Eukaryotic Cells 1: Immune system examples

Question 1

List and describe the microbe groups that are eukaryotic. List the other groups of eukaryotes that are important for this class.

Answer 1

• amoeba- moves by extending pseudopods.
• Giardia- protozoans that have two nuclei and multiple flagella.
• trypanosomes- protozoan cells that move with an undulating membrane.
• Protozoans- moves like an animal. It has some kind of motility, either by an undulating membrane, pseudopods, flagella or cilia. They divide by sexual and asexual reproduction. Some of them have complex life cycles. Like us, they’re chemoheterotrophs. Some protozoans are pathogenic, but most of them are not.
• fungi- They have long chains of eukaryotic cells that grow in tangled fibers. They have structures that release tiny, little spores.
  - Single celled fungi are called yeast and we might be familiar with yeast infections: thrush- a yeast infection in somebody’s throat. The fungi are a little different than the protozoans, because all fungi have cell walls. The cell wall consists of multiple layers. It consists of things like mannans and glucans, which are potent stimulators of the immune system, and also something else called chitin.
  - Most of the fungi that we might be familiar with are multicellular–they’re filamentous, they’re molds, but some fungi are unicellular. Just like the protozoans, and just like us they’re chemoheterotrophs. They release digestive enzymes outside of their cells, do external digestion and then absorb simple molecules by diffusion.
• algae- Green pigment in these multicellular or unicellular eukaryotes. while very few algae are capable of infecting, very few algae are truly pathogens, they can impact human health, because some are toxigenic and they can kill wildlife, they can kill fish, or they can cause shellfish poisoning and related diseases to humans.
• animals- the one that we’re perhaps going to emphasize the most; a small group of the animals…are microbes that we need to consider and that is the helminths.
  - Helminths are microbes. They are animals and we can in a sort of non-strict, non-formal way divide them up into tapeworms, flukes, and nematodes, or roundworms.
  - Humans fall in the kingdom of animals. And so all of our cells are eukaryotic animal cells like our white blood cells.
  - Pets or livestock also fall under the kingdom of animals.

Question 2

Briefly describe how eukaryotic cells are different from prokaryotic cells.

Answer 2

Eukaryotic cells are full of numerous compartments: endoplasmic reticulum, ribosomes, etc… Eukaryotic cells have a membrane-bound nucleus and prokaryotic cells do not. The nucleus is where eukaryotes store their genetic information.

Question 3

What is a vector?

Answer 3

A vector is an invertebrate animal capable of carrying a microbe. It’s an invertebrate (an organism, an animal that lacks a backbone) animal that is capable of carrying and transmitting a pathogen. Other invertebrate vectors to think about are things like ticks or fleas or lice. These are all examples of invertebrates that are capable of biting people and transmitting a pathogen that way.

Question 4

What is a zoonotic pathogen?

Answer 4

To be a host for a zoonotic disease, you have to be a vertebrate.

Question 5

A bacteria infects the gut of a tick. The tick bites a person and the bacteria then infects the person. Is this a zoonotic infection? Why or why not? What other terminology could be applied to this situation?

Answer 5

No, it’s not zoonotic because ticks don’t have vertebrates. It is considered a vector since the animal that caused the infection is an invertebrate.

Question 6

Fungi don’t do phagocytosis. Why not?

Answer 6

Fungi don’t do phagocytosis because they release digestive enzymes outside of their cells and do external digestion and then absorb simple molecules through diffusion (ex. A fungal cell releases enzymes outside of their cell to digest starch in bread and then absorb glucose). Phagocytosis requires the reshaping of the plasma membrane so that a large object, like a bacterial cell, can be taken in and digested. Bacteria cells are small compared to us but are large compared to dissolved sugars and proteins. Phagocytosis is the process by which a cell uses its plasma membrane to engulf a large particle, giving rise to an internal compartment called the phagosome.

Question 7

Besides holding chromosomes, what is the major function of the nucleus?

Answer 7

The nucleus helps regulate gene expression- refers to which coding genes are being transcribed and translated to make proteins, which coding genes are actively being used as instructions for proteins. Controlling which proteins the cell makes. And the cells of our body change which proteins they make over time. They respond to changing conditions, they adapt.

Question 8

Name one of the cytoskeletal networks described in the textbook.

Answer 8

There are three flavors of cytoskeleton: microtubules, intermediate filaments, and actin microfilaments.

Question 9

What are the functions of the cytoskeleton?

Answer 9

Cytoskeleton gives a cell its shape. Since the shape of some cells can change, what this really means is that the cytoskeleton is involved in cell movement. Inside the cell, the cytoskeleton allows for the movement of organelles inside the cell. You might say the cytoskeleton is involved in anchoring some organelles.

Question 10

What do transport proteins do?

