Download What is Life? Project PART 6: The molecules of life

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What is Life? Project PART 6: The molecules of life
Due Monday 9/17 (15 points)
Read the following text and answer the questions:
The Molecules of Life
All living things are composed of chemical compounds.
Cells consist mostly of water, but the rest of them consist mostly of carbon-based
molecules. Carbon can form large, complex, diverse molecules that are necessary for life
functions. Compounds that contain carbon are called organic compounds.
Carbon is an important molecular ingredient in all living things because of its unique
bonding ability. A carbon atom has 4 electrons in its outer shell that holds 8. This means
that carbon can complete its outer shell by sharing electrons with 4 other atoms in four
covalent bonds. Each carbon thus acts as an intersection from which an organic molecule
can branch off in up to four different directions. And because the carbon can use one or
more of its bonds to attach to other carbon atoms, it is possible to construct an endless
diversity of carbon skeletons.
Below are examples of different carbon molecules:
H
H–C–H
H
H
H
H
H–C–C–C–H
H
H
H
All of these examples are examples of carbon bonding to hydrogen.
1. Can you complete the following molecule by bonding hydrogen atoms?
(0.5 point)
H
H–C–
2. How would your molecule change if you added one more carbon atom? Draw it.
(0.5 point)
Below are examples of carbon molecules with double bonds:
H
H
H
H
H
H–C=C–C–C-H
H
H
H
H
H–C–C=C–C-H
H
H
H
3. Can you complete the following molecule by bonding hydrogen atoms?
(0.5 point)
H–C=C
Below are examples of carbon molecules that are arranged in rings:
Benzene
Fructose
Each type of organic molecule has a unique three-dimensional shape. Many vital processes
within living organisms rely on the ability of molecules to recognize one another based on
their shape. The unique properties of an organic molecule depend not only on its carbon
skeleton, but also on the atoms attached to the skeleton. Certain atoms that usually
participate in chemical reactions are called functional groups. These functional groups
usually behave the same way on different molecules. Functional groups help give each
molecule its unique properties.
Below are some common functional groups on organic molecules:
Hydroxyl group:
H
H
H – C – C – OH
H
H
Found in sugars and
alcohols
Carbonyl group:
H
O
H
H–C–C–C–H
H
H
H
Found in sugars
Amino group:
H
H
H–C–N
H
Carboxyl group:
H
O
H–C–C
H
Found in _____________.
H
OH
Found in amino acids and
fatty acids
5. What functional groups do you think you could find on amino acids (the
monomers of proteins)? (0.5 point)
Giant molecules from smaller building blocks
On a molecular scale, many of life’s molecules are gigantic; in fact, biologists call them
macromolecules. DNA is a macromolecule, as are the carbohydrates in starchy foods and
the proteins that compose your hair. Even though they are quite large, the structure of
most macromolecules can be easily understood because they are the polymers, large
molecules made by stringing together smaller molecules called monomers.
Cells link monomers together through a dehydration reaction, a chemical reaction that
removes a molecule of water.
Organisms not only make macromolecules, but they also have to break them down. For
example, many of the molecules in your food are macromolecules. You must digest these
giant molecules in order to make their monomers available for your cells, which can rebuild
the monomers into your own brand of macromolecules. Digestion occurs through the
process known as hydrolysis. Hydrolysis means to break down with water.
The diagram below shows the synthesis and digestion of polymers:
There are four main categories of molecules that we find in living things: carbohydrates,
proteins, lipids, and nucleic acids.
Carbohydrates
Carbohydrates are a chemical compound consisting of carbon, hydrogen, and oxygen.
Sugar, starch, and cellulose are all examples of carbohydrates. Usually the atoms of these
molecules are present in a ratio that is expressed by the formula CnH2nOn.
There are many types of carbohydrates. They have been placed into three groups:
monosaccharides, disaccharides, and polysaccharides.
6. What does the prefix “mono-“ mean? (0.5 point)
7. What does “di-“ mean? (0.5 point)
8. What does “poly-“ mean? (0.5 point)
9. What does saccharide mean? (0.5 point)
Sugars have been used for ages to make food sweeter. The most common dietary sugars
are glucose (or dextrose), fructose, and sucrose. Both glucose and fructose are
monosaccharides. Sucrose is a disaccharide. Common table sugar is sucrose, usually
obtained from sugarcane or sugar beets. Glucose is corn syrup. Glucose is also the sugar
used by the cells of our bodies for energy. Because it is the sugar that circulates in the
bloodstream, it is often called blood sugar. Fructose is found in honey and in some fruits,
but much of it is made from glucose. Corn syrup can be treated with enzymes to convert
much of the glucose to fructose. The result is high fructose corn syrup. Fructose is sweeter
than sucrose or glucose. Foods sweetened to the same degree with high-fructose corn syrup
have somewhat fewer calories than those sweetened with sucrose.
Glucose is an example of a monosaccharide.
Sucrose is an example of a disaccharide. When hydrolyzed, it will yield two
monosaccharide units: glucose and fructose.
Complex carbohydrates are polysaccharides. Starch and cellulose are examples of
polysaccharides. Starch and cellulose are both polymers of glucose. Starch is the main
energy storage system in plants. You can find roots and other plant organs. You observed
starch when you looked at the potato cells under the microscope. The amyloplasts, starch
storage sacks, turned purple with iodine.
