BACTERIOPHAGES Flashcards
4 different ways in which bacteria acquire new genetic information:
○ Conjugation
○ Transduction
○ Transformation
○ Lysogenic Conversion
viruses that infect bacteria
Like animal cells, bacteria can also be infected by viruses,called ______
bacteriophages.
_____ intracellular parasite, they must enter the cell to replicate.
Obligate
3 categories of bacteriophages based on their shape:
Icosahedron bacteriophages
Filamentous bacteriophages
Complex bacteriophages
categories of bacteriophages based on their shape:
it isa an almost spherical shape with 20 triangular facets; the smallest icosahedron phages are about 25 nm in diameter.
Icosahedron bacteriophages
categories of bacteriophages based on their shape:
It is a long tubes formed by capsid proteins assembled into a helical structure; they can be up to about 900 nm long
Filamentous bacteriophages
categories of bacteriophages based on their shape:
An icosahedral heads attached to helical tails; they may also possess base plates and tail fibers.
Complex bacteriophages
Like animal viruses, bacteriophages can be categorized by the type of nucleic acid that they possess; there are
■ Single-stranded DNA phages
■Double-stranded DNA phages,
■ Single-stranded RNA phages,
■ Double-stranded RNA phages
Bacteriophages can also be categorized by the events that occur after invasion of the bacterial cell: some are _____, whereas others are _______
virulent phages
temperate phages.
Phages in either category ____ enter the bacterial cell-rather, they ___ their nucleic acid into the cell.
It is what happens next that distinguishes virulent phages from temperate phages
do not
inject
______always cause lytic cycle, which ends with the destruction (lysis) of the bacterial cell.
○ the whole process (from ____ to ____) takes less than 1 hour.
Virulent bacteriophages
attachment to lysis
STEPS IN THE MULTIPLICATION OF BACTERIOPHAGES (LYTIC CYCLE)
Attachment (adsorption) Penetration Biosynthesis Assembly Release
WHAT OCCURS DURING THIS STEP
The phage attaches to a protein or polysaccharide molecule (receptor) on the surface of the bacterial cell.
Attachment (adsorption)
WHAT OCCURS DURING THIS STEP
The phage injects its DNA into the bacterial cell; the capsid remains on the outer surface of the cell.
Penetration
WHAT OCCURS DURING THIS STEP
Phage genes are expressed, resulting In the production of phage pieces or parts (I.e., phage DNA and phage proteins)
Biosynthesis
WHAT OCCURS DURING THIS STEP
The phage pieces or parts are assembled to create complete phages
Assembly
WHAT OCCURS DURING THIS STEP
The complete phages escape from the bacterial cell by lysis of the cell
Release
there is ___ uncoating in bacteriophages, unlike in animal viruses.
NO
The replicative cycle of bacteriophages is very similar to that of animal viruses except that bacteriophages do not actually enter the host cell, but rather ____ their nucleic acid into the cell.
inject
The first step in the lytic cycle is ______ of the phage to the surface of the bacterial cell.
- The phage can only attach to bacterial cells that possess the appropriate receptor-a protein or_____ on the surface of the cell that is recognized by a molecule on the surface of the phage.
- Most bacteriophages are species- and strain specific (must attach to a specific cell), meaning that they only infect a particular species or strain of bacteria. -
Ex. Tox gene that produces diphtheria toxin only attaches to a specific bacteria which is Corynebacterium diphtheria
Ex. The phage that infects C. diphtheriae is _________.
attachment (adsorption)
polysaccharide molecule
corynebacteriophage
Those that infect Escherichia coli are called
coliphages
Some bacteriophages can attach to _____one species of bacterium.
more than
The second step in the lytic cycle is called ______.
- the phage injects its DNA into the bacterial cell - acting much like a _____ needle
- the phage DNA “dictates” what occurs within the bacterial cell - sometimes described as the phage DNA taking over the host cell “machinery.”
- That’s why they are called “____”, because they cannot multiply on their own, they need to go inside a host cell.
penetration
hypodermic
infectious
The third step in the lytic cycle is called _____.
- the phage genes are expressed, resulting in the production (biosynthesis) of viral pieces.
- the host cell’s _____ (e.g., DNA polymerase and RNA polymerase), nucleotides, amino acids, and ribosomes are used to make viral DNA and viral proteins.
biosynthesis
enzymes
In the fourth step of the lytic cycle, called _______, the viral pieces are assembled to produce complete viral particles (virions).
- the viral DNA is packaged up into ______
assembly
capsids.
The final step in the lytic cycle, called _____, is when the host cell bursts open and all of the new virions (about 50 – 1,000) escape from the cell.
