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UNIT 1
BIOCHEMISTRY
Part 3
Hillis Textbook Chapter 2-3
Macromolecules
(Building Blocks of Life)
2007-2008
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 backbones 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!
CARBON
EVERYWHERE!
•Biomolecules are made of these strong bonds
with carbon as a central atom.
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
Cn ( H 2O) n
• 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
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.
Amphipathic: the lipid has a hydrophilic end and a hydrophobic tail.
Phospholipid—two fatty acids and a phosphate compound bound to glycerol
The phosphate group has a negative charge, making that part of the molecule
hydrophilic.
• In an aqueous environment,
phospholipids form a bilayer.
• The nonpolar, hydrophobic “tails”
pack together and the phosphatecontaining “heads” face outward,
where they interact with water.
• Biological cell membranes have this
structure: PHOSPHOLIPID
BILAYER
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.
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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