THE MOLECULES OF LIFE

Organic Molecules

ORGANIC MOLECULES FOUR MAIN CATEGORIES:

carbohydrates: fuel & building material

lipids: fats & oils

proteins: perform most cell functions

nucleic acids: information storage

ORGANIC vs. INORGANIC Carbon based molecules are called organic molecules.

Non-carbon based molecules—water, oxygen, and ammonia are inorganic molecules.

Carbon

Atomic Structure of Carbon

Carbon atoms can form four bonds

Connecting point for other atoms in four directions

Can produce endless variety of carbon skeletons that can bond with carbon or with other elements

CARBON BACKBONES Types of carbon backbones:

- straight chain

- branched chain

- can form double bonds

- can form ring structures

CARBON SKELETONS

FUNCTIONAL GROUPS Group of atoms within molecules—

determine properties of organic molecules

React in predictable ways with other molecules

Hydrophilic molecules: molecules that are attracted water

Hydrophobic molecules: molecules that do not mix with water

FUNCTIONAL GROUPS 4 most common functional groups:

1) hydroxyl group: (OH)

2) carbonyl group: (C=O)

3) carboxyl group: (O=C-OH)

4) amino group: (H-N-H)

HYDROCARBONS Organic molecules composed only of carbon and hydrogen

Many are important fuels

Methane found in natural gas is used to heat homes.

MONOMERS & POLYMERS Most biological molecules are large and are made up of smaller subunits

Monomer: molecular subunit that is building block of a larger molecule

Polymer: long chain of monomers

DEHYDRATION REACTION Also called condensation reaction Links monomers together forming

polymers or making polymer chains longer

Water molecule is removed in forming a polymer or making it longer

Same type of reaction occurs regardless of type of monomers being linked or type of polymer produced

DEHYDRATION REACTION

HYDROLYSIS REACTION Chemical reaction where polymers

are broken down to their monomers

Large polymers must be broken down to make monomers available to cells

Hydrolysis breaks the chemical bonds in polymers by adding water molecules reverse of dehydration/condensation

HYDROLYSIS REACTION

Short polymer MonomerHydrolysis

Dehydration

Longer polymer

DEHYDRATION vs. HYDROLYSIS Summary:

Dehydration: water is removed to build a polymer

Hydrolysis: Water is added to break down a polymer

CARBOHYDRATES ARE MADE UP OF SUGAR MOLECULES

Sugars contain carbon, hydrogen, and oxygen in the following ratio:

1 carbon : 2 hydrogen : 1 oxygen

Molecular formula of any carbohydrate is a multiple of the basic formula CH2O

HOW CELLS USE SUGARS Main fuel supply for cellular work

Other uses: - Provide raw material to make other organic molecules such as fats

- Used to make energy stockpiles

- Serve as building materials

MONOSACCHARIDES Sugars that contain just one sugar unit or monomer

Carbohydrate Monomer Unit monosaccharides

Examples: - glucose - fructose - galactose

DISACCHARIDES “double sugars”

Produced in dehydration reactions from two monosaccharides

Most common disaccharide is sucrose – table sugar—formed by linking glucose and fructose molecules

DISACCHARIDE

POLYSACCHARIDES 3 common types all glucose polymers:

Starch: found in plant cells—glucose storage molecule

Glycogen: found in animal cells—glucose storage—abundant in muscle and liver cells

Cellulose: used by plant cells for building material—makes up cell walls—not digestible by humans forms “bulk” in our diet

POLYSACCHARIDES

LIPIDS Commonly known as fats and oils Are hydrophobic do not mix with water Lipid Base Unit

Glycerol

Simplest fats are triglycerides Chain of 3 fatty acids (hydrocarbon molecules)

bonded to a glycerol molecule

Lipids Are Not Polymers

Polymer: repeating monomer

Macromolecule: The lipid base unit is not a monomer

TRIGLYCERIDES

FUNCTIONS OF LIPIDS Act as a boundary—they are a major

component of cell membranes

Circulate in the body acting as chemical signals to cells—some are hormones

Used to store energy in the body

Act to cushion and insulate the body

SATURATED FATS All the carbon atoms in fatty acid chains contain only single bonds

