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
What is the end result of AIDS caused by HIV that typically kills an individual?
When large numbers of helper T cells are destroyed by HIV, the function of the immune system is seriously compromised, and the individual becomes susceptible to infectious diseases called opportunistic infections that would not normally occur in a healthy person. For example, Pneumocystis jiroveci, a fungus that causes a type of pneumonia, is easily destroyed by a healthy immune system. However, in people with AIDS, Pneumocystis jiroveci pneumonia can be fatal.
What is an insidious feature of HIV replication involving its reverse transcriptase molecule?
The enzyme that copies the RNA genome into DNA, lacks a proofreading function.
Because reverse transcriptase lacks this function, it makes more errors and thereby tends to create mutant strains of HIV. This undermines the ability of the body to combat HIV because mutant strains may be resistant to the body’s defenses.
What is a compelling reason to understand the reproductive cycle of HIV and other disease-causing viruses?
This knowledge may be used to develop drugs that stop viral proliferation.
For example, in the U.S., the highest rate of AIDS-related deaths was approximately 17 per year per 100,000 people in 1994 and 1995. The current rate is about 4 to 5 deaths per year per 100,000 people, owing in part to the use of new antiviral drugs. These drugs inhibit viral proliferation, though they cannot eliminate the virus from the body.
What is a way scientists are combating HIV proliferation?
What are two challenges in AIDS research?
- Designing antiviral treatments, like inhibiting reverse transcriptase and inhibiting proteases which help form new capsids.
- A major challenge in AIDS research is to discover drugs that inhibit viral proteins without also binding to host cell proteins and inhibiting normal cellular functions. A second challenge is to develop drugs to which mutant strains will not become resistant. As mentioned, HIV readily accumulates mutations during viral replication. A current strategy is to treat HIV patients with a “cocktail” of three or four HIV drugs, making it less likely that any mutant strain will overcome all of the inhibitory effects.
How did viruses come into existence? Name a few hypotheses.
- Progressive Evolution from Genetic Elements Within Cells
A common hypothesis for the origin of viruses is that they evolved from macromolecules inside living cells. The precursors of the first viruses may have been RNA molecules or they may have been plasmids—small, circular DNA molecules that exist independently of chromosomal DNA.
- Regressive Evolution from Cells
Essentially, they came to fruition by the reduction of a trait or traits over time. They have minimal genetic information yet, over time, they have lost genes required for their independent existence.
- Parallel Evolution with Cells
They could have evolved parallel to the precursors of cellular DNA genomes during the earlier stages of evolution, termed the RNA world.
After a virus infects a host cell, the expression of viral genes leads to a series of steps called a viral ________ __________. These steps result in the production of new viruses.
Blank 1: reproductive or reproduction
Blank 2: cycle
A virus is a small infectious particle that consists of ______ acid enclosed in a(n) ________ coat.
Blank 1: nucleic
Blank 2: protein or polypeptide
What occurs in step 1 of the viral reproductive cycle?
Multiple choice question.
Assembly
Attachment
Synthesis
Integration
Attachment
Select all that apply
Viruses vary in which of the following characteristics?
Multiple select question.
Genome composition
Host range
Basic structure
Whether or not they rely on a living cell for replication
Small size
Genome composition
Host range
Basic structure
Once integrated into the chromosome, the phage DNA in a bacterium is called a(n) _________
Blank 1: prophage
Select all that apply
What is the function of the capsid and envelope in viruses?
Multiple select question.
enable host infection
weaken host immune defenses
protect genetic material
release genetic material
replicate genetic material
encase genetic material
enable host infection
protect genetic material
encase genetic material
During some viral reproductive cycles, the host cell, with its integrated phage DNA, undergoes repeated divisions without being destroyed. However, new phages are not made. This type of reproductive cycle is called the ________ cycle.
lysogenic
______ are viruses that specifically target bacteria.
Multiple choice question.
Bacteriophages
Bacteriocins
Phagocytes
Bacteriocides
Bacteriophages
While it exists as a prophage, a bacteriophage is in a type of viral reproductive cycle called the ______ cycle.
Multiple choice question.
lytic
paralytic
lysogenic
sexual
asexual
lysogenic
The series of steps that results in the production of new viruses is BEST described as the ______.
Multiple choice question.
viral life pathway
viral reproductive cycle
viral reproductive pathway
viral life cycle
viral reproductive cycle
What is a provirus?
Multiple choice question.
