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The Structure and Function
of Macromolecules
Chapter 5
• Macromolecules - larger molecules
made from smaller ones.
• 4 major classes of macromolecules:
carbohydrates, lipids, proteins, and
nucleic acids.
• 3 of these are polymers because
they are made from individual
building blocks called monomers.
• Monomers - joined together
through condensation or
dehydration reaction (form
macromolecules)
• Requires energy; uses covalent
bonds (links together monomers)
• Water produced.
Water produced
as by-product
• Hydrolysis breaks polymers into
monomers.
• Water added to polymer; breaks
bonds, creates monomers (i.e.
digestive process in animals)
Carbohydrates
• 1Carbohydrates - sugars
(monomers) and polymers.
• AMonosaccharides - simple sugars.
• BDisaccharides - double sugars
(monosaccharides linked together)
• CPolysaccharides - polymers of
monosaccharides.
• Sugars named with –ose.
• Monosaccharides needed for
cellular work.
• Help to synthesize other
macromolecules.
• 2 monosaccharides joined by
glycosidic linkage to form
disaccharide via dehydration.
• Maltose - 2 glucose molecules.
• Sucrose - 1 glucose, 1 fructose.
• Polysaccharides - energy storage.
• Starch - energy storage
polysaccharide for plants.
• Starch stored in plants plastids.
• Herbivores access starch for
energy.
• Animals store energy as glycogen.
• Humans - in liver and muscles.
• Cellulose – polysaccharide; plant cell
walls.
• Many herbivores cannot digest
cellulose (develop relationships with
microbes)
• Chitin - polysaccharide - makes up
exoskeleton of arthropods (like
crustaceans).
• Chitin - found in fungi; functions as
structural support.
Chitin is used in surgery
Lipids
• Lipids - no polymers (exception)
• Lipids nonpolar (no affinity for
water)
• Fat made from glycerol and fatty
acids.
• Glycerol - 3 carbon molecule with
hydroxyl group and fatty acid;
consists of carboxyl group attached
to long carbon skeleton.
• The 3 fatty acids in a fat can be
same or different.
• No carbon-carbon double bonds,
molecule is saturated fatty acid
(hydrogen at every possible
position)
• Form bad fats - solid at room
temperature (butter, lard)
No double-double bonds
• 1+ carbon-carbon double bonds molecule is unsaturated fatty acid formed by removal of hydrogen
atoms from carbon skeleton.
• Form good fats - liquid at room
temperature (oils)
• Purpose of fat - energy storage.
• Gram of fat stores 2X as much
energy as gram of polysaccharide.
• Fat also cushions vital organs.
• Layer of fat can also function as
insulation.
• Phospholipids - 2 fatty acids
attached to glycerol, phosphate
group at 3rd position.
• Fatty acid tails are hydrophobic,
phosphate group and attachments
form hydrophilic head.
• When phospholipids added to
water, self-assemble with
hydrophobic tails pointing toward
center, hydrophilic heads on
outside.
• Phospholipids in cell form bilayer;
major component of cell membrane.
Hydrophilic
Hydrophobic
• Steroids - lipids with carbon
skeleton consisting of 4 fused
carbon rings.
• Cholesterol - component in animal
cell membranes.
• Cholesterol – also forms hormones
(i.e. testosterone, estrogen)
Cholesterol
Proteins
• Proteins - support, storage,
transport, defenses, and enzymes.
• Made in ribosomes in cell.
• Proteins - amino acids linked
together to form polymer.
• 20 different amino acids that can
be linked together to form
thousands of different proteins.
• Amino acids link - polypeptides combine to form proteins.
• Amino acids made of hydrogen
atom, carboxyl group, amino group,
variable R group (or side chain).
• R group makes amino acids
different from one another.
• R groups have different properties
(i.e. hydrophobic) - form amino
acids with different properties.
• Amino acids joined by peptide
bonds when dehydration reaction
removes hydroxyl group from
carboxyl end of 1 amino acid and
hydrogen from amino group of
another.
• Shape of protein determines
function.
• Shapes - 3 dimensional determined by sequence of amino
acids.
• Primary structure of protein linear sequence of amino acids
determined by genetics; problem in
sequence can cause problem in
ending protein created.
• Secondary structure - hydrogen
bonds at regular intervals along
polypeptide backbone.
• Two shapes are usually formed:
alpha coils or beta sheets.
• Tertiary structure determined by
variety of interactions among R groups
and between R groups and polypeptide
backbone.
• Interactions include hydrogen bonds,
van der Waals forces, and ionic bonds.
• Disulfide bridges help stabilize form.
• Quarternary structure - joining of
2+ polypeptide subunits.
• Collagen and hemoglobin examples.
• Protein’s shape can change due to
environment.
• pH, temperature, or salinity (salt
concentrations) change - protein
can denature (starts to fall apart)
• Some proteins can return to
functional shape after
denaturation, others cannot,
especially in crowded environment
of cell.
Nucleic acids
• Amino acid sequence of polypeptide
programmed by a gene (regions of
DNA, polymer of nucleic acids)
• 2 types of nucleic acids: ribonucleic
acid (RNA) and deoxyribonucleic
acid (DNA).
• DNA gives information so RNA can
create proteins.
• Flow of genetic information - DNA > RNA -> protein.
• Protein synthesis occurs in
ribosomes.
• Monomers of nucleic acids nucleotides.
• Nucleotides made up of 3 parts:
nitrogen base, five-carbon sugar,
and phosphate group.
• Nitrogen bases, rings of carbon and
nitrogen, come in 2 types: purines
and pyrimidines.
• Pyrimidines - cytosine (C), thymine
(T), and uracil (U in RNA only).
• Purines - adenine (A) and guanine
(G).
• Pyrimidines - single six-membered
ring; purines - five-membered ring.
• In RNA - sugar is ribose; DNA sugar is deoxyribose.
• Difference between sugars is lack
of oxygen atom on carbon two in
deoxyribose.
• Nitrogen base sequence is
different for different genes.
• Genes are normally hundreds to
thousands of nucleotides long.
• The number of possible
combinations of the four DNA
bases is limitless.
• RNA single-stranded - linear shape.
• DNA forms double helix.
• Sugar and phosphate forms
backbone of double helix while
nitrogen bases form connection
between backbones.
• Adenine (A) always pairs with
thymine (T) guanine (G) with
cytosine (C).
• Due to six and five membered rings
–shapes are compatible.
• Know sequence of one side of
double helix - figure out other.
• Two strands are complementary.
http://www.emunix.emich.edu/~rwinning/genetics/pics/dna2.gif
• DNA used to show evolutionary
similarities between species.
• Two species that appear to be
closely-related based on fossil and
molecular evidence also more
similar in DNA and protein
sequences than more distantly
related species.