Through the Virtual Cell
--A Guided Tour--
We invite you to explore our virtual cell by taking a guided virtual tour of certain basic functions going on within the cell as well as the intracellular locations where these events occur.
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Welcome to the NDSU Virtual Cell. It’s time to climb into one of our cell submarines and take a virtual tour of our cellular landscape.
Out on the horizon, you should see a large blue object. That is the nucleus of the cell. It will be our first stop today. The nucleus is uniquely recognizable by the system of pores embedded within its outer membrane. Biological materials move in and out through the pores. They are the communication channel between the internal world of the nucleus and the cellular cytoplasm.
The nucleus contains the vast majority of the DNA in the cell. The DNA contains all of the genetic information necessary to carry out all of the functions of the cell, as well as the tissues and organs in which the cell can be found. That information is mobilized first by the process of transcription. Let’s pop inside and take a short look at the process. During this process, the DNA is used as a template to make RNA. Here, you can see that process in action. The final product of transcription is then spliced and modified into one of three RNA molecules: messenger RNA (or mRNA), transfer (or tRNA), or ribosomal (or rRNA). These are all important components of the process call translation that is used to make proteins.
If we follow the final RNA products out of the nucleus we can see them in action during the process of translation. Here you can see a particulate organelle called the ribosome. It is partially composed of the rRNA we just spoke of. Attached to it is the mRNA. As translation starts, a tRNA molecule binds to it and delivers the correct amino acid. As the protein grows, additional amino acids are brought into place by the correct tRNA molecules. The correct tRNA is determined by triplet codes found in the mRNA.
Proteins are the product of translation. Although some of these proteins stay within the cytoplasm, others are trafficked to different locations within the cell and some are exported from the cell. Most of this trafficking involves the endoplasmic reticulum (or ER) and the golgi apparatus.
We are now looking at the ER, or endoplasmic reticulum. Some of the cell’s ribosomes are attached to the ER and the proteins they manufacture are inserted directly into the space inside the ER. Those proteins can be packaged into vesicles which depart the ER and migrate to the golgi apparatus.
Here, the vesicles merge to form a golgi cisterna with the proteins located inside the cisterna’s membrane. As the cisterna matures, enzymes inside can modify the protein. This modification creates a molecular tag that is used to target the protein to a specific cellular location. Eventually, the cisterna will mature into the trans golgi network. From here vesicles can deliver proteins to cellular locations such as the endosome or the cell membrane where the proteins can be embedded or exported from the cell.
Once proteins have been translated, they can also be delivered to other organelles in the cell, such as the mitochondria and the chloroplast. Delivery here is by a different process. Some proteins are produced with transit peptides. These are specialized sequences on the end of the protein recognized by pores in the mitochondrial membrane. With the help of additional specialized proteins, the protein is delivered into the organelle. Transport to the chloroplast involves a similar process.
Mitochondria and chloroplasts are the sites for unique cellular processes. We’ll first look at the mitochondria. This organelle produces ATP, an energy molecule that is used by many other cellular processes. ATP is produced by a complex in the mitochondrial membrane called ATP synthase. The energy to produce ATP is provided by a gradient of protons (or hydrogen ions) found on the two sides of the membrane. Protons flow from the area of high proton concentration through the ATP synthase, to the area of low concentration. As they flow through ATP synthase, ATP is produced.
This gradient is produced by the action of the electron transport system. As electrons are passed from one carrier to another in the system, protons are pumped across the membrane. This creates the gradient required for ATP production. Here we see can see the electrons moving between the carriers.
Finally, we see an organelle only found within plant cells. This is the chloroplast. Here light energy from the sun is converted into chemical energy in the form of ATP. As with the electron transport system, electrons are passed from one carrier to another and protons are passed across the membrane. The gradient this creates produces ATP by a similar ATP synthase complex. It begins with a photon of light that produces the energy necessary to release an electron down the carrier chain. Here you can see the electron moving between the carriers along with ATP being produced by ATP synthase.
And that brings us to the end of our fly through. There are many processes going on within our virtual cell, and this trip featured only a few of the major functions. We are always working to expand our collection, and we hope you will return to explore our newest additions.
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