Carbohydrates Biomolecule #1

Carbohydrates Structure Compounds composed of carbon (C), hydrogen (H), and oxygen (O) are called carbohydrates. The monomer of a carbohydrate is a monosaccharide. Carb = Carbon hydro = water Carbohydrate = carbon + water general formula = CH2O; a ratio of 2 hydrogen to 1 oxygen like water H2O ribose C5H10O5 glucose C6H12O6 sucrose C12H22O11 glycogen C24H42O21 Most commonly form ring shapes but can also form straight chains.

Functions of Carbohydrates Carbohydrates are a central energy source in organisms, as well as functioning as cellular support in plants, fungi, and animals. Energy for metabolism (glucose) Short term energy storage (glycogen/starch) Structure: plants – cell wall (cellulose); animals – exoskeleton (chitin) Source of carbon for other molecules Cell surface markers – cell identification

1. Monosaccharide: Simple Sugars Examples of Carbohydrates 1. Monosaccharide: Simple Sugars Monosaccharides like glucose are the main source of energy in living things

2. Disaccharides-2 sugars 2 monosaccharides linked together by a condensation reaction Examples: Sucrose – Table Sugar glucose + fructose Lactose – Milk Sugar glucose + galactose Maltose – glucose + glucose

3. Polysaccharides: Complex Carbs Starch: Used by plants to store excess glucose (energy); Water soluble Cellulose: Used by plants as a cell wall building material (structure); Water insoluble Glycogen: Used by animals to store excess glucose (energy); Water soluble Chitin: Used by animals to create a hard outer covering; Water insoluble

 Figure 5.8 About 80 cellulose molecules associate Plant cells 0.5 m 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 and starch are both polymers of glucose, but the bonds which hold them together are different The difference in bonds creates differences in the molecules structure. Structure = Function

Cellulose is difficult to digest Animals can’t break the bonds between the glucose molecules –dietary fiber Animals that eat plants have bacteria in their stomachs that can break the bonds of cellulose- allow their hosts to digest plants Figure 5.9

Chitin, another important structural polysaccharide Is a polymer of a form of glucose with an attached functional group Is found in the exoskeleton of arthropods (a) The structure of the chitin monomer. O CH2OH OH H NH C CH3 (b) Chitin forms the exoskeleton of arthropods. This cicada is molting, shedding its old exoskeleton and emerging in adult form. (c) Chitin is used to make a strong and flexible surgical thread that decomposes after the wound or incision heals. Figure 5.10 A–C

= S T R U C E F U N C T I O

4. Other Uses for Carbohydrates Cell surface markers – carbohydrates attached to parts on the cell membrane where they act to identify the cell ABO blood groups are identified by carbohydrates on their surface