quiz 3- week 3/4 Flashcards
What is characteristic of Group 1 viruses?
Group 1 viruses have double-stranded DNA (dsDNA) genomes, which must be transcribed and translated.
How do Group 2 viruses replicate?
Group 2 viruses have single-stranded DNA (ssDNA) genomes, which must first make a complementary strand, then undergo transcription and translation.
How do Group 3 viruses differ from Group 4 viruses?
Group 3 viruses have double-stranded RNA (dsRNA) genomes that can be transcribed but not replicated, while Group 4 viruses have single-stranded positive RNA ((+) ssRNA) genomes, which can be directly translated into proteins.
What do Group 5 viruses require for replication?
Group 5 viruses have single-stranded negative RNA ((-) ssRNA) genomes and require RNA-dependent RNA polymerase, which is packaged within the virion.
What is the defining characteristic of Group 6 viruses (retroviruses)?
Group 6 retroviruses reverse-transcribe their RNA genome into double-stranded DNA (dsDNA) using reverse transcriptase, which is packaged in the virion.
What are the two types of DNA strands and their roles in transcription?
The template strand binds to RNA polymerase, while the coding strand has the same sequence as the RNA that gets translated.
What are the key steps in the lytic cycle of bacteriophages?
In the lytic cycle, the phage injects its genome into a bacterial cell, replicates, and lyses the cell to release new virions.
What happens during the lysogenic cycle of bacteriophages?
Phage DNA integrates into the bacterial genome and is propagated during bacterial replication. It may eventually exit the genome and enter the lytic cycle.
How do bacteria protect themselves from viral infection using genetic resistance?
Bacteria may stop producing receptor proteins, making it difficult for viruses to bind and infect them.
What is CRISPR, and how does it protect bacteria from viruses?
CRISPR is a system in bacterial genomes that contains sequences from viral genomes, allowing for a rapid immune response when encountering these sequences again.
What role do topoisomerases play in DNA supercoiling?
Topoisomerases alleviate DNA supercoiling; Type 1 cleaves one strand, while Type 2 (including DNA gyrase) cleaves both strands to manage coiling.
What is the difference between positive and negative supercoiling?
Positive supercoiling tightens the DNA coil, while negative supercoiling loosens it.
What is the significance of Dam methylase in DNA replication initiation?
Dam methylase methylates “A” in a GATC sequence to help bacteria distinguish old from new DNA strands and protect their own DNA from restriction enzymes.
How does SeqA regulate DNA replication initiation?
SeqA binds to hemimethylated DNA strands, inhibiting DnaA from starting another round of replication, and is removed once DNA is fully methylated.
What enzymes help with DNA proofreading during replication elongation?
DNA polymerases perform proofreading, detecting and fixing mistakes in real time during DNA replication.
How does unidirectional plasmid replication differ from bidirectional replication?
In unidirectional replication, the plasmid uses rolling circle replication, while in bidirectional replication, synthesis occurs at two replication forks, similar to chromosomal replication.
How do low copy number plasmids ensure segregation into daughter cells?
Low copy number plasmids use filaments to push copies toward opposite poles during cell division.
What are secondary chromosomes, and how do bacteria acquire them?
Secondary chromosomes carry essential genes, acquired when bacteria lose those genes on the primary chromosome but gain them on the secondary one.
How do nitrogen-fixing bacteria contribute to nitrogen availability?
They convert atmospheric nitrogen (N2) into usable forms like ammonia, ammonium, nitrite, or nitrate.
What role do heterocyst cells play in cyanobacteria like Anabaena?
Heterocysts are specialized cells for nitrogen fixation, providing organic nitrogen to vegetative cells, which in return supply carbon.
What is the function of mycelia in Streptomyces?
Under nutrient-rich conditions, cells form mycelia, and when nutrients are scarce, they form aerial hyphae that can sporulate and secrete antibiotics.
What is RNA interference (RNAi), and how does it protect against viruses?
RNAi machinery cuts double-stranded RNA, preventing viral replication by degrading viral RNA through anti-sense RNA binding to the viral RNA.
How do miRNAs regulate translation and protect against viral infections?
miRNAs bind to target mRNA, forming a double-stranded RNA that gets degraded, inhibiting translation and viral replication.
How do vaccines prime the immune system against viruses?
Vaccines introduce a dead viral particle, viral protein, or viral mRNA to stimulate an immune response, preparing the body to fight actual viral infections.
