12.2. Viruses

Virus

The viruses are microscopic particles acellular genetic material that are able to reproduce inside living cells.

They are not cellular beings, and are made up of:

A nucleic acid (DNA or RNA).
A protein capsid.
Sometimes a membranous envelope.

By domdomegg (Own work) [CC BY 4.0], via Wikimedia Commons

Viruses are said to be obligate intracellular parasites because they lack their own metabolism, since they do not have the necessary enzymes to do so. That is why they need the matter, energy and enzymes of the cell they parasitize.

Although the viral organization is simple, viruses contain the genetic information necessary to control their replication and synthesize the proteins they need, some of them structural, and others necessary for their reproduction.

Viruses are small structures that are responsible for transporting nucleic acid from one host cell to another. Viruses, outside the cell, are called virions. In the extracellular phase, viruses are inert, since they do not have the necessary enzymes to have their own metabolism.

Viruses adhere to the surface of the cells to which they are going to parasitize, and introduce their genetic material (DNA or RNA), where the new envelopes for the new viruses are reproduced and synthesized (intracellular phase), taking advantage of the matter, enzymes and energy of the parasitized cell. As we have said, they are obligate intracellular parasites.

Various types of viruses are distinguished, depending on the cell they parasitize. Thus, phages parasitic bacteria, plant viruses, plant cells, and animal viruses, which infect animal cells.

Viruses cause many diseases such as influenza, the hepatitis or AIDS, but it may also be beneficial. The biotechnology and genetic engineering can be used as virus vectors in the cloning of genes for therapeutic or industrial purposes. They have also had an important role in the evolution of living beings, by inserting themselves into the DNA of some organisms and carrying information to others.

Living beings perform the functions of nutrition, interaction and reproduction. Reproduction is the only function that viruses perform, even if it is using the matter, energy and mechanisms of the host cell, which is why we have said that they were considered obligate parasites. As they do not have their own metabolism or cellular organization, they are not considered living beings.

Biological song: Viruses (cell pirates). Julinky.

Questions that have come out in University entrance exams (Selectividad, EBAU, EvAU)

Cantabria, June 2021, question 6

Question 6 [1.25 POINTS]

Viruses: definition, composition and structure (drawing), lifestyle and role of viruses in nature. Why are viruses not considered living beings in biology?

Extremadura, June 2021, question 7

7.- In relation to viruses:

A. Briefly explain why a virus remains inert if it is not in contact with a host cell (0.5 points).
B. List two differences between viruses and prokaryotes. (0.5 points)
C. Give two arguments for and two against viruses being considered living organisms. (1 point).

Basque Country, June 2021, question 3A

In 2020, he awarded the Nobel Prize in Physiology or Medicine to three scientists, Harvey J. Alter, Michael Houghton, and Charles M. Rice, for their important contribution to the fight against blood-borne hepatitis that causes cirrhosis and liver cancer. This chronic infection, which affects 71 million people worldwide, is caused by the hepatitis C virus.

a) (1 point) Draw a diagram of the structure of a virus and indicate each of its components.

b) (0.5 points) Indicate the main differences between a virus and a bacterium.

c) (0.5 points) How do viruses multiply if their components do not show any metabolic activity? Give reasons for your answer.

d) (0.5 points) Are antibiotics effective in treating diseases caused by a virus? Give reasons for your answer.

Canary Islands, July 2021, question 18

18. A finger prick, a smartphone, and the new $ 34 device created by biomedical engineers at Columbia University (USA) are all it takes to detect the presence of the HIV AIDS virus and Syphilis bacteria Treponema pallidum in the blood. (Source: Science Translational Medicine).

a. Indicates the different types of viral nucleic acids, specify if they are single or double stranded.
b. Why do viruses need to invade a cell to multiply?
c. Viruses have two strategies of action: lytic cycle and lysogenic cycle. What difference is there in the result of each cycle?

