Page 50 - 2022-bfw-morris-1e

Many of us, when we feel tired, reach for a candy bar for
a quick energy boost. The energy in a candy bar comes from
sugars, which are quickly broken down to release energy.
©2022 BFW Publishers. PAGES NOT FINAL. For review purposes only - do not post.
Sugars are carbohydrates, which are organic molecules
that store energy in their chemical bonds. In addition, they
are sometimes attached to proteins on the surface of cells,
such as your red blood cells, and make up the external layer
of the cells in plants, algae, and bacteria.
Carbohydrates are sometimes called sugars. Table sugar
(sucrose) is a familiar example. Other carbohydrates include
the sugars glucose, galactose, and lactose (milk sugar). Fruit,
FIGURE 1.13 Polymer like that shown in FIGURE 1.14, contains a variety of sugars,
including fructose. Like proteins and nucleic acids, carbohy-
A polymer is a long chain of repeating subunits called monomers, similar
drates are composed of repeating units of individual sugars,
to this necklace made up of individual beads. Photo: LionGate/Alamy Stock Photo
called monosaccharides.
example, is mostly made up of proteins. Proteins are com- As we have seen, proteins, nucleic acids, and carbohy-
posed of subunits called amino acids. Returning to our drates all are polymers made up of smaller, repeating units.
necklace example, we would say that a protein is a necklace, Lipids are different. Instead of being defined by a chemical
and an amino acid is a bead. structure, they share a particular property: lipids are organic
A single cell has thousands of proteins with different molecules that are hydrophobic. Hydrophobic means “water
functions. For example, some proteins form scaffolds that fearing” and it describes nonpolar molecules that don’t dis-
help to determine the shape of cells. Other proteins serve solve in water. Instead, they tend to associate with other lipids
as chemical messengers, traveling from one cell to another and minimize their contact with water. Think of what hap-
to convey a message. Still other proteins accelerate the rate pens when oil, which is hydrophobic, is mixed with water.
of chemical reactions. These various functions depend on The oil forms droplets that minimize their contact with
the structure, or shape, of the protein. In fact, structure and water, as pictured in FIGURE 1.15. By contrast, hydrophilic
function are closely connected. As a result, scientists can means “water loving” and it describes polar molecules that
sometimes infer what a protein does by examining its shape. readily associate with and dissolve in water. For example,
Furthermore, anything that disrupts the shape of a protein when sugar is placed in water, it dissolves as the individual
will often disrupt its function. The shape of a protein is sugar molecules associate with water molecules.
determined by its sequence of amino acids. We will discuss Because they share a property rather than a structure, lip-
proteins in more detail in Module 4. ids are chemically and functionally diverse. Their hydrophobic
Nucleic acids are responsible for encoding and trans- property allows them to be effective membranes, or barriers,
mitting genetic information. There are two types of nucleic
acids. Module 0 mentioned deoxyribonucleic acid (DNA).
The second nucleic acid is ribonucleic acid (RNA). Like
proteins, nucleic acids are long polymers made up of repeat-
ing subunits, called nucleotides.
Nucleic acids are examples of informational molecules—
that is, large molecules that carry information in the sequence,
or order, of nucleotides that make them up. This molecular
information is much like the information carried by the let-
ters in an alphabet, but, in the case of nucleic acids, the infor-
mation is in chemical form. DNA is the genetic material in
all organisms. It is transmitted from parents to offspring, and
it contains the information needed to specify the amino acid FIGURE 1.14 Carbohydrates
sequence of proteins. RNA has multiple functions, but one Fruit, such as these items at a market, contains fructose along with
of its most important is in the synthesis of proteins. We will several other types of sugars. Sugars are types of carbohydrates.
discuss nucleic acids in more detail in Module 5. Photo: OGphoto/Getty Images

38 UNIT 1 CHEMISTRY OF LIFE

©2022 BFW Publishers. PAGES NOT FINAL. For review purposes only - do not post.

04_morrisapbiology1e_11331_Unit1_Mod1_26-42_3pp.indd 38 10/04/21 9:10 AM