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Cecie Starr
Christine Evers
Lisa Starr
www.cengage.com/biology/starr
Chapter 3
Molecules of Life
(Sections 3.1 - 3.3)
Albia Dugger • Miami Dade College
3.1 Fear of Frying
• Trans fats in hydrogenated vegetable oils raise blood
cholesterol more than any other fat, and directly alter the
function of arteries and veins
• Eating as little as 2 grams a day of hydrogenated vegetable
oils increases risk of atherosclerosis (hardening of the
arteries), heart attack, and diabetes
Trans fats, an unhealthy food
• The arrangement of hydrogen atoms around a double bond
makes a fat trans or cis
3.2 Molecules of Life—
From Structure to Function
• Only living things make the molecules of life—complex
carbohydrates and lipids, proteins, and nucleic acids
• All of these molecules are organic
• organic
• Type of compound that consists primarily of carbon and
hydrogen atoms
Carbon and Hydrocarbons
• Carbon chains or rings form the backbone of molecules of life
• An organic molecule that consists only of hydrogen and
carbon atoms is a hydrocarbon
• hydrocarbon
• Compound or region of one that consists only of carbon
and hydrogen atoms
Modeling an Organic Molecule
A glucose
B glucose
C glucose
D glucose
E glucose
carbon hydrogen oxygen nitrogen phosphorus
Fig. 3.2, p. 38
Functional Groups
• Most molecules of life have at least one functional group
• functional group
• A group of atoms bonded to a carbon of an organic
compound
• Imparts a specific chemical property such as polarity or
acidity
Common Functional Groups
Common
Functional
Groups
Stepped Art
Fig. 3.3, p. 38
What Cells Do
• Metabolic activities (mediated by enzymes) help cells stay
alive, grow, and reproduce
• metabolism
• All enzyme-mediated chemical reactions by which cells
acquire and use energy as they build and break down
organic molecules
• enzyme
• Compound (usually a protein) that speeds a reaction
without being changed by it
Building and Breaking Down
• Condensation reactions build polymers from monomers of
simple sugars, fatty acids, amino acids, and nucleotides
• Hydrolysis reactions release monomers by breaking apart
polymers
• monomers
• Molecules that are subunits of polymers
• polymer
• Molecule that consists of multiple monomers
Condensation
• Builds a large molecule
from smaller ones
• Enzyme removes –OH
group from one
molecule and -H atom
from another
• Covalent bond forms
between two molecules
– water also forms
Hydrolysis
• Splits a large molecule
into smaller ones by a
water-requiring reaction
• Enzyme attaches –OH
group and -H atom from
water at cleavage site
Hydrolysis
A Condensation. Cells build a large
molecule from smaller ones by this
reaction. An enzyme removes a hydroxyl
group from one molecule and a hydrogen
atom from another. A covalent bond forms
between the two molecules, and water
also forms.
B Hydrolysis. Cells split a large molecule
into smaller ones by this water-requiring
reaction. An enzyme attaches a hydroxyl
group and a hydrogen atom (both from
water) at the cleavage site.
Stepped Art
Fig. 3.4, p. 39
Animation: Condensation and hydrolysis
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Common Metabolic Reactions
Key Concepts
• Structure Dictates Function
• We define cells partly by their capacity to build complex
carbohydrates and lipids, proteins, and nucleic acids
• All of these organic compounds have functional groups
attached to a backbone of carbon atoms
Animation: Functional groups
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3.3 Carbohydrates
• Enzymes assemble complex carbohydrates such as cellulose,
glycogen, and starch from simple carbohydrate (sugar)
subunits
• Cells use carbohydrates for energy, and as structural
materials
• carbohydrate
• Molecule that consists primarily of carbon, hydrogen, and
oxygen atoms in a 1:2:1 ratio
Simple Sugars
• Monosaccharides (one
sugar unit) are the simplest
type of carbohydrate
• Components of the nucleic
acids DNA and RNA have
five carbon atoms
• Glucose has six
Short-Chain Carbohydrates
• An oligosaccharide is a short chain of covalently bonded
monosaccharides
• Disaccharides consist of two sugar monomers
• Lactose (glucose + galactose)
• Sucrose (glucose + fructose)
• Oligosaccharides with three or more sugar units are often
attached to lipids or proteins that have important functions in
immunity
Synthesis of a Sucrose Molecule
• Sucrose (common table sugar) is synthesized from
monomers of glucose and fructose in a condensation reaction
Synthesis of a Sucrose Molecule
glucose
+
fructose
sucrose
+
water
Stepped Art
Fig. 3.5b, p. 40
Complex Carbohydrates
• Polysaccharides, are straight or branched chains of many
sugar monomers—often hundreds or thousands
• Common polysaccharides: cellulose, glycogen, and starch
• All consist of glucose monomers
• Each has different chemical properties due to different
patterns of covalent bonds that link glucose monomers
Cellulose
• Tough structural
component of plants
• Chains of glucose units
stretch side by side and
hydrogen bond at many
-OH groups
• Hydrogen bonds
stabilize chains in tight
bundles of long fibers
Starch (Amylose)
• Main energy reserve in
plants, which store it in
roots, stems, leaves,
fruits, and seeds
• In amylose, a series of
glucose units form a
coiled chain
Glycogen
• In humans and other
animals, glycogen
stored in muscles and
liver functions as an
energy reservoir
Chitin
• Monomers are glucose
with nitrogen-containing
carbonyl group
• Long, unbranching
chains linked by
hydrogen bonds.
• Strengthens hard parts
of many small animals,
such as crabs
Key Concepts
• Carbohydrates
• Carbohydrates are the most abundant biological
molecules
• They function as energy reservoirs and structural
materials
• Different types of carbohydrates are built from the same
sugars, bonded in different patterns