Answer 10

Transport proteins are important for allowing things in and out of cells. Some things do not cross through the lipid portion of a membrane. And the transport proteins would allow things in–things like ions, things like glucose molecules to cross through membranes, by way of transport proteins.

Question 11

Find the diagram of the small intestines in the Eukaryotic Cells 1: Immune System Examples slides. The diagram has villus and crypt regions labeled. Dysregulation of transport across the intestinal wall can result in watery diarrhea. Which part of the transport story could be dysregulated to cause watery diarrhea–the villus portion or the crypt portion? How would it have to be dysregulated–overactive or inhibited?

Answer 11

Nutrients would be absorbed across the cells that make up the intestinal wall and enter the bloodstream. That kind of absorption mainly happens in the villus, And each of the cells on the villus have these little folds called microvilli to help increase their absorption surface area.

The intestinal villi are small finger like projections that extend into the lumen of the small intestine. Each villus has many microvilli projecting from its epithelial surface, collectively forming a brush border. Villi are specialized for absorption and have very thin walls which are single cell thick. The villi of the small intestine project into the intestinal cavity, greatly increasing the surface area for food absorption and adding digestive secretions.

Crypts are moat-like invaginations of the epithelium around the villi, and are lined largely with younger epithelial cells which are involved primarily in secretion. Crypt cells actively secrete electrolytes, leading to water secretion.

Question 12

Nearly all cells have MHC-1. What is the cellular location of MHC-1 when it is carrying out its function? What is the function of MHC-1?

Answer 12

T cell receptor looks for information on the surface of antigen presenting cells which have a different protein on their surface called MHC class one. The MHC one protein can present signs of infection; if there is a pathogen growing inside the cell, the MHC one will present antigens from that pathogen.

Question 13

A few specific cell types have MHC-2. Helper (CD4) T cells interact with MHC-2. What types of T cells interact with MHC-1? What do they use to interact with MHC-1?

Answer 13

T lymphocytes that are called cytotoxic or helper T cells will recognize those antigens. While some pathogens are really slick and they’re like, “I’m going to hide inside this human cell, but I don’t want the immune system to find me.” And so they tell that cell that they’re hiding in, “Stop putting MHC one on your surface, stop presenting antigens.” This is a way of the pathogen hiding in human cells. And so we have a fallback strategy, we have these natural killer cells that recognize any human cell that is no longer expressing MHC1.

Question 14

Name 2 molecules found on the surface of bacteria that allow immune system cells to quickly identify them as bacterial cells. How do the immune system cells detect them?

Answer 14

We have a white blood cell with these membrane proteins on its surface. One of those membrane proteins is called the CD 14 receptor. and the other one’s called a Toll-like receptor (TLR). What these proteins do is they recognize lipopolysaccharide. And they recognize lipoteichoic acid. Gram negative bacteria have an outer membrane that has LPS or lipopolysaccharide. And so this cell is capable of tasting and detecting that type of molecule. It’s a way for this cell to recognize bacteria. Gram positive bacteria do not have an outer membrane, and do not have lipopolysaccharide, but they do have lipoteichoic acids. And it turns out the cells can also recognize lipoteichoic acid.

Question 15

Immune system cells can easily detect most fungal cells. Propose a molecule that the immune system recognizes? What type of protein do the immune system cells use to identify fungal cells?

Answer 15

T cell proteins are a type of way that the immune system identifies fungal cells. The T lymphocytes that are called cytotoxic or helper T cells will recognize those antigens present in MHC-1. Cells recognize each other by the interaction of proteins that are embedded in their membranes and this is a key part of the function of the immune system.

Question 16

Complete the following sentences. In epithelial tissues, anchoring proteins connect _____ to each other and to the ____________.

Answer 16

cells

extracellular matrix

Question 17

What are the functions of tight junction proteins?

Answer 17

Tight junctions are these proteins that penetrate through the membranes of two neighboring cells that hold those cells so tightly together that water molecules cannot diffuse in between those cells easily. This is part of our waterproofing effect. If you have a bunch of cells that line a mucous membrane, then you can imagine water molecules and other molecules might slip in between those cells and penetrate into the body. And microbes might try to slip in between those cells and get into the body. And those tight junctions create this seal. It makes it hard for microorganisms to just slip in between our cells and enter into the body, into the bloodstream, into the lymphatics.

Question 18

Some bacteria secrete enzymes that digest the anchoring proteins in skin. State 2 possible consequences.

Answer 18

Microbes might try to slip in between those cells and get into the body. And those tight junctions/anchoring proteins create this seal. It makes it hard for microorganisms to just slip in between our cells and enter into the body, into the bloodstream, into the lymphatics. Once the integrity of the epidermis is compromised, bacterial proteases released from colonizing pathogens can significantly deter the immune system and lead to further tissue damage and to bacterial dissemination and infection.

