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CONCEPTS IN BIOLOGY
TWELFTH EDITION
Enger • Ross • Bailey
CHAPTER 3
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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3.1 Organic chemistry

All organic molecules contain carbon.
–

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Inorganic molecules do not contain carbon.
Biochemistry is the chemistry of living things.
Carbon: The central atom


Carbon is the central
atom in all organic
molecules.
Carbon has unique
bonding properties.
–
–
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Can combine with other
carbon atoms in long
chains.
Can form ring structures.
Carbon: The central atom

Carbon atoms participate in
four covalent bonds.
Has four electrons in the
outer energy level.
– Can double bond with
oxygen.
– Can triple bond with other
carbon atoms.
(e.g., gas acetylene, C2H2,
Hydrogen cyanid, HCN)
(See page 47)
–
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Isomers (See p. 47)

Several factors determine the properties of an
organic molecule.
–
–

The types of atoms in the molecule.
The 3-D arrangement of atoms within the molecule.
Organic molecules can have the same number and
composition of atoms, but can have different
arrangements.
–
These are called isomers.

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Molecules with the same empirical formula but different
structural formulas.
Hexose isomers (i.e., Structure
isomers)
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How Science Works 3.1 (See p. 50)
Generic Drugs and Mirror Image Isomers
The carbon skeleton

All organic molecules have a carbon skeleton.
–

This determines the overall shape of the molecule.
Organic molecules differ in these ways:
–
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–
The length and arrangement of the carbon
skeleton.
The kinds and location of atoms attached to it.
How the attached atoms are combined together
 These combinations are called functional
groups.
 Functional groups determine the chemical
nature of the molecule.
Functional groups
Macromolecules of life


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Macromolecules are very large organic
molecules.
The most important organic compounds
found in living things are:
 Carbohydrates
 Proteins
 Nucleic acids
 Lipids
Polymers




Carbohydrates, proteins and nucleic acids are polymers.
Polymers are combinations of smaller building blocks.
– The building blocks are called monomers.
Polymers are built via dehydration synthesis.
Polymers are broken apart via hydrolysis.
3.2 Carbohydrates

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Organic molecules composed of carbon, hydrogen
and oxygen.
All have the general formula CH2O.
Names end in –ose. (See p. 49 in Textbook)
Serve as the primary energy source for most living
things.
Also serve as structural support
– Plant cell walls
Important components of nucleic acids
– DNA
Simple sugars

Simple sugars are
described by the
number of carbons in
the molecule.
–
–
–

Examples of simple sugars:
–
–
–
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Triose-3 carbons
Pentose-5 carbons
Hexose-6 carbons
Glucose
Fructose
Galactose
Complex carbohydrates

When two or more simple sugars are
combined they form complex carbohydrates.
–
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Formed via dehydration synthesis
Disaccharides
–
Two simple sugars

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Trisaccharides
–
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Sucrose
Lactose
Maltose
Three simple sugars
Polysaccharides

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Contain many simple sugars
Examples of polysaccharides:
– Starch and glycogen
 Used for energy storage in plants (starch) and
animals (glycogen, (i.e., animal starch))
– Cellulose
 Important component of plant cell walls.
 Humans cannot digest cellulose; it is the fiber
in our diet.
– Helps facilitate movement of food through
the digestive tract.
Complex carbohydrates
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3.3 Proteins


Proteins are polymers
made of amino acids.
An amino acid contains:
–
–
–
–
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Central carbon
Amino group
Carboxyl group
Hydrogen
There are 20 different
amino acids. (See p. 53
Outlooks 3.2)
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The structure of proteins


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Amino acids are joined via dehydration synthesis.
– The bond formed between amino acids is called a
peptide bond.
Several amino acids joined together form
polypeptide chains.
Primary structure


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The sequence of amino acids in a polypeptide
constitutes the primary structure of the protein.
This sequence is dictated by information in genes
(DNA).
All levels of protein structure depend on the primary
sequence.
Secondary structure

Polypeptides twist and
fold into their secondary
structure.
– Some sequences of
amino acids twist into
a helix.
 This is called an
alpha helix.
– Some sequences of
amino acids remain
straight and fold back
on themselves.
 This is called a
beta-pleated sheet.
Tertiary structure

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The various alpha
helices and beta
pleated sheets interact
to form a globular
structure.
This globular structure
is unique for each
polypeptide.
Quaternary structure



Some proteins contain
more than one
polypeptide chain.
Each of these
polypeptides has its
own unique tertiary
structure.
– These polypeptides
interact to form a
more complex
globular structure.
Quaternary structure
can be stabilized by
disulfide bonds. (see
next page)
Form and function