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Skip navigation Biology 2nd Baccalaureate Biology 2nd Bac. 1. Bioelements and biomolecules. Water and mineral salts 1.1. Chemical bonds in biology 1.1.1. Intramolecular bonds 1.1.1.1. Covalent bond 1.1.1.2. Ionic bond 1.1.2. Intermolecular bonds 1.1.2.1. Van der Waals forces 1.1.2.2. Hydrogen bonds 1.2. The chemical basis of life: inorganic and organic components 1.2.1. Primary bioelements 1.2.2. Secondary bioelements 1.2.3. Trace elements 1.3. The immediate principles or biomolecules 1.3.1. Water 1.3.1.1. Chemical structure of water 1.3.1.2. Properties and functions of water 1.3.2. Mineral salts 1.3.2.1. Functions of salts in solution 1.3.2.2. Colloidal solutions and dispersions 1.3.2.3. Properties of colloidal dispersions 1.3.2.4. Diffusion, osmosis and dialysis 1.3.2.4.1. Diffusion 1.3.2.4.2. Osmosis 1.3.2.4.3. Dialysis 1.4. Bibliography 2. Glucides 2.1. Glucid concept 2.2. Classification of carbohydrates 2.3. Monosaccharides 2.3.1. Trioses 2.3.1.1. Spatial isomerism or stereoisomerism 2.3.2. Tetroses 2.3.3. Pentoses 2.3.3.1. Monosaccharide cyclization 2.3.4. Hexoses 2.4. The N-glucosidic and O-glucosidic bonds 2.4.1. Substances derived from monosaccharides 2.5. Disaccharides 2.6. Polysaccharides 2.6.1. Homopolysaccharides 2.6.1.1. Reserve homopolysaccharides 2.6.1.2. Structural homopolysaccharides 2.6.2. Heteropolysaccharides 2.6.3. Heterosides 2.7. General functions of glucides 2.8. Bibliography 3. Lipids 3.1. Lipid concept 3.2. Classification of lipids 3.2.1. Fatty acids 3.2.1.1. Saturated and unsaturated fatty acids 3.2.1.2. Chemical properties of fatty acids 3.2.1.3. Physical properties of fatty acids 3.2.1.4. Fatty Acid Functions 3.2.2. Saponifiable lipids or with fatty acids 3.2.2.1. Simple lipids 3.2.2.1.1. Acylglycerides 3.2.2.1.2. Cerides 3.2.2.2. Complex lipids 3.2.2.2.1. Phospholipids 3.2.2.2.2. Glycolipids 3.2.3. Unsaponifiable lipids or without fatty acids 3.3. Lipid functions 3.4. Bibliography 4. Proteins 4.1. Introduction to proteins 4.2. Amino acids 4.2.1. Classification of amino acids 4.2.2. Properties of amino acids 4.3. The peptide bond 4.4. Protein 4.4.1. Protein structure 4.4.1.1. Primary structure of proteins 4.4.1.2. Secondary structure of proteins 4.4.1.3. Tertiary structure of proteins 4.4.1.4. Quaternary structure of proteins 4.4.2. Protein properties 4.4.3. Classification of proteins 4.4.3.1. Holoproteins 4.4.3.2. Heteroproteins 4.4.4. Protein functions 4.5. Enzymes 4.5.1. Structure of enzymes 4.5.2. The active center of enzymes 4.5.3. General Mechanism of Enzyme Catalysis 4.5.4. Regulation of enzyme activity 4.5.5. Allosteric enzymes 4.5.6. Nomenclature and classification of enzymes 4.6. The vitamins 4.6.1. Fat-soluble vitamins 4.6.2. Water soluble vitamins 4.7. Bibliography 5. Nucleotides and nucleic acids 5.1. The chemical composition of nucleic acids 5.1.1. Components of nucleic acids 5.1.2. Concept, types and functions of nucleic acids 5.1.3. Nucleosides 5.1.4. Nucleotides 5.1.4.1. Nucleotide functions 5.1.5. Nucleic acids 5.2. Deoxyribonucleic acid (DNA) 5.2.1. DNA structure 5.2.1.1. Primary structure of DNA 5.2.1.2. Secondary structure of DNA 5.2.1.3. Tertiary structure of DNA 5.2.1.3.1. Tertiary structure of DNA in prokaryotes 5.2.1.3.2. Tertiary structure of DNA in eukaryotes 5.2.1.4. Quaternary structure of DNA 5.2.2. DNA types 5.2.3. Genetic material: chromatin and chromosomes 5.2.3.1. Karyotype and karyogram 5.3. Ribonucleic acid (RNA) 5.3.1. RNA types 5.3.1.1. Transfer RNA 5.3.1.2. Messenger RNA 5.3.1.3. Ribosomal RNA 5.3.1.4. Nucleolar RNA 5.3.1.5. Small nuclear RNA 5.3.2. Functions of ribonucleic acids 5.4. Bibliography 6. Cell morphology 6.1. Cell concept 6.1.1. Cell history 6.1.2. Cell theory 6.2. Levels of cellular