Unit 4 (Week 15 Genetics of Viruses and Bacteria) Flashcards
In bacterial meningitis, what do the meninges do?
They cause inflammation of the protective membranes that cover the brain and spinal cord.
Bacterial meningitis is up to six times more common among people living in close quarters, such as college dormitories.
What is a virus or microorganism that causes disease symptoms in its host?
A pathogen.
How do bacteria, even though they reproduce asexually, have their genetic variety enhanced?
A phenomenon called gene transfer, in which genes are passed from one bacterial cell to another.
Like sexual reproduction in eukaryotes, gene transfer enhances the genetic diversity observed among bacterial species.
[19.1 General Properties of Viruses]
What are nonliving particles with nucleic acid genomes?
Viruses
How does a virus or its genetic material replicate?
It must be taken up by a living cell.
What was the first discovered virus and subsequent viruses before 1900?
Tobacco mosaic virus (TMV), cattle disease (foot-and-mouth disease), and the first human virus, yellow fever.
TMV can spread the disease but spraying sap from one plant to another. Filtering the sap, the sap still caused the disease ruling out bacteria. Also, toxic chemical was thought to be the issue, but after several generations of the plants, the disease still remained which wouldn’t if it was a toxin since the toxin would be diluted.
What is a small infectious particle that consists of a nucleic acid enclosed in a protein coat?
A virus.
Researchers have identified and studied over 4,000 different types of viruses.
What similarities do all viruses share?
Small size and reliance on a living cell for replication.
What vary greatly in the characteristics of a virus?
The host range, structure, and genome composition.
{Information: Hosts and Characteristics of Selected Viruses]
Order = Virus or group of viruses, Host, Effect on Host, Nucleic Acid, Genome Size, and Number of Genes. (also saved on drive)
Virus or group of viruses Host Effect on host Nucleic acid* Genome size (kb)† Number of genes†
Phage λ
E. coli
Can exist harmlessly in the host cell or cause lysis
dsDNA
48.5
36
Phage T4
E. coli
Causes lysis
dsDNA
169
288
Tobacco mosaic virus (TMV)
Many plants
Causes mottling and necrosis of leaves and other plant parts
ssRNA
6.4
6
Baculoviruses
Insects
Most baculoviruses are species specific; they usually kill the insect
dsDNA
133.9
154
Influenza virus
Mammals
Causes classical “flu,” with fever, cough, sore throat, and headache
ssRNA
13.5
11
More Viruses
Epstein-Barr virus
Humans
Causes mononucleosis, with fever, sore throat, and fatigue
dsDNA
172
80
Adenovirus
Humans
Causes respiratory symptoms and diarrhea
dsDNA
34
35
Herpes simplex type II
Humans
Causes blistering sores around the genital region
dsDNA
158.4
77
HIV (type I)
Humans
Causes AIDS, an immunodeficiency syndrome eventually leading to death
ssRNA
9.7
9
What is a cell that is infected by a virus, fungus, or bacterium?
What about a species that can be infected by a specific virus?
A host cell.
A host species.
What is the number of species and cell types that a virus or bacterium can infect?
Host range
For example, TMV is known to infect over 150 different species of plants while yellow fever caused by the flavivirus infects the brain and CNS.
What do viruses range in size from?
20 nm to 400 nm in diameter.
For size comparison, a bacterium is 1,000 nm in diameter while most eukaryotic cells is 10 to 1,000 times bigger than that of a bacterium.
Over 50 million adenoviruses (75 nm) could fit into an average-sized human cell.
All viruses have a protein coat enclosing a virus’s one or more molecules of nucleic acid (DNA or RNA) called a?
Capsid.
Capsids have a variety of shapes, including helical and polyhedral.
What are the subunits of a capsid called?
Capsomers
What are the several different protein subunits of a capsid called?
Capsomers
What type of structure does TMV have?
Helical capsid with identical capsomers.
What type of structure does the adenovirus have?
It is polyhedral, meaning 6 sided. The corners have protein fibers with a terminal knob at the end
What is a structure enclosing a viral capsid that consists of a membrane derived from the plasma membrane of the host cell and embedded with virally encoded spike glycoproteins?
Viral envelope
T/F Viral envelopes of influenza viruses are lipid bilayers to include all other viruses.
