1. How the Cell Mobilizes to Release Antibodies

When you fight off a virus, your immune system produces antibodies. Antibodies are virus-killing proteins that are made by white blood cells called B cells, which secrete them by the millions into the bloodstream. As B cells produce antibodies, their appearance changes. Their cytoplasm becomes filled with endoplasmic reticulum (ER). There’s also a lot of Golgi Apparatus.

05_immature-b-cell-with-receptors
An immature B cell. The Y shaped membrane receptors are drawn vastly larger than they actually are.

06_plasma-cells-secreting-antibodies
A B cell that has matured into an activated “plasma cell,” secreting antibodies into the bloodstream. Note the ER and golgi in these cells.

What’s going on?

animal_cell_w-smooth-erv2     The ER is a vast internal network of channels separated from the rest of the cytoplasm by internal plasma membrane. The Golgi is similar, except for that instead of channels, the Golgi forms a series of flattened, elongated sacs, also bound by membranes. In the diagram at right, which we’ve extensively studied in previous tutorials, the ER is at 9 and 10, while the Golgi is shown at 3.

For the purpose of understanding the way that the ER, Golgi, and other organelles cooperate in various cell processes, we’re going to shift to much simpler diagram that only includes the parts we’re interested in.

04c_internal-membrane-sketch-gw-modified In the diagram to the left, the nucleus is shown at 1. The endoplasmic reticulum is at 2 and 3. The Golgi is at 5.

The left side of the ER is covered by many ribosomes, which are shown as dots in this illustration. Ribosomes are the cell’s protein factories: they’ll make any protein that they’re told to make, based on instructions they receive from the nucleus. ER with ribosomes is called Rough ER. ER without ribosomes is smooth ER, and we’ll discuss it more below.

Antibodies, like all proteins that will be exported out of the cell, are made at the rough ER (2). As the antibody is made, it gets put into the channels of the ER. It then moves to the Smooth ER (3). In the same way that bubbles can form from a soap film, the smooth ER will bud off a bubble of membrane, also known as a vesicle (shown at 4). A vesicle is the name we give to any small, membrane bound sac that’s transporting substances from one area of the cell to another.

This vesicle, containing the antibody, will merge with the Golgi Apparatus (5). The Golgi has enzymes that modify the antibody, getting the antibody into the exact form it will need to be in to bind with and help to neutralize the virus. When the Golgi is done, it buds off another vesicle (6). This vesicle will fuse with the cell membrane (8). As it does, the antibody will be dumped into the cell’s exterior. In this case, that means the bloodstream. The antibody (along with millions of other identical antibodies) will now float around in the blood and, hopefully, bind with the virus, helping to neutralize it (Note, in case you’re worried, number 7 was not used in this diagram).

2. Checking Understanding: The Endomembrane System

Let’s just work with this diagram a bit to make sure that you’re understanding it.

[qwiz random = “true” qrecord_id=”sciencemusicvideosMeister1961-endomembrane (AP)quiz 1″]

[h]Endomembrane quiz 1

[i]

[q]Which number is pointing to the nucleus?

[textentry single_char=”true”]

[c*]1

[f]Yes. The nucleus, the cell’s control center, is at number 1

[c]*

[f]No. Find the structure that’s closest to the center of the cell (furthest from the membrane.

[!!!]++++question 2 +++++[/!]

[q]Which number is pointing to where ribosomes are going to make the antibody that’s (hopefully) going to fight off the invading virus?

[textentry single_char=”true”]

[c*]2

[f]Yes. “2” is the rough ER, which is where ribosomes attached to the ER are making proteins.

[c]*

[f]No. You’re looking for the rough ER. Find ribosomes (black dots) attached to membrane.

[!!!]++++question 3 +++++[/!]

[q]After the antibody is made, it’s going to be enclosed within a bubble of membrane (a vesicle). Where is the membrane that’s going to make up that vesicle going to be made?

[textentry single_char=”true”]

[c*]3

[f]Yes. “3” is the smooth ER, which is where membrane (and other lipids) are synthesized.

[c]*

[f]No. You’re looking for the smooth ER, which is a network of membrane just outside of the rough ER, and which lacks ribosomes.

[!!!]++++question 4 +++++[/!]

[q]Which numbered part indicates a vesicle that’s going to transport the antibody from the ER to the Golgi?

[textentry single_char=”true”]

[c*]4

[f]Yes. “4” is a vesicle, a bubble of membrane, that’s transporting our developing antibody from the ER to the Golgi apparatus.

