Biology help !! DUE SOON !! Virus alive?

Question

project using the 7 chacteristics .. cell,reproduction,metabolism,homeostatasis. heredity(DNA)evolution and interdence .. well i think some are named differently and i need help on telling are viruses alive.. using the 7 char. of life .. like yes a virus has dna(heredity) ect .. please help im soo confused right now !!!!

Answer 1

Again, most virologists will tell you that viruses are alive and meet all the important criteria of life:

(Your criteria are out of date biology teacher)

There are 7 characteristics of life: homeostasis, organization, metabolism, growth, adaptation, response to stimuli, and reproduction.

Homeostasis - many bacteria don't maintain a stable internal environment, are they dead?

Organization - Viruses are organized, have you ever seen a crystal structure of a virion

Metabolism - no

Growth - yes virus particles grow and mature in the host cell

adaptation (evolution) - very much yes

response to stimuli - Viruses respond to stimuli, just not the stimuli you think of naturally. Viruses modulate their reproduction and life cycles based on the "stimuli" in the host cell

Reproduction - agreed yes

So the only characteristic that viruses fail to qualifiy as alive for is metabolism, and it could easily be argued that metabolism is the least important and most arbitrar characteristic of living organisms since viruses do a fine job of gathering energy from their environment (host cell).

Answer 2

2

Answer 3

Characteristics of Life incude the following:
1) Made of cells
2) Movement
3) Responsiveness (respond to a stimulus)
4) Metabolism
5) Digestion
6) Excretion
7) Reproduction
8) Growth

Viruses are not considered living because viruses are not made of cells, they rely solely on a host for all movement from place to place, they have no need to take in nourishment so therefore they do not digest or excrete. They do not grow and or develop. The only way a virus can reproduce itself is to insert its DNA into the living cells of other organisms. This DNA then takes over the cell's machinery and reproduces the virus inside the cell. When the cell becomes too full of "baby" viruses, it ruptures, spilling all the "baby" viruses into the surrounding tissue where they then attack other cells and continue the cycle.

Viruses can lie dorment for thousands of years. They withstand all kinds of temperatures and weather conditions. They do not "adapt" to their environments. Viruses just "are".

I like to think of viruses as the original "aliens from outer space", which is probably where they originated.

The only thing that viruses have in common with living things is that they possess DNA. Viral DNA contains codes only for viral reproduction. It takes a living host cell to provide everything else that the virus needs to reproduce itself. In a sense, you could consider a virus a parasite, but, unlike living parasites, their presence always results in the death of the host, but not the virus. Living parasites rarely kill their host because if they do, they die right along with the host. So, again, even if a virus acts "parasitic" in one sense of the word, it is very unlike living parasites in the outcomes.

So, as you can see, viruses do not contain the characteristics of living things. Therefore, viruses are not alive. (Think about this statement: If viruses are not "alive", how can you "kill" one?)

Hope this helps (I am a biology teacher, by the way.)

Answer 4

Hope this will do some good:
Viruses:
-can only be seen with an electron microscope
-they are NOT cells
-they carry out no life functions on their own
-can be stored for years (latent)
- parasites have negative affecy on organisms
-can reproduce

Answer 5

I would say no, because they do not aquire energy and they are unable to reproduce with out help from a host cell. I think in reality this question can go either way.

Answer 6

Sure, they can reproduce, but they cannot do so without a host. Viruses are in the gray area currently.

Answer 7

You know it may sound crazy, but I think viruses may have been the first forms of "life" and perhaps they evolved into prokaryotes which branched out and became eukaryotes. hmm... :)

Answer 8

no because viruses will not carry out any life functions on its own... think of it this way... feathers grow when they are on a bird but if you were to pluck it... it wouldn't grow or develop after that

Answer 9

A virus is a microscopic particle that can infect the cells of a biological organism. Viruses can only replicate themselves by infecting a host cell and therefore cannot reproduce on their own. At the most basic level, viruses consist of genetic material contained within a protective protein coat called a capsid; the existence of both genetic material and protein distinguishes them from other virus-like particles such as prions and viroids. They infect a wide variety of organisms: both eukaryotes (animals, fungi and plants) and prokaryotes (bacteria). A virus that infects bacteria is known as a bacteriophage, often shortened to phage. The study of viruses is known as virology, and those who study viruses are known as virologists. The word virus comes from the Latin, poison (syn. venenum).[1]

It has been argued extensively whether viruses are living organisms. Most virologists consider them non-living, as they do not meet all the criteria of the generally accepted definition of life. They are similar to obligate intracellular parasites as they lack the means for self-reproduction outside a host cell, but unlike parasites, viruses are generally not considered to be true living organisms. A definitive answer is still elusive because some organisms considered to be living exhibit characteristics of both living and non-living particles, as viruses do. For those who consider viruses living, viruses are an exception to the cell theory proposed by Theodor Schwann, as viruses are not made up of cells.