organization 6.2.1. General characteristics of cells 6.2.2. Prokaryotic cells 6.2.2.1. Prokaryotic cell morphology 6.2.2.2. Structure of prokaryotes 6.2.2.2.1. Bacterial capsule 6.2.2.2.2. Bacterial wall 6.2.2.2.3. Plasma membrane 6.2.2.2.4. Cytoplasm-Ribosomes-Inclusions 6.2.2.2.5. Bacterial DNA 6.2.2.2.6. Bacterial appendages 6.2.2.3. Bacteria Physiology 6.2.3. Eukaryotic cells 6.2.3.1. Animal and plant cell 6.2.3.1.1. Animal eukaryotic cell 6.2.3.1.2. Plant eukaryotic cell 6.2.3.2. Cell Evolution: Endosymbiont Theory 6.3. Size, shape and quantity 6.4. The plasma membrane 6.4.1. Chemical composition of the membrane 6.4.2. The structure of the membrane. The fluid mosaic model 6.4.3. Functions of the plasma membrane 6.4.4. Transport across the membrane 6.4.4.1. Small molecule transport 6.4.4.2. Macromolecule transport 6.4.5. Plasma membrane differentiations 6.5. The cell wall of plant cells 6.5.1. Chemical composition of the cell wall 6.5.2. Cell wall structure 6.5.3. Cell wall differentiations 6.5.4. Cell wall functions 6.6. Extracellular matrix or glucocalyx 6.7. Cytosol or hyaloplasm 6.8. The cytoskeleton 6.8.1. Microfilaments or actin filaments 6.8.2. Intermediate filaments 6.8.3. Microtubules 6.9. Cell membrane and organelle systems 6.9.1. Membrane systems 6.9.1.1. The endoplasmic reticulum 6.9.1.2. Golgi apparatus 6.9.2. Cell organelles 6.9.2.1. Lysosomes 6.9.2.2. Peroxisomes 6.9.2.3. Vacuoles 6.9.2.4. Mitochondria 6.9.2.4.1. Functions of the mitochondria 6.9.2.5. Plastids 6.9.2.5.1. Chloroplasts 6.9.2.6. Ribosomes 6.9.2.7. Centrosome 6.9.2.8. Cilia and flagella 6.10. Cell motility 6.11. The cell nucleus 6.11.1. Characteristics of the cell nucleus 6.11.2. The interphase nucleus 6.11.3. The mitotic nucleus or nucleus in division 6.12. Bibliography 7. Metabolism 7.1. Metabolism 7.1.1. Energetic Aspects of Cellular Chemical Reactions 7.2. Catabolism 7.2.1. Catabolism and obtaining energy 7.2.2. Carbohydrate catabolism 7.2.2.1. Glycolysis 7.2.2.2. Cellular respiration 7.2.2.2.1. Oxidative decarboxylation 7.2.2.2.2. Krebs cycle 7.2.2.2.3. Electron transport chain 7.2.2.2.4. Energy balance of cellular respiration 7.2.2.3. Fermentations 7.2.2.3.1. Alcoholic or ethyl fermentation 7.2.2.3.2. Lactic fermentation 7.2.2.3.3. Other types of fermentations 7.3. Anabolism 7.3.1. Autotrophic anabolism 7.3.2. Photosynthesis 7.3.2.1. Photochemical or light phase 7.3.2.1.1. Photosystems 7.3.2.1.2. Photophosphorylation 7.3.2.1.2.1. Non cyclic photophosphorylation 7.3.2.1.2.2. Cyclic photophosphorylation 7.3.2.2. Biosynthetic or dark phase 7.3.2.3. Factors influencing photosynthesis 7.3.2.4. Products of photosynthesis 7.3.3. Chemosynthesis 7.4. Bibliography 8. Cell reproduction 8.1. The cell cycle 8.1.1. Interphase 8.1.2. Cellular division 8.2. Cellular division 8.2.1. Mitosis 8.2.1.1. Prophase 8.2.1.2. Metaphase 8.2.1.3. Anaphase 8.2.1.4. Telophase 8.2.1.5. Cytokinesis 8.2.1.6. More on mitosis 8.2.2. Meiosis 8.2.2.1. Meiosis I 8.2.2.2. Meiosis II 8.2.3. Meiosis and sexual reproduction 8.2.4. Meiosis and life cycle 8.2.5. Biological importance of meiosis 8.3. Differences and similarities between mitosis and meiosis 8.4. Bibliography 9. Classical genetics 9.1. Genetics basics 9.2. Mendelian genetics 9.2.1. The method 9.2.2. Mendel's Laws 9.2.2.1. Mendel's first law or principle of uniformity in the first generation 9.2.2.2. Mendel's second law or principle of segregation 9.2.2.2.1. Backcross and test crossover 9.2.2.3. Mendel's third law or principle of independent combination 9.3. Gene interaction 9.3.1. Gene interaction between allelic genes 9.3.2. Gene interaction between non-allelic genes that influence for the same trait 9.4. Chromosomal theory of heredity 9.5. Ligation and recombination 9.6. Complex mendelism 9.6.1. Multiple allelism 