The Structure and Function of Macromolecules

II. Classes of Organic Molecules: What are the four classes of organic molecules? Carbohydrates Lipids Proteins Nucleic Acids

A. Carbohydrates Sugars Carbo = carbon, hydrate = water; carbohydrates have the molecular formula (CH 2 O) n Functions: Store energy in chemical bonds Glucose is the most common monosaccharide Glucose is produced by photosynthetic autotrophs

1. Structure of Monosaccharides An OH group is attached to each carbon except one, which is double bonded to an oxygen (carbonyl).

Classified according to the size of their carbon chains, varies from 3 to 7 carbons. Triose = 3 carbonsPentose = 5 carbonsHexose = 6 carbons

In aqueous solutions many monosaccharides form rings:

2. Structure of Disaccharides Double sugar that consists of 2 monosaccharides, joined by a glycosidic linkage. What reaction forms the glycosidic linkage? Condensation synthesis

Examples of Disaccharides: Lactose = glucose + galactoseSucrose = glucose + fructose

3. Polysaccharides Structure: Polymers of a few hundred or a few thousand monosaccharides. Functions: energy storage molecules or for structural support:

Starch is a plant storage from of energy, easily hydrolyzed to glucose units Cellulose is a fiber-like structural material - tough and insoluble - used in plant cell walls Glycogen is a highly branched chain used by animals to store energy in muscles and the liver. Chitin is a polysaccharide used as a structural material in arthropod exoskeleton and fungal cell walls.

B. Lipids Structure: Greasy or oily nonpolar compounds Functions: Energy storage membrane structure Protecting against desiccation (drying out) Insulating against cold Absorbing shocks Regulating cell activities by hormone actions

1. Structure of Fatty Acids Long chains of mostly carbon and hydrogen atoms with a -COOH group at one end. When they are part of lipids, the fatty acids resemble long flexible tails.

Saturated and Unsaturated Fats Unsaturated fats : –liquid at room temp –one or more double bonds between carbons in the fatty acids allows for “kinks” in the tails –most plant fats Saturated fats: –have only single C-C bonds in fatty acid tails –solid at room temp –most animal fats

Saturated fatty acid Unsaturated fatty acid

2. Structure of Triglycerides Glycerol + 3 fatty acids 3 ester linkages are formed between a hydroxyl group of the glycerol and a carboxyl group of the fatty acid.

3. Phospholipids Structure: Glycerol + 2 fatty acids + phosphate group. Function: Main structural component of membranes, where they arrange in bilayers.

Phospholipids in Water

4. Waxes Function: Lipids that serve as coatings for plant parts and as animal coverings.

5. Steroids Structure: Four carbon rings with no fatty acid tails Functions: Component of animal cell membranes Modified to form sex hormones

C. Proteins Structure: Polypeptide chains Consist of peptide bonds between 20 possible amino acid monomers Have a 3 dimensional globular shape

1. Functions of Proteins Enzymes which accelerate specific chemical reactions up to 10 billion times faster than they would spontaneously occur. Structural materials, including keratin (the protein found in hair and nails) and collagen (the protein found in connective tissue).

Specific binding, such as antibodies that bind specifically to foreign substances to identify them to the body's immune system. Specific carriers, including membrane transport proteins that move substances across cell membranes, and blood proteins, such as hemoglobin, that carry oxygen, iron, and other substances through the body.

Contraction, such as actin and myosin fibers that interact in muscle tissue. Signaling, including hormones such as insulin that regulate sugar levels in blood.

2. Structure of Amino Acid Monomers Consist of an asymetric carbon covalently bonded to: Hydrogen Amino group Carboxyl (acid) group Variable R group specific to each amino acid

Properties of Amino Acids Grouped by polarity Variable R groups (side chains) confer different properties to each amino acid: polar, water soluble. non-polar, water insoluble positively charged negatively charged.

3. Primary Structure Unique sequence of amino acids in a protein Slight change in primary structure can alter function Determined by genes Condensation synthesis reactions form the peptide bonds between amino acids

4. Secondary Structure Repeated folding of protein’s polypeptide backbone stabilized by H bonds between peptide linkages in the protein’s backbone 2 types, alpha helix, beta pleated sheets

5. Tertiary Structure Irregular contortions of a protein due to bonding between R groups Weak bonds: –H bonding between polar side chains –ionic bonding between charged side chains –hydrophobic and van der Waals interactions Strong bonds: –disulfide bridges form strong covalent linkages

5. Quaternary Structure Results from interactions among 2 or more polypeptides

Factors That Determine Protein Conformation Occurs during protein synthesis within cell Depends on physical conditions of environment –pH, temperature, salinity, etc. Change in environment may lead to denaturation of protein Denatured protein is biologically inactive Can renature if primary structure is not lost

D. Nucleic Acids Two kinds: –DNA: double stranded can self replicate makes up genes which code for proteins is passed from one generation to another –RNA: single stranded functions in actual synthesis of proteins coded for by DNA is made from the DNA template molecule

1. Nucleotide Monomer Structure Both DNA and RNA are composed of nucleotide monomers. Nucleotide = 5 carbon sugar, phosphate, and nitrogenous base Deoxyribose in DNARibose in RNA

2. Building the Polymer Phosphate group of one nucleotide forms strong covalent bond with the #3 carbon of the sugar of the other nucleotide.

3. Functions of Nucleotides Monomers for Nucleic Acids Transfer chemical energy from one molecule to another (e.g. ATP)

DNA: Double helix 2 polynucleotide chains wound into the double helix Base pairing between chains with H bonds A - T C - G

Summary of the Organic Molecules: