Genetic Systems of Viruses and Bacteria: Structure, Reproduction, and Gene Transfer

What is the first virus discovered?

The tobacco mosaic virus (TMV).

Why are viruses considered nonliving?

They do not exhibit all properties of living organisms, such as metabolism or reproduction without a host.

What is a virus composed of?

Nucleic acid enclosed in a protein coat.

What is the host cell?

A cell that is infected by a virus.

What is the host species?

A species that can be infected by a specific virus.

What is the range of virus sizes?

Viruses range from about 20 to 400 nm in diameter.

What is a capsid?

The protein coat that encloses the nucleic acid genome of a virus.

What is a viral genome?

The genetic material in a virus, which can be DNA or RNA, single or double stranded.

What are the basic steps of the viral reproductive cycle?

Attachment, Entry, Integration, Synthesis of viral components, Viral assembly, Release.

What happens during the attachment step of the viral reproductive cycle?

The virus attaches to the surface of a host cell.

What occurs during the entry step of the viral reproductive cycle?

The viral genome enters the host cell.

What is integration in the context of viral reproduction?

The viral genome is inserted into the host cell's chromosome.

What is the lysogenic cycle?

A reproductive cycle where the virus integrates into the host DNA and remains inactive.

What is the lytic cycle?

A reproductive cycle that leads to the lysis of the host cell and release of new viruses.

What is the role of integrase in viral reproduction?

Integrase cuts host chromosomal DNA and inserts the viral genome.

What is a prophage?

A phage that has integrated its DNA into the bacterial chromosome.

How does HIV integrate into the host genome?

HIV uses reverse transcriptase to create a complementary DNA strand that integrates as a provirus.

What is the significance of viral latency?

Viruses can remain dormant in the host genome for long periods before reactivating.

What are episomes in the context of viral latency?

Genetic elements that replicate independently but can integrate into host DNA.

What is the function of viral reverse transcriptase?

It synthesizes complementary DNA from viral RNA.

What happens during the synthesis of viral components?

Host cell enzymes replicate viral DNA and transcribe it into mRNA.

What is the outcome of the viral assembly step?

New viral particles are assembled from synthesized components.

How do enveloped viruses release from the host cell?

They bud from the host cell without causing lysis.

What is the difference between ss and ds in viral genomes?

ss refers to single-stranded, and ds refers to double-stranded nucleic acids.

What is the role of capsid proteins during viral assembly?

They may modify or serve as scaffolding for assembling the virus.

What influences the switch from the lysogenic to the lytic cycle?

Environmental conditions can trigger the switch.

What is the typical genome size of the TMV?

6400 base pairs with only six genes.

What is a bacteriophage?

A virus that specifically infects bacteria.

What are emerging viruses?

Emerging viruses are those that have arisen recently or are likely to have a greater probability of causing infection, often due to mutations in pre-existing viruses.

Name four examples of emerging viruses.

Coronavirus, Influenza virus, Zika virus, Human immunodeficiency virus (HIV).

What virus causes COVID-19?

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

What is the origin of SARS-CoV-2?

It is believed to be derived from a coronavirus found in bats.

When did the WHO declare COVID-19 a pandemic?

On March 11, 2020.

What is the structure of SARS-CoV-2?

It is an enveloped virus with an RNA genome.

What is the H1N1 virus known for?

It causes swine flu and is a strain of the influenza virus.

How many deaths does influenza cause annually in the U.S.?

Over 30,000 people.

What is the Zika virus and how is it spread?

Zika virus is a type of flavivirus spread by Aedes mosquitoes.

What serious condition can Zika virus infection during pregnancy cause?

Microcephaly, which is an abnormality where the infant's head is smaller than normal.

What does HIV stand for?

Human Immunodeficiency Virus.

What disease does HIV cause?

Acquired Immunodeficiency Syndrome (AIDS).

How is HIV primarily spread?

Through sexual contact between infected and uninfected individuals.

What is the estimated total number of deaths caused by AIDS since 1981?

About 40 million.

What type of cells does HIV destroy?

Helper T cells, which are crucial for the immune system.

What is a significant challenge in HIV replication?

The reverse transcriptase enzyme lacks a proofreading function, leading to high mutation rates.

What is one drug developed against HIV?

Azidothymidine (AZT), which inhibits reverse transcriptase.

What is the role of mRNA vaccines?

They provide active acquired immunity against infectious diseases by coding for viral proteins.

How do mRNA vaccines work?

They inject mRNA that codes for a viral spike glycoprotein, eliciting an immune response.

What happens to B cells after vaccination?

They increase in number and produce antibodies against the spike glycoprotein.

What are memory B cells?

B cells that persist for months or years and can rapidly proliferate upon re-exposure to the virus.

What distinguishes bacteria and archaea from eukaryotes?

Bacteria and archaea are prokaryotes that lack extensive internal compartmentalization.

What type of chromosome do most prokaryotes have?

A single circular, double-stranded DNA molecule.

What is the typical length of prokaryotic chromosomes?

A few million base pairs in length.

Where are nucleoids found in bacteria?

In the cytoplasm, tightly packed and in direct contact with it.