False. Typically yes for influenza viruses but some viruses may not have the viral envelope.
Although they help encasing and protecting the genetic material, what does the capsid and envelope also accomplish?
What helps viruses bind to the surface of a cell?
Enabling viruses to infect their hosts.
The protein fibers with a knob or spike glycoproteins.
What is a virus that infects bacteria?
Bacteriophages or phages.
They may have more complex protein coats, with accessory structures used for anchoring the virus to a host cell and injecting the viral nucleic acid
What is the genetic material of a virus?
The viral genome.
Answer the following questions on infections of the adenovirus.
- What plays an important role for the adenovirus’s ability to be accepted by the host cell?
- Why?
- Once connected via the CAR to the host cell, what process happens next?
- What forms to carry the virus but is then broken down by proteins provided by the viral capsid?
- Once released, what happens to the viral DNA?
- It’s capsid structure, primarily the protein fiber with a knob.
- The knob binds to a receptor on the host cell designated coxsackievirus and adenovirus receptor (CAR), because it can recognize either coxsackievirus or adenovirus.
- The adenovirus is taken into the host cell via receptor-mediated endocytosis.
- Vesicles
- During the breaking of the vesicles, the viral DNA makes it way to the nucleus and provides the information to make thousands of new viruses.
What are viruses referred as based on their nucleic acids?
DNA and RNA viruses. Can be single or double stranded.
Additionally, the nucleic acids can be linear or circular depending on the virus and can ALSO have more than one copy of the genome.
Pathogens are ______.
Multiple choice question.
extrachromosomal DNA segments found in bacteria
white blood cells that kill harmful bacteria
microorganisms that cause disease
chemicals that allow microorganisms to grow
microorganisms that cause disease
What do viruses use in order to replicate?
Multiple choice question.
A plasma membrane
A polyhedral capsid
A chaperone protein
A host cell
A host cell
What occurs when genes are passed from one bacterium to another?
Multiple choice question.
Gene expansion
Gene donation
Gene transfer
Gene accumulation
Gene transfer
A virus is a:
Multiple choice question.
living particle with a protein genome
nonliving particle with a nucleic acid genome
living particle with a nucleic acid genome
nonliving particle with a protein genome
nonliving particle with a nucleic acid genome
To replicate, a virus or its genetic material must be in a living _________
host, cell, organism, or host cell
Viruses and bacteria that cause disease symptoms in their hosts are called ________
pathogens or pathogenic
Which of the following describes a virus?
Multiple choice question.
A small infectious particle that is comprised almost entirely of protein
A small infectious particle comprised of nucleic acid enclosed in a protein coat
A non-infectious cell with a complex structure that includes cytoplasm, nucleic acid, ribosomes, and peptidoglycan
A small infectious particle that is comprised entirely of single-stranded, circular RNA
A small infectious particle comprised of nucleic acid enclosed in a protein coat
A virus uses the host’s cellular machinery to _________ its own genome.
replicate, copy, reproduce, or duplicate
Select all that apply
Identify the similarities that all viruses share.
Multiple select question.
Small size
Structure
Genome composition
Reliance on a living cell for replication
Host range
Small size
Reliance on a living cell for replication
Genes can be transmitted from one bacterial cell to another. This phenomenon is called gene ________
transfer
The function of the __________ and __________ is to encase and protect the genetic material and to enable viruses to infect their hosts.
Blank 1: capsid or viral capsid
Blank 2: envelope or viral envelope
Viruses are nonliving particles with a(n) _________ made of nucleic acids.
genome or genomes
Viruses that infect bacteria are known as ________, or simply ________.
bacteriophages or phages
[19.2 Viral Reproductive Cycles]
What is the series of steps that results in the production of new viruses during a viral infection?
Viral reproductive cycle
What is the first step of the viral reproductive cycle?
The virus attaches itself to the surface of the host cell.
This is typically very specific because proteins in the virus are recognized and bind to specific molecules on the cell surface.
Phage delta binds to E. Coli cells
HIV binds to white blood cells
The second step, entry, involves what action depending on the type of virus?
One or a few viral genes are expressed immediately due to the action of host cell enzymes and ribosomes.
Steps may be skipped and quickly lead to the production of new viruses or they may be prolonged, delaying the creation of new viruses.
For Step 3, the integration phase, answer the following questions.
