Animal Viruses: 3. Synthesis & Replication - Online Tutor, Practice Problems & Exam Prep

Animal viruses undergo a complex synthesis and replication process, which is crucial for their survival. This involves the production of viral structural proteins and enzymes, followed by the replication of the viral genome, which can be DNA or RNA. The mechanism of replication varies based on the genome type, including double-stranded DNA, single-stranded DNA, and various forms of RNA. A common requirement across all viruses is the generation of plus single-stranded RNA (mRNA), essential for protein synthesis by the host's ribosomes.

Animal Viruses: 3. Synthesis & Replication

In this video, we're going to continue to talk about animal viruses and animal virus infections by focusing specifically on the third step of an animal virus infection, which is synthesis and replication of the virus. After the entry and uncoating of a virus into a host animal cell, synthesis and replication of that virus can begin. There are two main events that are required for complete replication of a virus. The first main event is going to be the synthesis of viral structural proteins, including the capsid of the virus. It also includes the synthesis of viral enzymes and also viral replication enzymes that are needed for the second main event that's needed for replication of a virus, which is replication of the viral genome. The viral genome is going to be some form of nucleic acid, some type of DNA or RNA that we'll get to talk more about as we move forward in our course. Now, this replication of the viral genome is going to occur multiple times inside of the host cell, which means that many copies of the viral genome are going to be replicated.

If we take a look at our image down below, we can get a better understanding of animal virus synthesis and replication. Notice that over here on the left-hand side, we're showing you an infecting animal virus that has entered into our host cell here. This infecting virus is uncoating here where its protein coat is uncoating, and the viral genome here is being released into the cell's cytoplasm. After entry and uncoating of an animal virus into the host cell, synthesis, and replication can begin. If the viral genome were to be DNA, then this DNA would need to be transcribed, and it would create viral mRNA. The viral DNA is used to build viral mRNA, and the host cell's transcriptional machinery is utilized to allow for this transcription. Once the viral mRNA has been made, then the viral mRNA can be translated by the host cell's ribosome. The translation of this viral mRNA results in the synthesis of viral proteins.

Notice down below we have a collection of viral proteins that are being synthesized, including spike proteins and also proteins that make up part of the capsid of the animal virus. In addition to the structural proteins of the virus that are being synthesized, also viral enzymes and replication enzymes are going to be made, which is going to allow for the replication of the viral genome. Initially, we start with just one copy of the viral genome, but after viral genome replication, it creates many copies of the viral genome. After viral genome replication and synthesis of these viral proteins, these viral proteins and the viral genome can assemble to form new virus particles like what we have down below. The assembly of the virus is another step that we'll talk about later in our course. But for now, we're focusing on this third step of an animal virus infection, which is the synthesis of viral proteins and the replication of the viral genome. We'll get to talk a lot more about the synthesis and replication step as we move forward in our course. So I'll see you all in our next video.

Map of Lesson on Animal Virus Synthesis & Replication

In this video, we're going to introduce our map of the lesson on animal virus synthesis and replication, which is actually down below right here. And so what's really important to note is that animal viruses can actually have many different types of genomes. And these different types of genomes allow for variations in viral synthesis and replication. As we move forward in our course, we're going to talk about all of the different types of viral genomes, and we're going to talk about how those viral genomes allow for variations in viral synthesis and replication. Really what we're saying here is that the mechanism of viral synthesis and replication depends on the type of viral genome. Notice our map down below is really a map of the animal virus genome types.

Animal virus genomes can be broken up into 3 major groups. The first group over here on the far left are going to be the DNA viruses, which of course are going to be viruses that have a DNA genome, either a plus minus dsDNA genome, where "plus minus" and "ds" are just referring to the fact that it is a double-stranded DNA molecule that we'll get to talk more about later in our course. The "ds" here stands for double-stranded. As you can see here, we have a double-stranded DNA molecule. Or the DNA virus could have a single-stranded DNA genome or a plus ssDNA where the "ss" here stands for single stranded. Once again, we'll be able to talk more about these DNA virus genomes later in our course as we move forward.

Now the second major group of animal virus genomes are going to be the RNA viruses. RNA viruses of course are going to have an RNA genome. It could either be a plus ssRNA genome or a plus single-stranded RNA genome where the "ss" is single stranded as you see here. It could also be a minus ssRNA genome, where again the "ss" stands for single stranded. We'll differentiate between the plus and the minus later in our course as we move forward. Or the RNA virus could have a plus minus dsRNA, where, again, the "ds" is double-stranded RNA, which is very strange and unique, but it can occur in some viruses. Once again, we'll get to talk more about this later in our course.

