SCH4U Nucleic Acids
Fats and Oils
Page 131 # 2 - 6
132 # 4, 8
136 # 1 - 6
Section # 3, 6, 10, 12
Lipids: Hydrophobic molecules
P Large biological molecules do not form
polymers
P Little or no affinity for water
P Mostly hydrocarbons: nonpolar
P Most important lipids are fats, phospholipids
and steroids
Fats
P Fats form from glycerol and fatty acids
P Glycerol is 1,2,3-propanetriol
P Fatty acids have a carboxyl group attached
to a long carbon chain
P Fats are triesters (or triglycerides)
P Water hydrogen bonds to water and excludes
fat molecules that are not very polar
Fatty acid
(palmitic acid)
Glycerol
Dehydration reaction in the synthesis of a fat
Ester linkage
Fat molecule (triacylglycerol)
Fatty acids
P Vary in length and in number and location of
double bonds
P Saturated fatty acids have no double bonds
P Unsaturated fats have one or more double
bonds
P Major function of fats is energy storage
Saturated Fats
Made from saturated fatty acids
P Most animal fats are saturated
P Solid at room temperature
P May contribute to heart disease (cause
plaque deposits)
Stearic acid
Saturated fat and fatty acid.
Unsaturated Fats
Made from unsaturated fatty acids
P Plant fats and fish fats are usually
unsaturated
P Liquid at room temperature (called oils)
Unsaturated fats
Cis (good) and trans (bad) fatty acids
P Unsaturated fats
(and fatty acids) can
be hydrogenated
P Margarine is a
hydrogenated
vegetable oil
Hydrogenation
Reactions with lipids
P Lipids are long term energy storage
P Lipids produce twice as much energy per
gram as carbohydrates
P Reactions with strong bases produce soap
(saponification)
Phospholipids
Cell membranes
Hydrophilic
head
Hydrophobic
tails
WATER
WATER
Other lipids are steroids.
Examples include cholesterol, and the
sex hormones estrogen and
testosterone.
Lipid Steroids: Cholesterol
“Good” HDL and “Bad” LDL
P HDL (high
density
lipoproteins)
carry lipids to
the liver for
excretion
P LDL (low density
lipoproteins)
carry lipids from
the liver for to
tissues
Lipid Steroids: Sex Hormones
Synthetic steroids
Mimic natural steroids
Mark McGwire 70
Home runs
Oral Contraceptives
Progesterone suppresses ovulation
P Progesterone breaks down during digestion
P Synthetic estrogens are absorbed without
decomposing
Fat substitutes
Olestra is not absorbed into the body
P Molecule is too large to digest
P Nutrient uptake can be disrupted
Olestra Chemical Composition
P Olestra: sucrose polyester
instead of glycerol
P Six to eight fatty acids react with
sucrose
P It is a synthetic fat composed of
sucrose and edible oils.
P Olestra can be used as a fat
substitute
Why is Olestra Effective? Not effective?
P Olestra is not digested or absorbed.
P Adds no calories or fat to the diet.
P Passes through the body as opposed to
being absorbed by it.
P Lubricates digestive tract!
Nucleic acids store and transmit
hereditary information
• The amino acid sequence of a polypeptide is
programmed by a unit of inheritance called a gene
• Genes are made of DNA, a nucleic acid
The Roles of Nucleic Acids
• There are two types of nucleic acids:
– Deoxyribonucleic acid (DNA)
– Ribonucleic acid (RNA)
• DNA provides directions for its own replication
• DNA directs synthesis of messenger RNA (mRNA)
and, through mRNA, controls protein synthesis
• Protein synthesis occurs in ribosomes
The Structure of Nucleic Acids
• Nucleic acids are polymers called polynucleotides
• Each polynucleotide is made of monomers called
nucleotides
• Each nucleotide consists of a nitrogenous base, a
pentose sugar, and a phosphate group
• The portion of a nucleotide without the phosphate
group is called a nucleoside
LE 5-26a
5¢ end
Nucleoside
Nitrogenous
base
Phosphate
group
Nucleotide
3¢ end
Polynucleotide, or
nucleic acid
Pentose
sugar
Nucleotide Monomers
• Nucleotide monomers are made up of nucleosides
and phosphate groups
• Nucleoside = nitrogenous base + sugar
• There are two families of nitrogenous bases:
– Pyrimidines have a single six -membered ring
– Purines have a six-membered ring fused to a
five-membered ring
• In DNA, the sugar is deoxyribose
• In RNA, the sugar is ribose
Nitrogenous bases
Pyrimidines
Cytosine
C
Thymine (in DNA) Uracil (in RNA)
U
T
Purines
Adenine
A
Guanine
G
Pentose sugars
Deoxyribose (in DNA)
Nucleoside components
Ribose (in RNA)
Nucleotide Polymers
• Nucleotide polymers are linked together, building a
polynucleotide
• Adjacent nucleotides are joined by covalent bonds
that form between the –OH group on the 3 carbon of
one nucleotide and the phosphate on the 5 carbon on
the next
• These links create a backbone of sugar-phosphate
units with nitrogenous bases as appendages
• The sequence of bases along a DNA or mRNA
polymer is unique for each gene
The DNA Double Helix
• A DNA molecule has two polynucleotides spiraling
around an imaginary axis, forming a double helix
• In the DNA double helix, the two backbones run in
opposite 5 to 3 directions from each other, an
arrangement referred to as antiparallel
• One DNA molecule includes many genes
• The nitrogenous bases in DNA form hydrogen
bonds in a complementary fashion: A always with
T, and G always with C
LE 5-27
5¢ end
3¢ end
Sugar-phosphate
backbone
Base pair (joined by
hydrogen bonding)
Old strands
Nucleotide
about to be
added to a
new strand
5¢ end
New
strands
5¢ end
3¢ end
5¢ end
3¢ end
DNA Double Helix
• Base pairing by unique hydrogen bonds
• C - G and A - T pairs