The Structure and Function of Large Biological Molecules

Transcription

1 Chapter 5-1 & 5-2 The Structure and Function of Large Biological Molecules PowerPoint Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Polymerization Carbohydrates Overview: The Molecules of Life All living things are made up of four classes of large biological molecules: Carbohydrates Lipids Proteins nucleic acids Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Essential Question: Overview: The Molecules of Life How do cells synthesize and break down macromolecules? Within cells, small organic molecules are joined together to form larger molecules Macromolecules are large molecules composed of thousands of covalently connected atoms Molecular structure and function are inseparable Fig. 5-1 studying the structure of macromolecules Concept 5.1: Macromolecules are polymers, built from monomers A polymer is a long molecule consisting of many similar building blocks These small building-block molecules are called monomers Three of the four classes of life s organic molecules are polymers: Carbohydrates Proteins Nucleic acids 1

2 The Synthesis and Breakdown of Polymers Fig. 5-2 HO H HO H Dehydration synthesis (also called dehydration polymerization or a condensation reaction) occurs when two monomers bond together through the loss of a water molecule The hydroxyl group of one monomer and a hydrogen atom from the other monomer are removed A covalent bond forms between the two monomers The hydroxyl group and the hydrogen atom bond to produce a water molecule (dehydration) Short polymer Unlinked monomer Dehydration removes a water molecule, forming a new bond H 2O HO H Longer polymer Dehydration reaction in the synthesis of a polymer Condensation Polymerization Loss of water, formation of larger molecules Loss of water/ formation of larger molecules A-OH + H-B A-B + H 2 O The Synthesis and Breakdown of Polymers Fig. 5-2 HO H Enzymes are macromolecules that speed up the dehydration process Hydrolysis adds a water molecule, breaking a bond H 2O Polymers are broken down into monomers by hydrolysis, a reaction that is essentially the reverse of the dehydration reaction Water is split (hydro = water/ lysis = to split) by enzymes The covalent bond between the monomers is broken A hydroxyl group from water is added to one monomer and a hydrogen atom is added to the other Occurs during digestion HO H HO Hydrolysis of a polymer Hydrolysis Gain of water, breakdown of molecules into smaller units A-B + H 2 O H A-OH + H-B The name of the bond formed varies depending on which atoms wind up bonded together MONOMERS POLYMERS BOND Monosaccharides Glycerol, fatty acids Amino acids Nucleotides Polysaccharides (carbohydrates) Triglycerides (a type of lipid) Peptide chains (proteins) Nucleic acids (DNA & RNA) Animation: Polymers Glycosidic linkage Ester bonds Peptide bond Phosphodiester linkage Ester bonds join fatty acids to glycerol The bonding of a hydroxyl group to a carbon with a carbonyl Glycosidic linkage bonds two sugar monomers together Peptide bond the nitrogen of one amino acid is bonded to the carbon of the next amino acid to form polypeptides Sugar-phosphate bond the sugar of one nucleotide is bonded to the phosphate of another nucleotide to form nucleic acids 2

3 The Diversity of Polymers Each cell has thousands of different kinds of macromolecules 2 3 H HO Macromolecules vary among cells of an organism, vary more within a species, and vary even more between species An immense variety of polymers can be built from a small set of monomers Concept check 1. What are the four main classes of large biological molecules? 2. How many molecules of water are needed to completely hydrolyze a polymer that is ten monomers long? 3. Suppose you eat a serving of green beans. What reactions must occur for the amino acid monomers in the protein of the beans to be converted to proteins in your body? 4. What is the formula for a monosaccharide that has three carbons? 5. A dehydration reaction joins two glucose molecules to form maltose. The formula for glucose is C 6 H 12 O 6. What is the formula for maltose? C 3 H 6 O 3 6. The molecular formula for glucose is C 6 H 12 O 6. What would be the molecular formula for a polymer made by linking ten glucose molecules together by dehydration reactions? C 12 H 22 O 11 C 60 H 102 O 51 Essential Question 7. Enzymes that break down DNA catalyze the hydrolysis of the covalent bonds that join nucleotides together. What would happen to DNA molecules treated with these enzymes? a) The two strands of the double helix would separate. b) The phosphodiester linkages between deoxyribose sugars would be broken. c) The purines would be separated from the deoxyribose sugars. d) The pyrimidines would be separated from the deoxyribose sugars. e) All bases would be separated from the deoxyribose sugars. How do structures of biologically important molecules (carbohydrates, lipids, proteins, nucleic acids) account for their function? 3

