viruses Flashcards
(49 cards)
What are the characteristics of viruses?
Obligate parasites, contain DNA or RNA, can evolve but cannot carry out respiration, reproduction, respond to stimuli without host cell.
What is the structure of a T4 bacteriophage?
Double stranded DNA genome protected by icosahedral capsid head made of proteins; tail that is a long, hollow tube-like structure; contractile tail sheath; base plate; tail fibers and pins.
Describe the structure of a lambda phage.
Icosahedral capsid head made of protein, encases a double-stranded DNA genome; tail is non-contractile and flexible; tail fibers and base plate.
What are the stages of the life cycle of a T4 phage?
Attachment, Penetration, Replication, Maturation, Release.
What occurs during the attachment stage of the T4 phage life cycle?
Attachment sites on tail fibers adsorb to complementary receptor sites on bacterial surface.
What happens during the penetration stage of the T4 phage life cycle?
Phage releases lysozyme that digests bacterial cell wall, allowing the phage DNA to be injected into the bacteria.
What is involved in the replication stage of the T4 phage life cycle?
Phage proteins synthesized using host cell machinery; early phage proteins degrade host DNA and phage DNA is synthesized.
What is the maturation stage of the T4 phage life cycle?
Phage DNA and capsid assemble into a head, which assembles independently with tail and tail fibers.
What occurs during the release stage of the T4 phage life cycle?
Phage lysozyme breaks down the cell wall, resulting in lysis of the bacterial cell and release of newly formed virions.
What is the lysogenic life cycle of the lambda phage?
Linear phage DNA circularizes and inserts into host cell genome, forming a prophage that remains latent.
What triggers the activation of the lysogenic lambda phage?
Spontaneous induction by cellular protease that activates and destroys phage repressor proteins.
What is the structure of the influenza virus?
Negative strand RNA genome with 8 segments; RNA-dependent mRNA polymerase; glycoproteins embedded in envelope (80% hemagglutinin, 20% neuraminidase).
What are the stages of the influenza virus life cycle?
Attachment, Entry, Replication and Transcription, Protein Synthesis, Assembly, Release.
How does the influenza virus enter the host cell?
The virus enters via endocytosis, and the acidic pH in the endosome triggers fusion with the viral envelope.
What is the function of neuraminidase in the influenza virus life cycle?
Cleaves sialic acids to release new virions, preventing them from sticking to the cell.
How does Tamiflu work?
Tamiflu is a neuraminidase inhibitor that blocks the function of the viral neuraminidase enzyme, preventing the release and spread of new viruses.
What is the structure of the HIV virus?
Genome: (+) strand RNA; conical-shaped capsid containing reverse transcriptase, integrase, and protease; glycoproteins embedded in the envelope.
What are the stages of the HIV life cycle?
Entry, Replication, Activation, Release.
How does HIV replicate its RNA into DNA?
Reverse transcriptase makes a DNA strand using viral RNA as a template, forming double-stranded DNA.
What role do protease inhibitors play in HIV treatment?
Prevent the processing of viral proteins, blocking the assembly of mature viral particles.
What is antigenic drift?
Accumulation of mutations in the viral genome due to poor proofreading by RNA-dependent RNA polymerase.
What is antigenic shift?
Sudden, major change in a virus’s genome due to reassortment or recombination when two or more viruses co-infect a single host cell.
What features of influenza allow it to give rise to new subtypes?
Segmented genome, antigenic drift, antigenic shift, high mutation rate, ability to cross species.
What is the first step in the influenza life cycle?
Attachment: Haemagglutinin on the viral envelope recognises and binds to sialic acid receptors on the host cell surface.
This step is crucial for the virus to initiate infection by targeting the host cell.
