Parasites {virus, organism} can have DNA or RNA surrounded by protein.
nucleic acid
Virus has nucleic acid 4 to 250 genes long. Nucleic acid can be RNA or DNA, single or double-stranded.
injection
Protein coat has sites that attach to cell membrane. After attachment, protein coat contracts to inject nucleic acid into cell.
replication
After injection, viral genes can transcribe. Proteins from those viral genes prevent host-cell DNA transcription. Then cells transcribe viral genes whose proteins replicate virus and protect viral DNA from attack. Enzyme protects from attack by methylating sites that are vulnerable to attack by cell nucleases.
protein coat
After rod-like-virus nucleic acid replicates, nucleic acid binds protein-subunit disks at a site and then adds more subunit disks as nucleic acid folds into helix inside.
After sphere-like-virus nucleic acid replicates in cell, cell makes protein spheres, and enzyme inserts nucleic acid into protein sphere. One cell can make up to 200 viruses.
types
After assembly, virus can lyse cell and let viruses out to attack more cells. Virus can allow cell to remain packed with viruses, without bursting.
Viruses have protein coats {capsid}, with identical subunits hydrogen-bonded into symmetric structures. Special capsid proteins recognize cells by binding to cell-membrane proteins. After attachment, virus nucleic acid enters cell by injection through cell membrane, using energy from ATP.
Nucleic acids {bacteriophage}| can act like viruses in bacterial cells. It is DNA or RNA that has protein coat. It tries to enter cell from outside and then integrate into chromosome. Bacteriophages replicate in cell along with chromosome.
Viruses {RNA virus} can have RNA instead of DNA. RNA viruses can use RNA-directed RNA polymerase for direct RNA replication. RNA viruses can use RNA-directed DNA polymerase to make DNA from RNA and then make viral RNA from DNA. RNA viruses include polio, colds, foot-in-mouth disease, rabies, cancer retrovirus, and human immune deficiency virus.
Viruses {Sendai virus} can alter membranes and allow two cells to fuse, even if they are from different species.
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Date Modified: 2022.0225