4 Concept 5.2: Carbohydrates serve as fuel and building material Carbohydrates include sugars and the polymers of sugars The simplest carbohydrates are monosaccharides, or single sugars have molecular formulas that are usually multiples of CH 2 O Carbohydrate macromolecules are polysaccharides, polymers composed of many sugar building blocks Include cellulose, chitin, and glycoproteins Sugars soluble in water because of hydroxyl group Monosaccharides (simple sugars) (C 6 H 12 O 6 ) is the most common monosaccharide classified by The location of the carbonyl group (as aldose or ketose) The number of carbons in the carbon skeleton Have 3-7 carbons Fig. 5-3 Fig. 5-3a Trioses (C 3 H 6 O 3 ) Pentoses (C 5 H 10 O 5 ) Hexoses (C 6 H 12 O 6 ) Trioses (C 3 H 6 O 3 ) Pentoses (C 5 H 10 O 5 ) Hexoses (C 6 H 12 O 6 ) Ketoses Aldoses Glyceraldehyde Dihydroxyacetone Ribose Galactose Aldoses Glyceraldehyde Ribose Galactose Ribulose Fructose Fig. 5-3b Trioses (C 3 H 6 O 3 ) Pentoses (C 5 H 10 O 5 ) Hexoses (C 6 H 12 O 6 ) Though often drawn as linear skeletons, in aqueous solutions many sugars form rings Ketoses Dihydroxyacetone Monosaccharides serve as a major fuel for cells and as raw material for building molecules Ribulose Fructose 4

5 Fig. 5-4 Fig. 5-4a In aqueous solutions, the most common form for sugars is the ring (a) Linear and ring forms (b) Abbreviated ring structure (a) Linear and ring forms 36% of glucose is in the Alpha form in solution the -OH on carbon 1 is down In Beta glucose, the OH on carbon 1 is up/ 64% of glucose molecules in solution are Beta glucose Fig. 5-5 A disaccharide is formed when a dehydration reaction joins two monosaccharides This covalent bond between two monosaccharides is called a glycosidic linkage 1 4 glycosidic linkage alpha alpha Maltose Plant sugar (a) Dehydration reaction in the synthesis of maltose 1 2 glycosidic linkage Animation: Disaccharides alpha beta Fructose Sucrose (b) Dehydration reaction in the synthesis of sucrose Table sugar Polysaccharides Polysaccharides, the polymers of sugars, have storage and structural roles Formed from 3 or more monosaccharides Starch, glycogen, cellulose, chitin The structure and function of a polysaccharide are determined by its sugar monomers and the positions of glycosidic linkages Storage Polysaccharides Starch consists of long chains of glucose monomers that are digestible bonding produces helical molecules Amylose unbranched chains Amylopectin branched chains a storage polysaccharide of plants Surplus starch is stored as granules within chloroplasts and other plastids 5

6 Fig. 5-6 Chloroplast Starch Storage Polysaccharides Glycogen Long chains of glucose molecules that are extensively branched Amylose 1 µm Amylopectin Note the helical structure of amylose and amylopectin molecules a storage polysaccharide in animals Humans and other vertebrates store glycogen mainly in liver (1 day s worth) and muscle cells Starch: a plant polysaccharide Note the extensive branching of the long chains Mitochondria Glycogen granules 0.5 µm Glycogen Glycogen: an animal polysaccharide Structural Polysaccharides cellulose The most abundant organic molecule a major component of the tough wall of plant cells Digested only by some bacteria and fungi (NOT by animals) Made entirely of β glucose monomers Forms straight parallel strands (microfibrils) that are linked by hydrogen bonds between hydroxyl groups and hydrogen atoms. The microfibrils then intertwine to form cellulose fibrils which are strong building materials for plants. Animation: Polysaccharides Fig. 5-7 The difference in starches and cellulose is the type of glycosidic linkages Fig. 5-8 Cell walls Cellulose microfibrils in a plant cell wall Microfibril α and β glucose ring structures 10 µm 0.5 µm β Cellulose molecules Starch: 1 4 linkage of α glucose monomers Cellulose: 1 4 linkage of β glucose monomers β monomer 6

7 Digestion Cellulose-digesting Prokaryotes are found in the rumen of this cow Structural Polysaccharides The structure of these molecules affects animals ability to digest them Enzymes that digest starch by hydrolyzing α linkages can t hydrolyze β linkages in cellulose Cellulose in human food passes through the digestive tract as insoluble fiber and functions to stimulate the production of mucus, which aids in elimination of wastes from the digestive tract. Some microbes use enzymes to digest cellulose Many herbivores, from cows to termites, have symbiotic relationships with these microbes Chitin found in the exoskeleton of arthropods, in some sponges, & in the cell walls of many fungi Amino sugar Chitin forms the exoskeleton of arthropods. Chitin is used to make a strong and flexible surgical thread. Quick Quiz Quick quiz 1. What is the formula for a monosaccharide that has three carbons? C 3 H 6 O 3 2. Which term includes all others in the list? a) Monosaccharide b) Disaccharide c) Starch d) Carbohydrate e) Polysaccharide Quick Quiz Quick quiz 3. What would happen if a cow were given antibiotics that killed all of the prokaryotes in its stomach? It would starve 4. The enzyme amylase can break glycosidic linkages between glucose monomers only if the monomers are the α form. Which of the following could amylase break down? a) Glycogen, starch, and amylopectin b) Glycogen and cellulose c) Cellulose and chitin d) Starch and chitin e) Starch, amylopectin, and cellulose 7

8 Quick Quiz 5. Which types of organisms use chitin as a structural molecule? Arthropods (in their exoskeleton) Some sponges (in their skeletons) Some fungi (in their cell walls) 8