- What are viruses capable of carrying that cuts the host’s chromosomal DNA and inserts the viral genome into the chromosome?
- Once integrated, what does the phage DNA in a bacterium known as?
- When a bacterial cell divides with a prophage, and creates copies of the DNA strain to daughter cells along with the bacterial chromosomal DNA, what do you call this type of reproductive cycle?
- What does not happen in the lysogenic cycle? (2)
- What happens on occasion which leads to step 4, the synthesis of viral components?
- Enzyme called Integrase
- Prophage
- Lysogenic Cycle
- New phages are not created and the host cell is not destroyed.
- The prophage is excised from the bacterial chromosome.
How can an RNA virus integrate its genome into the host cell’s DNA?
What enzyme does HIV use to change its RNA to DNA?
What is this process called?
The viral genome must be copied into DNA.
Reverse transcriptase. A viral enzyme that catalyzes the synthesis of viral DNA starting with viral RNA as a template.
This process is called reverse transcription because it is the reverse of the usual transcription process, in which a DNA strand is used to make a complementary strand of RNA. The viral double-stranded DNA enters the host cell nucleus and is inserted into a host chromosome via integrase.
What do you call viral DNA that have become integrated into a chromosome of a host cell?
Provirus
What do you call viruses that is an RNA virus that utilizes reverse transcription to produce viral DNA that can be integrated into a chromosome of the host cell?
Retrovirus
In step 4, the Synthesis of Viral Components, what must happen to the prophage before new viral components are created?
What is required for this process?
It must be excised.
An enzyme called excisionase
What leads to the degradation of the host chromosomal DNA in bacteria?
After excision, the host cell enzymes make many copies of the phage DNA and transcribe the genes within these copies into mRNA.
Host cell ribosomes translate this viral mRNA into viral proteins. The expression of phage genes also leads to the degradation of the host chromosomal DNA.
In step 4, what is the difference between phage delta and HIV?
The provirus DNA is not excised from the host chromosome.
It is transcribed in the nucleus to produce many copies of viral RNA. These viral RNA molecules enter the cytosol, where they are used to make viral proteins and serve as the genome for new viral particles.
What happens after all of the viral components have been synthesized through the hijacking of the host cell?
The components must be assembled into new viruses.
How do viruses with simple structures assemble?
Self-assembly.
viral components spontaneously bind to each other to form a complete virus particle. An example of a self-assembling virus is TMV, which we examined earlier.
TMV capsid proteins assemble around a TMV RNA molecule, which becomes trapped inside the hollow capsid.
What are two examples of viruses that DO NOT self assemble in Step 5, the Viral Assembly?
Phage delta, a bacteriophage, and HIV.
How is phage delta assembled with the help of what?
Help from noncapsid proteins not found in the completed phage particle.
They can either help in the modification of capsid proteins or act as scaffolding for assembly of the capsid.
What are the two stages of HIV assembly?
First Stage - capsid proteins assemble around two molecules of viral RNA and molecules of reverse transcriptase and integrase.
Second Stage - the newly formed capsid acquires its outer envelope in a budding process. This second phase of assembly occurs during step 6, as the virus is released from the cell.
What must the bacteriophages do in order to be released from the bacteria?
The release of bacteriophages is a dramatic event. Because bacteria are surrounded by a rigid cell wall, the phages must burst, or lyse, their host cell to escape. After the phages have been assembled, a phage-encoded enzyme called lysozyme digests the bacterial cell wall, causing the cell to burst.
What consists of the lytic cycle?
Steps 1, 2, 4, 5, 6 are called the lytic cycle because they lead to a cell lysis (bursting of the cell).
How does new HIV particles escape the host cell?
This type of virus escapes by a mechanism called budding that does not lyse the cell. In the case of HIV, a newly assembled virus particle associates with a portion of the plasma membrane containing HIV spike glycoproteins.
The membrane enfolds the viral capsid and eventually buds from the surface of the cell. This is how the virus acquires its envelope, which is a piece of host cell membrane studded with viral glycoproteins.
What is the term used to describe a prophage or provirus that remains inactive for a long time?
Latent.
Most of the viral genes are silent during latency, and the viral reproductive cycle does not progress to step 4.
What is another name for latency in bacteriophages?
Lysogeny.
