12.2.1. Viral morphology

Viral morphology

The morphologically complete virus particle or virion is made up of a nucleic acid enveloped by a protein capsid. Some viruses also have a membranous envelope that surrounds them.

The viruses are composed of:

Nucleic acid

All viruses contain a nucleic acid that can be DNA (in DNA viruses) or RNA (in RNA viruses or retroviruses), but never DNA and RNA in the same virus. This nucleic acid can be circular or linear, and single-stranded or double-stranded. Nucleic acid can be made up of a single molecule, as in the case of DNA viruses, or segmented, as in some RNA viruses.

DNA viruses: Most DNA viruses have double-stranded DNA, and will take advantage of the cellular mechanism to replicate their DNA and synthesize the mRNA that produces the proteins necessary for the virus. Examples of viral DNA are adenoviruses, herpesviruses, and bacteriophage T4.
RNA viruses: There are several types, depending on whether the RNA sequence is directly translated into proteins (equivalent to mRNA, as in poliovirus) or not (complementary to mRNA, as rhabdoviruses). In this case, the RNA polymerase enzyme will form the mRNA, or, as in retroviruses, such as HIV, the reverse transcriptase enzyme, which forms DNA from viral RNA and integrates it into the host cell's DNA.

All viruses that have double-stranded RNA, and some single-stranded RNA, have several independent RNA molecules. They are said to have a fragmented genome. DNA viruses have only one DNA molecule.

The simplest viruses can only code for about eight proteins, but the most complex viruses can code for up to two hundred proteins. These proteins can be:

Structural proteins: are responsible for forming the capsid.
Enzymes proteins: they are involved in the synthesis of new viral nucleic acids.
Binding proteins: facilitate adherence to the host cell membrane.

Capsid

The capsid is a protein structure that surrounds and protects nucleic acid. It is formed by the union of capsomeres (globular proteins). Although its main function is to protect the nucleic acid, in viruses that are not enveloped by a membrane, it is also responsible for recognizing the cells it is going to parasitize.

The capsid is usually formed by the repetition of capsomeres with the same type of proteins, so the virus can create a complex capsid, with many capsomeres, with little genetic information. The more proteins you need to synthesize, the more genetic information you need, and the space for nucleic acid in a virus is very limited.

The term nucleocapsid refers to the genetic material wrapped in its capsid.

The capsomeres, to the joining, can form three types of capsids: icosahedral, helical and complex.

The icosahedral capsid is a polyhedral structure with 12 vertices, 20 triangular faces and 30 edges, in which the capsomeres are arranged to form an icosahedron. This arrangement allows to have a closed structure with few capsomeres.

For example, they are virus icosahedral the virus influenza and virus human warts.

Cápside icosaédrica By Dr. Richard Feldmann (photographer) (National Cancer Institute here) [Public domain], via Wikimedia Commons

The helical capsid is made up of capsomers arranged in a helical manner, forming a tubular structure inside which is the nucleic acid. They have this type of capsid, the tobacco mosaic virus (VMT), the rabies virus or the measles virus.

By Thomas Splettstoesser (www.scistyle.com) (Own work) [CC BY-SA 4.0], via Wikimedia Commons

The complex capsid is characteristic of bacteriophages, viruses specialized in parasitizing bacteria.

The virion has at least two parts:

An icosahedral head or nucleocapsid that contains the nucleic acid .

A tail (viruses that present a tail are called urophagi), of helical and contractile symmetry, ending in a basal plate equipped with spines and anchoring fibers (generally of a protein nature), adapted for the injection of nucleic acid into the inside the bacteria. At the base of the tail there may be enzymes and ATP, whose function is to destroy the bacterial wall.

Estructura de un virus bacteriófago

By NoeTico1516 (Own work) [CC BY-SA 4.0], via Wikimedia Commons

Enveloped virus

The viral envelope is a membranous structure that surrounds the viral capsid of some viruses. It usually comes from the host's plasma membrane. In addition, the envelope contains glycoproteins in its outer part that are encoded by the viral genome. These glycoproteins are involved in the recognition, in the adherence to the host cell and in inducing the penetration of the virion into the cell by phagocytosis.

The enveloped viruses do not necessarily have to destroy the host cell for her to leave because they can get out by budding and cause persistent infections, such as HIV, the virus flu, or the smallpox.

The viruses that have envelope called virus naked, such as virus polio and bacteriophage T4.

Interactive activity: Parts of a complex virus.

Fundamental ideas about viral morphology

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

The viruses are composed of:

A nucleic acid (DNA or RNA).
A protein capsid.
- Icosahedral.
- Helicolidal.
- Complex.
Sometimes a membranous envelope.

