The Chemical Basis for Life

(Bio.A.2)

Properties Of Water

• Polarity – uneven distribution of electrons between the hydrogen and oxygen atoms –Oxygen is bigger and attracts the electrons more than hydrogen

• Hydrogen bonds – slightly positive H atoms are attracted to slightly negative atoms like O

• Cohesion – H bonds allow water molecules to stick together–Surface tension

• Adhesion – H bonds allow water molecules to stick to other, polar molecules–Capillary action (ex. straws)

• High specific heat - water can absorb lots of heat energy without drastically changing its temperature

• Water stays in a liquid phase over much of the planet and therefore supports life

• Density of ice – allows ice to float• Most biological reactions require

water.

Carbon as a backbone

• Covalent bond – electrons are shared between atoms–Example H2O and CO2

• Carbon has the unique ability to make four covalent bonds

• Carbon is part of many biological molecules

COVALENT BOND #’S

• Atoms want to fill their electron shells. An atom wants to make just enough bonds to fill its shells.

• H makes one bond• O makes two bonds• C makes four bonds

Compounds

• Chemical Formulas - show how many and which atoms are in a compound – Ex. H2O

• Structural Formulas - show the arrangement of the atoms in a compound– Ex. H-O-H

• Isomers - molecules with the same chemical formula, but different structure (ex. propanol and isopropanol)

Isomers

MACROMOLECULES• Macromolecules – giant

molecules• Monomers (smaller units) join to

make polymers (macromolecules)

• The four major biological macromolecules–Carbohydrates –Lipids–Proteins –Nucleic acids

Carbohydrates• Structure

–Composed of C, H, and O with approximately twice as many H’s as O’s

–Building blocks (monomers) are sugars

• Function–Main source of energy

• Types of Carbohydrates–Monosaccharide – one sugar

• Example: glucose (C6H12O6)–Disaccharide – two sugars

joined• Example: lactose (C12H22O11)

–Polysaccharide – many sugars joined• Example: starch and fiber

Building and breaking down molecules• Dehydration synthesis - two

molecules joined together by losing a molecule of water

• Hydrolysis - larger molecules broken down into smaller molecules by the addition of water (ex. digestion)

Dehydration Synthesis

Hydrolysis

Lipids• Structure

–Composed of C, H, and O, but the # of H’s is much greater than the # of O’s

–Building blocks – no monomers• Functions:

– Energy storage, basic structure of plasma membranes, protection, insulation, and waterproof coverings

• Type of lipids – Fats and Oils

• Example: Fatty Acids (a long carbon chain with a –COOH at one end)

– Steroids • Examples: cholesterol,

testosterone, estrogen, Vitamin A, and cortisone

– Waxes• Example: ear wax

• Different types of fatty acids: –Saturated - all single,

covalent bonds in between carbons in chain

–Unsaturated - one double bond between carbons in chain

–Polyunsaturated - many double bonds between carbons in chain

Steroids

Protein

• Structure– Composed of C, H, & O as well as

nitrogen, N, and possibly sulfur– Building blocks (monomers) are

amino acids• Functions

–Proteins are building materials (like muscle and hair), act as enzymes, antibodies, transporters, and markers

Amino Acid Structure

Alanine Serine

General structure

Amino Acids

• There are 20 main amino acids.

• Each has same basic structure with the only difference being the “R” group

• Amino acids are linked by peptide bonds (formed by dehydration synthesis)

Nucleic Acids• Structure

–Composed of C, H, O, N, and P–Building blocks (monomers) are

nucleotides• Nucleotides consist of a sugar, a nitrogenous base, and a phosphate

• Functions–Genetics and energy transfer

• Types of Nucleic Acids–DNA, RNA, and ATP

Chemical Reactions

• Chemical reactions always involve breaking bonds in reactants and making bonds in products

• Some reactions release energy and therefore usually occur spontaneously

• Other reactions need energy to happen

• Activation energy – the minimum amount of energy needed to start any reaction

• Enzymes are catalysts which speed up chemical reactions

• Enzymes are proteins that lower activation energy and allow reactions to occur at normal temperatures

• Without enzymes, too much energy would be needed to start all of the thousands of reactions your body performs all of the time!

Reaction pathwaywith enzyme

Reaction pathwaywithout enzyme

Activation energywithout enzyme

Activation energywith enzyme

• Each enzyme is specific and has a specific shape

• Enzymes are not permanently changed and are not used up in the reaction

• Enzyme activity is affected by pH, temperature, and concentration levels–Most of your enzymes work best at 98.6°F

• Most enzyme names end in -ase • Reactants are called substrates. • Enzymes work on substrates (either

breaking them down or adding something to them.

• Example: Lactase (enzyme) breaks down lactose (substrate), which is the sugar in milk.

Enzyme Activity