When this occurs, both the prophage and its host cell are said to be lysogenic.
What is the significant difference in the lysogenic and lytic cycles in viral reproduction?
The end result either is the death of the cell or the cell duplicates with prophage or provirus DNA.
When the infected cells are lysogenic, they duplicate and may do for a long time. Once lysogeny ends, the viral DNA is expressed and enters the lytic cycle.
What isnt step 3 included in the lytic cycle?
This step CAN involve latent viral DNA or lysogeny which starts the lysogenic cycle and temporarily suspends the lytic cycle.
What is a bacteriophage that can follow either a lysogenic or lytic cycle?
A temperate phage.
What are bacteriophages that follows only the lytic cycle?
Virulent phage
What is a significant difference in what viral DNA can do in a temperate phage than a virulent phage?
Temperate phages, like phage delta, can integrate their nucleic acids in host DNA while virulent phages cannot.
What is an example of a virulent phage?
Phage T4 will always lyse a host bacterial E. coli cell.
What conditions can influence how long a phage remains in the lysogenic cycle?
Environmental
From the perspective of the bacteriophage, what are the primary advantages of the lytic and lysogenic cycles?
The advantage of the lytic cycle is that the phage can make many copies of itself and proliferate. However, sometimes the growth conditions may not be favorable to make new phages. The advantage of the lysogenic cycle is that the prophage can remain latent until conditions become favorable to make new phages.
What is a type of plasmid or viral genome that can integrate into a host chromosome or can replicate independently?
Give some examples.
Episome
Examples of viral genomes that exist as episomes include different types of herpesviruses that cause cold sores (usually herpes simplex type I), genital herpes (usually herpes simplex type II), and chickenpox (varicella-zoster).
A person infected with a given type of herpesvirus may have periodic outbreaks of disease symptoms when the virus switches from the latent, episomal form to the active form that produces new virus particles.
As an example, let’s consider the herpesvirus called varicella-zoster. The initial infection by this virus causes chickenpox, after which the virus may remain latent for many years as an episome. The disease called shingles occurs when varicella-zoster switches from the latent state and starts making new virus particles. Shingles begins as a painful rash that eventually erupts into blisters. The blisters follow the path of the neurons that carry the latent varicella-zoster virus. The blisters often form a ring around the back of the patient’s body. The name shingles is derived from a Latin word meaning girdle, referring to the observation that the blisters girdle a part of the body.
What is a virus that has arisen recently or has recently shown a greater probability of causing infection?
Emerging virus.
Because the base sequences of many viruses are already known, researchers have determined that emerging viruses typically result from mutations in pre-existing viruses.
New strains of influenza virus arise fairly regularly due to mutations. An example is the strain H1N1, also called swine flu. In the U.S., despite attempts to minimize deaths by vaccination, over 30,000 people die annually from influenza.
Another example of an emerging virus is Zika virus, an enveloped virus with a genome composed of single-stranded RNA. Its name comes from the Zika Forest of Uganda, where the virus was first isolated in 1947. Zika virus is primarily spread by mosquitoes of the genus Aedes. The most common symptoms of a Zika infection are fever, rash, joint pain, and conjunctivitis. In most people, the illness is usually mild, but in rare cases, a Zika infection in an adult can cause a more serious illness called Guillain-Barré syndrome. In addition, Zika virus infection during pregnancy can result in serious brain abnormalities, including the condition microcephaly, in which the infant’s head is smaller than normal.
What is a retrovirus that is the causative agent of acquired immune deficiency syndrome (AIDS)?
Human Immunodeficiency Virus (HIV)
HIV Facts
HIV is primarily spread by sexual contact between infected and uninfected individuals, but it can also be spread by the transfusion of HIV-infected blood, by the sharing of needles among drug users, and from infected mother to unborn child. Since AIDS was first recognized in 1981, the total number of AIDS deaths has been nearly 40 million, making it one of the most deadly diseases in human history. More than 0.6 million of these deaths have occurred in the U.S. In 2016, over 30 million people were living with HIV; approximately 3 million of them were infected that year. In that same year, nearly 2 million died from AIDS. Worldwide, nearly 1 in every 100 adults between ages 15 and 49 is infected. In the U.S., about 50,000 new HIV infections occur each year, 70% of those infections in men and 30% in women.
None
