Bio 178 Lecture 5
The Chemical Building Blocks of Life (2)
Reading
•
Chapter 3
Quiz Material
•
Questions on P 60
•
Chapter 3 Quiz on Text Website
(www.mhhe.com/raven7)
Outline
• Nucleic Acids (Cntd.)
• Lipids
• Carbohydrates
DNA Structure
Double Helix
• 2 strands joined together that is then twisted into a
helical shape.
• The strands are antiparallel.
Outside of Helix
Sugar-phosphate backbone.
Inside of Helix
• Nitrogenous bases linked by hydrogen bonds.
• Only A can pair with T and C with G.
DNA Structure
What sequence will pair with AGCTTCAG?
TCGAAGTC
Why will only certain bases pair?
• Width of helix
• Hydrogen bonding
RNA Structure
DNA Versus RNA
DNA
Sugar Type
#of Strands
Base Types
RNA
Adenosine Triphosphate
ATP
Lipids
Molecules that are insoluble in water but soluble in oil.
1. Phospholipids
Composition
3 subunits:
• Glycerol
• 2 fatty acids
• Phosphate group (this may have an attached charged
organic molecule also)
Phospholipids are Amphipathic Molecules
Lipids
2. Fats
Characteristics
Lipids that lack a polar component.
Composition
2 subunits - 3 fatty acids and glycerol.
Functions
• Energy storage (X 2 starch)
• Compact
• Protection
• Warmth
Saturated & Unsaturated Fats
Saturated & Unsaturated Fats
Polyunsaturated Fats
When a fatty acid has >1 double bond.
Atherosclerosis
Plaques of fat and cholesterol (amongst other substances)
that develop on the internal lining of blood vessels,
impeding blood flow).
Lipids
3. Terpenes
Long-chain lipids that are components of some biologically
active pigments.
Eg. Chlorophyll.
Lipids
4. Steroids
Have 4 carbon rings.
Eg. Cholesterol, testosterone, estrogen.
Carbohydrates
Molecules that contain C, H, and O atoms bonded together
to form monomers known as monosaccharides.
1. Monosaccharides
Example - Glucose
• C6H12O6
• Form rings in an aqueous environment
• Functions in energy storage
Glucose
Sugar Isomers
Isomers - Molecules that have the same empirical formula
but different 3D structures.
Structural Isomers
Eg. Fructose
Identical chemical groups bonded to different C atoms.
Stereoisomers
Eg. Galactose
Identical chemical groups bonded to the same C atoms but
in different orientations (mirror images).
Carbohydrates
2. Disaccharides
Example - Sucrose
Transport Disaccharides
Plants
Sucrose - Enzymes for sucrose metabolism only present in
the destination tissue  less likely to be metabolized en
route than glucose.
Animals
Lactose - Milk sugar. Adults have reduced quantities of
lactase  ensuring that most of the energy from lactose is
reserved for the progeny.
Carbohydrates
3. Polysaccharides
(a) Storage Polysaccharides
Polymers of monosaccharides that convert soluble forms of energy
into insoluble ones for storage.
• Plants
Starch - Polymers of glucose. 2 types:
• Amylose - Unbranched.
• Amylopectin - Branched (short branches).
• Animals
Glycogen - Branched (long branches).
-Glucose
OH group on C1 below the plane of the ring.
Eg. Starch
-Glucose
OH group on C1 above the plane of the ring.
Polysaccharides
(b) Structural Polysaccharides
• Cellulose
Glucose polymer that consists of all -glucose subunits.
Component of plant cell walls.
Breakdown requires special enzymes.
• Chitin
Modified form of cellulose with a N group on the glucose
subunits.
Exoskeleton of arthropods and fungal cell walls.