[c]*

[f]No. Look for a small bubble of membrane in-between the ER and the Golgi.

[!!!]++++question 5 +++++[/!]

[q]The antibody is going to have to be modified and packaged for export before it can be released from the cell into the bloodstream. Which numbered part is where this modification and packaging is going to happen?

[textentry single_char=”true”]

[c*]5

[f]Yes. “5” is the Golgi apparatus. Within these flattened sacs of membrane, enzymes modify proteins and prepare them for shipping to their final destination.

[c]*

[f]No. Look for the series of flattened sacs between the membrane and the ER.

[!!!]++++question 6 +++++[/!]

[q]After modification of the protein, the Golgi will bud off a vesicle that will bring the antibody to the membrane for export from the cell. Which number shows a vesicle that’s budding off from the Golgi complex?

[textentry single_char=”true”]

[c*]6

[f]Yes. “6” shows a vesicle that’s budding off from the Golgi.

[c]*

[f]No. Find the vesicle just outside the Golgi body, in between the Golgi and the membrane (and don’t pick # 7).

[!!!]++++question 7 +++++[/!]

[q]To be exported from the cell, our antibody is going to be transported (within a vesicle) to the membrane. The vesicle will fuse with the membrane, and dump the antibody out of the cell (in this case, into the bloodstream). Which number shows a vesicle that’s fusing with the membrane, dumping its contents outside?

[textentry single_char=”true”]

[c*]8

[f]Yes. “8” shows a vesicle that’s fusing with the membrane.

[c]*

[f]No. Find the vesicle that’s fused with the membrane, forming a kind of pocket within the membrane, with arrows indicating that materials are being dumped outside of the cell.

[x][restart]

[/qwiz]

3. Interactive reading: Introducing Lysosomes

[qwiz qrecord_id=”sciencemusicvideosMeister1961-lysosomes (AP)I.R.”]

[h]Interactive Reading: Introducing Lysosomes

[i]Consider the Amoeba, a eukaryotic, single-celled organism found in freshwater lakes and streams, where it preys on bacteria and scavenges small pieces of organic matter. In this tutorial, you’ll learn about how it uses lysosomes to digest its food.

04a_chaos_carolinense-amoeba
An amoeba. Size can range from 700 – 2000 microns (source: Wikipedia)

[q topic = “info”]The process by which an amoeba engulfs its prey is called phagocytosis.

The process begins at “A”. The amoeba extends part of its membrane to surround its prey (2). The extension is called a pseudopod (“false foot), and is shown at 1. In this same diagram, you can also see two other organelles. For our purposes, the most important of these is number 3: lysosome. The lysosome contains digestive enzymes which would be harmful to the cell if they were floating in the cytoplasm (because they would digest the cell). Click “next question” to continue.

[q]In “B” you can see what happens when the pseudopods completely surround the prey. At this point, the prey is enclosed in a food vacuole (5). In “C,” the lysosome fuses with the food vacuole. The enzymes in the lysosome attack the prey, breaking it down to simple monomers.

Which number is the lysosome?

[textentry single_char=”true”]

[c*]3

[f]Yes. “3” is the lysosome

[c]*

[f]No. Find the vesicle that’s going to fuse with the ingested food. That’s the part that’s filled with digestive enzymes.

[q]Which number is a pseudopod?

[textentry single_char=”true”]

[c*]1

[f]Yes. “1” is the pseudopod.

[c]*

[f]No. Find the extension of the membrane that’s about the surround and engulf the prey.

[q]Which number is a food vacuole?

[textentry single_char=”true”]

[c*]5

[f]Yes. “5” is a food vacuole.

[c]*

[f]No. Find the membrane “bubble” (actually a large vesicle) that forms when the pseudopod surround the prey.

[q topic – “info”]In “C,” the lysosome (3) fuses with the food vacuole (5). The enzymes in the lysosome attack the prey, breaking it down to simple monomers. Number 4, by the way, is the nucleus, which is not directly involved in this process (though it did code for the enzymes that are in the lysosome).

Click “next question” to continue.

[q]In “D”, those monomers are released into the cytoplasm, where the cell can use them for food or energy. In “E” the lysosome has been inactivated. The food molecules are in the cytoplasm, and molecules or particles that can’t be digested are released from the cell.

Which letter shows the moment when the food vacuole and the lysosome fused together?

