Carbon and the Molecular Diversity of Life 3 Carbon and the Molecular Diversity of Life

Concept 3.2: 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 Some molecules that serve as monomers also have other functions of their own © 2016 Pearson Education, Inc. 2

The Synthesis and Breakdown of Polymers Cells make and break down polymers by the same mechanisms A dehydration reaction occurs when two monomers bond together through the loss of a water molecule Polymers are disassembled to monomers by hydrolysis, a reaction that is essentially the reverse of the dehydration reaction These processes are facilitated by enzymes, which speed up chemical reactions © 2016 Pearson Education, Inc. 3

Animation: Polymers © 2016 Pearson Education, Inc.

(a) Dehydration reaction: synthesizing a polymer Figure 3.7 (a) Dehydration reaction: synthesizing a polymer 1 2 3 Short polymer Unlinked monomer 1 2 3 4 Longer polymer (b) Hydrolysis: breaking down a polymer Figure 3.7 The synthesis and breakdown of polymers 1 2 3 4 1 2 3 © 2016 Pearson Education, Inc.

(a) Dehydration reaction: synthesizing a polymer Figure 3.7-1 (a) Dehydration reaction: synthesizing a polymer 1 2 3 Short polymer Unlinked monomer Figure 3.7-1 The synthesis and breakdown of polymers (part 1: dehydration) 1 2 3 4 Longer polymer © 2016 Pearson Education, Inc.

(b) Hydrolysis: breaking down a polymer Figure 3.7-2 (b) Hydrolysis: breaking down a polymer 1 2 3 4 Figure 3.7-2 The synthesis and breakdown of polymers (part 2: hydrolysis) 1 2 3 © 2016 Pearson Education, Inc.

The Diversity of Polymers Each cell has thousands of different macromolecules 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 © 2016 Pearson Education, Inc. 8

Concept 3.3: Carbohydrates serve as fuel and building material Carbohydrates include sugars and the polymers of sugars The simplest carbohydrates are monosaccharides, or simple sugars Carbohydrate macromolecules are polysaccharides, polymers composed of many sugar building blocks © 2016 Pearson Education, Inc. 9

Sugars Monosaccharides have molecular formulas that are usually multiples of CH2O Glucose (C6H12O6) is the most common monosaccharide Monosaccharides are classified by the number of carbons in the carbon skeleton and the placement of the carbonyl group © 2016 Pearson Education, Inc. 10

product of glucose in cells Figure 3.8 Triose: three-carbon sugar (C3H6O3) Pentose: five-carbon sugar (C5H10O5) Glyceraldehyde An initial breakdown product of glucose in cells Ribose A component of RNA Hexoses: six-carbon sugars (C6H12O6) Figure 3.8 Examples of monosaccharides Glucose Fructose Energy sources for organisms © 2016 Pearson Education, Inc.

product of glucose in cells Figure 3.8-1 Triose: three-carbon sugar (C3H6O3) Figure 3.8-1 Examples of monosaccharides (part 1: triose) Glyceraldehyde An initial breakdown product of glucose in cells © 2016 Pearson Education, Inc.

Pentose: five-carbon sugar (C5H10O5) Figure 3.8-2 Pentose: five-carbon sugar (C5H10O5) Figure 3.8-2 Examples of monosaccharides (part 2: pentose) Ribose A component of RNA © 2016 Pearson Education, Inc.

Hexoses: six-carbon sugars (C6H12O6) Figure 3.8-3 Hexoses: six-carbon sugars (C6H12O6) Figure 3.8-3 Examples of monosaccharides (part 3: hexoses) Glucose Fructose Energy sources for organisms © 2016 Pearson Education, Inc.

Though often drawn as linear skeletons, in aqueous solutions many sugars form rings Monosaccharides serve as a major nutrients for cells and as raw material for building molecules © 2016 Pearson Education, Inc. 15

(a) Linear and ring forms Figure 3.9 (a) Linear and ring forms Figure 3.9 Linear and ring forms of glucose (b) Abbreviated ring structure © 2016 Pearson Education, Inc.

This covalent bond is called a glycosidic linkage A disaccharide is formed when a dehydration reaction joins two monosaccharides This covalent bond is called a glycosidic linkage © 2016 Pearson Education, Inc. 17

Animation: Disaccharides © 2016 Pearson Education, Inc.

Glucose Fructose Figure 3.10-s1 Figure 3.10-s1 Disaccharide synthesis (step 1) © 2016 Pearson Education, Inc.

Glucose Fructose 1– 2 glycosidic linkage Sucrose Figure 3.10-s2 Figure 3.10-s2 Disaccharide synthesis (step 2) Sucrose © 2016 Pearson Education, Inc.

Polysaccharides Polysaccharides, the polymers of sugars, have storage and structural roles The structure and function of a polysaccharide are determined by its sugar monomers and the positions of glycosidic linkages © 2016 Pearson Education, Inc. 21

Storage Polysaccharides Starch, a storage polysaccharide of plants, consists entirely of glucose monomers Plants store surplus starch as granules Most animals have enzymes that can hydrolyze plant start, making glucose available as a nutrient © 2016 Pearson Education, Inc. 22

Glycogen is a storage polysaccharide in animals Humans and other vertebrates store glycogen mainly in liver and muscle cells © 2016 Pearson Education, Inc. 23

Animation: Polysaccharides © 2016 Pearson Education, Inc.

