Table of contents

1. Introduction to Biology2h 42m
2. Chemistry3h 37m
3. Water1h 26m
4. Biomolecules2h 23m
5. Cell Components2h 26m
6. The Membrane2h 31m
7. Energy and Metabolism2h 0m
8. Respiration2h 40m
9. Photosynthesis2h 49m
10. Cell Signaling59m
11. Cell Division2h 47m
12. Meiosis2h 0m
13. Mendelian Genetics4h 44m
14. DNA Synthesis2h 27m
15. Gene Expression3h 6m
16. Regulation of Expression3h 31m
17. Viruses37m
- Viruses
  37m
18. Biotechnology2h 58m
19. Genomics17m
- Genomes
  17m
20. Development1h 5m
21. Evolution3h 1m
22. Evolution of Populations3h 53m
23. Speciation1h 37m
24. History of Life on Earth2h 6m
25. Phylogeny2h 31m
26. Prokaryotes4h 59m
27. Protists1h 12m
28. Plants1h 22m
29. Fungi36m
- Fungi
  19m
- Fungi Reproduction
  17m
30. Overview of Animals34m
- Overview of Animals
  34m
31. Invertebrates1h 2m
32. Vertebrates50m
33. Plant Anatomy1h 3m
34. Vascular Plant Transport1h 2m
- Water Potential
  1h 2m
35. Soil37m
- Soil and Nutrients
  20m
- Nitrogen Fixation
  16m
36. Plant Reproduction47m
- Flowers
  33m
- Seeds
  14m
37. Plant Sensation and Response1h 9m
38. Animal Form and Function1h 19m
39. Digestive System1h 10m
- Digestion
  1h 3m
- Blood Sugar Homeostasis
  7m
40. Circulatory System1h 49m
41. Immune System1h 12m
42. Osmoregulation and Excretion50m
- Osmoregulation and Excretion
  50m
43. Endocrine System1h 4m
- Endocrine System
  1h 4m
44. Animal Reproduction1h 2m
- Animal Reproduction
  1h 2m
45. Nervous System1h 55m
- Neurons and Action Potentials
  1h 8m
- Central and Peripheral Nervous System
  46m
46. Sensory Systems46m
- Sensory System
  46m
47. Muscle Systems23m
- Musculoskeletal System
  23m
48. Ecology3h 11m
49. Animal Behavior28m
- Animal Behavior
  28m
50. Population Ecology3h 41m
51. Community Ecology2h 46m
52. Ecosystems2h 36m
53. Conservation Biology24m
- Conservation Biology
  24m

17. Viruses

Viruses

General Biology

17. Viruses

Viruses

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0:50 minutes

Problem 4

Textbook Question

What features distinguish the seven major categories of viruses?

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Identify the type of nucleic acid present: Viruses can contain either DNA or RNA as their genetic material, which can be single-stranded or double-stranded. This is a fundamental characteristic used to classify viruses.

Determine the capsid symmetry: Viruses have protein shells called capsids that encase their genetic material. The symmetry of the capsid can be helical, icosahedral, or more complex forms.

Check for the presence of an envelope: Some viruses have an outer lipid membrane called an envelope, derived from the host cell membrane. The presence or absence of this envelope is another distinguishing feature.

Assess the mode of replication: Different viruses have unique replication cycles and mechanisms. Understanding whether a virus integrates into the host genome or replicates in the cytoplasm can help categorize it.

Examine the host range: Viruses are often specific to particular types of host cells. The host range, whether it infects animals, plants, bacteria, or other organisms, is a critical classification criterion.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Virus Classification

Viruses are classified into categories based on various features, including their genetic material (DNA or RNA), structure (enveloped or non-enveloped), and replication methods. The seven major categories include DNA viruses, RNA viruses, retroviruses, and others, each with distinct characteristics that influence their behavior and interaction with host cells.

Viral Structure

The structure of a virus is crucial for its classification and function. Viruses can be categorized as either enveloped, which have a lipid membrane surrounding their capsid, or non-enveloped, which lack this outer layer. This structural difference affects their stability in the environment and their mechanisms of infection.

Host Range and Tropism

The host range refers to the variety of hosts that a virus can infect, while tropism indicates the specific types of cells within those hosts that a virus can target. Understanding these concepts is essential for distinguishing between virus categories, as different viruses have evolved to infect specific hosts and cell types, influencing their pathogenicity and transmission.

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Related Practice

Textbook Question

Emerging viruses arise by

a. Mutation of existing viruses.

b. The spread of existing viruses to new host species.

c. The spread of existing viruses more widely within their host species.

d. All of the above.

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Textbook Question

In the viral replicative cycle, what reaction do viral proteases catalyze?

Select True or False for each statement.

T/F They catalyze polymerization of amino acids into peptides.

T/F They catalyze folding of long peptide chains into functional proteins.

T/F They catalyze cutting of polyprotein chains into functional proteins.

T/F They catalyze breaking of peptide bonds

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Textbook Question

To cause a human pandemic, the H5N1 avian flu virus would have to

a. Spread to primates such as chimpanzees.

b. Develop into a virus with a different host range.

c. Become capable of human-to-human transmission.

d. Become much more pathogenic.

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Textbook Question

A bacterium is infected with an experimentally constructed bacteriophage composed of the T2 phage protein coat and T4 phage DNA. The new phages produced would have

a. T2 protein and T4 DNA.

b. T4 protein and T2 DNA.

c. T2 protein and T2 DNA.