UNIT 1BIOCHEMISTRYPart 3

2007-2008Hillis Textbook Chapter 2-3

Macromolecules(Building Blocks of Life)

MACROMOLECULES OF LIFE

•BIOMOLECULES – macromolecules essential for living things to survive.

•Heterotrophs get biomolecules from the food that they consume (typically). This is why eating food is critical to survival.

•Autotrophs can produce them on their own by special processes (ex. Photosynthesis).

•Macromolecules•Most biological molecules are polymers

(poly, “many”; mer, “unit”), made by covalent bonding of smaller molecule called monomers.

•These large molecules are make of carbon back-bones which gives them the “organic” term.

Remember why carbon is so important?

•Carbon has FOUR electrons capable of sharing, which means it can form FOUR covalent bonds!

•Biomolecules are made of these strong bonds with carbon as a central atom.

CARBON EVERYWHERE!

Polymers are formed and broken apart in reactions involving water.

• Condensation Reaction or Dehydration synthesis —removal of water links monomers together. Requires enzymes and energy input.

REMOVE WATER TO BUILD! MONOMER TO POLYMER• Hydrolysis—addition of water breaks a polymer into monomers.

Requires enzymes and releases energy.ADD WATER TO BREAK! POLYMER TO MONOMER

Carbohydrates• formed by linking similar sugar monomers

(monosaccharides) to form polysaccharides• Source quick energy use and “first choice” storage of

energy.• Recognition or signaling molecules that can trigger

specific biological responses

nn OHC )( 2

Monosaccharides are simple sugars.Pentoses are 5-carbon sugars

Ribose and deoxyribose are the backbones of RNA and DNA.

Hexoses (C6H12O6) include

glucose, fructose and galactose.

• Monosaccharides are covalently bonded by condensation reactions that form glycosidic linkages.

• Sucrose is a disaccharide.

• Oligosaccharides are small polysaccharides (3-6 sugars)

• Many have additional functional groups.• They are often bonded to proteins and lipids on cell

surfaces, where they serve as recognition signals (they stick out of the cell membrane like street signs).

• Polysaccharides are large polymers of monosaccharides; the chains can be branching.

• Starches—a branched family of polysaccharides of glucose found in plants

• Glycogen—highly branched polymer of glucose; main energy storage molecule in mammals (found in the liver cells).

• Cellulose—the most abundant carbon-containing (organic) biological compound on Earth; stable and unbranched; good structural material

Lipids •formed by interactions of lipid monomers, such

as fatty acids and glycerol backbones.•Contain hydrocarbons (composed of C and H

atoms); they are insoluble in water because of many nonpolar covalent bonds.

•When close together, weak but additive van der Waals interactions hold them together.

Store energy in C—C and C—H bonds•Play structural role in cell membranes •Fat in animal bodies serves as thermal

insulation

Triglycerides (simple lipids) • Fats—solid at room temperature• Oils—liquid at room temperature• They have very little polarity and are extremely

hydrophobic.

Triglycerides consist of: • Three fatty acids—nonpolar hydrocarbon chain attached to a polar carboxyl (—COOH) (carboxylic acid)• One glycerol—an alcohol with 3 hydroxyl (—OH) groups• Synthesis of a triglyceride involves three condensation reactions.

• Fatty acid chains can vary in length and structure.• In saturated fatty acids, all bonds between carbon

atoms are single; they are saturated with hydrogens.• In unsaturated fatty acids, hydrocarbon chains

contain one or more double bonds. These acids cause kinks in the chain and prevent molecules from packing together tightly.

• In an aqueous environment, phospholipids form a bilayer.

• The nonpolar, hydrophobic “tails” pack together and the phosphate-containing “heads” face outward, where they interact with water.

• Biological cell membranes have this structure: PHOSPHOLIPID BILAYER

Amphipathic: the lipid has a hydrophilic end and a hydrophobic tail.

Phospholipid—two fatty acids and a phosphate compound bound to glycerolThe phosphate group has a negative charge, making that part of the molecule hydrophilic.

Nucleic acids

•from four kinds of nucleotide monomers

•polymers are specialized for storage, transmission, and use of genetic information.

DNA = deoxyribonucleic acid

RNA = ribonucleic acid

Nucleotide: Pentose sugar + N-containing base + phosphate group

Bases:

• Pyrimidines—single rings

• Purines—double rings

Sugars:

• DNA contains deoxyribose

• RNA contains ribose• Nucleotides bond in

condensation reactions to form phosphodiester linkages.

• Nucleic acids grow in the 5′ to 3′ direction.

Function: Protein synthesis

Function:Genetic Code

Proteins•Formed from different combinations of 20

amino acid monomers•Amino and carboxylic acid functional groups

allow them to act as both acid and base.•The R group differs in each amino acid.•They are grouped according to properties

conferred by the R groups.

Major functions of proteins:• Enzymes—catalytic proteins • Defensive proteins (e.g., antibodies) • Hormonal and regulatory proteins—control

physiological processes• Receptor proteins—receive and respond to

molecular signals • Storage proteins store amino acids• Structural proteins—physical stability and

movement• Transport proteins carry substances (e.g.,

hemoglobin) • Genetic regulatory proteins regulate when, how,

and to what extent a gene is expressed

•Amino acids are linked in condensation reactions to form peptide linkages or bonds.

•Polymerization takes place in the amino to carboxyl direction.

•Polypeptides or proteins •range in size from insulin, •which has 51 amino acids, •to huge molecules such as •the muscle protein titin, with •34,350 amino acids.

Primary structure of a protein—the sequence of amino acids

Secondary structure—regular, repeated spatial patterns in different regions, resulting from hydrogen bonding

• α (alpha) helix—right-handed coil• β (beta) pleated sheet—two or more polypeptide chains are

extended and aligned

Tertiary structure—polypeptide chain is bent and folded; results in the definitive 3-D shape. The outer surfaces present functional groups that can interact with other molecules.

Interactions between R groups determine tertiary structure.• Disulfide bridges hold a folded polypeptide together (sulfur bonds)• Ionic interactions form salt bridges •Hydrophobic side chains can aggregate•van der Waals interactions between hydrophobic side chains•Hydrogen bonds stabilize folds

Secondary and tertiary protein structure derive from primary structure. Denaturing—heat or chemicals are used to disrupt weaker interactions in a protein, destroying secondary and tertiary structure.The protein can return to normal when cooled—all the information needed to specify the unique shape is contained in the primary structure.

• Quaternary structure—two or more polypeptide chains (subunits) bind together by hydrophobic and ionic interactions, and hydrogen bonds.

• These weak interactions allow small changes that aid in the protein’s function.

Factors that can disrupt the interactions that determine protein structure (denaturing):•Temperature •Concentration of H+ •High concentrations of polar substances •Nonpolar substances