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The protein’s overall shape determines its
job.
If a protein is not shaped properly, it likely
will not work properly.
Example:
– Sickle cell anemia (See p.54, p. 159)
– A mutation in the gene causes the
protein to have a different shape.
(Point mutation, see p. 158))
– This shape change results in a change
in function. (CJD &BSE, p. 56)
Denaturation:
– When heat or other environmental
conditions break the bonds that
stabilize tertiary structure. (See p. 56)
Types of proteins


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Structural proteins
– Important in maintaining the shape of cells and
organisms.
– Collagen
Regulatory proteins
– Determine what activities will occur in a protein.
– Enzymes and hormones
Carrier proteins
– Transport molecules from one place to another.
– Lipoproteins
3.4 Nucleic acids



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The complex organic
polymer molecules.
Store and transfer
information within a cell.
Include DNA and RNA
Are made of
nucleotides.
–
–
–
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5-carbon sugar
phosphate group
nitrogenous group.
Nucleotides
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DNA vs. RNA
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DNA

Each DNA molecule is made of two strands.
–
–
Held together by hydrogen bonds between the nitrogenous
bases.
The bases pair according to base pair rules. (See Fig. 3.17)

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The two DNA strands are twisted on each other,
forming a double helix. (See Fig. 3.17)
Each DNA strand is divided into segments. (See p.57)
–
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Each segment forms a gene. (p. 57,Book, chapter)
Genes are the recipes for proteins.
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Adenine - thymine
Cytosine - guanine
The sequence of nucleotides in a gene dictate the order of
amino acids in a polypeptide.
The structure of DNA
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DNA and chromosomes

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Each DNA strand has many genes.
Each DNA strand is called a chromosome.
Human cells have 46 chromosomes in
each cell.
–
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Each cell copies all of these chromosomes
before it divides to pass along to daughter
cells.
The functions of DNA
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DNA is able to:
– Replicate itself
– Mutate (change chemically)
– Store information and transmit it to
offspring
– Direct synthesis of proteins
RNA
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RNA is a single stranded molecule.
Contains uracil instead of thymine.
Base pairs with itself and DNA
–
–

A-U
G-C
RNA is found in three different forms:

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
mRNA (messenger RNA)
rRNA (ribosomal RNA)
tRNA (transfer RNA)
3.5 Lipids
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Commonly called fats.
Large and nonpolar
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Do not dissolve in water
Dissolve in other nonpolar molecules like acetone
Usually have very few oxygen atoms
There are three types of lipids:
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True fats (e.g. pork chop fat and oils)
Phospholipids (membrane components)
Steroids (most hormones)
True (neutral) fats
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Used to provide energy.
The building blocks of
fats
– A glycerol molecule
– Three fatty acids.
Saturated vs. unsaturated lipids

If the carbon skeleton of a fatty acid has as
much hydrogen as possible, the fat is called
a saturated fat.
–
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Saturated fats are found in animal tissues and tend to be
solid at room temperature.
If the carbons of a fat have double bonded
carbon molecules in them, the fat is called
unsaturated fat.
–
–
–
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Unsaturated fats are frequently plant fats and are liquids at
room temperature.
A polyunsaturated fat has several double bonds.
Fats are important energy storage molecules.
Saturated and unsaturated fatty
acids
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45
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Phospholipids

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Are complex organic
molecules that
resemble fats but
contain phosphate
groups.
Phospholipids are the
major components of
cell membranes.
–
47
Some are known as
lecithins. (See p.62,
p. 63 Outlooks)
Diagram of a Lipoprotein
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December 4, 2006 (New York Times)
End of Drug Trial Is a Big Loss for Pfizer
By ALEX BERENSON
The news came to Pfizer’s chief scientist, Dr. John L.
LaMattina, as he was showering at 7 a.m. Saturday: the
company’s most promising experimental drug, intended
to treat heart disease, actually caused an increase in
deaths and heart problems. Eighty-two people had died
so far in a clinical trial, versus 51 people in the same trial
who had not taken it.
Within hours, Pfizer, the world’s largest drug maker, told
more than 100 trial investigators to stop giving patients
the drug, called torcetrapib. Shortly after 9 p.m. Saturday,
Pfizer announced that it had pulled the plug on the
medicine entirely, turning the company’s nearly $1 billion
investment in it into a total loss.
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Pfizer's shares fell by 10.6% to $24.90 by the close of
trade on Wall Street.
Steroids
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Nonpolar molecules that are arranged in rings of carbon.
Steroids are important components of cell membranes.
– Cholesterol (See p.62)
Steroids often serve as hormones and serve in
regulation of body processes.
– Testosterone