Virus Vs Bacteria – Their Differences And Similarities

Both viruses and bacteria can be classified as germs. This is because they are both incredibly small being organisms/microbes/agents that are capable of causing issues like disease for humans, plants, animals, and other living beings.

Virus Vs Bacteria - Their Differences And Similarities

While there are a few significant similarities between both bacteria and viruses (their incredibly small size which is hard for most people to comprehend) there are just as many factors that make these two germs very different from each other.

To find out all of the main similarities and differences between viruses and bacteria so you can properly identify which is which as well as some extra information to help you work out the functions of each, keep reading to learn all of this!

One of the most important differences between the two of these organisms is that bacteria are officially classified as living things, and viruses do not fit under this classification.

Viruses are not considered completely not living however and have a classification somewhere in between living and nonliving things.

This difference in particular for bacteria and viruses is attributed to the differences in structure between the two organisms as well as the significant differences in how the two reproduce.

The most important differences and distinguishing qualities of both viruses and bacteria can be found in how they are structured. The next section will go into the differences in structure of these different organisms.

The Structural Differences Of Viruses And Bacteria

Defining Characteristics Of The Cell Wall In Viruses And Bacteria

The cell wall is considered the outer layer of the cell with this layer sometimes labeled as the coating, or capsule. While viruses are not officially seen as cells, similarly to bacteria, they have an outer layer similar to an envelope that is used to hold the inner components of this particle.

In spite of this similarity, these cell walls are very different when considering what distinguishes them between viruses and bacteria.

Comparing bacteria to viruses will show that most bacteria (close to 90% of known bacteria) have a cell wall which is made of a peptidoglycan layer.

This is also called murein, and the peptidoglycan layer is classified as a polysaccharide which is made of N-acetylmuramic acid as well as acetylglucosamine, these two alternate and create long chains.

As well as these 2 compounds, this layer is also made of four amino acids that are known as a tetrapeptide, and these cross-link with the aforementioned chains.

As previously mentioned, most bacteria contain a cell wall structure that will be made of peptidoglycan, and the contents of this will vary between types of bacteria which makes it so the bacteria can be divided into 2 main categorizations.

These are Gram-positive bacteria which tend to have a thicker layer of peptidoglycan, and then Gram-negative bacteria which will have a thinner layer of peptidoglycan.

When considering bacteria that have a cell wall, the structure will perform a variety of functions which are very important for proper cell function.

These roles include something as important as the cell maintaining its shape, making sure the cell is protected from any osmotic pressure, regulating the movement of any substances that come in and out of the cell, as well as much more.

Defining Characteristics Of Cell Membrane (Cytoplasmic Membrane) In Viruses And Bacteria

As well as having a cell wall, bacteria all tend to have a membrane made out of a cytoplasmic material which is usually located directly underneath the cell wall.

This layer is also sometimes called the plasma membrane, and this membrane acts as a lipid bilayer which is composed of about 40% phospholipid and then 60% proteins.

This part of the cell is often characterized by having a hydrophilic head (or a glycerol head) as well as a hydrophobic region which the tail of the structure will be composed of.

Comparing this to the cell wall of the organism, a cytoplasmic membrane can be characterized by its more fluid mosaic being much less static than the structure of the cell wall.

As well, it containing key components of the cell, the membrane also works to regulate which substances and materials go in and out of the cell in conjunction with the cell wall.

Defining Characteristics Of The Capsid In Viruses And Bacteria

In comparison to bacteria, one of the most defining characteristics of viruses is that they use a capsid instead of the cell membrane which bacteria use.

Compared to a membrane, a capsid is instead a shell made from protein that is used to enclose the nucleic acid that is in a virus.

As previously referenced, the cytoplasmic membrane that is used by bacteria is classified as a lipid bilayer that is made from both proteins and phospholipids (but can also contain a variety of other components).

A capsid on the other hand is made from proteins split in subunits that are called capsomeres and dependent on the virus, the capsid could be composed of just a single or perhaps a double protein shell which contains a few different structural species of protein.

Similarly to a cell membrane, a capsid of a virus is used to enclose the nucleic materials and other contents of the virus, however it does not control the movement of substances going in and out of a cell like a cytoplasmic membrane does.

It is instead a more robust complex, and this makes it distinct from the more dynamically acting cytoplasmic membrane.

Defining Characteristics Of The Viral Envelope In Viruses And Bacteria

As well as having a capsid to make it stand out from bacteria. Viruses also use an envelope which is used to surround the capsid. Viruses that use this system are known as enveloped viruses which of course separates them from viruses without an envelope.