- the lytic cycle ends with lysis of the host cell. - Lysis is caused by an enzyme (referred to as an _____) that is coded for by a phage gene.
- At the appropriate time – after assembly – the appropriate viral gene is expressed, the enzyme is produced, and the bacterial cell wall is destroyed.
- a phage gene codes for an enzyme that interferes with cell wall synthesis, leading to weakness and, finally, collapse of the cell wall.
release
endolysin
They do not immediately initiate the lytic cycle, but rather, their DNA remains integrated into the bacterial cell chromosome, generation after generation.
- Similar to proviruses, the bacteriophage genome is referred to as a______.
Temperate phages (lysogenic phages)
prophage
Bacteriophages are involved in two of the four major ways in which bacteria acquire new genetic information.
(1) lysogenic conversion
(2) transduction
__________
- After temperate phages (also known as lysogenic phages) inject their DNA into the bacterial cell, the phage DNA integrates into (becomes part of) the bacterial chromosome but does not cause the lytic cycle to occur. -
This situation – in which the phage genome is present in the cell but is not causing the lytic cycle to occur – is known as _______.
Lysogenic Conversion
lysogeny
During lysogeny, all that remains of the phage is its DNA; in this form, the phage is referred to as a ______.
prophage
The bacterial cell containing the prophage is referred to as a________
lysogenic cell or lysogenic bacterium.
Each time a lysogenic cell undergoes binary fission, the phage DNA is replicated along with the bacterial DNA and is passed on to each of the daughter cells.
- Thus, the daughter cells are also _______
lysogenic cells.
Although the prophage does not usually cause the lytic cycle to occur, certain events (e.g., exposure of the bacterial cell to ______ or certain chemicals) can trigger it to do so
ultraviolet light
While the prophage is integrated into the bacterial chromosome, the bacterial cell can produce gene products that are coded for by the _____ genes.
prophage
The bacterial cell will exhibit new properties – a phenomenon known as ___________
lysogenic conversion (or phage conversion).
A medically related example of lysogenic conversion – _______.
diphtheria
Diphtheria is caused by a toxin – called diphtheria toxin – that is produced by a Gram-positive bacillus named __________
Corynebacterium diphtheriae.
The C. diphtheriae genome does not normally contain the gene that codes for diphtheria toxin.
- Only cells of C. diphtheriae that contain a _____ can produce diphtheria toxin because it is actually a phage gene (called the tox gene) that codes for the toxin.
prophage
Strains of C. diphtheriae capable of producing diphtheria toxin are called _________, and those unable to produce the toxin are called __________.
toxigenic strains
nontoxigenic strains
A nontoxigenic C. diphtheriae cell can be converted to a toxigenic cell as a result of ______
lysogeny
The phage that infects C. diphtheriae – the phage having the tox gene in its genome – is called a ___________
corynebacteriophage.
Other medically related examples of lysogenic conversion involve _____________
Streptococcus pyogenes, Clostridium botulinum, and Vibrio cholerae.
Only strains of S. pyogenes that carry a prophage are capable of producing erythrogenic toxin – the toxin that causes ___________
scarlet fever.
Only strains of C. botulinum that carry a prophage can produce _______
botulinal toxin
Only strains of V. cholerae that carry a prophage can produce ________.
cholera toxin
_________ (or phage) A virus that infects bacteria
Bacteriophage
A bacterial cell with bacteriophage DNA integrated into its chromosome
Lysogenic cell (or lysogenic bacterium)
When a bacterial cell has acquired new phenotypic characteristics as a result of lysogeny
Lysogenic conversion
When the bacteriophage DNA Is Integrated Into the bacterial chromosome; the bacteriophage DNA replicates along with the chromosome
Lysogeny
The sequence of events in the multiplication of a virulent bacteriophage; ends with lysis of the bacterial cell
Lytic cycle
The name given to the bacteriophage when all that remains of It Is Its DNA, Integrated Into the bacterial chromosome
Prophage
A bacteriophage that always causes the lytic cycle to occur
Virulent bacteriophage
(2) Transduction
- Involves bacteriophages; means “_______.”
- Some bacterial genetic material may be carried across from one bacterial cell to another by a bacterial virus.
- This phenomenon may occur after infection of a bacterial cell by a ________
- The viral DNA combines with the bacterial chromosome, becoming a ______. - If a stimulating chemical, heat, or ultraviolet light activates the prophage, it begins to produce new viruses via the production of phage DNA and proteins.
- As the chromosome disintegrates, small pieces of bacterial DNA may remain attached to the maturing phage DNA.
