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.
