3 Biological Molecules 1

Chapter 3 At a Glance 3.1 Why Is Carbon So Important in Biological Molecules? 3.2 How Are Organic Molecules Synthesized? 3.3 What Are Carbohydrates? 3.4 What Are Lipids? 3.5 What Are Proteins? 3.6 What Are Nucleotides and Nucleic Acids?

OH H HO CH2OH O Carbohydrates energy molecules

Carbohydrates are composed of C, H, O (CH2O)x C6H12O6 Function: fast energy u energy storage raw materials u structural materials Monomer: sugars ex: sugars, starches, cellulose (CH2O)x C6H12O6 carb = carbon hydr = hydrogen ate = oxygen compound sugar

Sugars 6 5 3 Most names for sugars end in -ose Classified by number of carbons 6C = hexose (glucose) 5C = pentose (ribose) 3C = triose (glyceraldehyde) Glyceraldehyde H OH O C H OH HO O Ribose CH2OH OH H HO CH2OH O Glucose 6 5 3

3.3 What Are Carbohydrates? Carbohydrate molecules are composed of C, H, and O in the ratio of 1:2:1 If a carbohydrate consists of just one sugar molecule, it is a monosaccharide Two linked monosaccharides form a disaccharide A polymer of many monosaccharides is a polysaccharide Carbohydrates are important energy sources for most organisms Most small carbohydrates are water-soluble due to the polar OH functional group

3.3 What Are Carbohydrates? There are several monosaccharides with slightly different structures The basic monosaccharide structure is a backbone of 3–7 carbon atoms Most of the carbon atoms have both a hydrogen (-H) and a hydroxyl group (-OH) attached to them Most carbohydrates have the approximate chemical formula (CH2O)n where “n” is the number of carbons in the backbone When dissolved in the cytoplasmic fluid of a cell, the carbon backbone usually forms a ring

3.3 What Are Carbohydrates? There are several monosaccharides with slightly different structures (continued) Glucose (C6H12O6) is the most common monosaccharide in living organisms

Figure 3-5 Depictions of glucose structure 6 5 4 3 2 1 Chemical formula Linear, ball and stick 6 6 5 5 4 1 4 1 3 3 2 2 Ring, ball and stick Ring, simplified 9

Figure 3-4 Sugar dissolving in water hydrogen bond hydroxyl group 10

ACTIVITY Build GLUCOSE C6 H12 O6 BUILD RIBOSE C5 H10 O5

USE DEHYDRATION SYNTHESIS TO BUILD A DISACCHARIDE RELEASE THE ENERGY OF THE SUGAR BY BREAKING THE BOND USING HYDROLYSIS

3.3 What Are Carbohydrates? There are several monosaccharides with slightly different structures (continued) Additional monosaccharides are Fructose (“fruit sugar” found in fruits, corn syrup, and honey) Galactose (“milk sugar” found in lactose) Ribose and deoxyribose (found in RNA and DNA, respectively)

Table 3-1 14

Carbon atoms can attach to functional groups - determine characteristics and reactivity of molecule functional groups- are more reactive than carbon backbone because they are less stable carboxyl

Figure 3-6 Some six-carbon monosaccharides 5 5 2 4 1 4 3 3 1 2 fructose galactose 16

Figure 3-7 Some five-carbon monosaccharides 5 5 4 1 4 1 3 2 3 2 Note “missing” oxygen atom Missing functional Group- hydroxyl ribose deoxyribose 17

3.3 What Are Carbohydrates? Disaccharides consist of two monosaccharides linked by dehydration synthesis The fate of monosaccharides inside a cell can be Some are broken down to free their chemical energy Some are linked together by dehydration synthesis

3.3 What Are Carbohydrates? Disaccharides consist of two monosaccharides linked by dehydration synthesis (continued) Disaccharides are two-part sugars They are used for short-term energy storage When energy is required, they are broken apart into their monosaccharide subunits by hydrolysis

Figure 3-8 Synthesis of a disaccharide glucose fructose sucrose dehydration synthesis 20