Cellulose microfibrils in a plant cell wall Figure 3.11 Storage structures (plastids) containing starch granules in a potato tuber cell Amylose (unbranched) Amylopectin (somewhat branched) Glucose monomer 50 mm (a) Starch Muscle tissue Glycogen granules in muscle tissue Glycogen (extensively branched) Cell wall 1 mm Figure 3.11 Polysaccharides of plants and animals (b) Glycogen Cellulose microfibrils in a plant cell wall Cellulose molecule (unbranched) Plant cell, surrounded by cell wall 10 mm Microfibril Hydrogen bonds 0.5 mm (c) Cellulose © 2016 Pearson Education, Inc.

Storage structures (plastids) containing starch granules in a potato Figure 3.11-1 Storage structures (plastids) containing starch granules in a potato tuber cell Amylose (unbranched) Amylopectin (somewhat branched) Glucose monomer 50 mm Figure 3.11-1 Polysaccharides of plants and animals (part 1: starch) (a) Starch © 2016 Pearson Education, Inc.

Storage structures (plastids) containing starch granules in a potato Figure 3.11-1a Storage structures (plastids) containing starch granules in a potato tuber cell Figure 3.11-1a Polysaccharides of plants and animals (part 1a: plastids containing starch granules, micrograph) 50 mm © 2016 Pearson Education, Inc.

Glycogen granules in muscle Glycogen tissue (extensively branched) Figure 3.11-2 Glycogen granules in muscle tissue Glycogen (extensively branched) 1 mm (b) Glycogen Figure 3.11-2 Polysaccharides of plants and animals (part 2: glycogen) © 2016 Pearson Education, Inc.

Glycogen granules in muscle tissue 1 mm Figure 3.11-2a Figure 3.11-2a Polysaccharides of plants and animals (part 2a: glycogen granules, micrograph) 1 mm © 2016 Pearson Education, Inc.

Cellulose microfibrils in a plant cell wall Cellulose molecule Figure 3.11-3 Cellulose microfibrils in a plant cell wall Cellulose molecule (unbranched) Microfibril Hydrogen bonds 0.5 mm (c) Cellulose Figure 3.11-3 Polysaccharides of plants and animals (part 3: cellulose) © 2016 Pearson Education, Inc.

Cell wall Plant cell, surrounded 10 mm by cell wall Figure 3.11-3a Figure 3.11-3a Polysaccharides of plants and animals (part 3a: plant cell wall, micrograph) 10 mm © 2016 Pearson Education, Inc.

Cellulose microfibrils in a plant cell wall Figure 3.11-3b Cellulose microfibrils in a plant cell wall Figure 3.11-3b Polysaccharides of plants and animals (part 3b: cellulose microfibrils, micrograph) 0.5 mm © 2016 Pearson Education, Inc.

Structural Polysaccharides The polysaccharide cellulose is a major component of the tough wall of plant cells Like starch and glycogen, cellulose is a polymer of glucose, but the glycosidic linkages in cellulose differ The difference is based on two ring forms for glucose © 2016 Pearson Education, Inc. 33

(a)  and b glucose ring structures Figure 3.12 (a)  and b glucose ring structures  Glucose b Glucose Figure 3.12 Starch and cellulose structures (b) Starch: 1–4 linkage of  glucose monomers (c) Cellulose: 1–4 linkage of b glucose monomers © 2016 Pearson Education, Inc.

 Glucose b Glucose (a)  and b glucose ring structures Figure 3.12-1 Figure 3.12-1 Starch and cellulose structures (part 1: ring structures)  Glucose b Glucose © 2016 Pearson Education, Inc.

(b) Starch: 1–4 linkage of  glucose monomers Figure 3.12-2 Figure 3.12-2 Starch and cellulose structures (part 2: starch linkage) (b) Starch: 1–4 linkage of  glucose monomers © 2016 Pearson Education, Inc.

(c) Cellulose: 1–4 linkage of b glucose monomers Figure 3.12-3 Figure 3.12-3 Starch and cellulose structures (part 3: cellulose linkage) (c) Cellulose: 1–4 linkage of b glucose monomers © 2016 Pearson Education, Inc.

Starch (and glycogen) are largely helical In starch, the glucose monomers are arranged in the alpha () conformation Starch (and glycogen) are largely helical In cellulose, the monomers are arranged in the beta () conformation Cellulose molecules are relatively straight © 2016 Pearson Education, Inc. 38

In cellulose, some hydroxyl groups on its glucose monomers can hydrogen-bond with hydroxyl groups of other cellulose molecules Parallel cellulose molecules held together this way are grouped into microfibrils, which form strong building materials for plants © 2016 Pearson Education, Inc. 39

Some microbes use enzymes to digest cellulose Enzymes that digest starch by hydrolyzing  linkages can’t hydrolyze  linkages in cellulose Cellulose in human food passes through the digestive tract as insoluble fiber Some microbes use enzymes to digest cellulose Many herbivores, from cows to termites, have symbiotic relationships with these microbes © 2016 Pearson Education, Inc. 40

Chitin, another structural polysaccharide, is found in the exoskeleton of arthropods Chitin also provides structural support for the cell walls of many fungi © 2016 Pearson Education, Inc. 41