Last but not least, the third group of animal virus genomes that we're going to talk about are the reverse transcribing viruses, which have the ability to reverse transcribe. We'll get to talk more about what that means and more details about those genomes as we move forward in our course. But for now, this here concludes our brief lesson on our map of the lesson on animal virus synthesis and replication. We're going to cover this map by following the leftmost branches first. We'll talk about the DNA viruses first, then we'll talk about the RNA viruses, and then last but not least, we'll talk about the reverse transcribing viruses. I'll see you all in our next video.

All of the following are types of animal viruses except which of these answers?

• A. Reverse transcribing viruses.
• B. Phage viruses.
• C. DNA viruses.
• D. RNA viruses.

Types of RNA Virus Genomes

This video, we're going to talk more about the types of animal virus genomes. And so recall from our last lesson video that the synthesis and replication mechanism of an animal virus actually depends on the type of viral genome that the virus has. And so really, there are 5 main types of viral genomes that viruses can have. And notice that we have those 5 types numbered down below, and the numbers in the text correspond with the numbers that you see down below in the image. Now, what you'll notice is that each of these viral genomes is going to have either a plus and or a minus, indication. And we need to recall from way back in some of our previous lesson videos that the plus strands are going to be coding strands. And coding strands are going to directly encode the message for building a product. Now the minus strands, on the other hand, are going to be non-coding strands, or in other words, they are template strands. And so they do not directly encode the message for building a product. Instead, these minus strands are going to be complementary to the plus strands. Now the very first type of viral genome that we have listed here is the plus-minus dsDNA. Now every time we see ds moving forward, you should note that this represents double-stranded. And so this is plus-minus double-stranded DNA. And so the plus-minus double-stranded DNA is a double-stranded DNA molecule, as we have learned about it in our previous lesson videos. And so, it is going to have one plus strand or one coding strand and one minus strand or one non-coding or template strand. And so this double-stranded DNA molecule, if it is a viral genome, is going to be expressed by following the normal central dogma of biology, which means that the double-stranded DNA molecule of the virus is going to be transcribed into an mRNA, and then that mRNA will be translated into protein. And so if we take a look at our image down below, notice on the left-hand side over here, we're focusing in on the plus-minus double-stranded DNA molecule. And so notice that the original molecule at the top here is a double-stranded DNA molecule, it has a plus strand and a minus strand. And so, this viral genome, if it is a plus-minus dsDNA molecule, double-stranded DNA molecule, then it is going to be expressed via the normal central dogma of biology, which means that it will be transcribed to form a messenger RNA, and we'll learn that messenger RNA is actually synonymous with plus ssRNA, where the ss is standing for single-stranded RNA or just single-stranded. And so we have plus ssRNA synthesis, which is really just transcription, and, that's the formation of the plus ssRNA, the messenger RNA. And then this, messenger RNA, of course, will be translated using the host ribosome's machinery to form, the synthesis of viral proteins. Now, we'll get to talk a lot more about this process as we move forward in our course, but right now this is the introduction to plus-minus double-stranded DNA being a possibility for a viral genome. Now the second type of viral genome that we have listed is going to be ssDNA. And, ss is going to stand for single-stranded as we move forward through our course. And so this ssDNA is going to be single-stranded DNA, and it could either be a plus single-stranded DNA or a coding single-stranded DNA, or it could be a minus single-stranded DNA. And we'll get to talk more details about the mechanism of how the single-stranded DNA is expressed as we move forward in our course. But really, this ssDNA, which can be either plus or minus, is gonna be a single-stranded DNA molecule. And we're going to learn that it is going to need to be converted into plus-minus dsDNA before it can actually be replicated and synthesized and the viral proteins can be synthesized. And so notice that the second one that we have right here is going to represent our plus or minus single-stranded DNA. And so notice that we only have one single strand of DNA. And what we're going to learn is that before it can be replicated and sy