When it comes to viruses that use this envelope system, the envelope is considered a glycoprotein layer. In spite of this, the envelope is made of 2 separate lipid layers using protein molecules, this is also known as the lipoprotein bilayer.

Studies done on this viral envelope layer have shown that the envelope layer can actually originate from the infected host cells and here a new virus particle will be wrapped in the envelope as they get released from the infected host cell.

As time goes on, it is shown that viruses are able to add their own unique proteins onto this envelope layer which makes it easier for them to survive as well as making it easier for the virus to infect more new cells.

Using this envelope, it is easier for the virus to fuse to the membrane of a host cell which will make it much easier for them to enter and subsequently infect this cell.

Other Defining Structural Characteristics Between Viruses And Bacteria

As well as these more specific components, there are still more structural factors that can be used to differentiate viruses and bacteria.

An example of this is how the surface layer of some bacteria consist of more unique components that do not appear on viruses. These unique components could be pili, or flagella, or any similar component. 

These structural factors that are unique to bacteria are usually used for mobility, for the purpose of improving adhesion or attachment to the cell which makes them more pathogenic.

An example of this is pili on bacteria which are used to improve the bacteria ability to attach to a host cell and then make it easier for the bacteria to invade the host cell.

For bacteria that live in a more free environment, flagella are useful for use in swimming through an aquatic environment.

Viruses do not use structural components like flagella or pili, but they can possess something similar like a tail sheath or a similar protein attachment.

These are used to make it easier for them to attach to a surface protein or a structure similar to viral spikes, for the host cell to once again make the role of invading the host cell significantly easier. 

Some bacteria may have an outer capsule which is present similar to how some viruses have a viral envelope. This outer capsule is often compared to the aforementioned cell wall or the cell membrane.

This capsule layer is sometimes called the slime layer and is defined as a polysaccharide layer which is shown to aid the organism in the role of developing a resistance to different drugs used to attack them.

On top of this, this outer capsule is utilized to protect its bacteria from any desiccation which will allow the bacteria to much more effectively survive in harsher environments and their conditions. Viruses do not have a capsule structure like this.

Cellular Components Of Viruses And Bacteria

Generally speaking, the structural qualities of a virus are quite simple, and it is usually just the nucleic acid and the capsid with an outer viral envelope for the viruses that use this system.

As well as this there are the viruses that have an attachment structure to make the goal of infecting host cells easier. 

Compared to these viruses, bacteria are more likely to contain some organelles that are used to perform unique functions with the goal of allowing the organisms to gain energy from its surroundings to help it grow and then reproduce.

Because of this, bacteria are considered living, because of the roles they have in different cellular mechanisms involved in growing and reproducing.

We will now list some of these cellular components of both bacteria and viruses,

Genetic Material Of Viruses And Bacteria

A similarity between viruses and bacteria is that both of them use genetic material in the form of nucleic acid. For bacteria, this genetic material will be contained inside a chromosome which takes the form of a strand of DNA.

While these do not contain a nucleus, the generic material that these organisms have is contained in an area which is called the nucleoid. 

As well as this nucleoid, the bacteria also use a plasmid which is an extrachromosomal molecule of the DNA. Generally speaking, this plasmid will exist in a circular and double-stranded DNA molecule which is capable of replicating by itself.

Viruses on the other hand, contain nucleic acid which is in the form of either DNA or RNA. Different from bacteria however, it that viruses do not have any plasmid (the extrachromosomal DNA)

Differences In The Ribosome

As well as the differences in genetic material, generally speaking, bacteria will have ribosomes that will be composed into 2 subunits. These ribosomes are nucleoprotein particles which are involved in the translation of mRNA for use for protein synthesis.

Different from any ribosome that will be found in any eukaryotic cells, the bacterial ribosomes will not be bound to a specific cellular organelle or structure.

Because of this they will be distributed freely within the cytoplasm. Different from bacteria, viruses will not contain ribosomes and because of this rely solely on their organelles or any host cells for use in protein synthesis.

Other Structures Which Define Viruses And Bacteria

As previously mentioned, there are different types of bacteria and these contain a variety of different additional organelles or structures which include structures like pili, flagella, and fimbriae. These are usually used for the purpose of movement or attachment to other cells.

Bacterial cells will also contain protoplasm or cytoplasm which is where metabolic actions as well as replication will take place. In this cytoplasm there is a variety of different substances which include waste materials, gases, as well as water amongst other things.

