eukaryotic cell membranes • Opposing properties of a phospholipid molecule give rise to cell membrane structure • Two layers of lipids (lipid bilayer) • Hydrophobic tails sandwiched between hydrophilic heads

11. Phospholipids and Cell Membranes • Head is hydrophilic –tails are hydrophobic • Lipid bilayer— the structural foundation of all cell membranes

12. hydrophilic head one layer of lipids one layer of lipids two hydrophobic tails Fig. 3.10, p. 42

13. Waxes • wax • Water-repellent mixture with long fatty-acid tails bonded to long-chain alcohols or carbon rings • Functions: • Covers exposed surfaces of plants • Protects and lubricates skin and hair • Honeycomb

14. Steroids • steroid • Lipid with four carbon rings and no fatty acid tails • Found in all eukaryotic cell membranes • Cholesterol, the most common steroid in animal tissue, is remodeled into many molecules: • Bile salts (which help digest fats) and vitamin D • Steroid hormones (estrogens and testosterone)

15. Estrogen and Testosterone • Estrogen and testosterone • Steroid hormones derived from cholesterol

16. Steroid Functions • Steroid hormones cause different traits to arise in males and females of many species, such as wood ducks (Aix sponsa)

17. Key Concepts • Lipids • Lipids function as energy reservoirs and as waterproofing or lubricating substances • Some are remodeled into other compounds such as vitamins • Lipids are the main structural component of all cell membranes

18. Animation: Fatty acids To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

19. Animation 2.2: Triglyceride formation To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

20. 3.5 Proteins—Diversity in Structure and Function • Structurally and functionally, proteinsare the most diverse molecules of life • The shape of a protein is the source of its function • protein • Organic compound that consists of one or more chains of amino acids (polypeptides)

21. Amino Acids • Cells make thousands of different kinds of proteins from only twenty kinds of monomers (amino acids) • amino acid • Small organic compound that is a subunit of proteins • Consists of a carboxyl group, an amine group, and a characteristic side group (R), all typically bonded to the same carbon atom

22. Amino Acids • Generalized structure of amino acids: Twenty amino acids are used in eukaryotic proteins

23. Amino Acids Stepped Art Fig. 3.12, p. 44

24. Building Proteins • Protein synthesis involves covalently bonding amino acids into a chain polypeptide linked by peptide bonds • polypeptide • Chain of amino acids linked by peptide bonds • Primary structure of a protein • peptide bond • Bond that joins the amine group of one amino acid and the carboxyl group of another in a protein

25. Polypeptide Formation • Condensation: A peptide bond forms between the carboxyl group of the methionine and the amine group of the serine • Additional amino acids are added to the carboxyl end

26. methionine serine arginine glutamine serine methionine methionine serine Polypeptide Formation Stepped Art Fig. 3.13, p. 44

27. Animation: Peptide bond formation To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

28. Protein Structure • Polypeptides (primary structure) twist into loops, sheets, and coils (secondary structure) that can pack further into functional domains (tertiary structure) • Many proteins, including most enzymes, consist of two or more polypeptides (quaternary structure) • Fibrous proteins aggregate into much larger structures

29. Primary and Secondary Structure • Primary structure (polypeptide) twists into secondary structure

30. Tertiary and Quaternary Structure • Tertiary structure forms functional domains • Hemoglobin has quaternary structure (4 globin chains)

31. Aggregate Proteins • Many proteins aggregate by thousands into much larger structures, such as keratin filaments that make up hair

32. arginine lysine glycine glycine Tertiary structure occurs when a chain’s coils and sheets fold up into a functional domain such as a barrel or pocket. In this example, the coils of a globin chain form a pocket. 3 Many proteins aggregate by the thousands into much larger structures, such as the keratin filaments that make up hair. 5 A protein’s primary structure consists of a linear sequence of amino acids (a polypeptide chain). Each type of protein has a unique primary structure. Secondary structure arises as a polypeptide chain twists into a coil (helix) or sheet held in place by hydrogen bonds between different parts of the molecule. The same patterns of secondary structure occur in many different proteins. 2 1 Some proteins have quaternary structure, in which two or more polypeptide chains associate as one molecule. Hemoglobin, shown here, consists of four globin chains (green and blue). Each globin pocket now holds a heme group (red). 4 Polypeptide Formation Stepped Art Fig. 3.14.1-4, p. 45

33. Animation: Secondary and tertiary structure To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

34. Combined Proteins • Enzymes often attach sugars or lipids to proteins • Glycoproteins allow a tissue or body to recognize its own cells • Lipoproteins carry fats and cholesterol through the bloodstream • Low-density lipoprotein (LDL) • High-density lipoprotein (HDL)

35. 3.6 Importance of Protein Structure • A protein’s structure dictates its function so, if a protein unravels (denatures), it loses its function • denature • To unravel the shape of a protein or other large biological molecule • Caused by shifts in pH or temperature, exposure to detergent or some salts that disrupt hydrogen bonds, and other molecular interactions responsible for protein shape

36. Prions • Priondiseases, are the result of misfolded proteins • Mad cow disease (bovine spongiform encephalitis, BSE) • Creutzfeldt–Jakob disease (vCJD) in humans • Scrapie in sheep • prion • Infectious protein • MisfoldedPrPC protein

37. PrPC Protein Becomes a Prion • The PrPC protein misfolds into an unknown conformation • Prions cause other PrPC proteins to misfold • Misfolded proteins aggregate into long fibers

38. Conformational change ? PrPC protein prion protein Fig. 3.16, p. 46

39. Variant Creutzfeldt–Jakob Disease • Charlene Singh: • Diagnosed in 2001 • Died in 2004 • Brain tissue shows characteristic holes and prion protein fibers radiating from several deposits

40. Key Concepts • Proteins • Structurally and functionally, proteins are the most diverse molecules of life • They include enzymes and structural materials • A protein’s function arises from and depends on its structure

41. ANIMATION: Globin and hemoglobin structure To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

42. ANIMATION: Sickle-Cell Anemia To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

43. 3.7 Nucleic Acids • Nucleotidesare small organic molecules consisting of a sugar, a phosphate group, and a nitrogen-containing base • nucleotide • Monomer of nucleic acids; has five-carbon sugar, nitrogen-containing base, and phosphate groups

44. A Nucleotide Monomer • ATP, a nucleotide monomer of RNA, and also an essential participant in many metabolic processes

45. Nucleic Acids • Nucleotides are monomers of DNA and RNA, which are nucleic acids • nucleic acid • Single- or double-stranded chain of nucleotides joined by sugar–phosphate bonds; for example, DNA, RNA

46. A Nucleic Acid • A chain of nucleotides is a nucleic acid • The sugar of one nucleotide is covalently bonded to the phosphate group of the next, forming a sugar–phosphate backbone

47. ANIMATION: Nucleotide Subunits of DNA To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

48. DNA and RNA • DNA (Deoxyribonucleic acid) • DNA encodes heritable information that guides the synthesis of RNA and proteins • Consists of two nucleotide chains twisted in a double helix • RNA (Ribonucleic acid) • RNAs interact with DNA and with one another to carry out protein synthesis

49. DNA • DNA consists of two chains of nucleotides, twisted into a double helix • Hydrogen bonding maintains the three-dimensional structure

50. Other Nucleotides • Some nucleotides have additional functions • Example: ATPenergizes many kinds of molecules by phosphate-group transfers • ATP Adenosine triphosphate • Nucleotide that consists of an adenine base, a five-carbon ribose sugar, and three phosphate groups