3.3 What Are Carbohydrates? Disaccharides consist of two monosaccharides linked by dehydration synthesis (continued) Examples of disaccharides include Sucrose (table sugar)  glucose  fructose Lactose (milk sugar)  glucose  galactose Maltose (malt sugar)  glucose  glucose

Simple & complex sugars OH H HO CH2OH O Glucose Monosaccharides simple 1 monomer sugars glucose Disaccharides 2 monomers sucrose Polysaccharides large polymers starch

Building sugars Dehydration synthesis monosaccharides disaccharide H2O maltose | glucose | glucose | maltose glycosidic linkage

Building sugars Dehydration synthesis monosaccharides disaccharide H2O | glucose | fructose | sucrose (table sugar) sucrose = table sugar

GLUCOSE + FRUCTOSE = sucrose

3.3 What Are Carbohydrates? Polysaccharides are chains of monosaccharides Storage polysaccharides include Starch, an energy-storage molecule in plants, formed in roots and seeds Glycogen, an energy-storage molecule in animals, found in the liver and muscles Both starch and glycogen are polymers of glucose molecules

Figure 3-9 Starch structure and function starch grains Potato cells A starch molecule Detail of a starch molecule 27

3.3 What Are Carbohydrates? Polysaccharides are chains of monosaccharides (continued) Many organisms use polysaccharides as a structural material Cellulose (a polymer of glucose) is one of the most important structural polysaccharides It is found in the cell walls of plants It is indigestible for most animals due to the orientation of the bonds between glucose molecules

Animation: Carbohydrate Structure and Function

Figure 3-10 Cellulose structure and function Cellulose is a major component of wood A plant cell with a cell wall A close-up of cellulose fibers in a cell wall Hydrogen bonds cross-linking cellulose molecules bundle of cellulose molecules cellulose fiber Alternating bond configuration differs from starch Detail of a cellulose molecule 30

3.3 What Are Carbohydrates? Polysaccharides are chains of monosaccharides (continued) Chitin (a polymer of modified glucose units) is found in The outer coverings of insects, crabs, and spiders The cell walls of many fungi

Figure 3-11 Chitin structure and function 32

Polysaccharides Polymers of sugars Function: costs little energy to build easily reversible = release energy Function: energy storage starch (plants) glycogen (animals) in liver & muscles structure cellulose (plants) chitin (arthropods & fungi) Polysaccharides are polymers of hundreds to thousands of monosaccharides

Breakdown of Polysaccharides Release of energy hydrolysis Polysaccharide + H2O  Monosaccharides Starch + H2O  Glucose + Glucose + Glucose + Glucose hydrolysis

Polysaccharide diversity Molecular structure determines function in starch in cellulose isomers of glucose structure determines function…

Cellulose Most abundant organic compound on Earth herbivores have evolved a mechanism to digest cellulose most carnivores have not that’s why they eat meat to get their energy & nutrients cellulose = undigestible roughage Cross-linking between polysaccharide chains: = rigid & hard to digest The digestion of cellulose governs the life strategy of herbivores. Either you do it really well and you’re a cow or an elephant (spend a long time digesting a lot of food with a little help from some microbes & have to walk around slowly for a long time carrying a lot of food in your stomach) Or you do it inefficiently and have to supplement your diet with simple sugars, like fruit and nectar, and you’re a gorilla. But it tastes like hay! Who can live on this stuff?!

Cow Gorilla can digest cellulose well; no need to eat other sugars can’t digest cellulose well; must add another sugar source, like fruit to diet The digestion of cellulose governs the life strategy of herbivores. Either you do it really well and you’re a cow or an elephant (spend a long time digesting a lot of food with a little help from some microbes & have to walk around slowly for a long time carrying a lot of food in your stomach) Or you do it inefficiently and have to supplement your diet with simple sugars, like fruit and nectar, and you’re a gorilla. APBioTOPICS/20Biochemistry/MoviesAP/Macromolecule-Lifewire.swf

Helpful bacteria Caprophage Ruminants How can herbivores digest cellulose so well? BACTERIA live in their digestive systems & help digest cellulose-rich (grass) meals Caprophage I eat WHAT! Tell me about the rabbits, again, George! Ruminants