9.6.1.1. Lethal genes 9.6.2. Pleiotropy 9.6.3. Expressiveness and genetic penetrance 9.7. Sex-linked inheritance 9.7.1. Y-linked inheritance 9.7.2. X-linked inheritance 9.8. Heredity influenced by sex 9.9. Bibliography 10. Molecular genetics 10.1. DNA as hereditary material 10.2. DNA replication 10.2.1. The need for DNA replication 10.2.2. First hypotheses about DNA duplication 10.2.3. Meselson and Stahl experiment 10.2.4. The sense of growth of the new strands 10.2.5. Mechanism of DNA replication 10.2.5.1. Replication in prokaryotes 10.2.5.2. Replication in eukaryotes 10.2.6. Error correction 10.2.7. Enzymes involved in replication 10.3. Gene concept 10.4. "One gene-one enzyme" theory 10.5. Transcription 10.5.1. Mechanism of transcription 10.5.1.1. Transcription in prokaryotes 10.5.1.2. Eukaryotic transcription 10.6. Translation or protein biosynthesis 10.6.1. The genetic code 10.6.2. Mechanism of translation of RNA to proteins 10.6.2.1. Translation in eukaryotes 10.7. Regulation of gene expression 10.8. Bibliography 11. Genetics and evolution 11.1. Mutations 11.2. Types of mutations 11.2.1. Gene or point mutation 11.2.2. Chromosomal or structural mutation 11.2.3. Mutation at the genomic level 11.3. Causes of mutations 11.4. Evolutionary implications of mutations 11.5. Metabolic implications of mutations 11.6. Bibliography 12. Microbiology and biotechnology 12.1. Microbiology 12.2. Viruses 12.2.1. Viral morphology 12.2.2. Viral physiology 12.2.2.1. Lytic cycle 12.2.2.2. Lysogenic cycle 12.2.2.3. Cycles of viruses of special interest 12.2.2.3.1. Flu virus life cycle 12.2.2.3.2. Life cycle of the AIDS virus 12.3. Other acellular forms 12.3.1. Viroids 12.3.2. Prions 12.4. Biotechnology 12.5. Bibliography 13. Immunology 13.1. Infection concept 13.2. Defense mechanisms against infections 13.2.1. Nonspecific mechanisms 13.2.1.1. Primary barriers: external defenses 13.2.1.2. Secondary barriers: internal defenses 13.2.2. Specific mechanisms 13.3. Immunity and immune system 13.3.1. Components of the immune system 13.3.2. Concept and nature of antigens 13.4. The immune response 13.4.1. Humoral immune response: the antibodies 13.4.1.1. Antibody-producing cells: B lymphocytes 13.4.1.2. Antibodies 13.4.1.2.1. Types of antibodies 13.4.1.2.2. Antigen-antibody reaction 13.4.1.3. Immune memory: primary and secondary responses 13.4.2. Cellular immune response: T lymphocytes 13.5. Types of immunity 13.5.1. Natural immunity 13.5.2. Artificial immunity 13.6. Immune system disorders 13.6.1. Autoimmunity 13.6.2. Hypersensitivity 13.6.3. Immunodeficiency 13.6.4. Transplants and the phenomenon of rejections 13.7. Bibliography « Previous \| Next » 12.2. Viruses Virus The viruses are microscopic particles *acellular* genetic material that are able to reproduce inside living cells. They are not cellular beings, and are made up of: A nucleic acid (DNA or RNA). A protein capsid. Sometimes a membranous envelope. By domdomegg (Own work) [CC BY 4.0], via Wikimedia Commons Viruses are said to be obligate intracellular parasites because they lack their own metabolism, since they do not have the necessary enzymes to do so. That is why they need the matter, energy and enzymes of the cell they parasitize. Although the viral organization is simple, viruses contain the genetic information necessary to control their replication and synthesize the proteins they need, some of them structural, and others necessary for their reproduction. Viruses are small structures that are responsible for transporting nucleic acid from one host cell to another. Viruses, outside the cell, are called virions. In the extracellular phase, viruses are inert, since they do not have the necessary enzymes to have their own metabolism. Viruses adhere to the surface of the cells to which