Download Julie Little Virginia Highlands Community College Ricin

Julie Little
Virginia Highlands Community College
Ricin - A Forced Review
Goal: At VHCC, we cover the immune system at the very end of the second semester. By then, most
students have forgotten many important details covered in beginning of the first semester (ex. Cell
Biology). After lecturing on the immune system, I will describe Dr. Seth Pincus’ research showing how
ricin kills humans and how antibodies can protect us. After the lecture, I will provide the students with
the following worksheet to complete. This worksheet will force the student to review their chemistry
and Cell Biology.
RICIN
( not just a cool toxin but a great way to force you to review all the stuff you wanted to forget! )
Your final is cumulative! So how much of the first semester do you remember? Work through this
worksheet using the first four chapters in your textbook. And you thought ricin was so cool a few
minutes ago. Have fun! Due next lecture.
1. Ricin is a protein weighing around 60,000-65,000 Daltons. When introduced into the body, it
binds to glycoproteins and glycolipids.
a. What is a Dalton?
b. How much (in Daltons) does one atom of hydrogen weigh? How much does one
molecule of water weigh?
c. What is the monomer of a protein?
d. Describe the levels of protein structure. For each level, name a protein in the human
body that exhibits that structure.
e. What is a glycoprotein? What is a glycolipid?
f. Where in your body do you find glycoproteins and glycolipids?
g. Why do cells need glycoproteins and glycolipids (what do they use them for)?
h. How do glycoproteins and glycolipids end up in the gylcocalyx?
2. Ricin enters cells via endocytosis. Three things can occur after ricin enters the cell. Sometimes,
the cell spits the ricin out to protect itself. Sometimes, the ricin that enters the cell is
transported to a lysosome for degradation. If the ricin that enters the cell is taken to a Golgi
body, the cell will die.
a. Name three passive ways a substance (any substance) can enter a cell.
b. For each way listed in #2a, describe what type of substance would use that method of
entry.
c. Name two active ways a substance enters a cell and give actual example of substances
that use the active pathways in the human body.
d. What is a lysosome? Where do they come from? How do they break down substances
within the cell that need to be broken down?
3. If the ricin is transported to the Golgi bodies within a cell, retrograde transport occurs and the
ricin is eventually transported to the cell ribosomes. Once this occurs, apoptosis is definite.
a. What does retrograde transport mean?
b. If you are a substance in the Golgi body and you move back through the endomembrane
system, where will you end up?
c. Why are ribosomes so important to the cell (what do they make)?
d. Name 5 proteins in the human body. Where were these proteins made (specifically)?
(Ex. Albumin is made by ribosomes inside liver cells OR Glucagon is made by ribosomes
inside pancreas cells.)
e. What structure (molecule) in the cell directly gives the ribosome its directions on how to
make the ribosome’s final product?
f. Where did #3e originate?
Ricin – A Forced Review
Answer Sheet
1.
Chemistry-related questions:
a.
A Dalton (da) is a unit of measurement used to weigh atoms and molecules. One Dalton
is approximately equal to one Atomic Mass Unit (u). Each proton and each neutron
weighs one Atomic Mass Unit while electrons (for all intents and purposes) weigh zero
Atomic Mass Units.
b.
Hydrogen atom: Since one hydrogen atom consists of a single proton (weighing 1 u), a
single electron (weighing 0 u), and no neutrons, it weighs one Atomic Mass Unit (u) or 1
Dalton (da).
Water molecule: A water molecule consists of 2 hydrogen atoms and one oxygen atom.
To find out how much a water molecule weighs, you need to determine how much each
atom in the molecule weighs. A hydrogen atom weighs 1da (previously determined).
An oxygen atom has 8 protons (collectively weighing 8da), 8 electrons (collectively
weighing 0da), and 8 neutrons (collectively weighing 8da). Therefore, the total weight
in Daltons for an oxygen atom is 16da. If you add the atomic weights together
(hydrogen atom = 1da times 2 +one oxygen atom at 16da), you will find that a water
molecule weighs 18da.
c.
The monomers of proteins are amino acids.
d.
Proteins have four levels of structure: primary, secondary, tertiary, and quarternary.
The primary structure of a protein involves the linear sequence of amino acids and is
determined by the cell’s DNA. All proteins have primary structure. The secondary
structure of a protein involves the coiling or pleating of a protein with primary structure.