Question 19

Some pathogens disrupt the function of tight junctions in the intestines. State 2 possible consequences.

Answer 19

tight junction is a kind of waterproofing protein that prevents water from diffusing
past cells through the spaces between them so without it, pathogens could invade
the cells more easily.

Question 20

What are 2 functions of the Golgi apparatus?

Answer 20

Golgi has two main functions. It’s going to modify any of the proteins that arrive at the gold G apparatus, namely the sugar chains on those proteins are going to be modified if it’s going to be a glycoprotein. The Golgi’s other main function is to sort proteins based upon their destination. So this mixture of proteins with various destinations arrives at the Golgi. Golgi apparatus is really like the post office of the cell that sorts things out so that all proteins that go into a common destination, end up in the same vesicle.

Question 21

Where is the nuclear pore complex located? What does it do normally?

Answer 21

The way that messenger RNA gets out of the nucleus is through the nuclear pore or nuclear pore complex which are these little gates in the envelope of the nucleus.

Question 22

Protein X is secreted by a eukaryotic cell. Starting with the mRNA for protein X, describe the steps in its synthesis and secretion.

Answer 22

So the ribosome, which always starts translation in the cytosol can stay in the cytosol to build a cytosolic protein, or it can become attached to the ER if it’s going to build a secreted or membrane protein. The secreted or membrane protein gets built in the ER, and it either gets attached to the membrane of the ER or it goes into the hollow space inside of the ER called the lumen of the ER. Eventually a mixture of proteins in the ER membrane and in the lumen of the ER. a mixture of proteins gets carried away from the ER in a little bubble. And so this is now called the vesicle, this thing that’s about to break free from the ER and it then goes to the Golgi apparatus.

Question 23

Protein W is found in the cytosol of a eukaryotic cell. Starting with the mRNA for protein W, describe the steps in its synthesis.

Answer 23

Whether they are healthy cells or whether they are infected cells, they’re going to be making proteins. A sample of those proteins is taken–say 1% of the protein molecules in the cell. The cell sends that sample, that 1% of all those protein molecules, to a structure in the cytosol called the proteasome. The proteasome takes that sampling of proteins and it starts this quality control process that the body uses to look for infection. It takes those proteins and it digests them into short segments of 12 to 15 amino acids. We’re going to call those peptides. So the proteasome is this sort of enzymatic garbage disposal inside of the cell. And it takes a sampling of the proteins in it digest them so that they end up in these pieces of protein called peptides, that are only 12 to 15 amino acids long. Those peptides, then get transported to the ER. And they get connected to a protein called MHC one.

Question 24

MHC-1 proteins on a cell’s surface display many different peptides. Where do the peptides come from and how do they come to be associated with MHC-1? How does MHC-1 get to the surface of a human cell?

Answer 24

so if this is the surface of the cell, and this is my plasma membrane, what we’re going to end up with is this protein that I like to draw like this–this is our MHC one protein And what it’s holding, what it’s pinching and that little cup like structure is a little peptide. It’s presenting to the immune system a fragment of the proteins that it has inside it. And so it has many different proteins that it’s building. And so it’s going to have peptides from different proteins which are going to have slightly different shapes and it’s going to be presenting them on the surface of the cell. TC interrogate each cell’s MHC I with a T-cell receptor (each TCR recognizes 1
foreign peptide) TC cells do not recognize self peptides. If a peptide is recognized, it is foreign, indicating that foreign proteins are being made in the cell. Example: viral
Proteins. Example: intracellular pathogenic bacteria proteins.

Question 25

Our definition of antigen is not yet complete. What is our working definition of antigen at this point?

Answer 25

An antigen is a molecule that is recognized as foreign by a lymphocyte. Any molecule that lymphocytes- which is a type of white blood cell, would recognize as not being human as being a foreign molecule.

Question 26

Which types of pathogens are detected with the help of MHC-1?

Answer 26

viral proteins

intracellular pathogenic bacteria proteins

Question 27

What do cytotoxic (CD8) T cells do?

Answer 27

Cytotoxic T cells have on their surface some kind of protein called the T cell receptor. Some other cell of the human body, just about every other cell of the human body, is then going to be holding up various peptide antigens in MHC one. And so if this T cell receptor, which should only be able to recognize foreign peptides, if this T cell receptor recognizes that peptide being held by MHC one then this T cell knows that this cell is infected. If this cell is infected, then some of the peptides on its surface will be foreign. It will be antigens. The T cell receptor only recognizes foreign. And so when the cytotoxic T cell recognizes that foreign peptide, it’s going to say we have a problem here, and it’s going to send signals to that infected cell that will trigger death, it will send the death signal. This is just about the cytotoxic T cells, the T sub c cells. It has nothing to do with the helper T cells.

Question 28

What do natural killer cells do? Are they redundant to CD8 T cells or are they complementary? Explain.

