12.2.2.1. Lytic cycle

Lytic cycle of viruses

The lytic cycle is so named because the cell infected by a virus dies by rupture (lysis in Greek), when the new viral copies are released. The lytic cycle is the main method of viral reproduction and involves the destruction of infected cells. The lithic cycle consists of the following phases:

Fixation or adsorption phase

The virus binds to the host cell stably. The binding is specific, since the virus recognizes protein, lipoprotein or glycoprotein molecular complexes, present in cell membranes, which act as receptors that allow the adhesion of virions.

In the binding or adsorption phase, the virus binds to the host cell surface. Proteins in the capsid (or envelope or caudal fibers) bind to receptors on the host cell.

The fixation in the bacteriophages is carried out through the tips of the caudal fibers by means of chemical bonds and then, mechanically, they drive the spines into the bacterial wall.

Other viruses, especially plants, do not attach to specific sites in the cell, but take advantage of areas of rupture or wounds to penetrate, or by the action of transmitting arthropods, mainly insects.

Ciclo lítico

Lytic Cycle | for ap bio flashcards | xxoverflowed | Flickr. (s. f.). Recuperado 17 de febrero de 2017, a partir de https://www.flickr.com/photos/hixtine/6374709127

Penetration phase

The penetration of the nucleic acid of the virus into the cell can be in several ways:

By injection, as in bacteriophages and certain naked animal viruses (polio viruses). The bacteriophage pierces the cell wall of the bacteria with lysozyme enzymes from its base plate. It then contracts the tail sheath and injects the DNA through the hole, while the capsid, tail, and attachment plate do not enter the bacteria.
By endocytosis: viruses that infect cells animale s intact are introduced inside the cell in a vesicle endocytosis. Inside the cell, the virus breaks the membrane of the vesicle with the help of some hydrolytic enzymes and reaches the cytoplasm.
By fusion of the viral envelope (in enveloped viruses ) with the plasma membrane of the cell.
Directly through pores or breakdown areas of the cell surface, as is the case with many plant viruses.

If the nucleocapsid also penetrates into the cell, decapsidation occurs, rupturing the capsid and releasing the nucleic acid into the cytoplasm.

Eclipse phase (replication and synthesis of viral components)

It is called the eclipse phase because in this phase no copies of the virus are observed in the cell, but the RNA synthesis and transcription necessary to generate the capsid protein copies is taking place. The continuous formation of viral nucleic acids and bacterial DNA destroying enzymes also occurs.

The metabolism cell is canceled and is used to synthesize the elements of the virus. The nucleic acid of the virus uses nucleotides and RNA polymerase from the host cell to synthesize mRNA which, in turn, will synthesize endonuclease enzymes that destroy cellular DNA. Afterwards, the nucleic acid of the virus will be duplicated and the proteins (capsomeres) of the new viruses will be synthesized.

The two main functions of the eclipse stage are:

Synthesis of virus proteins.
Replication of viral nucleic acid.

The retroviruses, viruses having RNA as nucleic acid, such as the HIV, causing the acquired immunodeficiency syndrome (AIDS), have two identical copies of single stranded RNA, which replicates via an intermediate form of dsDNA. The reverse transcriptase or reverse transcriptase enzyme is responsible for synthesizing DNA from RNA.

Viruses with RNA have much more variability than those with DNA, since RNA polymerase makes more reading errors than DNA polymerase. This implies that RNA viruses have more changes and it is more difficult to find vaccines against them.

Assembly phase

In the assembly phase, newly synthesized viral components unite to form new viruses. The capsomeres come together to form the capsid and the viral nucleic acid is packaged within it.

Lysis or release phase

In the lysis or release phase, the new viruses leave the cell by breaking (lysis) the bacterial wall, by the action of the enzyme endolysin. These new viruses can already infect a new cell. Lysis leads to cell death.

In the release phase, enveloped viruses take their membrane from the newly ruptured cell, after inserting into it proteins encoded by the virus genome.

Video: Lithic cycle (without sound).

Fundamental ideas about the lytic cycle of viruses

In the lytic cycle of a virus, the host cell dies by rupture (lysis), when the new copies of the virus are released.

The lithic cycle consists of several phases:

Fixation or adsorption. There is great specificity.
Penetration. It can be in several ways:
- By injection: in bacteriophages.
- By endocytosis: in animal cells.
- By fusion of the viral envelope: in enveloped viruses.
- Directly through pores or break zones: in plant viruses.
Eclipse phase (replication and synthesis of viral components).
- The phase of highest metabolic activity, necessary to synthesize viral mRNA.
- Synthesis of the capsomeres of the virus.
- Viral DNA replication.
Assembly of new viruses.
- Formation of the capsid from capsomeres.
- The viral DNA molecules enter the capsid.
Lysis or release.
- The new virions go outside and can infect other cells.