What is a unique feature of archaea compared to bacteria?

Archaea typically do not cause infectious diseases and can occupy extreme environments.

How much must a typical bacterial chromosome be compacted?

About 1000-fold.

What are the two processes involved in the compaction of bacterial DNA?

Formation of loop domains and DNA supercoiling.

What proteins help form loops in bacterial DNA?

Nucleoid-associated proteins.

What enzymes control the degree of DNA supercoiling?

Topoisomerases.

How is the archaeal chromosome organized?

Some have bacterial-like nucleoid-associated proteins, while others have eukaryotic-like histone proteins.

What are plasmids?

Small, circular pieces of DNA that exist independently of the bacterial chromosome.

What is the origin of replication in plasmids?

Plasmids have their own origin of replication allowing independent replication.

What are the four categories of plasmids?

Resistance plasmids, degradative plasmids, virulence plasmids, and fertility plasmids.

What is the primary method of reproduction in prokaryotes?

Binary fission.

What is a strain in the context of prokaryotic cells?

A lineage that is genetically different from another lineage within a species.

What are the three ways gene transfer can occur between prokaryotic cells?

Conjugation, transformation, and transduction.

What is conjugation in bacteria?

Direct physical interaction that transfers genetic material from a donor to a recipient cell.

What is transformation in bacteria?

The uptake of DNA from the environment by a living bacterial cell.

What is transduction in bacteria?

Transfer of bacterial genes from one bacterium to another via bacteriophages.

What is a fertility factor (F factor)?

A type of plasmid that allows donor strains to transfer genetic material during conjugation.

What is the role of competence factors in transformation?

They facilitate the binding and uptake of DNA fragments into competent bacterial cells.

What is horizontal gene transfer?

The transfer of genes between the same or different species without being offspring.

What is vertical gene transfer?

The transfer of genes from one generation to the next among individuals of the same species.

What is the medical relevance of horizontal gene transfer?

It can lead to the acquisition of antibiotic resistance, such as MRSA.

What can happen during an error in the phage lytic cycle?

Bacteriophages can incorporate bacterial DNA and transfer it to another bacterium.

What is the significance of plasmids in bacteria?

They can provide growth advantages but are not usually necessary for survival.

What is the structure of archaeal chromosomes?

They can be organized like bacteria or wrapped around histone proteins like eukaryotes.

What is the size range of plasmids?

From a few thousand base pairs to 100,000 to 500,000 base pairs.

How do plasmids replicate during binary fission?

Plasmids replicate independently and copies are distributed into daughter cells.

What is the role of nucleoid-associated proteins in bacteria?

They help compact bacterial DNA into loop domains.

What is the effect of mutations on prokaryotic genetic diversity?

Mutations can alter the genome and affect cell traits.

What are the six stages of the phage reproductive cycle?

Attachment, entry, integration, synthesis of viral components, viral assembly, and release.

How does a phage attach to a bacterial cell?

The phage binds specifically to proteins in the outer bacterial cell membrane.

What happens during the entry stage of the phage reproductive cycle?

The phage injects its DNA into the bacterial cytoplasm.

What is integration in the context of phage reproduction?

Phage DNA may integrate into the bacterial chromosome via integrase.

What triggers the switch from the lysogenic cycle to the lytic cycle?

The phage DNA is excised from the bacterial chromosome.

What occurs during the synthesis of viral components in the lytic cycle?

Phage DNA directs the synthesis of viral components, circularizes, and degrades host chromosomal DNA.

What is the role of lysozyme in the phage reproductive cycle?

Lysozyme causes cell lysis, releasing new phages from the broken cell.

What are the stages of the HIV reproductive cycle?

Attachment, entry, integration, synthesis of viral components, viral assembly, and release.

How does HIV attach to a host cell?

Spike glycoproteins bind to receptors on the host cell plasma membrane.

What is the process of uncoating in HIV infection?

Some capsid proteins are removed by cellular enzymes, releasing RNA and reverse transcriptase.

What happens during the integration stage of HIV reproduction?

Viral RNA is reverse transcribed into double-stranded DNA and integrated into the host cell chromosome.

What is the significance of the provirus in HIV infection?

The integrated provirus may remain latent for a long time.

What is the function of the lipid nanoparticle in mRNA vaccines?

It encapsulates mRNA coding for viral spike glycoprotein for delivery into cells.

What is binary fission in bacteria?

A method of asexual reproduction where a mother cell divides to form two daughter cells.

What are the three mechanisms of gene transfer between bacterial cells?

Conjugation, transformation, and transduction.

What occurs during conjugation in bacteria?

A donor cell transfers genetic material to a recipient cell through a conjugation bridge.

How does transformation occur in bacteria?

A DNA fragment binds to a receptor, is cut into smaller pieces, and one strand is imported into the cell.

What is transduction in bacterial gene transfer?

A bacteriophage transfers DNA from one bacterium to another during infection.

What is the F factor in bacterial conjugation?

A plasmid that facilitates the transfer of genetic material between bacterial cells.

What happens during the transfer of an F factor?

One strand of the F factor DNA is cut and transferred to the recipient cell while the donor synthesizes a complementary strand.