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Chapter 21: Problem 9

To get a visual look at the internal structure of virions, scientists must use a(n) ____. a. scanning electron microscope b. transmission electron microscope c. porcelain filter d. light microscope

Short Answer

Expert verified
b. transmission electron microscope

Step by step solution

01

- Understanding Virions

Virions are entire virus particles, consisting of an outer shell and genetic material inside. To observe their internal structure, we need a microscope powerful enough to see inside these tiny particles.
02

- Comparing Microscopes

Determine which of the given microscopes is capable of providing the internal details of virions. Scanning electron microscopes (SEMs) produce detailed surface images, while transmission electron microscopes (TEMs) can visualize the inside of cells at a molecular level. Light microscopes have much lower resolution, and porcelain filters are not visualization tools.
03

- Choosing the Correct Microscope

Since we need to look at the internal structure of virions, the microscope that can provide detailed internal views at the molecular level is the transmission electron microscope (TEM).
04

- Conclusion

The appropriate tool to visualize the internal structure of virions, considering their tiny size and the need for internal detail, is the transmission electron microscope.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Virions
Virions are the complete, infective forms of viruses. They contain genetic material, either DNA or RNA, which is crucial for replication once inside a host cell. Virions are very small, often between 20 and 300 nanometers in diameter. Because of their small size and intricate structure, studying them requires powerful microscopes.

To fully understand and observe virions, knowing their components is essential:
  • The capsid: A protein shell that surrounds the genetic material.
  • The envelope (in some viruses): A lipid layer that encases the capsid, often derived from the host cell membrane.
  • Glycoproteins: Often embedded in the envelope, these proteins help the virus attach to and penetrate host cells.
Understanding virions is critical for developing vaccines and antiviral drugs, as these therapies often target specific structural components of the virus.
Microscopy
Microscopy is the use of microscopes to view objects that cannot be seen with the naked eye. There are various types of microscopes, each suitable for different applications.

Some common kinds include:
  • Light Microscopes: These use visible light to magnify samples. They are great for viewing larger cells and tissues but lack the resolution to see viruses or their internal structures.
  • Scanning Electron Microscopes (SEM): They provide detailed surface images of samples by scanning them with a focused beam of electrons. Though useful for surface details, SEMs cannot penetrate samples to show internal structures.
  • Transmission Electron Microscopes (TEM): TEMs use electrons to pass through thin slices of a sample, providing information about internal structures at a molecular level. This makes them perfect for studying the internal features of virions.
By choosing the appropriate type of microscope, scientists can obtain the necessary detail to further understand and research various microscopic entities.
Virus Structure
The structure of a virus is critical for its function and infectivity. Viruses consist of several key components that facilitate infection and replication within host cells.

Key structural elements include:
  • Genetic Material: The core of the virus, containing either DNA or RNA, encodes the information required for viral replication and takes over the host cell's machinery.
  • Capsid: The protective protein coat surrounding the genetic material, composed of protein subunits called capsomeres. The capsid ensures the genetic material is delivered to the host cell.
  • Envelope (in many viruses): A lipid membrane that surrounds some viruses' capsids, often stolen from the host cell's membrane. The envelope may contain viral proteins necessary for the infection process.
  • Spikes or Glycoproteins: Protrusions on the surface of some viruses, which help them attach to and enter host cells. These structures are often targets for immune responses and vaccine development.
Understanding virus structure is essential for virology. It aids in developing treatments by identifying which parts of the virus to target, whether through vaccination, antiviral drugs, or other methods.

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Most popular questions from this chapter

Three-dimensional (3D) structures, or folding, of proteins have been shown to contain more information about evolutionary relationships than the sequences of DNA nucleotides that encode the proteins. Amino acid sequences of rabbit skeletal muscle actin (375 amino acids) and bovine ATPase (386 amino acids) have only 39 locations in common. However, the 3D structure of these proteins are nearly identical (Flaherty et al., Proc. Natl. Acad. Sci. USA, 1991). As information about the 3D folding of proteins and the number of sequenced whole genomes has increased, folding has been shown to be an evolutionarily conserved property. A. Analyze these data to refine the following model: The evolutionary history of life on Earth can be inferred from variations over time of the nucleotide sequence of a gene. By applying a classification scheme based on protein folding, Nasir and Caetano-Anoll茅s (Sci. Adv. 2015) have determined the number of folding families that viruses share with the three domains. Approximately 60% of the folding patterns found in viruses were common to all three domains, as shown below. Fewer than 10% were unique to viruses. viruses have been discovered, each a double-stranded DNA virus with more than one million bases, with some encoding nucleotides and amino acids. However, none encode ribosomes, so these viruses are still dependent on a marine bacteriovore (amoeba or flagellate) host for replication. Hypotheses regarding the origin of life on Earth need to account for the relationship between proteins and genetic information. Proteins are required to read and write genetic information, but genetic information is required to synthesize proteins. Which of these systems evolved first, and if neither came first, how could they evolve simultaneously? The RNA-first model is based on the idea that ribosomal RNA both encodes and synthesizes proteins. B. Describe a hypothesis for the origin of life on Earth that combines the dual functionality of RNA and the function of retroviral reverse transcriptase to propose a mechanism leading to an ancient, acellular lineage of very large, double-stranded DNA viruses and a first DNAbased cellular life form. C. Like viruses, the nucleus of a eukaryote uses the machinery of the cell to transcribe DNA and synthesize proteins. Evaluate the possibility of the origin of Eukarya by specialization of a very large double-stranded DNA virus.

Which of the following statements about prions is true? a. Prions are larger than viruses. b. Prions contain DNA and RNA. c. The PrPCis the normal form of the protein. d. The PrPSCis folded abnormally

Influenza A virus is the most pathogenic of the human influenza viruses. Its envelope encloses a protein complex (vRNP) and eight, single-stranded, negative RNA (the complement of a positive RNA strand that can be transcribed by a ribosome) segments (vRNA). Each segment encodes one or two proteins that support viral replication. On the outer surface of the envelope are proteins that recognize and bind to host receptors. A. Annotate the representation below to briefly describe each process associated with a numbered label. B. Describe influenza A viral replication as a process regulated by either positive or negative feedback and justify your selection. The human-acquired immunodeficiency syndrome (AIDS) and many cancers are cause by double-stranded RNA retroviruses C. Contrast the processes of viral replication of HIV and influenza A virus. D. Explain the difference in the effects of infection by HIV and influenza A virus on host genetic variability. E. Measured mutation rates for influenza A virus and HIV are nearly identical (Sanjuan et al., Jour. Virology, 2010). Explain this observation even though host error-checking operates in one of these replication modes

Which of the following statements about viroids is true? a. Viroids are single-stranded RNA particles. b. Viroids reproduce only outside of the cell. c. Viroids produce proteins. d. Viroids affect both plants and animals

What characteristics do viroids and viruses have in common? a. They both replicate within a host cell and contain nucleic acids. b. They both replicate within a host cell and do not contain nucleic acids. c. They both replicate within a host cell and contain proteins. d. They both replicate within a host cell and contain only RNA.
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