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 (CH2O)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 carbons Pentose = 5 carbons Hexose = 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 + galactose Sucrose = 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 DNA Ribose 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: