Microbiology unit 3
RNA retroviruses use_____________.
viral reverse transcriptase to make a DNA copy that is integrated into the host genome and then host RNA polymerase transcribes it.
What recognizes viral mRNA and prevents further viral gene expression.
A _____ virus cycle leads only to cell lysis, and a _____ virus cycle involves phage genome integration into the host genome.
List the steps from HIV retroviral genome replication to protein synthesis.
- (+)ssRNA genome
- Reverse transcriptase
- dsDNA genome
- Integration into host genome
- RNA polymerase II transcription
- Translation of viral proteins by host ribosomes
In the________the phages have transition host cell machinery for phage progeny production, as a consequence of diverted resources the host cell replication slows.
Prion diseases, which affect the brain, are thought to be caused by_____________.
misfolded proteins that act as a template for further protein misfolding
HIV, which only infects humans, is considered to have a______host range, whereas rabies virus, which can infect a number of animals and humans, is considered to have a______host range.
Human papillomavirus (HPV) is a double-stranded DNA virus that enters the cytoplasm before undergoing uncoating. Although the virus is replicated by host DNA polymerase in the nucleus, viral replication is closely tied to epithelial cell differentiation. In particular, viral DNA replication is inhibited until_______are differentiated into_________, which are ready to be shed from the epithelial layer, increasing the likelihood that HPV will be transmitted to a new host.
basal cells; keratinocytes
The enzyme reverse transcriptase (RT) is found in__________.
some DNA and some RNA viruses.
PrPSc does have a higher proportion of__________, and this could be a viable hypothesis as to why this protein is more resistant to methods of control.
beta pleated sheets
What is a prophage?
A phage genome integrated into a host genome.
What type of virus can integrate into the host genome to form a prophage.
________are naked nucleic acids, usually RNA, devoid of a protein capsid. Some plant viroids are ribozymes, capable of catalytic action.
The Baltimore classification of viral genomes is based on what?
The composition of the genome, and the route used to express messenger RNA (mRNA).
Viral genomes may comprise____________.
double or single-stranded DNA or double or single-stranded RNA.
The innate immune system recognizes double-stranded RNA (dsRNA), an indicator of viral replication in the host cell, and signals the immune response with________.
A gene for a __________ is likely to be encoded in the viral genome.
What is the ability to infect a particular type of cell within the host?
What is a set of short DNA sequences that allow the bacterium to “remember” past infections?
Reverse transcriptase catalyzes _____ production from a _____ template.
Which viral genome is likely to require an RNA-dependent RNA polymerase for transciption upon viral entry?
(–) sense single-stranded RNA
All strains of human papillomavirus (HPV) are capable of integrating their double-stranded DNA viral genome into host basal cells while waiting for keratinocyte differentiation before initiating viral replication for virion shedding. As a consequence of the integrated genome, HPV strains that more readily transform host cells are more likely to cause an increased expression of viral_________.
A temperate phage is one that___________.
can undergo lysogeny.
_________is a process by which bacteria transfer DNA via formation of a pilus. This process requires cell-to-cell contact.
What is a structural gene?
A string of nucleotides that can be used as a template to produce an RNA that codes for a protein.
A collection of prokaryotic genes and operons located at different positions on a chromosome but that have a unified biochemical function is known as a__________.
Eukaryotic genomes comprise mostly __________, whereas prokaryotes have mostly __________.
noncoding DNA; coding DNA
Functional units of DNA sequences include structural genes, which are nucleotide sequences that encode an RNA molecule, and_________sequences that regulate the expression of structural genes.
During rolling-circle replication, RepA binds to the ori and nicks one strand of the DNA. The_____ end of the nicked DNA serves as a primer and is extended by DNA polymerase, while the_____ end is coated with single-stranded DNA-binding proteins and replicated using RNA and DNA polymerases.
What are constitutive genes?
"Housekeeping genes"; they are always expressed.
transcribed continually as opposed to a facultative gene, which is only transcribed when needed.
What are the types of regulatory proteins?
Represses and activators; repression/ induction/ corerepressor/ derepression
Inactive repressor= gene expression
To induce or derepress is to_______
Turn on gene expression.
Induction involves the______operon
Derepression involves the______operon
The activator can only itself become active through the use of_______.
A low level of______transcription always occurs. Why?
lacZYA; Lactose permease (lacY) transports lactose must be expressed.
Absence of lactose= ?
Repression, transcription blocked
Presence of allolactose=?
Induction, RNA polymerase binds; transcription allowed.
lac operon transduction is also controlled by_______, a regulatory molecule that binds to cAMP regulatory protein (CRP)
bind lac promoter, increasing transcription
Cellular cAMP levels fluctuate based on the cell's_______.
As [glucose] increases [cAMP]______
Glucose turns off the lac operon via________.
What occurs during inducer exclusion?
Glucose blocks the entry of lactose
Genes of a biosynthetic pathway for tryptophan synthesis.
Low or no tryptophan present=
Derepression; transcription proceeds.
Acts as corepressor; binds aporepressor
Is a secondary strategy for regulating tryptophan synthesis.
In order to transfer, an F factor must have what?