[textentry single_char=”true”]

[c*]c

[f]Yes. “c” shows a lysosome that has fused with food vacuole.

[c]*

[f]No. Find the first stage when the food vacuole (5) and the lysosome (3) have become one membrane enclosed entity. Your answer will be a letter (a, b, c, d, or e)

[q topic = “info”]So, now we know about lysosomes. But here’s a question. If the enzymes inside a lysosome can digest bacteria, they must be pretty dangerous.What I mean by that is that the same enzymes that could digest the proteins, carbohydrates, lipids and nucleic acids in a bacterial cell could probably digest many of those same substances in a eukaryotic cell. How does the cell safely get those enzymes inside the lysosome? You’ll find your answer below.

[/qwiz]

4. Making Lysosomes

The hydrolytic enzymes in lysosomes are dangerous, and can’t be directly exposed to the cytoplasm (or else the cell would wind up digesting itself). In the diagram below, 7 represents a lysosome. What would have to happen in order for a cell to safely get one of these enzymes into a lysosome?

04c_internal-membrane-sketch-gw-modified

Take the following steps and put them into correct order in the table below.

[qwiz qrecord_id=”sciencemusicvideosMeister1961-Putting Hydrolytic Enzymes into a Lysosome”]

[h]Putting hydrolytic enzymes into a lysosome

[q labels = “top”]

Step One __________________________________________________
Step Two __________________________________________________
Step Three __________________________________________________
Step Four __________________________________________________
Step Five __________________________________________________

[l]Enzyme goes to Golgi for modification and activation

[fx] No. Please try again.

[f*] Good!

[l]Golgi buds off a vesicle that goes to a lysosome.

[fx] No. Please try again.

[f*] Great!

[l]Instructions go from nucleus to a ribosome

[fx] No, that’s not correct. Please try again.

[f*] Great!

[l]Ribosome makes the enzyme inside the rough ER

[fx] No. Please try again.

[f*] Correct!

[l]Smooth ER makes a vesicle containing the enzyme

[fx] No, that’s not correct. Please try again.

[f*] Great!

[/qwiz]

5. The Endomembrane System: The Whole Shebang

[qwiz random = “true” qrecord_id=”sciencemusicvideosMeister1961-endomembrane (AP)quiz 2″]

[h]The endomembrane system

[i]Use what you’ve learned above to identify the parts and function of the endomembrane system, as shown below.

07b_nucleus_er_golgi_lysosome_membrane-lettered
Source: Wikipedia

[!!] ++++question 1 [/!!!]

[q]Which number below is pointing to the nuclear membrane (also called the nuclear envelope)?

[textentry single_char=”true”]

[c*]A

[f]Yes. “A” is pointing to the nuclear membrane.

[c]*

[f]No. Find the membrane that’s surrounding the nucleus (towards the center of the cell)

[!!] ++++question 2 [/!!!]

[q] Which number below is pointing to a nuclear pore?

[textentry single_char=”true”]

[c*]B

[f]Great job. “B” is pointing to a nuclear pore.

[c]*

[f]No. To find a nuclear pore, you have to find a kind of “hole” in the nuclear membrane.

[!!] ++++question 3 [/!!!]

[q] Which number below is pointing to the rough ER?

[textentry single_char=”true”]

[c*]C

[f]Nice. “C” is pointing to the rough E.R.

[c]*

[f]No. To find the rough ER, find the network of channels that has ribosomes attached to it. The ribosomes are represented by the small purple spheres, shown at “E.”

[!!] ++++question 4 (d) [/!!!]

[q] Which number below is pointing to the Golgi complex/apparatus/body?

[textentry single_char=”true”]

[c*]D

[f]Good job! “D” is pointing to the Golgi apparatus

[c]*

[f]No. To find the Golgi, find the series of flattened sacs that’s in between the ER and the cell membrane.

[!!] ++++question 5 (e) [/!!!]

[q] Which number below is pointing to a ribosome?

[textentry single_char=”true”]

[c*]E

[f]Excellent. “E” is pointing to a ribosome.

[c]*

[f]No. To find the ribosomes (the cell’s protein factories), look for structures that are in the rough ER, but not in the smooth ER or the Golgi bodies.

[!!] ++++question 6 (f) [/!!!]

[q] Which number below is pointing to a protein?

[textentry single_char=”true”]

[c*]F

[f]Way to go! “F” is pointing to a few proteins.