Answer 28

natural killer cells detect missing MHC-1 and trigger apoptosis of cells that are
not displaying MHC-1. I would consider the complementary to CD8T cells since they both detect infected cells and trigger/cause cell death.

Question 29

Briefly define and describe apoptosis.

Answer 29

the self destruct sequence of the infected cell, something we call apoptosis. The infected cell will digest its own DNA and fragment itself into little pieces called blebs. So the infected cells then destroyed, meaning it’s no longer a good hiding place for the pathogen and it no longer can serve as a factory for making viruses. So this is part of our defense against intracellular pathogens. We present peptide fragments on a membrane protein. We detect foreign peptide fragments with a membrane protein. And we trigger apoptosis or cell suicide or programmed cell death, when we recognize those foreign proteins. And so this death signal triggers apoptosis. Which can be called cell suicide, but perhaps better called programmed cell death.

Question 30

Which type of human cell secretes antibodies? What are 2 other names for antibodies?

Answer 30

Plasma cells secrete antibodies. Antibodies are also called gamma globulins, and immunoglobulins. It all means the same thing.

Question 31

Diagram a typical antibody. What type of molecule is it (polysaccharide, lipid, etc)? What are the important structural features of an antibody? What are the functions of those parts of an antibody?

Answer 31

•Most types of antibodies have a Y-shaped
structure, composed of 4 polypeptide chains

•The ends of the Y are 2 identical structures,
called antigen binding sites, that bind to
specific foreign molecules called anitgens

•The base of the Y is called the constant
fragment, or Fc

•When antibody molecules bind to foreign
molecules (antigens) on the surface of
microbes, those microbes are marked for
destruction

Question 32

What is an Fc receptor? What does it do?

Answer 32

The base of the Y is called the constant
fragment, or Fc. White blood cells such as macrophages use their Fc
receptors to detect the clusters of antibodies sticking out from the capsule

Question 33

How do capsules delay recognition of bacterial cells by the immune system? Explain in detail. Explain how antibodies relate to capsules and immune system recognition.

Answer 33

•A capsule normally hides a bacterial cell from
white blood cells because the WBCs do not detect
the capsule as foreign

•However, the adaptive immune system can
eventually make antibodies that bind to the
polymers in the capsule

•White blood cells such as macrophages use their Fc
receptors to detect the clusters of antibodies
sticking out from the capsule

Question 34

Define: opsonization. (This was not discussed in lecture, though it is in the text and the slides.)

Answer 34

The ability of antibodies to increase phagocytosis of a specific pathogen is called
Opsonization. The binding of antibodies to antigens opsonizes the pathogen
(increases the phagocytosis of the pathogen).

Question 35

Describe the steps of phagocytosis, as performed upon a pathogen by a white blood cell. Be sure to name all of the compartments and at least 4 classes of proteins involved in the process. HINT: one class of proteins involved are acid hydrolases.

Answer 35

In phagocytosis, a white blood cell is going to come along and eat those cell fragments that are formed when this infected cell undergoes apoptosis. So the pieces of the cell get digested through phagocytosis.

•One way white blood cells fight infection is by phagocytosis
(amoebas also do this process for a different reason—to
eat!)
•Detect invader with membrane proteins (a small number
microbial surface molecules can be directly recognized, or
the Fc region of antibodies can be recognized)
•WBC extends portions of cell (pseudopods) to surround
invader, creating a compartment called a phagosome.
•Lysosome compartment contains inactive digestive
enzymes (acid hydrolases)
•Lysosome membranes have proton (H+) pumps
•Lysosome and phagosome fuse to make
phagolysosome
•Pumps are activated, phagolysosome becomes
acidified
•Acid hydrolase enzymes become active
•Invader is digested (usually)

Question 36

Describe how a pathogen might defeat phagocytosis at 4 different points in the process.

Answer 36

•Avoid recognition by hiding recognizable
molecules (Ex. Secrete a capsule)
•Escape from phagosome before digestion occurs
(Ex. using lipases or cytolysin toxins)
•Prevent phagosome from fusing with lysosome
(Ex. Using a secreted protein that disrupts host
cytoskeleton)
•Prevent phagolysosome from becoming acidified
(Ex. Inhibiting proton pumps)

Question 37

Explain pinocytosis and receptor-mediated endocytosis. Compare and contrast phagocytosis, pinocytosis, and receptor-mediated endocytosis in terms of the size and specificity of the things taken in by a cell.

Answer 37

•Phagocytosis = cell eating; solid particles (cells, etc) visible
in phagosome
•Pinocytosis = cell drinking; smaller compartments
(vesicles)
•Receptor-mediated endocytosis: molecules bind to
membrane proteins (receptors) and are pulled inside when
vesicles form
•Pinocytosis and RM endocytosis vesicles move to
endosomes; endosomes acidify and become similar to
phagolysosomes