For viruses, there is a chance that cytoplasm will not be present. Because viruses do not have the same number of structures or organelles that are present within bacteria, they instead have attachment structures.

An example of these are tail fibers, or glycoprotein spikes which are used to attach them to the host cell.

This is because of their simple structure which is almost wholly dedicated to transferring any genetic material to its host cell for the purpose of transcription as well as reproduction.

Differences In The Size Of Viruses And Bacteria

One of the most significant differences to take into account when comparing viruses and bacteria is the difference they have in size.

While there has been a lot of study into viruses which show that they can sometimes be relatively large compared to others (an example of this being the mimivirus which is 750 nm in diameter), generally speaking, viruses are significantly smaller than bacteria.

To put it in perspective, some of the smaller viruses are only 20 to 30 nm measuring their diameter (these being members of the Picornaviridae and Parvoviridae family) but on average most viruses are somewhere between 10 and 300 nm.

In comparison to this, bacteria get much larger, and they can range in size anywhere between 0.2 and 2.0 micrometers in diameter. The largest measured bacteria was a sizeable 750 um or 0.75 mm in diameter.

Generally speaking, small viruses can get up to 200 times smaller than average bacteria. Because of this tiny size, it is also much easier for viruses to infect bacteria.

Viruses that do this are known as bacteriophages, and they inject their nucleic material into the host bacteria and are therefore able to take over their reproductive capabilities and instead make copies of themselves.

Differences In The Activity Of Viruses And Bacteria

Differences In The Activity Of Viruses And Bacteria

Due to the significant distinguishing factors in the genetic structure of bacteria and viruses, they also act differently. The following section will go in-depth into the activities done by these two organisms and what makes them unique from each other.

Replication Of Viruses And Bacteria

Replication is in reference to the process in which a DNA molecule is copied, which then leads to the production of two identical copies. For bacteria, this process can be described as starting with the origin of replication located on the DNA strand.

Here the DNA strand becomes unwound through the work of the enzyme Helicase. Then another enzyme called DNA Gyrase will ensure that the double-stranded area which is located behind the replication are has no chance of supercoil.

After this, both of the strands will be ready once the replication fork is also stable, and then polymerase DNA will be used as a catalyst for the additional new nucleotides which are on the now growing daughter DNA strands.

This will then end up with the creation of 2 new DNA strands which will then coil and for a helix and then the cell will be able to divide into two. This process makes it, so the daughter cells will have the exact genetic material of its parent cell.

For viruses, they do not possess the same machinery bacteria have to be able to replicate this form of replication.

They instead utilize the machinery of their host cell for this purpose and replication is therefore only possible when inside a host cell. This is done by using endocytosis or sometimes utilizing any surface molecules attached to the host cell.

After the entry process, a virus can uncoat allowing it to fully release its genetic material and then use the machinery of its host cell. The material of the nuclei will be able to use this to replicate and create new strands.

Because of the different genetic material between different viruses it is worth remembering that this process and transcription is different dependent on this.

After use of the host cell for successful replication the present virions will assemble in the form of nucleic acid and structural proteins to take the form of a nucleocapsid and the new viral particles will move onto new cells to repeat this process.

Disease-Causing Mechanisms Of Viruses And Bacteria

It is worth remembering that not all bacteria spread or cause disease. However, for the ones that do, they act as intracellular pathogens, and they do not actually depend on the host cell for developing.

So some parasitic bacteria do not actually need to invade cells to cause any disease. An example of this is Clostridium botulinum which releases toxins which will affect tissues and cells.

Viruses on the other hand are obligate intracellular parasites which means they need to have a host cell to reproduce. After they enter and reproduce within a cell, this will affect the processes of the cell but will also rupture it as the virus grows.

This can cause significant damage to cells and a good example of this is in respiratory issues like flu and tonsillitis.

Translation Of Viruses And Bacteria

Translation is the process in which mRNA information is decoded for use in protein synthesis. For viruses components of a host cell are needed to make viral components.

This is because viruses do not have the capability of translating mRNA into protein so need to use the host cell. Bacteria do not face this issue due to having ribosomes and enzymes to allow immediate decoding and protein production from mRNA.

Summarizing The Similarities Of Viruses And Bacteria

So while this article has made the differences of the viruses and bacteria clear there are some key similarities to keep in mind.

This includes them both lacking any membrane-bound organelles, the fact that they both have a microscopic size (in spite of bacteria being significantly bigger), the fact that both can be used to spread diseases, and both are used to carry genetic material.

So while you should keep the significant differences in mind, the similarities should also be considered!

Jennifer Dawkins

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