Common Themes of All Virus Genomes

This video we're going to talk about some common themes of all virus genomes. And so regardless of the viral genome type, all viruses must complete 2 tasks. The first task is they must all recreate their original genome type, regardless of what that original genome type was. For example, a double stranded RNA virus is going to contain a double stranded RNA genome as its original genome. And so this double stranded RNA virus must recreate the double stranded RNA genome in order for it to replicate properly. Now the second main task that every virus must accomplish is that every virus must make plus single-stranded RNA (ssRNA). Recall that plus ssRNA is the same thing as mRNA or messenger RNA as we've talked about it before in our previous lesson videos. And so all of these different viruses must make this plus ssRNA or messenger RNA because the messenger RNA is what can be directly translated into protein. And so all of these viruses, regardless of the viral genome type, must eventually make plus ssRNA or mRNA, and that is in order for the host cell's ribosome to synthesize viral proteins. What you'll notice up above in this image once again is that regardless of the type of viral genome, all viral genomes must accomplish the task of making plus ssRNA at some point. They must all make plus ssRNA or messenger RNA at some point in order to synthesize proteins. Notice that that is a common theme across all of these different types of viral genomes, regardless of the type that they are. And so that is something important to keep in mind. In addition, to making plus ssRNA as a common theme, all of them eventually must recreate their original genome. We'll talk about the mechanisms of how each of these different types of animal virus genomes is able to replicate, as well as synthesize viral proteins as we move forward in our course. But for now, this year concludes our common themes of all virus genomes, how they must all recreate their original genome type, and how they must all eventually make plus single-stranded RNA (ssRNA) or messenger RNA. And so I'll see you all in our next video.

Here’s what students ask on this topic:

What are the main steps involved in the synthesis and replication of animal viruses?

The synthesis and replication of animal viruses involve several key steps. After the virus enters the host cell and uncoats, the first main event is the synthesis of viral structural proteins, including the capsid and viral enzymes. This is followed by the replication of the viral genome, which can be DNA or RNA. The viral genome is transcribed into mRNA using the host cell's transcriptional machinery. The mRNA is then translated by the host's ribosomes to produce viral proteins. These proteins and replicated genomes assemble to form new virus particles. The specific mechanisms can vary depending on whether the virus has a DNA or RNA genome.

How do DNA and RNA viruses differ in their replication mechanisms?

DNA and RNA viruses differ significantly in their replication mechanisms. DNA viruses typically enter the host cell nucleus, where their DNA is transcribed into mRNA by the host's transcriptional machinery. This mRNA is then translated into viral proteins. RNA viruses, on the other hand, usually replicate in the cytoplasm. Positive-sense RNA viruses can be directly translated by host ribosomes, while negative-sense RNA viruses must first be transcribed into positive-sense RNA. Double-stranded RNA viruses have both positive and negative strands and use the positive strand as mRNA. Reverse transcribing viruses, like retroviruses, convert their RNA into DNA, which then integrates into the host genome.

What is the role of mRNA in the replication of animal viruses?

mRNA plays a crucial role in the replication of animal viruses. Regardless of the type of viral genome (DNA or RNA), all viruses must produce mRNA to synthesize viral proteins. mRNA serves as the template for protein synthesis, which is carried out by the host cell's ribosomes. For DNA viruses, the viral DNA is transcribed into mRNA. For RNA viruses, positive-sense RNA can act directly as mRNA, while negative-sense RNA must be transcribed into positive-sense RNA. The production of mRNA ensures that the viral proteins necessary for replication and assembly are synthesized, enabling the virus to propagate within the host.

What are the different types of viral genomes found in animal viruses?

Animal viruses can have various types of genomes, which influence their replication mechanisms. The main types include: 1) Double-stranded DNA (dsDNA), which follows the central dogma of biology (DNA to mRNA to protein). 2) Single-stranded DNA (ssDNA), which must be converted to dsDNA before transcription. 3) Positive-sense single-stranded RNA (ssRNA), which can be directly translated into proteins. 4) Negative-sense ssRNA, which must be transcribed into positive-sense RNA before translation. 5) Double-stranded RNA (dsRNA), which contains both positive and negative strands. Additionally, reverse transcribing viruses, like retroviruses, convert their RNA into DNA, which integrates into the host genome.

Why is the generation of plus single-stranded RNA (mRNA) essential for all viruses?

The generation of plus single-stranded RNA (mRNA) is essential for all viruses because mRNA is the template for protein synthesis. Viral proteins are necessary for the replication and assembly of new virus particles. Regardless of the type of viral genome (DNA or RNA), all viruses must produce mRNA to utilize the host cell's ribosomes for translating viral proteins. For DNA viruses, the viral DNA is transcribed into mRNA. For RNA viruses, positive-sense RNA can act directly as mRNA, while negative-sense RNA must be transcribed into positive-sense RNA. This common requirement ensures that the viral proteins needed for replication are synthesized.