they are going to parasitize, and introduce their genetic material (DNA or RNA), where the new envelopes for the new viruses are reproduced and synthesized (intracellular phase), taking advantage of the matter, enzymes and energy of the parasitized cell. As we have said, they are obligate intracellular parasites. Various types of viruses are distinguished, depending on the cell they parasitize. Thus, phages parasitic bacteria, plant viruses, plant cells, and animal viruses, which infect animal cells. Viruses cause many diseases such as influenza, the hepatitis or AIDS, but it may also be beneficial. The biotechnology and genetic engineering can be used as virus vectors in the cloning of genes for therapeutic or industrial purposes. They have also had an important role in the evolution of living beings, by inserting themselves into the DNA of some organisms and carrying information to others. Living beings perform the functions of nutrition, interaction and reproduction. Reproduction is the only function that viruses perform, even if it is using the matter, energy and mechanisms of the host cell, which is why we have said that they were considered obligate parasites. As they do not have their own metabolism or cellular organization, they are not considered living beings. Biological song: Viruses (cell pirates). Julinky. Questions that have come out in University entrance exams (Selectividad, EBAU, EvAU) Cantabria, June 2021, question 6 Question 6 [1.25 POINTS] Viruses: definition, composition and structure (drawing), lifestyle and role of viruses in nature. Why are viruses not considered living beings in biology? Extremadura, June 2021, question 7 7.- In relation to viruses: A. Briefly explain why a virus remains inert if it is not in contact with a host cell (0.5 points). B. List two differences between viruses and prokaryotes. (0.5 points) C. Give two arguments for and two against viruses being considered living organisms. (1 point). Basque Country, June 2021, question 3A In 2020, he awarded the Nobel Prize in Physiology or Medicine to three scientists, Harvey J. Alter, Michael Houghton, and Charles M. Rice, for their important contribution to the fight against blood-borne hepatitis that causes cirrhosis and liver cancer. This chronic infection, which affects 71 million people worldwide, is caused by the hepatitis C virus. a) (1 point) Draw a diagram of the structure of a virus and indicate each of its components. b) (0.5 points) Indicate the main differences between a virus and a bacterium. c) (0.5 points) How do viruses multiply if their components do not show any metabolic activity? Give reasons for your answer. d) (0.5 points) Are antibiotics effective in treating diseases caused by a virus? Give reasons for your answer. Canary Islands, July 2021, question 18 18. A finger prick, a smartphone, and the new $ 34 device created by biomedical engineers at Columbia University (USA) are all it takes to detect the presence of the HIV AIDS virus and Syphilis bacteria Treponema pallidum in the blood. (Source: Science Translational Medicine). a. Indicates the different types of viral nucleic acids, specify if they are single or double stranded. b. Why do viruses need to invade a cell to multiply? c. Viruses have two strategies of action: lytic cycle and lysogenic cycle. What difference is there in the result of each cycle? Licensed under the Creative Commons Attribution Share Alike License 4.0 « Previous \| Next » These pages are semi-automatically translated from the web Biology 2nd Baccalaureate. Biología de 2º de Bachillerato (biologia-geologia.com). You can make any suggestion, question, comment, ..., in our forum 2º Bachillerato Biología - Foro de biologia-geologia.com
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