Classification
For more details on this topic, see Virus classification.
In taxonomy, the classification of viruses is rather difficult due to the lack of a fossil record and the dispute over whether they are living or non-living. They do not fit easily into any of the domains of biological classification and therefore classification begins at the family rank. However, the domain name of Acytota has been suggested. This would place viruses on a par with the other domains of Eubacteria, Archaea, and Eukarya. Not all families are currently classified into orders, nor all genera classified into families.

As an example of viral classification, the chicken pox virus belongs to family Herpesviridae, subfamily Alphaherpesvirinae and genus Varicellovirus. It remains unranked in terms of order. The general structure is as follows.

Order (-virales)
Family (-viridae)
Subfamily (-virinae)
Genus (-virus)
Species (-virus)
The International Committee on Taxonomy of Viruses (ICTV) developed the current classification system and put in place guidelines that put a greater weighting on certain virus properties in order to maintain family uniformity. In determining order, taxonomists should consider the type of nucleic acid present, whether the nucleic acid is single- or double-stranded, and the presence or absence of an envelope. After these three main properties, other characteristics can be considered: the type of host, the capsid shape, immunological properties and the type of disease it causes.

In addition to this classification system, the Nobel Prize-winning biologist David Baltimore devised the Baltimore classification system. This places a virus into one of seven Groups, which distinguish viruses based on their mode of replication and genome type. The ICTV classification system is used in conjunction with the Baltimore classification system in modern virus classification.


[edit] Structure
A complete virus particle, known as a virion, is little more than a gene transporter, consisting of nucleic acid surrounded by a protective coat of protein called a capsid. A capsid is composed of proteins encoded by the viral genome and its shape serves as the basis for morphological distinction. Virally coded protein units called protomers will self-assemble to form the capsid, requiring no input from the virus genome - however, a few viruses code for proteins which assist in the construction of their capsid. Proteins associated with nucleic acid are known as nucleoproteins, and the association of viral capsid proteins with viral nucleic acid is called a nucleocapsid.

Replication
Viral populations do not grow through cell division, because they are acellular; instead, they use the machinery and metabolism of a host cell to produce multiple copies of themselves. They may have a lytic or a lysogenic cycle, with some viruses capable of carrying out both. A virus can still cause degenerative effects within a cell without causing its death; collectively these are termed cytopathic effects. Released virions can be passed between hosts through either direct contact, often via body fluids, or through a vector. In aqueous environments, viruses float free in the water.

In the lytic cycle, characteristic of virulent phages such as the T4 phage, host cells will be induced by the virus to begin manufacturing the proteins necessary for virus reproduction. As well as proteins, the virus must also direct the replication of new genomes, the technique used for this varies greatly between virus species but depends heavily on the genome type. The final viral product is assembled spontaneously, though it may be aided by molecular chaperones. After the genome has been replicated and the new capsid assembled, the virus causes the cell to be broken open (lysed) to release the virus particles. Some viruses do not lyse the cell but instead exit the cell via the cell membrane in a process known as exocytosis, taking a small portion of the membrane with them as a viral envelope. As soon as the cell is destroyed the viruses have to find a new host.

In contrast, the lysogenic cycle does not result in immediate lysing of the host cell, instead the viral genome integrates into the host DNA and replicates along with it. The virus remains dormant but after the host cell has replicated several times, or if environmental conditions permit it, the virus will become active and enter the lytic phase. The lysogenic cycle allows the host cell to continue to survive and reproduce, and the virus is passed on to all of the cell’s offspring.


A falsely coloured electron micrograph of multiple bacteriophagesBacteriophages infect specific bacteria by binding to surface receptor molecules and then enter the cell. Within a short amount of time, sometimes just minutes, bacterial polymerase starts translating viral mRNA into protein. These proteins go on to become either new virions within the cell, helper proteins which help assembly of new virions, or proteins involved in cell lysis. Viral enzymes aid in the breakdown of the cell membrane, and in the case of the T4 phage, in just over twenty minutes after injection over three hundred phages will be released.

Animal DNA viruses, such as herpesviruses, enter the host via endocytosis, the process by which cells take in material from the external environment. Frequently after a chance collision with an appropriate surface receptor on a cell, the virus penetrates the cell, the viral genome is released from the capsid and host polymerases begin transcribing viral mRNA. New virions are assembled and released either by cell lysis or by budding off the cell membrane.

Animal RNA viruses can be placed into about four different groups depending on their mode of replication. The polarity of the RNA largely determines the replicative mechanism, as well as whether the genetic material is single-stranded or double-stranded. Some RNA viruses are actually DNA based but use an RNA-intermediate to replicate. RNA viruses are heavily dependent upon virally encoded RNA replicase to create copies of their genomes.

Reverse transcribing viruses are viruses that replicate using reverse transcription, which is the formation of DNA from an RNA template. Those viruses containing RNA genomes use a DNA intermediate to replicate, whereas those containing DNA genomes use an RNA intermediate during genome replication. Both types of reverse transcribing viruses use the reverse transcriptase enzyme to carry out the nucleic acid conversion.