OriT and tra genes
The recipient of Hfr conjugation_______becomes an F+ cell
Genes for the capsid proteins are found in the________.
In the CRISPR system of bacteria, the spacer is a(n)______________.
Piece of phage DNA
Most structural genes of bacteria are grouped together and transcribed from a single________; immediately following this sequence is the_______that interacts with a regulatory protein to affect transcription of the genes.
The difference between generalized and specialized transduction is____________.
that in generalized transduction, any DNA can be moved, but with specialized transduction, only certain DNA near the phage site can be moved.
The operator of an bacterial operon serves was a_______element.
Bacterial operons possess a______promoter.
The transcript of a bacterial operon will be an_______of all the structural genes contained in a single polynucleotide sequence.
The information flow of retroviruses is____________.
RNA to DNA to RNA to protein
Retroviruses can form a_________.
Retroviruses can remain in the proviruses state while simultaneously_____________.
initiating production of new viral particles.
________is a mechanism of virus exit that leads to acquisition of the envelope around the viral particles
________is a mechanism that allows for the viral genome to be freed from the capsid.
Within a host, receptor molecules can also determine the_________, or tendency to infect a particular tissue type.
Formation of daughter cells is an example of_________.
vertical gene transfer or transmission?
Slow release of bacteriophage progeny from a bacterial host cell__________and___________.
does not kill the host cell; is a feature particular to filamentous phage.
Tissue specificity; relevant for animal viruses
_________are proteins that infect animals; they have no nucleic
In cows prions cause degenerative brain disease called________or mad cow disease. In humans it causes_______.
spongiform encephalopathy; Creutzfield‐ Jacob disease
Viroids alter gene expression in____________.
The international committee of taxonomy of viruses is based on what?
Genome, Capsid ssymmetry, Envelope, host range, and viroid size.
_____________dictate when lysogeny converts to the lytic cycle.
Define Vertical gene transfer.
the generational passing of genes from parent to offspring
__________is type of horizontal gene transfer that involves transfer of genes by bacteriophages. There are two types: generalized and specialized.
Which of the following events must precede transfer of chromosomal genes by specialized transduction?
___________is a simple transposable element that consists of a transposase gene flanked by short, inverted repeats that are the target of transposase.
An insertion sequence (IS)
An insertion sequence contains a gene for which enzyme?
__________are mobile DNA elements that can rearrange with in a larger DNA molecule.
Transposable elements differ from plasmids in that only plasmids________.
may exist autonomously, not integrated into host DNA.
Which type of DNA uptake is dependent on viruses?
Transduction (requires bacteriophages)
direct transfer of DNA from one bacterial cell to another
the uptake of DNA from the environment
during conjugation, the orientation of the will determine which of the flanking chromosomal genes are transferred first.
integrated F factor
regions exhibiting_____________would be suggestive of recently acquried foreign DNA.
different codon usage and GC content
________refers to the ability to perform transformation.
Natural transformation requires specific protein complexes called__________.
Which specific feature of replicative transposition distinguishes it from nonreplicative transposition?
During replicative transposition, the entire transposon is replicated.
In bacteria, a partially diploid strain may result from_____________.
acquisition of an F' factor or specialized transduction.
__________probably evolved first as a DNA repair mechanism, but it also determines the fate of sequences acquired by transformation, conjugation, and transduction.
Which type of DNA uptake is dependent on transferable plasmids?
_________acts to terminate transcription that is already underway, but unnecessary, under conditions of excess tryptophan.
Phase variation is when______________.
reversible flipping of a DNA segment enables a pathogen to turn on and off cell surface proteins.
What is the fastest and most easily reversible way for a cell to alter its physiology?
modification of an existing protein
“Virulent” phages only carry out______.
During_______Phage particles reproduce & exit without harming the host cell. Host cells grow slowly, but don’t die
slow release cycle
Bacterial host defenses may include__________which cleaves viral DNA sequences lacking methylation
For RNA viruses Genome replication; synthesis of viral proteins; and viral assembly all occur__________.
outside the nucleus
The genome of (+) RNA viruses can serve as a template for__________.
The genome of (-) RNA viruses can serve as a template for__________.
The genome of retroviruses can serve as a template for__________.
Lysogeny occurs in certain bacteria; the equivalent process in an animal cell is best represented by a_________
promoter + operator + structural genes=
Define Fertility factor or F factor
F’ (F prime) factor formation:
integrated F factor is excised from host chromosome along with some host DNA; extra genes expressed as part of the F’ plasmid.
_________is high‐frequency recombination strain
For Hfr Formation___________.
integration occurs at insertion sequences (IS); areas of homo‐ logy between plasmid & chromosome.
Define Specialized Transduction.
transfer of a few closely linked genes.
_________the process of mobilizing the transposable element within or between DNA molecules.
Control sequences in DNA do not code for proteins, but rather____________
they serve to regulate gene function
Plasmids that are copied vie rolling circl replication do not undergo____________.
The presence of competence factors, the formation of translocation in the cell membrane, and the presence of extracellular DNA all indicate_____________.
the cell is ready to carry out transformation