Download Compounds of Living Things

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CHAPTER 11
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Date
The Chemistry of Living Things
SECTION
2 Compounds of Living Things
California Science
Standards
BEFORE YOU READ
After you read this section, you should be able to answer
these questions:
8.3.c, 8.6.c
• Why is water important for living things?
• How does salt help your body cells function?
• What are four complex organic compounds needed
by living things?
Why Is Water Important for Living Things?
Water is one of the simplest compounds that all living
things need. In fact, about 70% of your body weight is due to
water. Water is found everywhere in your body. It is inside
your cells. It surrounds your tissues and joints, and it is inside
your blood vessels. Although you may not realize it, the water
you drink helps your body do many important things.
"RAINÈ
"ONEÈ
+IDNEYÈ
The percentage of water is not the same in
different parts of your body.
-USCLEÈ
"LOODÈ
Water helps you control your body temperature. It
stores heat and insulates your body in cold surroundings.
On a hot day, water cools your body. It does this by
evaporating from your skin in the form of sweat.
Water make the joints in your body move more easily. Water
surrounds your bones and joints and delicate organs such as
the eyes and brain. Water cushions these parts from shock.
Water has other functions in your body. It transports
many nutrients and other substances around your body.
As your body produces waste, water also helps dilute the
waste and remove it. In addition, water is needed by your
cells to make the molecules you use for energy.
STUDY TIP
Memorize When you come
across new vocabulary
words, create flashcards to
help you remember their
meanings. Write each word
on one side of an index card.
Then, write its definition (and
other important facts) on the
other side.
Math Focus
1. Analyze Data If a human
body has about 10 pounds of
blood, how much does the
water in the blood weigh?
Show your work.
READING CHECK
2. Identify Name five ways
that your body needs water
in order to function properly.
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Compounds of Living Things continued
Animals have salt in their bodies. Therefore,
they need to have a certain amount of salt
in their diets.
CALIFORNIA
STANDARDS CHECK
8.6.c Students know that living
organisms have many different
kinds of molecules, including
small ones, such as water and
salt, and very large ones, such
as carbohydrates, fats, proteins,
and DNA.
3. Explain When athletes
exercise very hard, it is
important for them to replace
salts lost from their bodies.
How can low amounts of
salts affect electrical signals in
your body?
Why Do Living Things Need Salt?
Why is the deer licking salt in the figure above? The
deer must replace the salt that is lost from its body. If
you’ve ever tasted sweat or tears, you know that your body
also contains salt. There are different types of salt. The salt
you usually eat is sodium chloride. There are other salts
that are made of elements such as potassium and calcium.
All of these salts are present in your body and have vital
functions. Salts help transport materials in and out of the
cells. Cells use a difference in electrical charge inside and
outside the cell membrane to move materials in and out.
Cells use the charges carried by salt ions to do this.
Salts are also used to conduct electrical signals
throughout your body. This is especially important for
nerve cells, muscle cells, and heart cells.
What Organic Compounds Do Living
Things Need?
READING CHECK
4. Identify What four
complex compounds are
needed by the human body?
Living things require simple compounds such as water
and salts. They also need large complex compounds. Can
you think of some examples? You may have read about
carbohydrates and proteins on food labels. Cells need
carbohydrates, lipids, proteins, and nucleic acids in order
to function.
Eating well-balanced meals is important
for your body. Carbohydrates, proteins,
and lipids come from different foods.
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Compounds of Living Things continued
SECTION 2
CARBOHYDRATES
Compounds made of one or more molecules of simple
sugar are called carbohydrates. Small sugar molecules
can join together to form complex carbohydrates. The figure below shows a glucose (simple sugar) molecule and
a sucrose (table sugar) molecule. You can see that the
sucrose is made of two simple sugars joined together.
Glucose is a simple sugar. Sucrose is a more-complex sugar.
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Glucose molecule
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TAKE A LOOK
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5. Identify How many
simple sugar molecules make
up one molecule of sucrose?
Sucrose molecule
A complex carbohydrate can be made of thousands of
simple sugars arranged in a long chain of repeating units. This
chain is called a polymer.
Cells use carbohydrates as an energy source. For example,
your body breaks down carbohydrates and stores some of the
energy in muscle cells in the form of molecules called
glycogen. Carbohydrates also have other uses in cells.
Cellulose, a type of carbohydrate, forms cell walls that give
plants their rigid structure.
READING CHECK
6. Describe What is a
polymer?
LIPIDS
Lipids are organic compounds that do not dissolve in water.
Lipids are fat-soluble; that is, they dissolve in fats. Examples
of lipids include fats, oils, and waxes. Like carbohydrates, they
are required by living things. Though too much fat in your diet
is unhealthful, some fat is important to help you maintain good
health.
Lipids are large molecules made mostly of carbon and
hydrogen atoms. Saturated fats are lipids with only single
bonds between the carbon atoms. Unsaturated fats are lipids
that contain double bonds.