- During the assembly of the virus particle, one or more bacterial genes may be incorporated into some of the mature bacteriophages.
to carry across
temperate bacteriophage.
prophage
two of four major ways in which bacteria acquire new genetic information.
the remaining 2 __________has nothing to do with bacteriophage
Conjugation and Transformation
It is the transfer of genetic material from 1 cell to another via a sex pilus
Conjugation
acquiring of naked gene from the environment
Transformation-
_______
- some viruses such as HIV (retroviruses) and some DNA viruses are capable of inserting the viral genome into the host cell DNA.
- In this case, the viral genome is referred to as a _____.
- This process allows the virus to cause a latent infection and to avoid causing an immune response that may eliminate the virus.
- The viral genome is replicated with the host cell genome during cell division and can remain latent through many host cell generations.
- Later, they can exit the host cell genome to undergo ______.
- It has been estimated that up to 8% of the human genome may exist in the form of __________.
provirus
viral replication
endogenous retroviruses
_____ – short naked fragments of ssRNA (about 300-400 nucleotides in length) that can interfere with the metabolism of plant cells and stunt the growth of plants, sometimes killing the plants in the process.
Viroids
They are transmitted between plants in the same manner as viruses. Plant diseases thought or known to be caused by ______ include potato spindle tuber (producing small, cracked, spindle-shaped potatoes), citrus exocortis (stunting of citrus trees), and diseases of chrysanthemums, coconut palms, and tomatoes.
viroids
Thus, no animal diseases have been discovered that are caused by _____.
viroids
_____- infectious RNA particles
_____- complete viral particle (including nucleic acid and capsid)
Viroids
Virions
______ – small infectious proteins causing fatal neurologic diseases in animals and humans in which the brain becomes riddled with holes (becomes sponge-like)
○ They are thought to be transmitted by consumption of food contaminated with the agent.
Prions
Prions Diseases in Humans
○ CJ Disease – Creutzfeldt-Jakob disease
○ Variant of CJ disease
○ Gerstmann-Stäussler-Scheinker syndrome
○ Fatal familial insomnia
○ Kuru
Prions Diseases in Animals:
○ Scrapie ○ Bovine spongiform encephalopathy ○ Chronic wasting disease ○ Transmissible mink encephalopathy ○ Feline spongiform encephalopathy ○ Ungulate spongiform encephalopathy
The mechanism by which prions cause disease remains a mystery, although it is known that prions convert normal protein molecules into nonfunctional ones by causing the normal molecules to ______.
- The functional role of these proteins in their native state is not cutTendy known.
- It is believed that the unfolding of the protein causes cell damage with the resulting _____ appearance of brain tissue. Interestingly, no inflammatory response typical of an infectious process occurs with ___.
change their shape
sponge-like
TSE
Of all infectious agents, _____ are believed to be the most resistant to destruction.
- They retain their infectivity after treatment with disinfectants and heat.
prions
Only prolonged exposure to ______ has been demonstrated to inactivate prions.
sodium hydroxide
Great care must be taken by health care personnel when encountering patients with suspected ______, especially pathologists performing autopsies involving the manipulation of the brain or eyes since these are the tissues with the highest concentration of prions
TSE
They are difficult to develop and use because of viruses are produced within host cells, but quite a few drugs have been found to be effective in certain viral infections.
Antiviral agents
______ – first antiviral agent effective against human immunodeficiency virus (HIV) (the causative agent of acquired immune deficiency syndrome or acquired immunodeficiency syndrome [AIDS] – introduced in 1987.
Zidovudine (known as azidothymidine)
A variety of additional drugs for the treatment of HIV infection were introduced subsequently.
● Certain of these antiviral agents are administered simultaneouslys in combinations referred to as ____.
Unfortunately such ____ are quite expensive, have significant side effects, and some strains of HlV have become resistant to some of the drugs.
cocktails
What is the disease that is also known as fifth disease?
caused by Parvovirus B19 - Erythema infectiosum
What virus is responsible for Kaposi’s sarcoma?
Herpesvirus 8 (HHV-8)
What virus is responsible for Exanthem subitum?
Herpesvirus 6 (HHV-6)
other name for Exanthem subitum
Roseola
A lesion in the oral mucosa consisting of irregular red spots with a bluish white spec in the center – presence of this is diagnostic of measles – appears 2-3 days before the rash.
Koplik spots
Virus responsible for shingles -
Varicella zoster
What herpes virus is responsible for conjunctivitis and keratitis?
HSV-1
What family of viruses does yellow fever disease belong to?
Flavivirus (Family flaviviridae)
What type of hepatitis virus belongs to flaviviridae?
Hepatitis C virus
What virus is responsible for infectious mononucleosis?
Epstein-Barr virus
Enteroviruses particularly ________, is responsible for acute hemorrhagic conjunctivitis.
Enterovirus 17,