A mutant virus that cannot complete its assembly process
A virus that is not capable of causing disease
The viral DNA that has integrated in a eukaryotic chromosome
The viral DNA that has integrated in a prokaryotic chromosome
The viral DNA that has integrated in a eukaryotic chromosome
In the first step of a viral reproductive cycle, the virus must _______ to the surface of a host cell.
Blank 1: attach, bind, adhere, or adsorb
The lytic cycle is named such because it leads to ______.
Multiple choice question.
budding
cell lysis
formation of a prophage
integration
cell lysis
What is the term that best describes phage DNA that has been integrated in a bacterial chromosome?
Multiple choice question.
Phagocyte
Lysophage
Prophage
Phagosome
Prophage
When lysogeny occurs, the prophage and its host cell are said to be __________.
Blank 1: lysogenic or latent
The repeated divisions that occur during the integration phase of the phage λ reproductive cycle are called the ______ cycle.
Multiple choice question.
lytic
asexual
lysogenic
cryptic
lysogenic
A viral reproductive cycle that includes the production of a prophage is the __________ cycle.
Blank 1: lysogenic
During the past few decades, what emerging virus has caused over 30 million deaths worldwide?
Multiple choice question.
ebola hemorrhagic fever virus
hantavirus
human immunodeficiency virus
foot-and-mouth disease virus
influenza virus
human immunodeficiency virus
The viral DNA in a eukaryotic cell, once integrated, is called a(n) _______.
provirus
Antiviral drugs ______.
Multiple choice question.
inhibit viral attachment to host cells
eliminate viruses from the body
inhibit viral proliferation inside host cells
stimulate the body to produce antibodies against viruses
eliminate susceptible host cells
inhibit viral proliferation inside host cells
The lytic cycle contains all of these steps EXCEPT ______.
Multiple choice question.
synthesis
integration
release
assembly
attachment
entry
integration
______ are small, circular DNA molecules that exist independently of chromosomal DNA.
Multiple choice question.
Prions
Capsids
Cysts
Plasmids
Viroids
Plasmids
When a ______ bacterium prepares to divide, it copies the prophage DNA along with its own DNA, so each daughter cell inherits a copy of the prophage.
Multiple choice question.
pleomorphic
pleiotropic
lysogenic
lytic
lysogenic
What are nonliving agents that are simpler than viruses and what are they composed of?
Viroids and prions.
Viroids consist primarily of RNA and prions are composed solely of protein.
For Viroids, how many nucleotides make up its single-stranded circular RNA molecule?
A few hundred nucleotides in length.
What do viroids infect?
Plant cells, and depend entirely on host enzymes for their replication.
[Focus on Viroids: Answer the Questions]
Where are viroids replicated?
Does the RNA genomes of viroids make proteins?
What disease involved with the first discovery of a viroid?
Host cell nucleus or the chloroplast.
No.
The potato spindle tuber disease.
What was a significant discovery in the 1960s by British researchers Tikvah Alper and John Stanley Griffith , where when preparing animals with certain neurodegenerative diseases with radiation?
They suggested that the infectious agent was a protein.
They remained infectious even after radiation exposure that would destroy any RNA or DNA.
Why, in the 1970s, did American neurologist Stanley Prusiner, began to search for a causative agent in a neurodegenerative disease?
He was moved by the death of a patient.
In 1982, Prusiner isolated a disease-causing particle composed entirely of protein, which he called a prion. The term was based on his characterization of the particle as a proteinaceous infectious agent. In 1997, Prusiner was awarded the Nobel Prize in Physiology or Medicine for his work on prions.
Why do prion diseases arise?
From the ability to induce abnormal folding in normal protein molecules.
The prion exists in a disease-causing conformation designated PrPSc
The superscript Sc refers to scrapie, an example of a prion disease. A normal conformation of this same protein, which does not cause disease, is termed PrPC. The superscript C stands for cellular. The normal protein is encoded by an individual’s genome, and it is expressed at low levels in certain types of neurons.
[Informational] How does someone contract a prion disease?
A healthy person may become “infected” with the abnormal protein by eating meat of an animal with the disease. Unlike most other proteins in the diet, the prion escapes digestion in the stomach and small intestine and is absorbed into the bloodstream. After being taken up by neurons, the prion gradually converts the cell’s normal proteins to the abnormal conformation. As a prion disease progresses, the PrPSc proteins are deposited as dense aggregates that form tough fibrils in the cells of the brain and peripheral nervous tissues, causing the disease symptoms. Some of the abnormal proteins are also secreted from infected cells, where they travel through the bloodstream. In this way, a prion disease spreads through the body like many viral diseases.
