Chapter 13: Viruses

antigenic shift

In ____ ____, a new strain of virus can be formed by the reassortment of different strains that infected the same cell.

prophage

In a lysogenic infection, the integrated DNA is called the _____, and it is integrated along with the host cell chromosome. When the lysogen (infected host cell) divides, the prophage is passed on to daughter cells.

mismatch repair and restriction-modification

In which 2 processes is the methylation of the DNA strand involved?

conversion

Lysogenic ______ is a change in the phenotype of a lysogen as a consequence of the specific pathogen it carries.

superinfection

Lysogens are morphologically identical to uninfected cells, but there are differences: 1- immunity to ______ (infection by the same type of phage) 2- lysogenic conversion

operator

Lysogens are protected from superinfection because the repressor that blocks the excision proteins will also bind to the _____ of incoming phage DNA.

small

Most viruses are extremely ____--they can be 100-1000x smaller than the cells they infect. They range in size--form 10 nm (only as few as 10 genes) to 800 nm.

site specific recombination

When the DNA of a temperate phage is being incorporated into bacterial genome, it is said to be integrated through ______ _______ ______.

metabolic, slowly, productive

While cells infected by filamentous phages do not suffer immediate costs (no lysis), there are _____ costs, causing these cells to grow more ______. → both lytic and filamentous phage infections are classified as ______ due to the continuous production of phage particles

more, bacterial

-When correcting a mismatch in mismatch repair, the ______ methylated strand is the "correct" / template strand. -In restriction-modificaiton systems, the methylated stand represents the _____ DNA (helps distinguish between self and non-self).

capsid, enzymes, nucleocapsid, capsomeres

A virion consists of nucleic acid surrounded by a ____ (protein coat). The coat serves to: → protect the nucleic acid → carry ____ required for infection of host cell The capsid together with the nucleic acid it enclose is called a ______. -Capsids are made of identical protein subunits called ____.

receptor, restriction, CRISPR

Bacterial defense mechanisms against viruses include: 1- altering _____ sites 2- ______ modification systems 3- _____ system

lytic, productive

By definition, _____, or virulent phages leave the host cell at the end of infection by lysing the cell. These viral infections result in the formation of new viral particles, and are called ____ infections.

resistant

Cells hat do not have the receptors that the virus attaches onto are _____ to infection by that virus.

dsDNA, often, host enzyme

Characteristics of DNA viruses: -must go through _____ intermediate before replication can start (if not initially) -replication ______ occurs in cell nucleus -most use the _____ ______ for genome replication (some use their own because they will not have to wait for cell to reach S phase in cell cycle)

cytoplasm, replicase, carry

Characteristics of RNA viruses: -replication usually occurs in _______ -must use virally-encoded _____ enzyme for genome replication -ss(-) ssRNA and (+/-) dsRNA viruses must _____ their own replicase enzyme before infection

RT

Characteristics of Reverse Transcribing Viruses: -viral ____ enzyme synthesizes DNA from RNA template -dsDNA is integrated → host genome (provirus) -leads to latent or productive infections -provirus cannot be eliminated

endocytosis

Enveloped viruses enter the host cell by one of the following mechanisms: 1- fusion with host membrane (enveloped) 2- ______ (non-enveloped)

acute, persistent

HIV infections have features of both ____ and _____ infections.

induction

Phage ____ is the process by which the infection change form from the lysogenic to the lytic cycle (allowing the phage to escape from a damaged hot). This may occur 1 of 10,000 lysogen replications, but is more often seen when the lysogen is affected by a mutagen that causes it to activate SOS system > protease break down repressor that blocks excision enzyme > viral DNA excised > lytic cycle

budding, apoptosis

Release: -Enveloped viruses leave by ____ -non-enveloped viruses leave when the host cell dies, often though _____

proofreading, antigenic drift

Replicases lack a ______ ability and thus tend to make mistakes. In the case of influenza, this leads to ____ ______.

