Chapter 3 Molecules of Life (Sections 3.1 - 3.3)

3.2 Molecules of Life— From Structure to Function Only living things make the molecules of life—complex carbohydrates and lipids, proteins, and nucleic acids All of these molecules are organic organic Type of compound that consists primarily of carbon and hydrogen atoms

Carbon and Hydrocarbons Carbon chains or rings form the backbone of molecules of life An organic molecule that consists only of hydrogen and carbon atoms is a hydrocarbon hydrocarbon Compound or region of one that consists only of carbon and hydrogen atoms

Modeling an Organic Molecule

Functional Groups Most molecules of life have at least one functional group functional group A group of atoms bonded to a carbon of an organic compound Gives a specific chemical property such as polarity or acidity. The following table gives examples of functional groups. One example is a phosphate group, found on DNA and the energy molecule, ATP.

Common Functional Groups Figure 3.3 Common functional groups. Such groups impart specific chemical characteristics to organic compounds. Stepped Art Fig. 3.3, p. 38

What Cells Do Metabolic activities (mediated by enzymes) help cells stay alive, grow, and reproduce metabolism All enzyme-mediated chemical reactions by which cells acquire and use energy as they build and break down organic molecules

Building and Breaking Down Condensation reactions build polymers from monomers of simple sugars, fatty acids, amino acids, and nucleotides Hydrolysis reactions release monomers by breaking apart polymers monomers Molecules that are subunits of polymers polymer Molecule that consists of multiple monomers

Condensation Builds a large molecule from smaller ones Enzyme removes –OH group from one molecule and -H atom from another Covalent bond forms between two molecules – water also forms Figure 3.4 Two common metabolic processes by which cells build and break down organic molecules.

Hydrolysis Splits a large molecule into smaller ones by a water-requiring reaction Enzyme attaches –OH group and -H atom from water at cleavage site

Hydrolysis A Condensation. Cells build a large molecule from smaller ones by this reaction. An enzyme removes a hydroxyl group from one molecule and a hydrogen atom from another. A covalent bond forms between the two molecules, and water also forms. B Hydrolysis. Cells split a large molecule into smaller ones by this water-requiring reaction. An enzyme attaches a hydroxyl group and a hydrogen atom (both from water) at the cleavage site. Figure 3.4 Two common metabolic processes by which cells build and break down organic molecules. Stepped Art Fig. 3.4, p. 39

Animation: Condensation and hydrolysis To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

Key Concepts Structure Dictates Function We define cells partly by their capacity to build complex carbohydrates and lipids, proteins, and nucleic acids All of these organic compounds have functional groups attached to a backbone of carbon atoms

3.3 Carbohydrates Enzymes assemble complex carbohydrates such as cellulose, glycogen, and starch from simple carbohydrate (sugar) subunits Cells use carbohydrates for energy, and as structural materials carbohydrate Molecule that consists primarily of carbon, hydrogen, and oxygen atoms in a 1:2:1 ratio

Simple Sugars Monosaccharides (one sugar unit) are the simplest type of carbohydrate Components of the nucleic acids DNA and RNA have five carbon atoms Glucose has six

Short-Chain Carbohydrates Disaccharides consist of two sugar monomers Lactose (glucose + galactose) Sucrose (glucose + fructose)

Synthesis of a Sucrose Molecule Sucrose (common table sugar) is synthesized from monomers of glucose and fructose in a condensation reaction Figure 3.5 The synthesis of a sucrose molecule is an example of a condensation reaction. You are already familiar with sucrose—it is common table sugar.

Complex Carbohydrates Polysaccharides, are straight or branched chains of many sugar monomers—often hundreds or thousands Common polysaccharides: cellulose, glycogen, and starch All consist of glucose monomers Each has different chemical properties due to different patterns of covalent bonds that link glucose monomers

Cellulose Tough structural component of plants Chains of glucose units stretch side by side and hydrogen bond at many -OH groups Hydrogen bonds stabilize chains in tight bundles of long fibers

Starch (the Amylose part) Main energy reserve in plants, which store it in roots, stems, leaves, fruits, and seeds In amylose, a series of glucose units form a coiled chain

Glycogen In humans and other animals, glycogen stored in muscles and liver functions as an energy reservoir

Chitin Monomers are glucose with nitrogen-containing carbonyl group Long, unbranching chains linked by hydrogen bonds. Strengthens hard parts of many small animals, such as crabs Figure 3.7 Chitin. This polysaccharide strengthens the hard parts of many small animals, such as crabs.

Key Concepts Carbohydrates Carbohydrates are the most abundant biological molecules They function as energy reservoirs and structural materials Different types of carbohydrates are built from the same sugars, bonded in different patterns