The
Molecules of Life [Ch. 3]
Four
major groups of macromolecules are essential for the life of the cell:
carbohydrates, lipids, proteins and nucleic acids. These four categories
of molecules consist of very large organic compounds with an enormous variety
in terms of function. Fortunately, the basic concept of their structure
is a simple one: a large number of building blocks (monomers) are joined
together with covalent bonds to form larger molecules (polymers). Their
unique structures give them a variety of different functions within living
systems. Natural selection and the process of evolution is the source of
variety in structure and function in these molecules.
Review Questions: [continue
to the links or the outline]
-
It is often stated that life is
made of organic compounds. What exactly is meant by that statement?
-
The carbon atoms and other elements
are joined to form different functional groups. How does different functional
groups affect the different properties (charged, non-charged, bulky, small,
polar, non-polar etc.) of a molecule?
-
How do monomers form polymers
via dehydration synthesis?
-
How are polymers broken down to
monomers via hydrolysis?
-
Note: You need to be able to
recognize different types of monomers and polymers. E.g. assume the test
has a figure of fructose. You should be able to recognize it as a monosaccharide
(simple sugar). A figure of any of the twenty amino acids should be recognized
as an amino acid and so on.
-
What is a monosaccharide? Give
examples of, and recognize figures of, monosaccharides (simple sugars).
-
What is a disaccharide? Examples?
-
Understand the concept of polysaccharides.
Describe the following three examples of polysaccharides (including their
source and function): Starch, glycogen and
cellulose.
-
What is a lipid (definition)?
-
How do hydrophobic and hydrophilic
compounds differ from each other?
-
What is the function of fats and
oils in living organisms?
-
Fats are often referred to as
triglycerides. Describe the basic components of a triglyceride.
-
What is the difference between
unsaturated and saturated fatty acids?
-
Can you give examples of where
one can expect to find unsaturated and saturated fats? Is there a reason
for why either of these fats/oils dominate in those organisms?
-
There are other types of lipids
than triglycerides. Some examples are phospholipids, waxes and steroids.
Briefly describe how these differ from each other as well as their function
in biological systems.
-
What is an anabolic steroid?
-
Proteins are very important macromolecules.
Give six examples of the different functions proteins can have within an
organism.
-
What are the building blocks for
proteins? How many different kinds of these building blocks are available
for human proteins?
-
Sketch an amino acid. Would you
recognize it on a test?
-
How are amino acids joined together
to form a peptide?
-
What is the connection between
the shape of a protein and its function?
-
What is denaturation? What causes
denaturation? How does the process of denaturation affect the function
of a protein?
-
Define the primary structure of
a protein.
-
Define the secondary structure
of a protein (local folding into a helix or a sheet).
-
Define the tertiary structure
of a protein. It is crucial that you understand how the shape of a protein
determines its function.
-
Define the quaternary structure
of a protein (more than one polypeptide unite to form the protein e.g.
hemoglobin). Do all proteins have a quaternary structure?
-
Who is Linus Pauling? How did
he contribute to our knowledge of macromolecules?
-
What is the role of nucleic acids
in living organisms?
-
There are two different types
of nucleic acids in a cell. What are they and how do they differ from each
other in structure and function?
-
What is adenosine triphosphate
(ATP)?
-
What is the function of DNA?
-
What are
the building blocks of nucleic acids?
-
Describe how the building blocks
(nucleotides) are joined together with covalent bonds to form a macromolecule
(nucleic acids).
-
Know the general structure of
the double helix and the concept of base pairing (A with T, G with C).
-
What is the complementary sequence
to the following DNA sequence: ATC CTA AAC GTA?
Lecture Outline
Macromolecules: We
will look at four major groups of macromolecules: carbohydrates/ lipids/
proteins and nucleic acids. These very large molecules fulfill important
roles in the cellular realm.
The building blocks of macromolecules
are referred to as monomers. The macromolecule itself is a polymer.
The process by which the monomers
are joined together to form the polymer is called a condensation
reaction.
The breakdown of the polymer
to form the monomers is called hydrolysis.
Carbohydrates
"Carbon water" - since
they are formed by the elements C, H and O. If these atoms are counted
in a sugar molecule they will form a multiple of C and H2O. All the molecules
in this group (from the small sugar molecules to the enormous starch molecules
(macromolecule)) are referred to as carbohydrates.
The building blocks of carbohydrates
are referred to as monosaccharides (or simple sugars). Examples of such
sugars are glucose, fructose and galactose. |
 |
Disaccharides are two monosaccharides
joined together (e.g. sucrose, lactose or maltose)
Monosaccharides and disaccharides
are joined together to form polysaccharides.
