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obligate intracellular parasites (hypotrophs.tend to be host specific,and are often categorized according to the type of organisms they infect.


A complete virus particle as it exists outside of its host is called a_______. a virus is the infective form.


the science or study of viruses


A virus that infects bacteria is called a____________meaning bacteria eater


a virus that infects E. coli is called a

virus structure


nucleic acid core

can be either DNA or RNA (double stand complimenaty and anti parellel or
single-stranded) can be ccc-dna or linerar. may be 1 segment or many genes 4-400.


The protein coat surrounding the nucleic acid core of a virus is called a____________-


capsid is made of units called___________


Capsomers are made up of smaller units called


additional layer, outside their protein capsid,made of protein and lipids like those found in cell membranes

tail assembly

Just below the nucleocapsid is a collar, and below that the tail core surrounded by a tail sheath. At the base of the tail core is a structure called a base plate, equipped with tail pins and tail fibers

Bacteriophages can be divided into two categories

cytolytic bacteriophage

cytolytic bacteriophage

is one that causes cell lysis, so kills its host


(avirulent or asymptomatic) bacteriophage does not kill its host (at least not right away


incorporate itself into the chromosome of its host.

T-even coliphages Life Cycle:


Adsorption I

The binding of a virus to the cell surface of its host is called_______.nteraction between the tail fibers of the virus and receptors on the host cell surface (viruses are host specific). then tail pins attach

Penetration II

the viral nucleic acid core enters the host
cell via the hollow tail core

Latent period III

the viral nucleic acid is transcribed and translated.The viral genome is transcribed in segments or in a sequence as follows:

Immediate early phage genes

enzymes used to transcribe viral DNA., and enzymes chop us the hosts cells dna

Delayed early phage genes

These genes encode enzymes used to replicate the viral genome. hundred of times

Late phage genes

These genes encode the proteins needed to build the viral capsid and the tail assembly

Assembly or maturation IV

the viral components are assembled (put together) to form new virions.


Some of the proteins come together by
themselves and others require assistance from other proteins called


new virions are
released into the environment

Bacteriophage lambda

A temperate phage known as_______.These bacteriophages can reside within the
host without causing damage, and may become incorporated into the host chromosome,
i.e., can exist as prophages.

Bacteriophage lambda

has a
double-stranded DNA genome that may be represented as a loop being closed by
overlapping cohesive termini called a a cosmid

cI gene

is expressed. This gene codes for a repressor protein that can block the transcription of the viral lytic genes.


gene of E. coli codes for a proteolytic enzyme that catalyses the cleavage and inactivation of
the cI repressor protein. The RecA gene is activated when the E. coli cells are stressed

phenotypic changes,

The presence of viral genes within a bacterial population will sometimes result in_____

lysogenic conversion

the phenotype of the bacteria is influenced by the expression of viral genes. This phenomenon is referred to as

toxin production.

A characteristic of bacteria that is often attributed to the expression of viral genes is ___

lysogenic cell

A bacterium that is carrying a prophage may be referred to as a

virus classification

all viruses should be classified according to
their own, shared properties rather than according to the organisms they infected

Human Immunodeficiency Virus (HIV)

is a diploid, single-stranded RNA type virus
known as a retrovirus because it has the ability to reverse transcribe the information of its
viral genome from RNA into DNA


primary targets is T4 lymphocytes


After the virus nucleocapsid enters the host, the capsid is removed (uncoating occurs) and
the viral genome is released within the cytoplasm of the host cell

reverse transcriptase

(RNA dependent DNA polymerase), also contained within the viral capsid, then causes the viral RNA to be reverse transcribed into DNA


Once the viral genome has been converted into a DNA format, it can become integrated into the chromosome of its host to form a


The integration of the viral DNA into the host
cell chromosome requires a second enzyme, also coded for by the viral genome, called


The virus particles exit the host cell by means of a process called


are plant pathogens made up of short, circular, single-stranded RNA molecules (usually around 246-375 bases in length) that are not surrounded by a protein coat


Prions are proteinaceous infectious particles,can be transmitted through ingestion

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