The Structure and Function of Large Biological Molecules

1. The Structure and Function of Large Biological Molecules Chapter 5

2. The Molecules of Life • Living things made up of 4 classes of large biological molecules (macromolecules) : 1. Carbohydrates 2. Lipids 3. Proteins 4. Nucleic acids • Molecular structure and function are linked • Unique, emergent properties

3. Macromolecules are polymers, built from monomers • polymer-long molecule of many building blocks • monomers - single unit Sucrose

4. The Diversity of Polymers • Each cell has thousands of different macromolecules • built from monomers • Macromolecules vary among cells, among species, and between species

5. Carbohydrates serve as fuel and building material • Carbohydrates= sugars and sugar polymers • Monosaccharides = single sugars • Ex. glucose (C6H12O6) • major fuel for cells • raw material for building molecules

6. Sugars often form rings (in aqueous solution) (a) Linear and ring forms (b) Abbreviated ring structure

7. Disaccharide = two sugars • Ex. lactose, sucrose, maltose

8. Polysaccharides • Polysaccharides - polymers of sugars = starch • storage and structural roles • The structure and function of a polysaccharide are determined by its sugar monomers and the positions of glycosidic linkages

9. Storage Polysaccharides • Starch • plants store starch • Glucose polymer • Glycogen • Animals store glycogen (glucose polymer) • Humans in liver and muscle cells

10. Mitochondria Chloroplast Starch Glycogen granules 0.5 µm 1 µm Glycogen Amylose Amylopectin (a) Starch: a plant polysaccharide (b) Glycogen: an animal polysaccharide Amylose - unbranched Amylopectin - branched Glycogen is more branched than starch

11. Structural Polysaccharides • Cellulose=component of tough wall of plant cells • polymer of glucose (glycosidic linkages differ from starch) • The difference is based on two ring forms for glucose:

12. Enzymes digest cellulose in some animals • Cows, termites, have symbiotic relationships with microbes that digest cellulose • In humans, cellulose is indigestible fiber Mastigophoran, anaerobic, methane

13. Chitin in the exoskeleton of arthropods and in fungi (a) (c) (b) Chitin forms the exoskeleton of arthropods. The structure of the chitin monomer. Chitin is used to make a strong and flexible surgical thread. Cicada exoskeleton

14. Lipids are hydrophobic • Lipids - fats, phospholipids, steroids Triglyceride= 3 fatty acids joined glycerol

15. Saturated fats • maximum number of H possible (no double bonds) • Solid at room T (animal fats) • Unsaturated fats • one or more double bonds • Liquid at room T (plant, fish oils) (a)

16. Coronary artery disease associated with diet rich in saturated fats

17. Hydrogenation • process of converting unsaturated fats to saturated fats by adding hydrogen • Extends shelf life, prevents oil separation • Ex. margarine, peanut butter

19. The good news: • Fats store energy (adipose cells) • Cell membranes need lipid • Lipid cushions and insulates

20. Steroids • Steroids– • Ex. estrogen, testosterone • Cholesterol • Steroid in animal cell membranes • Synthesized in the liver

21. Proteins • Proteins = more than 50% of dry mass of cells • Protein functions • structural support –collagen • pigment - melanin • transport - hemoglobin • cellular communications • movement • defense against foreign substances-antibodies

23. Enzymes • All are proteins • catalyst speeds up chemical reactions • reusable • specific to each reaction • essential to life • Heat or chemicals may denature • animation

24. Polypeptides • Polypeptides • polymers built from set of 20 amino acid building blocks • may be a few or thousands long • protein • one or more polypeptides • has a function

25. Peptide Protein

27. Protein Structure and Function • proteins consists of one or more polypeptides twisted, folded, and coiled into unique shape Groove Groove (a) (b) A ribbon model of lysozyme A space-filling model of lysozyme

28. Antibody protein Protein from flu virus • sequence of aa determines a 3D structure • structure determines function

29. Four Levels of Protein Structure 1 5 • Primary structure=unique sequence of amino acids 10 15 20 25

30. β pleated sheet • Secondary structure = coils and folds •  helix and  pleated sheet • H-bonds Example: spider silk Strong as steel Stretchy α helix

31. Tertiary structure determined by interactions between amino acids • hydrogen bonds • ionic bonds • hydrophobic interactions • disulfide bridges (covalent bonds)

32. Tertiary structure

33. α Chains • Quaternary structure two or more polypeptide chains may form one macromolecule • ex. hemoglobin • activity β Chains Hemoglobin

34. A patient with sickle cell disease

35. Denaturation of proteins • Denaturation • Loss of protein structure  biologically inactive • pH, heat, chemicals

36. The Roles of Nucleic Acids Deoxyribonucleic acid (DNA) replicates prior to cell division contains codes for proteins (genes)

37. Nucleic acids hold a code • Gene • unit of inheritance • code for protein primary structure • composed of DNA

38. The Structure of Nucleic Acids Nitrogenous bases Pyrimidines • Nucleotides G,A,T,C building blocks (monomers) • Pyrimidines (cytosine, thymine, and uracil) • Purines (adenine and guanine) Cytosine (C) Uracil (U, in RNA) Thymine (T, in DNA) Purines Adenine (A) Guanine (G) (c) Nucleoside components: nitrogenous bases

39. Nucleotides contain sugar • DNA deoxyribose • RNA ribose (ribonucleic acid) Sugars Deoxyribose (in DNA) Ribose (in RNA) (c) Nucleoside components: sugars

40. DNA Polymers Sugar phosphate backbone

41. The DNA Double Helix • A DNA molecule has 2 strands that form double helix • hydrogen bonds between: • adenine (A) thymine (T) • guanine (G) cytosine (C) • DNA replication • Before a cell divides

42. DNA, Proteins and Evolution • DNA is inherited • Cell to cell • Parent to offspring • Closely related species more similar in DNA sequence than more distantly related species • Human/human 99.1 % • Human/chimp 98.5% • Molecular biology used to assess evolutionary relatedness