Cellulose is the structural material of plants. Plant cell walls are made of polysaccarhrides
called cellulose. The cellulose molecules are assembled into fibrils that make up the main
fabric of cell walls. Wood is composed of cellulose and other polymers.
Starch and cellulose differ in the connecting links between the glucose units. Humans can
digest starch, but not cellulose. Starch is hydrolyzed to glucose when it is digested. The
body then metabolizes the glucose, using it as a source of energy. Glucose is broken down
through a complex set of more than 50 chemical reactions to produce carbon dioxide and
water with the release of energy.
C6H12O6 + 6 O2 Æ6 CO2 + 6 H2O + Energy
These reactions are essentially the reverse of photosynthesis. In this way, animal organisms
are able to make use of the energy from the sun that was captured by plants in the process
of photosynthesis.
We can eat cellulose, but we cannot digest it. We get no nutrient value from it. It is just
fiber. Certain bacteria have such enzymes, however, and they are present in grazing
animals, such as cows, and in termites. These animals can also convert cellulose to
glucose.
10. Cut out the sugars on the attached colored paper. In the space below, tape and
label the following saccharides. For each bond you make, be sure to show the
water formed as well.
• Glucose, a monosaccharide
• Fructose, a monosaccharide
• Sucrose, a disaccharide consisting of glucose and fructose
• Starch, a polysaccharide consisting of three or more glucose
(2 points)
Proteins
Proteins are an important molecular component of all living things. Your body contains tens
of thousands of different proteins. Each protein has a unique three-dimensional shape that
corresponds to a specific function. Proteins make up many of the structures in your body;
every time you look at your hair, your toenails, your skin, and your muscles, they’re all
protein. Proteins are found within the plasma membrane and other membranes of the cell.
These proteins are called membrane proteins. Proteins also make up the cytoskeleton of
the cell. Not only do proteins help maintain cell structure, but they also help change the
rate of chemical reactions in cells and organisms. Special proteins, called enzymes, can
change the rate of the reaction without being used in the process.
Proteins are made up of Amino Acids. The 20 amino acids make up all the proteins in your
body. Some amino acids the body can make by itself, others must be eaten as part of your
diet. The amino acids that must be eaten are called “Essential Amino Acids”. Vegetarians
must be especially careful that their diet includes these essential amino acids, as they are
most commonly found in eggs and meats.
11. Cut out the amino acids on the attached colored paper. In the space below,
tape and label the following molecules. For each bond, make sure you show the
water formed as well.
•
•
•
Alanine, an amino acid
Valine-tryptophan, a dipeptide
Use all the rest to create a large polypeptide (1. 5 points)
12. What do you think “peptide” means? (0.5 point)
Lipids
Lipids are another important class of organic molecules. Lipids are partially made of fats,
and partially made from alcohol. The fats are called “fatty acids” and the alcohol is glycerol.
The fatty end of these molecules will not dissolve in water, but the glycerol end will. For this
reason when you drop lipids in water, they form little balls, with the glycerol ends touching
the water, and the fatty ends in the middle.
The plasma membrane, as well as other membranes in the cell, is composed mostly of lipids
and proteins. The lipids belong to a special category called phospholipids. They are related
to dietary fats but have only two fatty acid tails instead of three. A phospholipid has a
phosphate group in place of the third fatty acid.
13. To build a lipid, you need to combine three fatty acids and one glycerol
molecule. Cut out the appropriate molecules from the “Pieces” paper. Label each
part of the lipid as “Fatty Acid” or “Glycerol.” For each bond you make, be sure to
show the water formed as well. There should be three waters formed for each
lipid you make.
(1 point)
Nucleic Acids
DNA is a nucleic acid. DNA is the chemical in your body that carries the genes used to
determine your hair color, eye color, skin color, gender and many other things. When
something is cloned, scientists must start with a good copy of that animal’s DNA.
The building blocks of nucleic acids are nucleotides. Nucleotides stack in a special way. They
stack in pairs, like a big zipper. Then, if the long chain is “unzipped”, each side can be used
to make a whole new side, resulting in two chains exactly like the first one. The sequence of
nucleotides in a long chain is actually an instruction manual for making proteins. You will
learn more about DNA and other nucleic acids, like RNA, later in the semester.
14. Cut out the nucleotides. In the space below, create a double strand of DNA. Be
sure to match them up appropriately by shape!
(1 point)
15. Now choose one organelle/structure of the cell to investigate in more detail.
You will find this organelle’s chemical composition (Is it a fat, protein, sugar, or
nucleic acid?) You will draw an enlarged picture of the organelle and show the
macromolecules, and atoms that compose these macromolecules on your cell
poster. Please do your drawing IN PENCIL.
(5 points)
Resources:
Boyes, Lee. Poly Bio Chem Activity. Unpublished Lesson. 2007.
Campbell, N. A., Reece, J. B., and Simon, E. J. Essential Biology with Physiology. 2nd Ed.
Pearson/Benjamin Cummings, 2007. 36-50.
Hill, J. W., and Kolb, D. K. (2001). Chemistry for Changing Times. 9th Ed. Upper Saddle
River, New Jersey: Prentice Hall.
Moniz de Sá, Mário. Langara College. Biology 2315 Lecture Notes. “Chapter 1: An
Introduction to Biochemistry”. January, 2007. September 16, 2007.
http://www.langara.bc.ca/biology/mario/Assets/Hy-dehydrationRx.jpg