HIV

Some infections can be productive chronic and latent (depending on the cell). An example of a virus that produces such an infection is _____.

host, matrix, more

Some viruses have a lipid bilayer envelope outside of the capsid. They obtain this envelope form the ___ cell. They have ____ protein in which the nucleocapsid is suspended in under the envelope. Most viruses are naked and do not have an envelope. → In general, enveloped viruses are _____ susceptible to disinfectants, since the envelope is damaged, making the virus non-infectious.

early, nuclease, RNA, late

Synthesis of Phage Proteins and Genome: -Within minutes after injection, viral genes are transcribed and translated. The first phage proteins produced are called ____ proteins and are important for phage multiplication These include: 1- ____ that degrades host cell DNA 2- proteins that modify the host cells' ____ pol so that it cannot recognize bacterial DNA → Soon after the infection, no bacterial genes are expressed --Toward the end of the end of the infection cycle, structural proteins that make up the phage are synthesized = ____ proteins

burst size

The ___ _____ is the number of phage particles released at the end of the infection of a lytic phage. For the T4 model system, it is about 200.

difficult

The fact viruses they are obligate intracellular parasites makes them ____ to study. -They cannot be grown in pure culture -they are often too small to see with light microscope (visualized only with electron microscope)

viridae, virus

The family name of viruses typically ends with ______ The genre name of viruses typically ends with _______

genome, synthesis, lyses

The infection cycle of lytic T4 phage: 1- adsorbs onto E. coli surface receptors 2- ____ entry: tail contracts and injects viral genome into cell, capsid remains outside 3- _____: all phage components are made, and genome is replicated, host DNA degraded 4- assembly: mature virions form 5- release: bacterial cell ____, mature phages leave

replicase

The majority of RNA viruses are single stranded, and they replicate in the cytoplasm with a virally encoded ______ enzyme (RNA pol).

entire

The mechanism an animal virus uses to enter its host cell depends in part on whether the virion is enveloped or non-enveloped. In all cases, the _____ virion is taken into the cell. This differs from most phages, where only nucleic acid enters and the capsid stays outside the bacterium.

temperate, integrase, repressor

The model system for the ____ phage is λ, which has a linear chromosome. When the phage enters the lysogenioc cycle, it uses an enzyme called _____ to insert the DNA at a specific site. The lytic infection may begin when a viral protein excises the viral DNA → the ____ protein prevents the expression of the gene required for excision, and therefore is necessary to maintain lysogenic state

glycoproteins

The receptors to which animal viruses bind are typically _______ projecting from the plasma membrane.

acute, persistent

The relationship between viruses and their hosts can be: 1- _____: sudden onset of symptoms with short duration 3- _____; can continue with our without symptoms for years (or even lifetime of host) → there are 2 types of persistent infections: chronic and latent

chronic, latent, provirus

There are 2 types of persistent infections: 1- _____: continuous production of low levels of viral particles 2- _____: virus remains silent in host cell's genome, but it can reactivate to cause a productive infection (silent viral genome is a _____)

complex, phages

There are 3 main virus shapes: -icosahedral (appear circular, but actually have 20 triple sides) (ex. adenovirus) -helical (appear cylindrical, their nucleic acid is in helical form) -_____ (have multiple components)-an example are ___, which have icosahedral head and helical trial

proteins

There is no evidence that viroids encode for ______ or mRNAs.

T4

This ___ phage is the model system for the lytic virus.

RNA, RT, reassortment, recombination

Viral Evolution: -fast replication leading to many progeny -_____ and ____ viruses tend to have high mutation rates (due to enzymes being used for genomic replication) → _______ can occur in the case of coinfection (influenza segmented virus and antigenic shift) → ____ may occur btw virus and the host genome → antigenic drift - when antigens change due to genome mutations in antigen genes

inert

Viruses are _____ particles, incapable of metabolism, replication, or motility. Although they are infectious agents, they are not organisms because they do not fit the definition of life.

phages

Viruses are separated into 2 groups based on what types of cells they infect. In general, they are all called viruses, but those specific to bacteria are called _____.

never

Viruses contain only a single type of nucleic acid--DNA or RNA--but _____ both. -the genome may be single or double stranded -it may be linear, circular, or segmented

receptor, spikes

Viruses have specific protein components that facilitate their adsorption onto specific ____ sites on host cells. → Phages often have tail fibers → animal viruses often have _____

Filamentous, slowly, M13, replicative

____ phages are ssDNA phages that look like long fibers. They cause productive infections, but they are not considered lytic phages because the host cell does not ultimately die. Infected cells grow more _____ than uninfected cells. -____ is the model system for this type of phage. It infects by attaching to a protein on the F pilus of E. coli. Its ssDNA genome then enters the cytoplasm of the bacterial cell, where DNA pol makes a complementary strand. The dsDNA is called the ____ form (RF).

Temperate

____ phages have het option of either directing a lytic infection or incorporating their DNA into the host cell genome (lysogenic infection).

retroviruses

_____ (such as HIV) have a (+) strand RNA genome and carry a reverse transcriptase with them.