Lipids have many roles in living things. One role is to store
energy. When carbohydrates or glycogen are not available, cells
use energy stored in your body fat. Fat layers under your skin
and around your organs also protect and insulate your body.
The vitamins A, D, E, and K are necessary for good
health. They are fat-soluble, so they need fat to work
properly. They are also stored in your body fat.
Critical Thinking
7. Infer Vitamins A, D, E, and
K can reach dangerous levels
in a person’s body if he or
she takes too many vitamin
supplements. What do you
think is the reason?
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Compounds of Living Things continued
PROTEINS
READING CHECK
Proteins are organic compounds made of building
blocks called amino acids. Most proteins are large molecules made of long-chain polymers of amino acids. Each
type of protein in a cell has its own special structure.
This structure depends on the way the amino acid chains
fold together. Think of folding a shirt while doing laundry.
There are different ways to fold it. With proteins, the way
one is folded affects its function in the body.
There are only 20 different types of amino acids, the
protein building blocks. However, the possible combinations of amino acids are almost limitless. For example, a
simple prokaryotic bacteria such as Escherichia coli has
over 1,000 different proteins.
8. Identify What are
proteins made of?
Human hair
Peanuts
Red blood cells
Proteins play a variety of important roles in living organisms.
READING CHECK
9. Identify What is the
protein that carries oxygen to
your body cells?
Proteins have a wide range of important functions in
living things. The figure above shows some examples of
different proteins. Keratin protein in hair is strong and
lightweight. Nuts are foods dense in proteins that store
energy.
Your body has other unique proteins that help keep
you healthy. One important protein in red blood cells is
hemoglobin. Hemoglobin carries oxygen to all the cells in
your body. It also carries away carbon dioxide.
Many hormones are proteins. For example, insulin is
a protein hormone that helps control the level of sugar
in your blood. This is important for maintaining a steady
flow of energy.
Antibodies in your body are also made of proteins.
Antibodies attach to and destroy bacteria.
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Compounds of Living Things continued
NUCLEIC ACIDS
The largest organic compounds made by living things
are nucleic acids. Nucleic acids are made up of sugars,
phosphates, and nucleotides. Nucleotides are molecules
made of carbon, oxygen, hydrogen, nitrogen, and
phosphorus. Four different nucleotides are found in the
nucleic acid known as DNA. They are adenine, thymine,
guanine, and cytosine.
'
#
10. Identify What are
nucleic acids made of?
"ASEPAIR
' #
4
!
!DENINE
!
4
'
#
4HYMINE
4
!
!
4
'UANINE
3UGARPHOSPHATE
BACKBONE
READING CHECK
'
#
4
!
!
4
'
#
4
!
!
4
DNA is a complex molecule
that looks like a twisted ladder.
The bases are found in pairs
between the two sides of the
DNA ladder.
#YTOSINE
Nucleic acids store genetic information. They are
sometimes called “the blueprints of life.” This is because
they carry all the information needed for a cell to make
all of its proteins. If the protein code in a nucleic acid is
changed, the proteins it affects will not function normally.
Think of the differences in eye color between you and your
friends. They are due to differences in the nucleotide patterns
for proteins that make up the eye. The differences in nucleotide sequences result in different traits and different species.
TAKE A LOOK
11. Identify Which base is
always paired with thymine?
Say It
Predict Report to the class
on what might happen if
there were a change in the
nucleic acids needed to
make hemoglobin.
DNA AND RNA
There are two different types of nucleic acids: DNA
and RNA. A model of DNA is shown above. DNA is the
genetic material found in the nuclei of your cells. DNA
exists in long-chain polymers. If you stretched out the
DNA in a human cell, it would stretch about six feet!
When a cell needs to make a certain protein, it copies
a small part of the DNA onto another type of nucleic acid
called RNA. The RNA is moved out of the nucleus and
into the cytoplasm. The RNA directs the organization of
amino acids into a specific protein.
READING CHECK
12. Describe What
instructions does RNA contain?
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The Chemistry of Living Things
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Section 2 Review
Date
8.3.c, 8.6.c
SECTION VOCABULARY
carbohydrate a class of energy-giving nutrients
that includes sugars, starches, and fiber;
contains carbon, hydrogen, and oxygen
lipid a type of biochemical that does not
dissolve in water; fats and steroids are lipids
Wordwise The root lip means “fat.”
nucleic acid a molecule made up of subunits
called nucleotides
protein a molecule that is made up of amino
acids and that is needed to build and repair
body structures and to regulate processes in
the body
1. Infer How does water act as your body’s “shock cushion” ?
2. Fill In Complete the Spider Map of the compounds discussed in this section that
are vital for living things. Below each compound, tell if it is a small molecule or a
large molecule.
Compounds
living things
depend on
3. Identify Long-chain proteins and long-chain carbohydrates are examples of the
type of molecule called a
.
4. Classify What can both carbohydrates and lipids provide for the body?
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The Chemistry of Living Things