[c]*

[f]No. Proteins could be in the rough ER (where they’re being manufactured by ribosomes), in the smooth ER (where they’ll be packaged into vesicles), or in the Golgi (where they’ll be modified, sorted, and sent to other destinations).

[!!] ++++question 7 (G) [/!!!]

[q] Which number below is pointing to the smooth ER?

[textentry single_char=”true”]

[c*]G

[f]Terrific! “G” is pointing to the smooth E.R.

[c]*

[f]No. The smooth ER is ER without ribosomes.

[!!] ++++question 8 (H) [/!!!]

[q] Which number below is pointing to a vesicle bringing some material from the ER to the Golgi?

[textentry single_char=”true”]

[c*]H

[f]Awesome! “H” is pointing to a vesicle that’s transporting some material from the ER to the Golgi.

[c]*

[f]No. A vesicle is any small bubble of membrane that’s transporting something (usually a protein) from one location to another. To answer this question, look for a vesicle in-between the ER and the Golgi.

[!!] ++++question 9 (I) [/!!!]

[q] Which number below is pointing to a vesicle that would be bringing a “finished” protein either to a lysosome, or, alternatively, to the membrane for export out of the cell?

[textentry single_char=”true”]

[c*]I

[f]Correct. “I” is pointing to a vesicle that has budded off from the Golgi apparatus. Depending on surface markers on the vesicle, it could be headed for a lysosome (where it would deliver hydrolytic enzymes) or to the cell membrane (where it could export materials from the cell).

[c]*

[f]No. To answer this question, look for a vesicle that’s budded off from the golgi (so that it would be on the Golgi’s outside), and look for arrows pointing to what could be a lysosome or the cell’s membrane.

[!!] ++++question 10 (J) [/!!!]

[q] Which number below is pointing to a part that could be a lysosome?

[textentry single_char=”true”]

[c*]J

[f]That’s right. “J” is pointing to a lysosome. “Hydrolytic enzymes” gives it away.

[c]*

[f]No. To answer this question, look for a an organelle that contains enzymes that could be used for digestion of food particles and recycling of worn out organelles.

[!!] ++++question 11 (C) [/!!!]

[q] Which number below is pointing to a part that produces proteins for export from the cell, or incorporation into lysosomes, or incorporation into the cell membrane?

[textentry single_char=”true”]

[c*]C

[f]Nice. This description refers to the rough ER, at letter C.

[c]*

[f]No. To answer this question, look for the rough ER.

[!!] ++++question 12 (G) [/!!!]

[q] Which number below is pointing to a part that produces lipids for making vesicles, or for making new cell membrane? This part also has enzymes that can help detoxify certain poisons.

[textentry single_char=”true”]

[c*]G

[f]Good work! This description refers to the smooth ER, at letter G.

[c]*

[f]No. To answer this question, look for the smooth ER.

[!!] ++++question 13 (D) [/!!!]

[q] Which number below is pointing to a part that acts as the cell’s packaging and sorting center (kind of like the post office?)

[textentry single_char=”true”]

[c*]D

[f]Yes. This description refers to the Golgi complex (or “body” or “apparatus,” at letter D.

[c]*

[f]No. To answer this question, look for the Golgi Apparatus. It’s a series of flattened sacs between the ER and the membrane.

[!!] ++++question 14 [/!!!]

[q] Which number below is pointing to the passageway through which a messenger RNA molecule would leave the nucleus, where it’s first made, and move towards a ribosome?

[textentry single_char=”true”]

[c*]B

[f]Great job. “B” is pointing to a nuclear pore, which allows messages to leave the nucleus and head toward the cytoplasm, where they can carry out DNA instructions.

[c]*

[f]No. This question is asking about a nuclear pore. To find a nuclear pore, you have to find a kind of “hole” in the nuclear membrane.

[!!] ++++question 16 [/!!!]

[q] Which number below is pointing to the robotic particle that can translate instructions from DNA in the nucleus into proteins ?

[textentry single_char=”true”]

[c*]E

[f]Good job. “E” is pointing to a ribosome. Ribosomes are like little nano-robots, capable of taking DNA instructions and using them to synthesize proteins.

[c]*

[f]No. This question is asking about ribosomes. To find a ribosome, find a particle that’s embedded in the rough ER, but not found in the smooth ER, or the Golgi.

[x][restart]

[/qwiz]

Next steps

  1. Continue on to The Evolution of Cellular Compartmentalization (the next tutorial in this module)
  2. Return to the Cell Parts and Functions Menu