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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 » 12.2.2.1. Lytic cycle Lytic cycle of viruses The lytic cycle is so named because the cell infected by a virus dies by rupture (lysis in Greek), when the new viral copies are released. The lytic cycle is the main method of viral reproduction and involves the destruction of infected cells. The lithic cycle consists of the following phases: Fixation or adsorption. Penetration. Eclipse phase (replication and synthesis of viral components). Assembly of new viruses. Lysis or release. Fixation or adsorption phase The virus binds to the host cell stably. The binding is specific, since the virus recognizes protein, lipoprotein or glycoprotein molecular complexes, present in cell membranes, which act as receptors that allow the adhesion of virions. In the binding or adsorption phase, the virus binds to the host cell surface. Proteins in the capsid (or envelope or caudal fibers) bind to receptors on the host cell. The fixation in the bacteriophages is carried out through the tips of the caudal fibers by means of chemical bonds and then, mechanically, they drive the spines into the bacterial wall. Other viruses, especially plants, do not attach to specific sites in the cell, but take advantage of areas of rupture or wounds to penetrate, or by the action of transmitting arthropods, mainly insects. Lytic Cycle \| for ap bio flashcards \| xxoverflowed \| Flickr. (s. f.). Recuperado 17 de febrero de 2017, a partir de https://www.flickr.com/photos/hixtine/6374709127 Penetration phase The penetration of the nucleic acid of the virus into the cell can be in several ways: By injection, as in *bacteriophages* and certain naked animal viruses (polio viruses). The bacteriophage pierces the cell wall of the bacteria with lysozyme enzymes from its base plate. It then contracts the tail sheath and injects the DNA through the hole, while the capsid, tail, and attachment plate do not enter the bacteria. By endocytosis: viruses that infect *cells* animale s intact are introduced inside the cell in a vesicle endocytosis. Inside the cell, the virus breaks the membrane of the vesicle with the help of some hydrolytic enzymes and reaches the cytoplasm. By fusion of the viral envelope (in *enveloped viruses* ) with the plasma membrane of the cell. Directly through pores or breakdown areas of the cell surface, as is the case with many *plant viruses. If the nucleocapsid* also penetrates into the cell, decapsidation occurs, rupturing the capsid and releasing the nucleic acid into the cytoplasm. Eclipse phase (replication and synthesis of viral components) It is called the eclipse phase because in this phase no copies of the virus are observed in the cell, but the RNA synthesis and transcription necessary to generate the capsid protein copies is taking place. The continuous formation of viral nucleic acids and bacterial DNA destroying enzymes also occurs. The metabolism cell is canceled and is used to synthesize the elements of the virus. The nucleic acid of the virus uses nucleotides and RNA polymerase from the host cell to synthesize mRNA which, in turn, will synthesize endonuclease enzymes that destroy cellular DNA. Afterwards, the nucleic acid of the virus will be duplicated and the proteins (capsomeres) of the new viruses will be synthesized. The two main functions of the eclipse stage are: Synthesis of virus proteins. Replication of viral nucleic acid. The retroviruses, viruses having RNA as nucleic acid, such as the HIV, causing the acquired immunodeficiency syndrome (AIDS), have two identical copies of single stranded RNA, which replicates via an intermediate form of dsDNA. The reverse transcriptase or reverse transcriptase enzyme is responsible for synthesizing DNA from RNA. Viruses with RNA have much more variability than those with DNA, since RNA polymerase makes more reading errors than DNA polymerase. This implies that RNA viruses have more changes and it is more difficult to find vaccines against them. Assembly phase In the assembly phase, newly synthesized viral components unite to form new viruses. The capsomeres come together to form the capsid and the viral nucleic acid is packaged within it. Lysis or release phase In the lysis or release phase, the new viruses leave the cell by breaking (lysis) the bacterial wall, by the action of the enzyme endolysin. These new viruses can already infect a new cell. Lysis leads to cell death. In the release phase, enveloped viruses take their membrane from the newly ruptured cell, after inserting into it proteins encoded by the virus genome. Video: Lithic cycle (without sound). Fundamental ideas about the lytic cycle of viruses In the lytic cycle of a virus, the host cell dies by rupture (lysis), when the new copies of the virus are released. The lithic cycle consists of several phases: Fixation or adsorption. There is great specificity. Penetration. It can be in several ways: By injection: in bacteriophages. By endocytosis: in animal cells. By fusion of the viral envelope: in enveloped viruses. Directly through pores or break zones: in plant viruses. Eclipse phase (replication and synthesis of viral components). The phase of highest metabolic activity, necessary to synthesize viral mRNA. Synthesis of the capsomeres of the virus. Viral DNA replication. Assembly of new viruses. Formation of the capsid from capsomeres. The viral DNA molecules enter the capsid. Lysis or release. The new virions go outside and can infect other cells. 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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Fixation or adsorption phase

Penetration phase

Eclipse phase (replication and synthesis of viral components)

Assembly phase

Lysis or release phase