Include animal fats such as butter

Solids at room temperature

UNSATURATED FATS Have at least one double bond between the carbon atoms in one of the fatty acid chains

Found in fruits, vegetables, fish, corn oil, olive oil, and other vegetable oils

Liquids at room temperature

SATURATED vs. UNSATURATED

STEROIDS Carbon skeleton forms four fused

rings

Classified as lipids are hydrophobic

Some act as chemical signals or hormones estrogen and testosterone

Some form structural components of cells cholesterol

EXAMPLES OF STEROIDS

CHOLESTEROL Essential molecule found in all cell membranes

Serves as base molecule from which other steroids are produced

Has bad reputation cholesterol containing substances in blood are linked to cardiovascular disease

FUNCTIONS OF PROTEINS Form structures—hair, fur, muscles

Provide long-term nutrient storage

Circulate and defend the body against microorganisms (antibodies)

Act as chemical signals—hormones

Help control chemical reactions in cells--enzymes

PROTEIN STRUCTURE Polymers formed from monomers

called amino acids

Amino acids bond together to form chains called a polypeptides

Sequence of amino acids makes each polypeptide unique

Each protein is composed of one or more polypeptides

Formation of a Peptide Bond

AMINO ACID STRUCTURE

Figure 5-12: All amino acids consist of a central carbon bonded to an amino group, a carboxyl group, and a hydrogen atom. The fourth bond is with a unique side group – called the “R” group. Differences in side groups convey different properties to each amino acid.

PROTEIN SHAPE Functional proteins consist of

precisely twisted, coiled, and shaped polypeptides

Proteins cannot function correctly if shape is altered

Sequence and types of amino acids in the polypeptides affect protein shape

Surrounding environment—usually aqueous—plays a role in protein shape

DENATURATION Denaturation: loss of normal protein shape

Changes in temperature, pH, or other environmental conditions may cause proteins to become denatured

If the protein shape is changed, protein cannot function normally

ENZYMES Provide a way for reactions to occur at cell’s normal temperature

Enzymes lower energy requirement for a chemical reactions in cells so they can occur at normal cell temperatures

Enzymes are highly selective catalysts

ACTIVATION ENERGY Activation energy: minimum energy

required to start chemical reaction

Chemical bonds in reactants must be weakened to start most reactions

Catalysts: compounds that speed up chemical reactions without getting involved in the reaction.

Activation Energy

HOW ENZYMES WORK Substrate: specific reactant acted on by an enzyme

Active site: specific region of the enzyme that the substrate fits into

Substrate binds to enzyme’s active site where the substrate undergoes a change

HOW ENZYMES WORK Shape of an enzyme fits the shape

of only specific reactant molecules

As substrate enters, active site of enzyme changes slightly to form snug attachment

Attachment weakens chemical bonds in substrate lowering activation energy required for reaction to proceed

ACTIVE SITE MODEL

HOW ENZYMES WORK Once products of chemical reaction

are released, enzyme’s active site is ready to accept another reactant molecule

Recycling is a key characteristic of enzymes—they are not “used up” catalyzing a single reaction

Nucleic Acids

Nucleic acids are molecules that store information for cellular growth and reproduction

There are two types of nucleic acids:

- deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) These are polymers consisting of long chains of monomers

called nucleotides A nucleotide consists of a nitrogenous base, a pentose sugar

and a phosphate group:

Nitrogen Bases

The nitrogen bases in nucleotides consist of two general types:

-Purines: adenine (A) and guanine (G)

-Pyrimidines: cytosine (C), thymine (T) and Uracil (U)

Phosphodiester Bond

Nucleotides are linked together in a nucleic acid by a strong covalent bond called a phosphodiester bond.

DNA and RNA