Polysaccharides: large polymers
of simple sugars connected with covalent bonds
Examples:
-
starch (storage of energy ion
plants)
-
glycogen (storage of energy in
animals [liver, muscle] (remember that most of the energy in animals is
stored in the form of fat [triglycerides]); branched structure for faster
access)
-
cellulose (structural carbohydrates
in plants and algae in their cell walls) [all of the three carbohydrates
above are made of glucose units as monomers]
-
chitin (structural component of
fungi (cell walls) and in exoskeletons of arthropods [e.g. insects and
crustaceans]
|
starch (energy storage
in plants) |
glycogen (energy
storage in animals esp in muscle tissue and the liver) |
cellulose (structural component
in plants (cell walls)) |
Lipids
A group of several types of
molecules. They are all referred to as lipids since they cannot be dissolved
in water. They are hydrophobic ("water fearing").
In contrast a hydrophilic
("water loving") compound is attracted to water.
Understand the difference
between hydrophobic versus hydrophilic characteristics in a molecule.
We are studying A. Fats, B.
Phospholipids and C. Steroids in this section.
A. Triglycerides
or Fats/oils (components: glycerol + three fatty acids)
There are two
major types of fatty acids: unsaturated versus saturated fatty acids; these
are the building blocks of fats.
The presence
of double bonds in an otherwise uniforms chain of carbon and hydrogen atoms
cause kinks in the molecular structure.
Unsaturated
fatty acids are prominent in triglycerides with an origin from plants. |
 |
FATS: (glycerol + three
fatty acids) [triglycerides] (to the right)
Biological roles:
-
energy storage (2x energy/weight
compared to carbohydrates). It is not surprising that animals were selected
for using fat for energy storage since it is an efficient form of storing
energy relative to its weight. Plants tend to use starch instead for storing
energy. Why do you think that is?
-
insulation: especially prominent
in some mammals and birds. Recall the example from class (penguins and
seals).
-
padding (some organs have extra
padding of fat)
The diagram to the right compares
a saturated versus an unsaturated fat molecule. Notice the "bulky" aspect
of the unsaturated fat. What do you think are some possible consequences
of this "bulkiness"? In which organisms do you tend to find unsaturated
fats? Why do you think that is? |
 |
B. Phospholipids
(glycerol + two fatty acids + phosphate group [polar])
the molecules
form a bilayer in water. One part of the molecule is hydrophobic while
the other is hydrophilic (this is often referred to as amphipathic).
Phospholipids is
a basic structural component of the cell membrane. You will learn more
about membranes later. They serve as selective barriers.
C. Steroids
Some hormones are
steroids (estrogen/ testosterone)
Another example
is cholesterol is an important structural componment of cell membranes
in animals (it stabilizes the fluidity of the membrane).
Proteins:
Crucial functions in
the organism
Examples:
-
structural proteins (e.g. keratin
in hair, nails and skin)
-
enzymes (e.g. amylase that breaks
down starch to maltose)
-
antibodies (immunoglobulins [Ig])
-
hormones (not all) (e.g. insulin
and human growth hormone)
-
clotting factors in blood
-
transport proteins (e.g. hemoglobin
transporting oxygen)
-
membrane proteins
|
Amino
acids are the building blocks of proteins.
The
figure above shows the basic structure of an amino acid
(R is the variable side chain
that strongly influences the property of
the amino acids (see below))
There are 20 different kinds
of amino acids in the human species
(you do not need to
memorize them!).
Each amino acid has different chemical properties
(large vs small, hydrophobic
vs hydrophilic) |
The amino acids are
joined by peptide bonds (a type of covalent bond) to form a polypeptide.
The amino acid sequence will
determine the three-dimensional structure of the protein which ultimately
is linked to its function. Since life is waterbased their behavior relative
to water is very important. The protein folds into a unique structure as
it is exposed to a water environment.
The structure of proteins
can be viewed as primary, secondary, tertiary and quaternary structure
The three dimensional shape
of the protein very important for its function.
This shape is influenced
by the solvent (water) as well as surrounding solutes, pH and temperature.
Even physical pressure can affect the shape. This is not something that
is critical for us, but for deep sea fish it is a critical issue.
Denaturation of proteins (caused
by temperature or chemicals) may inactivate the protein (may be irreversible)
by changing its tertiary structure.
Nucleic acids
function: information
carriers and information storage
deoxyribonucleic acid
(DNA)
ribonucleic acid (RNA)
building block: nucleotides
(a 5-carbon sugar + a phosphate + a nitrogenous base)
4 bases in DNA: adenine,
thymine, guanine, cytosine (A T G and C)
4 bases in RNA: adenine,
uracil, guanine, cytosine (A U G and C)
link the nucleotides
to form a polynucleotide (a nucleic acid) |
 |
After
reading these chapters you will have the fundamental knowledge to approach
biology on a cellular level. Remember to not be intimidated by complex
terminology. You are learning a lot of new concepts
and structures. It is necessary to use labels to be able to study the cellular
realm and journey further into the field of biology.
Links:
