The Structure and Function of Macromolecules Chapter 5 The Structure and Function of Macromolecules Part A

Macromolecules Are large molecules composed of smaller molecules Are complex in their structures

Biological Macromolecules There are four classes of large molecules in cells: Carbohydrates Lipids Proteins Nucleic acids

Most macromolecules are polymers, built from monomers Three of the classes of life’s organic molecules are polymers Carbohydrates Proteins Nucleic acids

A polymer Is a long molecule consists of many similar or identical building blocks called monomers Monomers are linked by covalent bonds

The Synthesis and Breakdown of Polymers Monomers form larger molecules by: condensation reactions called: dehydration reactions (a) Dehydration reaction in the synthesis of a polymer HO H 1 2 3 4 H2O Short polymer Unlinked monomer Longer polymer Dehydration removes a water molecule, forming a new bond Figure 5.2A

(b) Hydrolysis of a polymer Polymers can disassemble by Hydrolysis (b) Hydrolysis of a polymer HO 1 2 3 H 4 H2O Hydrolysis adds a water molecule, breaking a bond Figure 5.2B

Carbohydrates serve as: Immediate source of food energy (fuel) Building material for other molecules (energy source) They include both: Sugars (monomers) and Sugar polymers

Carbohydrates Carbohydrates include: Monosaccharides: Disaccharides: Single or simple sugars Disaccharides: Double sugars Polysaccharides: Long chain of sugar units

Sugars Monosaccharides Are the simplest sugars Can be used for fuel (cellular) Can be converted into other organic molecules Can be combined into polymers Named according to: No. of C atoms, or Funtional group

Examples of monosaccharides Triose sugars (C3H6O3) Pentose sugars (C5H10O5) Hexose sugars (C6H12O6) H C OH H C OH HO C H H C OH C O HO C H H C O Aldoses Glyceraldehyde Ribose Glucose Galactose Dihydroxyacetone Ribulose Ketoses Fructose Figure 5.3

Monosaccharides May be linear Can form rings (in aqueous solution) 4C H C OH HO C H H C O C 1 2 3 4 5 6 OH 4C 6CH2OH 5C H OH 2 C 1C 3 C 2C 1 C CH2OH HO 3 2 (a) Linear and ring forms. Chemical equilibrium between the linear and ring structures greatly favors the formation of rings. To form the glucose ring, carbon 1 bonds to the oxygen attached to carbon 5. Figure 5.4

Disaccharides Consist of two monosaccharides A dehydration reaction Monosaccharisdes are joined by: a covalent bond, also called glycosidic linkage

Example of Disaccharides Maltose: Malt sugar Made of two glucose units Sucrose: Table sugar Made of glucose & fructose Lactose: Milk sugar Made of glucose & galactose

Examples of disaccharides Dehydration reaction in the synthesis of maltose. The bonding of two glucose units forms maltose. The glycosidic link joins the number 1 carbon of one glucose to the number 4 carbon of the second glucose. Joining the glucose monomers in a different way would result in a different disaccharide. Dehydration reaction in the synthesis of sucrose. Sucrose is a disaccharide formed from glucose and fructose. Notice that fructose, though a hexose like glucose, forms a five-sided ring. (a) (b) H HO H OH OH O CH2OH H2O 1 2 4 1– 4 glycosidic linkage 1–2 glycosidic linkage Glucose Fructose Maltose Sucrose Figure 5.5

Polysaccharides Polysaccharides Are polymers of sugars Serve many roles in organisms

Storage Polysaccharides Starch Consists entirely of glucose monomers The major storage form of glucose in plants Glycogen Consists of glucose monomers Is the major storage form of glucose in animals Stored in: Liver muscles

(a) Starch: a plant polysaccharide Chloroplast Starch Amylose Amylopectin 1 m (a) Starch: a plant polysaccharide Figure 5.6

(b) Glycogen: an animal polysaccharide Mitochondria Giycogen granules 0.5 m (b) Glycogen: an animal polysaccharide Glycogen Figure 5.6

Cellulose Is a polymer of glucose Has different glycosidic linkages than starch Indigestible by humans & simple stomach animals due to lack of cellulase enzyme Digestible by ruminant animals thru microbes (c) Cellulose: 1– 4 linkage of  glucose monomers H O CH2OH OH HO 4 C 1 (a)  and  glucose ring structures (b) Starch: 1– 4 linkage of  glucose monomers  glucose  glucose Figure 5.7 A–C

Is a major component of the tough walls that enclose plant cells Cell walls Cellulose microfibrils in a plant cell wall  Microfibril CH2OH OH O Glucose monomer Parallel cellulose molecules are held together by hydrogen bonds between hydroxyl groups attached to carbon atoms 3 and 6. About 80 cellulose molecules associate to form a microfibril, the main architectural unit of the plant cell wall. A cellulose molecule is an unbranched  glucose polymer. Cellulose molecules Figure 5.8

Cellulose is difficult to digest Cows have microbes in their stomachs to facilitate this process Figure 5.9

Lipids Lipids: Are the one class of large biological molecules They do not consist of polymers Share the common trait of being hydrophobic Include fats, phospholipid, and steroids

Fats perform essential functions in the human body: Stored form of energy Cushioning (internal organs) Insulation (skin)

(a) Dehydration reaction in the synthesis of a fat Fats Fats Are constructed from two types of smaller molecules, a single glycerol and usually three fatty acids H O H H H H H H H H H H H H H H H H O H C OH Glycerol Fatty acid (palmitic acid) HO O (a) Dehydration reaction in the synthesis of a fat Ester linkage Figure 5.11 (b) Fat molecule (triacylglycerol)

Fatty acids Vary in the: Length of their chains Number and locations of double bonds they contain

(a) Saturated fat and fatty acid Saturated fatty acids Have the maximum number of hydrogen atoms possible Have no double bonds Form fats (solid at room temp.) (a) Saturated fat and fatty acid Stearic acid Figure 5.12

(b) Unsaturated fat and fatty acid Unsaturated fatty acids Have one or more double bonds Form fat that is liquid (oils) at room temp. (b) Unsaturated fat and fatty acid cis double bond causes bending Oleic acid Figure 5.12

Phospholipids Phospholipids Have only two fatty acids (tail of the molecule) Have a phosphate group instead of a third fatty acid (head of the molecule)

(a) Structural formula (b) Space-filling model Phospholipid structure: A polar hydrophilic “head” A non polar hydrophobic “tails” CH2 O P CH C Phosphate Glycerol (a) Structural formula (b) Space-filling model Fatty acids (c) Phospholipid symbol Hydrophobic tails Hydrophilic head Hydrophobic tails – Hydrophilic head Choline + Figure 5.13 N(CH3)3

The structure of phospholipids Results in a bilayer arrangement found in cell membranes Hydrophilic head WATER Hydrophobic tail Figure 5.14

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