Molecules of Life Chapter 3
3.1 Molecules of Life
Molecules of life are synthesized by living cells
• Carbohydrates
• Lipids
• Proteins
• Nucleic acids
Structure to Function
Molecules of life differ in three-dimensional
structure and function
• Carbon backbone
• Attached functional groups
Structures give clues to how they function
Organic Compounds
Consist primarily of carbon and hydrogen atoms
• Carbon atoms bond covalently with up to four
other atoms, often in long chains or rings
Functional groups attach to a carbon backbone
• Influence organic compound’s properties
Processes of Metabolism
Cells use energy to grow and maintain
themselves
Enzyme-driven reactions build, rearrange, and
split organic molecules
Building Organic Compounds
Cells form complex organic molecules
• Simple sugars → carbohydrates
• Fatty acids → lipids
• Amino acids → proteins
• Nucleotides → nucleic acids
Condensation combines monomers to form
polymers
Key Concepts:
STRUCTURE DICTATES FUNCTION
We define cells partly by their capacity to build
complex carbohydrates and lipids, proteins, and
nucleic acids
The main building blocks are simple sugars, fatty
acids, amino acids, and nucleotides
These organic compounds have a backbone of
carbon atoms with functional groups attached
3.2 Carbohydrates –
The Most Abundant Ones
Three main types of carbohydrates
• Monosaccharides (simple sugars)
• Oligosaccharides (short chains)
• Polysaccharides (complex carbohydrates)
Carbohydrate functions
• Instant energy sources
• Transportable or storable forms of energy
• Structural materials
Fig. 3.8, p. 39
c Glycogen. In animals, this
polysaccharide is a storage form
for excess glucose. It is
especially abundant in the liver
and muscles of highly active
animals, including fishes and
people.
Structure of
cellulose
Key Concepts:
CARBOHYDRATES
Carbohydrates are the most abundant biological
molecules
Simple sugars function as transportable forms of
energy or as quick energy sources
Complex carbohydrates are structural materials
or energy reservoirs
3.3 Greasy, Oily – Must Be Lipids
Lipids
• Fats, phospholipids, waxes, and sterols
• Don’t dissolve in water
• Dissolve in nonpolar substances (other lipids)
Lipid functions
• Major sources of energy
• Structural materials
• Used in cell membranes
Fats
Consists of –
• Glycerol and fatty acids
• Lipids with one, two, or three fatty acid tails
• Saturated – solid at room temp
• Unsaturated - liquid at room temp
• cis -same side
• trans - opposite side
Triglycerides (neutral fats )
• Three fatty acid tails
• Most abundant animal fat (body fat)
• Major energy reserves
Key Concepts:
LIPIDS
Complex lipids function as energy reservoirs,
structural materials of cell membranes, signaling
molecules, and waterproofing or lubricating
substances
3.4 Proteins –
Diversity in Structure and Function
Proteins have many functions
• Structures
• Nutrition
• Enzymes
• Transportation
• Communication
• Defense
Four Levels of Protein Structure
1. Primary structure
• Amino acids joined by peptide bonds form a
linear polypeptide chain
2. Secondary structure
• Polypeptide chains form
sheets and coils
3. Tertiary structure
• Sheets and coils pack into functional domains
Four Levels of Protein Structure
3. Tertiary structure
• Sheets and coils pack into functional domains
Four Levels of Protein Structure
4. Quaternary structure
• Many proteins (e.g. enzymes) consist of two or
more chains
Other protein structures
• Glycoproteins
• Lipoproteins
• Fibrous proteins
3.5 Why is Protein Structure
So Important?
Protein structure dictates function
Sometimes a mutation in DNA results in an
amino acid substitution that alters a protein’s
structure and compromises its function
• Example: Hemoglobin and sickle-cell anemia
Fig. 3.19, p. 45
VALINE HISTIDINE LEUCINE GLUTAMATE VALINE THREONINE PROLINE
sickle cell
normal cell
b One amino acid substitution results in the
abnormal beta chain in HbS molecules. Instead
of glutamate, valine was added at the sixth
position of the polypeptide chain.
c Glutamate has an overall negative charge; valine
has no net charge. At low oxygen levels, this
difference gives rise to a water-repellent, sticky
patch on HbS molecules. They stick together
because of that patch, forming rodshaped clumps
that distort normally rounded red blood cells into
sickle shapes. (A sickle is a farm tool that has a
crescent-shaped blade.)
Denatured Proteins
If a protein unfolds and loses its three-
dimensional shape (denatures), it also loses its
function
Caused by shifts in pH or temperature, or
exposure to detergent or salts
• Disrupts hydrogen bonds and other molecular
interactions responsible for protein’s shape
Key Concepts:
PROTEINS
Structurally and functionally, proteins are the
most diverse molecules of life
They include enzymes, structural materials,
signaling molecules, and transporters
3.6 Nucleotides, DNA, and RNAs
Nucleotide structure, 3 parts:
• Sugar
• Phosphate group
• Nitrogen-containing base
Nucleotide Functions:
Reproduction, Metabolism, and Survival
DNA and RNAs are nucleic acids, each
composed of four kinds of nucleotide subunits
ATP energizes many kinds of molecules by
phosphate-group transfers
Other nucleotides function as coenzymes or as
chemical messengers
DNA, RNAs, and Protein Synthesis
DNA (double-stranded)
• Encodes information about the primary structure
of all cell proteins in its nucleotide sequence
RNA molecules (usually single stranded)
• Different kinds interact with DNA and one another
during protein synthesis