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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 » 12.2.1. Viral morphology Viral morphology The morphologically complete virus particle or virion is made up of a nucleic acid enveloped by a protein capsid. Some viruses also have a membranous envelope that surrounds them. The viruses are composed of: Nucleic acid All viruses contain a nucleic acid that can be DNA (in DNA viruses) or RNA (in RNA viruses or retroviruses), but never DNA and RNA in the same virus. This nucleic acid can be circular or linear, and single-stranded or double-stranded. Nucleic acid can be made up of a single molecule, as in the case of DNA viruses, or segmented, as in some RNA viruses. DNA viruses: Most DNA viruses have double-stranded DNA, and will take advantage of the cellular mechanism to replicate their DNA and synthesize the mRNA that produces the proteins necessary for the virus. Examples of viral DNA are adenoviruses, herpesviruses, and bacteriophage T4. RNA viruses: There are several types, depending on whether the RNA sequence is directly translated into proteins (equivalent to mRNA, as in poliovirus) or not (complementary to mRNA, as rhabdoviruses). In this case, the RNA polymerase enzyme will form the mRNA, or, as in retroviruses, such as HIV, the reverse transcriptase enzyme, which forms DNA from viral RNA and integrates it into the host cell's DNA. All viruses that have double-stranded RNA, and some single-stranded RNA, have several independent RNA molecules. They are said to have a fragmented genome. DNA viruses have only one DNA molecule. The simplest viruses can only code for about eight proteins, but the most complex viruses can code for up to two hundred proteins. These proteins can be: Structural proteins: are responsible for forming the capsid. Enzymes proteins: they are involved in the synthesis of new viral nucleic acids. Binding proteins: facilitate adherence to the host cell membrane. Capsid The capsid is a protein structure that surrounds and protects nucleic acid. It is formed by the union of capsomeres (globular proteins). Although its main function is to protect the nucleic acid, in viruses that are not enveloped by a membrane, it is also responsible for recognizing the cells it is going to parasitize. The capsid is usually formed by the repetition of capsomeres with the same type of proteins, so the virus can create a complex capsid, with many capsomeres, with little genetic information. The more proteins you need to synthesize, the more genetic information you need, and the space for nucleic acid in a virus is very limited. The term nucleocapsid refers to the genetic material wrapped in its capsid. The capsomeres, to the joining, can form three types of capsids: icosahedral, helical and complex. The icosahedral capsid is a polyhedral structure with 12 vertices, 20 triangular faces and 30 edges, in which the capsomeres are arranged to form an icosahedron. This arrangement allows to have a closed structure with few capsomeres. For example, they are virus icosahedral the virus influenza and virus human warts. By Dr. Richard Feldmann (photographer) (National Cancer Institute here) [Public domain], via Wikimedia Commons The helical capsid is made up of capsomers arranged in a helical manner, forming a tubular structure inside which is the nucleic acid. They have this type of capsid, the tobacco mosaic virus (VMT), the rabies virus or the measles virus. By Thomas Splettstoesser (www.scistyle.com) (Own work) [CC BY-SA 4.0], via Wikimedia Commons The complex capsid is characteristic of bacteriophages, viruses specialized in parasitizing bacteria. The virion has at least two parts: An icosahedral head or nucleocapsid that contains the nucleic acid . A tail (viruses that present a tail are called urophagi), of helical and contractile symmetry, ending in a *basal plate* equipped with spines and *anchoring fibers* (generally of a protein nature), adapted for the injection of nucleic acid into the inside the bacteria. At the base of the tail there may be enzymes and ATP, whose function is to destroy the bacterial wall. By NoeTico1516 (Own work) [CC BY-SA 4.0], via Wikimedia Commons Enveloped virus The viral envelope is a membranous structure that surrounds the viral capsid of some viruses. It usually comes from the host's plasma membrane. In addition, the envelope contains glycoproteins in its outer part that are encoded by the viral genome. These glycoproteins are involved in the recognition, in the adherence to the host cell and in inducing the penetration of the virion into the cell by phagocytosis. The enveloped viruses do not necessarily have to destroy the host cell for her to leave because they can get out by budding and cause persistent infections, such as HIV, the virus flu, or the smallpox. The viruses that have envelope called virus naked, such as virus polio and bacteriophage T4. Interactive activity: Parts of a complex virus. Fundamental ideas about viral morphology The viruses are microscopic particles *acellular* genetic material that are able to reproduce inside living cells. The viruses are composed of: A nucleic acid (DNA or RNA). A protein capsid. Icosahedral. Helicolidal. Complex. Sometimes a membranous envelope. 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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Viral morphology

Nucleic acid

Capsid

Enveloped virus