Molecules of Life
Chapter 2
Part 2
2.6 Organic Molecules
 The molecules of life – carbohydrates, proteins,
lipids, and nucleic acids – are organic molecules
 Organic
• Type of molecule that consists primarily of carbon
and hydrogen atoms
Some Elemental Abundances
Modeling an Organic Molecule
Building Organic Molecules
 Carbon atoms bond covalently with up to four
other atoms, often forming long chains or rings
 Enzyme-driven reactions construct large
molecules from smaller subunits, and break
large molecules into smaller ones
From Structure to Function
 Cells assemble large polymers from smaller
monomers, and break apart polymers into
component monomers
 Metabolism
• All the enzyme-mediated chemical reactions by
which cells acquire and use energy as they build
and break down organic molecules
Monomers and Polymers
 Monomers
• Molecules that are subunits of polymers
• Simple sugars, fatty acids, amino acids,
nucleotides
 Polymers
• Molecules that consist of multiple monomers
• Carbohydrates, lipids, proteins, nucleic acids
Condensation and Hydrolysis
 Condensation (water forms)
• Process by which an enzyme builds large
molecules from smaller subunits
 Hydrolysis (water is used)
• Process by which an enzyme breaks a molecule
into smaller subunits by attaching a hydroxyl to
one part and a hydrogen atom to the other
Condensation and Hydrolysis
Condensation and hydrolysis
Functional groups
2.7 Carbohydrates
 Cells use carbohydrates for energy and
structural materials
 Carbohydrates
• Molecules that consist primarily of carbon,
hydrogen, and oxygen atoms in a 1:2:1 ratio
Complex Carbohydrates
 Enzymes assemble complex carbohydrates
(polysaccharides) from simple carbohydrate
(sugar) subunits
 Glucose monomers can bond in different
patterns to form different complex carbohydrates
• Cellulose (a structural component of plants)
• Starch (main energy reserve in plants)
• Glycogen (energy reserve in animals)
Some Complex Carbohydrates
Animation: Structure of starch and
cellulose
Animation: Examples of
monosaccharides
2.8 Lipids
 Lipids are greasy or oily nonpolar organic
molecules, often with one or more fatty acid tails
 Lipids
• Fatty, oily, or waxy organic compounds
 Fatty acid
• Consists of a long chain of carbon atoms with an
acidic carboxyl group at one end
Fats
 Fats, such as triglycerides, are the most
abundant source of energy in vertebrates –
stored in adipose tissue that insulates the body
 Fat
• Lipid with one, two, or three fatty acid tails
 Triglyceride
• Lipid with three fatty acid tails attached to a
glycerol backbone
Saturated and Unsaturated Fats
 Saturated fats pack more tightly than
unsaturated fats, and tend to be more solid
 Saturated fat
• Fatty acid with no double bonds in its carbon tail
 Unsaturated fat
• Lipid with one or more double bonds in a fatty
acid tail
Fatty Acids
 Saturated, unsaturated, cis, and trans fatty acids
carboxyl
group
cis
double
bond
long
carbon
chain
A stearic acid
B linolenic acid
C oleic acid
trans
double
bond
D elaidic acid
Fig. 2-14, p. 32
Phospholipids
 Phospholipids are the main structural
component of cell membranes
 Phospholipid
• A lipid with a phosphate group in its hydrophilic
head, and two nonpolar fatty acid tails
Phospholipids
one layer
of lipids
one layer
of lipids
B a lipid bilayer
Fig. 2-15b, p. 32
Waxes
 Waxes are part of water-repellent and lubricating
secretions in plants and animals
 Wax
• Water-repellent lipid with long fatty-acid tails
bonded to long-chain alcohols or carbon rings
Steroids
 Steroids such as cholesterol occur in cell
membranes or are remodeled into other
molecules (such as steroid hormones, bile salts,
and vitamin D)
 Steroid
• A type of lipid with four carbon rings and no fatty
acid tails
Steroids
Phospholipid structure
2.9 Proteins
 A protein’s function depends on its structure,
which consists of chains of amino acids that
twist and fold into functional domains
 Protein
• Organic compound that consists of one or
more chains of amino acids
Amino Acid
 Amino acid
• Small organic compound with a carboxyl group,
amine group, and a characteristic side group (R)
Peptide Bonds
 Amino acids are linked into chains by peptide
bonds
 Peptide bond
• A bond between the amine group of one amino
acid and the carboxyl group of another
 Polypeptide
• Chain of amino acids linked by peptide bonds
Polypeptide Formation
Protein Synthesis
1. Primary structure (polypeptide formation)
• A linear sequence of amino acids
2. Secondary structure
• Hydrogen bonds twist the polypeptide into a coil
or sheet
3. Tertiary structure
• Secondary structure folds into a functional shape
Protein Synthesis
4. Quaternary structure
• In some proteins, two or more polypeptide chains
associate and function as one molecule
• Example: hemoglobin
5. Fibrous proteins may aggregate into a larger
structure, such as keratin filaments
• Example: hair
1) A protein’s primary structure consists of a linear sequence of amino acids (a polypeptide chain).
2) Secondary structure arises when a polypeptide chain twists into a coil (helix) or sheet held in place
by hydrogen bonds between different parts of the molecule. The same patterns of secondary structure
occur in many different proteins.
lysine glycine glycine arginine
2
1
3
4
3) Tertiary structure occurs when a chain’s coils and sheets fold up into a
functional domain such as a barrel or pocket. In this example, the coils of
a globin chain form a pocket.
4) Some proteins have quaternary structure, in
which two or more polypeptide chains associate as
one molecule. Hemoglobin, shown here, consists
of four globin chains (green and blue). Each globin
pocket now holds a heme group (red).
5
5) Many proteins aggregate by the thousands into larger structures, such
as the keratin filaments that make up hair.
Protein Structure
Stepped Art
Fig. 2-18, p. 35
The Importance of Protein Structure
 Changes in a protein’s structure may also alter
its function
 Denature
• To unravel the shape of a protein or other large
biological molecule
Misfolded Proteins: Prion Disease
 Prion
• A misfolded protein that becomes infectious
• Example: mad cow disease (BSE) in cattle
• Example: vCJD in humans
Variant Creutzfeldt-Jakob Disease (vCJD)
2.10 Nucleic Acids
 Nucleotide
• Monomer of nucleic acids
• Has a five-carbon sugar, a nitrogen-containing
base, and phosphate groups
 Nucleic acids
• Polymers of nucleotide monomers joined by
sugar-phosphate bonds (include DNA, RNA,
coenzymes, energy carriers, messengers)
ATP
 The nucleotide ATP can transfer a phosphate
group and energy to other molecules, and is
important in metabolism
 Adenosine triphosphate (ATP)
• Nucleotide that consists of an adenine base, fivecarbon ribose sugar, and three phosphate groups
• Functions as an energy carrier
Functions of DNA and RNA
 DNA encodes heritable information about a cell’s
proteins and RNAs
 Different RNAs interact with DNA and with one
another to carry out protein synthesis
DNA and RNA
 Deoxyribonucleic acid (DNA)
• Nucleic acid that carries hereditary material
• Two nucleotide chains twisted in a double helix
 Ribonucleic acid (RNA)
• Typically single-stranded nucleic acid
• Functions in protein synthesis
A Nucleotide and Nucleic Acid
2.11 Impacts/Issues Revisited
 Our enzymes can’t easily break down trans fats
in processed foods, which causes health
problems – several countries will not import
foods made in the US that contain trans fats