All proteins exhibit secondary structure. The tertiary structure of a protein occurs when
the protein coils over about itself in a glob-like manner. Tertiary structure appears to be
random but it is not. Enzymes exhibit tertiary structure. An example of an enzyme in
the human body is helicase, the enzyme that uncoils and separates DNA during
replication. Quarternary structure of a protein involves at least two different
polypeptide chains coming together to form a protein. In the human body, hemoglobin
is a great example of a protein exhibiting quarternary structure. For hemoglobin, 4
different polypeptide chains (each exhibiting tertiary structure and looking rather globlike) come together to form the molecule. Another example of a quarternary protein is
collagen, the most abundant protein in the human body. Collagen consists of three
different polypeptide chains (each exhibiting secondary structure) twisting together to
form a strong, firm protein.
e.
A glycoprotein is a large molecule made of protein and carbohydrates. A glycolipid is a
molecule made of lipids and proteins.
2.
f.
Glycoproteins and glycolipids are found embedded within all of our the cells’ plasma
membranes. The carbohydrate and lipid portions (respectively) stick out into the
extracellular fluid creating the cell’s glycocalyx. Other glycoproteins found in the human
body that are not embedded within the plasma membrane include mucins (made in the
mucous membranes), antibodies, and blood plasma.
g.
Cells use glycoproteins and glycolipids in the glycocalyx in several different ways:
a. Identification – They act as self-markers of cells to prevent the body’s immune
system from attacking the body’s own cells.
b. Protection – antibodies are classified as glycoproteins.
c. Energy – glycolipids are used as energy sources.
d. Attachments sites – chemicals (various ligands) attach to glycoproteins and
glycolipids to cause a change within the cell. Ex. second messenger systems.
h.
The protein portion of the glycoproteins and glycolipids is made by a ribosome. Once
made, the protein portion enters the rough endoplasmic reticulum, where it is modified
(by adding a carbohydrate or lipid). Once modified, the newly made glycoproteins and
glycolipids are transported to the Golgi apparatus for further modification and sorting.
Once completed and sorted, the glycoproteins and glycolipids are packaged into the
walls of a vesicle which buds off of the Golgi apparatus. The vesicle travels to the
plasma membrane via the cytoskeleton system. Once the vesicle reaches the plasma
membrane, it fuses with the plasma membrane.
Cell Biology related questions:
a. Simple diffusion, facilitated diffusion, osmosis, and filtration.
b. Simple diffusion – small, nonpolar substances; facilitated diffusion – small, charged or
polar particles; osmosis – water; filtration – water and small solutes dissolved in the
water (no large proteins)
c. Active transport – ex. Na+/K+ pump that transports sodium out of the cell against its
concentration and potassium into the cell against its concentration gradient;
endocytosis –many hormones, growth factors, and proteins (and ricin!); exocytosis –
cellular wastes, cell products (ex. hormones, mucus), and ricin!
d. Lysosomes are cell organelles that function in intracellular digestion and clean-up. They
are packed full of acid hydrolases (enzymes) to break down degraded organelles, foreign
materials that enter the cell, and food substances. They originate from the Golgi
apparatus.
3.
Cell Biology related question:
a. Retrograde transport inside a cell means moving against the grain. For instance,
retrograde movement inside a neuron implies movement of a substance is moving from
an axon back into the cell body (substances usually flow from the cell body to the axon
to the axonal terminals). In the case of ricin, retrograde transport implies reverse
movement through the cell’s endomembrane system. Ricin is brought into the cell,
transported to the Golgi apparatus, then sent through the endoplasmic reticulum, and
then finally to the ribosomes. Normal flow is from ribosome  ERGolgi apparatus.
b. In the ribosomes.
c. Ribosomes make proteins.
d. I asked the student to name 5 proteins in the human body and list where they are
specifically made. I cannot make an answer key for this question b/c there are too many
possible answers. However, I am looking for the name of a protein, the cell that makes
it, and which organelle inside the cell makes it. For example, antibodies are made by
the ribosomes of white blood cells or thyroid stimulating hormone is made by the
ribosomes of the anterior pituicytes.
e. The mRNA delivers instructions to the ribosome of how to make each protein.
f.
The mRNA was made off of the DNA inside the nucleus.
Sources:
Marieb, E.N. and Hoehn, K. 2007. Human Anatomy and Physiology 7th Ed. :San Fransisc, CA: Prentice
Hall.
Stoker, H.S. 2004. General, Organic, and Biological Chemistry, 3rd Ed. New York, New York: Houghton
Mifflin.
http://en.wikipedia.org/wiki/Atomic_mass_unit
http://en.wikipedia.org/wiki/Glycoprotein
http://en.wikipedia.org/wiki/Glycolipids