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Lacking the structures and metabolic machinery found in cells, most __ are little more htan genes packaged in protein coats.
True or False:
Viruses can reproduce ad carry out metabolic activities outside a host cell.
Viruses lead a __.
__ stunts the growth of tobacco plants and gives their leaves a mootle,d or mosaic, coloration.
- borrowed life
- tobacco mosaic disease
In 1883, __ a German scientist, discovered that he could transmit the disease from plant ot plant by rubbing sap extracted from diseased leaves onto healthy plants.
__ filtered bacteria, assuming they caused the disease.
__ showed that unlike bacteria used in the lab, the mysterious agent of the mosaic disease couldn't be cultivated on nutrient media in test tubes or petri dishes. They could only reproduce in a host.
The tiniest viruses are only __ nm in diameter. And the largest can't be seen under a microscope. Stanley's discovery that some viruses could be __ was exciting.
If viruses aren't cells, what are they?
- infectious particles consisting of nucleic acid enclosed in a protein coat and in some cases a membranous envelope
Viruses' genomes may consist of _ (4)_.
- A virus is called a __ or a __ depending on which nucleic acid makes up its genome.
- single stranded DNA
- double stranded DNA
- single stranded RNA
- double stranded RNA
- DNA virus
- RNA virus
True or False:
In either case, the genome is usually organized as a single linear or circular molecule of nucleic acid, althought he genomes o some viruses consist of multiple molecules of nucleic acid.
The proteins hell enclosing the viral genome is called a __. Depending on the type of virus, it can be __, __ or more complex in shape.
- rod shaped
Capsids are built from a large number of protein subunits called __, but the number of differnet kinds of proteins in a capsid is usually small.
Rod-shaped viruses are often called __, polyhedral with 20 triangular facets and other similarly shaped viruses are referred toas __.
- helical viruses
Some viruses have accessory structures htat help them infect their hosts. For ex., a __ surrounds the capsids of flu viruses and many othe viruses. These __, which are derived from the embranes of the host cell, contain hlost cell phospholipids and membrane proteins. They also contain __ and __ of viral origin. Some viruses carry a few viral enzyme molecules within their capsids.
- membranous envelope
- viral envelopes
Man of the complex capsids are found among the viruses that infecct bacteria, called __ or __.
The three most common (T2, T4, T6) are very similar in struccture. Their __ have elongated __ heads enclosing their DNA.
-- Attached to the head is a protein tail piece with fibers by which the phages attach to a bacterium.
- bacteriophages or phages