Concept explainers
The Boundaries of Life
If viruses aren't a form of life, what are they? A virus by itself is an inert particle that doesn't approach the complexity of a cell. The simplest virus, such as that causing smallpox (FIG. 1.14), consists of a protein coat that surrounds genetic material. The uncomplicated structure of viruses, coupled with amazing advances in
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Biology: Life on Earth with Physiology (11th Edition)
- Researchers have recently discovered giant viruses that are 1 μm in length, the same size as some bacterial cells. The genomes of these viruses contain over 2 million base pairs of DNA, which is more DNA than is found in many bacterial genomes, and their genomes contain hundreds—in some cases, thousands—of genes. Given these observations and what you know about viruses, should viruses be considered living or nonliving? Give arguments for and against considering viruses as living organisms.arrow_forwardTRUE/FALSEAll viruses are unable to resist the proteolytic activity (or digestive ordeal) once they are inside our cell organelles called proteasomes and lysosomes. True or False: The presence of at least one membrane is required for any organism to be considered alive.arrow_forwardViruses display many of the characteristics of living organisms. In particular, they reproduce, creating new virus particles. During reproduction, viruses make copies of their genetic material, and some of the copies contain mutations that are beneficial to the virus. For example, HIV (human immunodeficiency virus), the virus that causes the disease AIDS (acquired immunodeficiency syndrome) mutates so often that its surface proteins change faster than we can develop antiviral drugs. New drug-resistant strains of HIV are appearing constantly. However, viruses can reproduce only after entering a living cell of an organism, because viruses hijack the cell’s machinery and use it to produce new viruses. Where does that combination of characteristics place viruses on the scale of nonlife to life? Are viruses living organisms? Nonliving? If neither of those categories fits the properties of viruses, how should they be classified?arrow_forward
- O O O A new virus is discovered. Its RNA genome encodes several proteins, including a reverse transcriptase enzyme. What can you conclude about replication of this virus? Its replication involves a double-stranded RNA intermediate Its replication involves a DNA copy of its genome Its replication depends entirely on cellular enzymes Its replication is entirely independent of cellular enzymes 00 A deficiency in Base Excision Repair (BER) would primarily sensitize you to mutations caused by radiation, X-rays O Chemicals in smoke, and UV radiation O Unavoidable, spontaneously occurring DNA damagearrow_forwardThe cell is the basic unit of all living things, and viruses which are generally not considered living but have the ability to infect cells. Describe how the structure of a virus compares to the structure of a cell. You should explain (not list) at least two similarities and two differences between features of cells and viruses including a brief explanation of the function of those structures. Explain why viruses need cells.arrow_forward#7arrow_forward
- All HPV are non-enveloped double stranded DNA viruses. Their genomes are circular and approximately 8 kilobase pairs in size. Most encode eight major proteins, 6 located in the “early” region and 2 in the “late” region. The “early” proteins are regulatory in function.... Can you please elaborate about the HPV genome in more detail that what I posted above? Thanks.arrow_forwardAre viruses considered as cells? why or why not?arrow_forwardWhy are viruses are not regarded as true living cells?arrow_forward
- Because viruses lack some of the traits seen in all living things, many scientists do not believe viruses to be genuinely "alive." Using a few characteristics of live organisms as examples, explain why viruses may not be truly "alive."arrow_forwardAs a general rule, viruses are not considered to be alive based on several reasons. One such reason is that some viruses use RNA as their genetic material instead of DNA. Which of the five biological themes does this violate? Briefly explain why.arrow_forwardSelect all the following statements that are TRUE regarding viruses: □ All viruses are potentially dangerous to humans because any virus can infect any host. □ Viruses are fastidious pathogens that require complex growth media. □ Viruses are noncellular particles that take over the metabolism of a cell to generate more virus particles. □ Viruses are genomes made of RNA and DNA that lack many protein. □ Viruses can infect all other known life forms on earth, from Archaea to humans.arrow_forward
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