Chapter 5 The Molecules of

Life

5.1 Carbon is the main ingredient of organic

molecules.• Life without carbon would be as unlikely as life

without water. Other than water, most molecules of a cell are carbon-based. These “biochemicals” are composed of a carbon backbone of carbon atoms bonded to one another. Atoms of other elements may branch off this carbon backbone.

Why are carbon atoms so common in living

things?• Carbon has only 4 electrons in its highest energy

level.

• The energy level can hold 8 electrons.

• So carbon can form up to 4 bonds with other atoms.

• Carbon can form bonds with one or more other carbon atoms, producing an endless variety of carbon skeletons.

• Organic molecules: • Carbon based molecules.

• Inorganic molecules:• Non based carbon molecules.• Ex. Water H20, Oxygen 02, and Ammonia NH3

• A group of atoms within a molecule that interacts in predictable ways with other molecules is called a functional group.

• The carbon skeleton and the attached functional groups determine the properties of an organic molecule.

Functional Group• Ex. Hydroxyl groups are hydrophilic.

• These molecules tend to become surrounded by water molecules in an aqueous environment.

Monomers and Polymers

• Biomolecules may be composed of hundreds or millions of atoms. The large molecules are built from many smaller molecules.

• The small molecules are called monomers. • Long chains of combined monomers create

polymers.

Building Polymer Chains

• Building up:

• Each time a monomer is added to a chain, a water molecule is released.

Breaking Polymer Chains

• We eat many molecules in our food that are polymers.

• We must break them down to make energy for our cells.

• Cells will break the bonds between monomers by adding water to them. This is called a hydrolysis reaction. Hydro= water lysis=break down

Hydrolysis Reaction

Summary• Water is removed to build a polymer.

• Monomer + Monomer - Water = Polymer

• Water is added to break down a polymer.

• Polymer + Water = Monomer + Monomer

Macromolecules• There are four macromolecules

• Carbohydrates

• Lipids

• Proteins

• Nucleic Acids

• Imagine you are preparing for a big race or sport event.

• What does your body need to give you energy?

• Carbohydrates

• What should you eat?• Pasta

5.2 Carbohydrates• Carbohydrates is an organic compound made up of

sugar molecules.

• Sugars are made of • 1 carbon• 2 hydrogen's• 1 oxygen

All carbohydrates end with –ose Ex. Glucose

• Monosaccharide: • Mono= one• Simple sugars containing one sugar unit.

• Ex. Glucose, fructose, and galactose.

• Glucose is the main fuel supply for cells. It is much like a car engine burning gasoline.

• Cells break down glucose molecules and use it for energy.

• Disaccharides:• Di= two • Double sugar.

• Ex. Sucrose

• Glucose (monomer) + Fructose (monomer) = Sucrose (polymer)

• Sucrose can be found in plants specifically in sap.

• Polysaccharides:• Poly= many• These are your complex carbohydrates.

• Ex. Starch

Animal Cells• Animal cells do not contain starch.

• Animals store excess sugar in the form of a polysaccharide called glycogen.

• When the body needs energy, it breaks down glycogen to release glucose.

Plant Cells• Polysaccharide in plant cells use cellulose to

serve as building materials.

• Cellulose is used to protect cells and stiffen the plant.

• They form cable like fibers.

• Most animals cannot digest cellulose because we lack the molecule that breaks the bonds between glucose monomers in cellulose.

• Cellulose is commonly referred to as “fiber”

• Fiber passes through our body unchanged.

• Helps keep our digestive track healthy.

5.3 Lipids• Why do you have to shake well before using a

bottle of salad dressing?

• The oil is a lipid and lipids do not mix well with water. Lipids are hydrophobic.

• When salad dressing bottle sits the oil and vinegar separates.

Types of Lipids• Fats:• Consists of a three carbon backbone called

glycerol attached to three fatty acids.

• Fat is used for storing energy and providing insulation for your body.

Types of Fats• Saturated fat: ( bad fat)• Contain the maximum possible number of

hydrogen atoms. • Solid at room temperature.• Ex. Lard, butter.

• Unsaturated fat:• Contains less than the maximum number of

hydrogen bonds. • Ex. Olive oil, vegetable oil.

Steroids• Steroid:• Lipid molecule which the carbon skeleton forms

four fused rings.

• Circulate our body as chemical signals.

Ex. Estrogen, testosterone.

5.4 Proteins • Proteins:• Polymer constructed from a set of 20 kinds of

monomers called amino acids.

• Are responsible for almost all of the day to day functioning in organisms.

• Function:• Form structures such as hair and fingernails.• Defend body from microorganisms.• Acts as signals.

• Amino acid:• Monomer consists of a central carbon atom

bonded to four partners.

• Will always have an Amino group, Carboxyl group, and a varying side group.

Building a Protein• Cells create proteins by linking amino acids

together into a chain called a polypeptide.

• Body can make a variety of proteins by arranging different amino acids in different orders.

• Each unique order makes unique proteins

Protein Shape• A protein in the simple form of amino acids linked

together cannot function properly.

• Compare a long strand of yarn and a finished sweater.

• A sweater is not bundled yarn but yarn that is carefully knitted into a particular shape.

• Likewise, proteins consists of one or more polypeptides precisely twisted, folded, and coiled in a unique shape.

• An unfavorable change in temperature, pH, or some other quality of the environment can cause a protein to unravel and lose its shape. This is called

• denaturation.

• When you fry an egg, the egg white changed from a clear liquid to solid white during cooking because heat denatures egg proteins.

5.5 Enzymes• To start a chemical reaction, it is first necessary to

weaken chemical bonds in the reactant molecules.

• The activation process requires that the molecules absorb energy.

• To burn a candle you need to provide initial energy with a match.

• This start up energy is called activation energy. • Activation energy:• Activates the reactants and triggers a chemical

reaction.

• Cellular reactions depend on the assistance of catalysts.

• Catalyst:• Compounds that speed up chemical reactions.

• The main catalysts of chemical reactions in organisms are specialized proteins called enzymes.

• Enzymes lower the activation energy to the reacting molecules.

How Enzymes Work• The shape of an enzyme fits the shape of only

particular reactant molecules. A specific reactant acted upon by an enzyme is called the substrate.

• The substrate fits into a particular region of the enzyme called the active site.

• Once connected the reactions occurs.