None
What are prion diseases termed as?
Disease Description
Scrapie
A disease of sheep and pigs characterized by intense itching, causing the animals to scrape themselves against trees or other objects, followed by neurodegeneration.
Mad cow disease
Begins with changes in posture and temperament, followed by loss of coordination and neurodegeneration.
Chronic wasting disease
A disease of deer (genus Odocoileus) and Rocky Mountain elk (Cervus elaphus). A consistent symptom is weight loss over time. The disease is progressive and fatal.
Transmissible spongiform encephalopathies (TSEs)
A _______ is a small infectious particle composed primarily of RNA without a protein coat. A ______ is composed primarily of protein.
Blank 1: viroid
Blank 2: prion
What are viroids?
Multiple choice question.
RNA molecules that infect animal cells
RNA molecules that infect plant cells
Protein molecules that infect animal cells
DNA molecules that infect plant cells
Protein molecules that infect plant cells
RNA molecules that infect plant cells
Prions are particles made of ______ that infect ______ cells.
Multiple choice question.
protein ; animals
RNA ; animal
RNA ; plant
protein ; plants
protein ; animals
What do many bacteria exist as?
Unicellular organisms
However, some of them may remain associated with each other after cell division, forming pairs, chains, or clumps.
T/F Bacteria are widespread on Earth, and numerous species are known to cause various types of infectious diseases, such as bacterial meningitis.
True
Although a bacterial cell usually has a single type of chromosome, it can have what?
More than one copy of the chromosome.
Actually, the number of copies depends on the bacterial species and on growth conditions, but a bacterium typically has one to four identical chromosomes.
What is the site in a bacterial cell where the genetic material (DNA) is located?
The nucleoid
Unlike the eukaryotic nucleus, the bacterial nucleoid is not a separate cellular compartment bounded by a membrane. The DNA in a nucleoid is in direct contact with the cytoplasm of the cell.
How is a nucleoid different from a nucleus found in a eukaryotic cell?
A nucleoid is not a membrane-bound organelle. It is simply a site where a bacterial chromosome is found. A cell nucleus in a eukaryotic cell has an envelope with a double membrane.
What do bacterial chromosomes contain? Think structure, macromolecules, and length.
Double-stranded DNA with many different proteins. They are usually circular and are typically a few million base pairs (bp) long.
For example, the chromosome of Escherichia coli has approximately 4.6 million bp, and the Haemophilus influenzae chromosome has roughly 1.8 million bp.
Typically, how many genes does a bacterial chromosome have?
What accounts for the largest part of bacterial DNA?
A few thousand throughout the chromosome.
Gene sequences, primarily those that encode proteins.
What is a few hundred base pairs long, exists as a single point on bacterial chromosomes, and functions as the initiation site for the assembly of several proteins that are required for DNA replication?
Origin of replication
In order for bacterial DNA to fit inside a bacterium, how much does the DNA need to be compacted?
1,000 fold.
What are the two processes involving DNA compaction within bacteria?
Formation of loops and DNA supercoiling.
What in bacteria, is a chromosomal segment that is folded into a loop by attachment to proteins; a means of compacting a bacterial chromosome?
Loop Domains.
Looking at a photo, the proteins in this compaction technique for a very tight circle inside the circular DNA. This creates anchor points for the chromosome, typically looping it (E. coli) 400-500 times with 10,000 bp each.
This type of compaction equates to 10-fold reduction in size.
What is the process that compacts a chromosome through twisting of the DNA molecule to form additional coils?
DNA supercoiling
This compaction process is similar to what happens to a rubber band if you twist it in one direction. Because the two strands of DNA already coil around each other, the formation of additional coils due to twisting is referred to as supercoiling.
What bacterial enzyme twists the DNA and control the degree of DNA supercoiling?
Topoisomerases
What exists separately from chromosomal bacterial DNA that is small, circular pieces of DNA?
Plasmids
Plasmids occur naturally in many strains of bacteria and in a few types of eukaryotic cells, such as yeast.
What is the range in size for plasmids and how many genes do they have?
The smallest plasmids consist of just a few thousand base pairs and carry only a gene or two.
The largest are in the range of 100,000 to 500,000 bp and carry several dozen or even hundreds of genes.
What does the origin of replication in plasmids determine?
How many plasmids can be found in each bacterial cell. Some can have up to 100 plasmids while other bacterial species may have only 1 or 2.
Describe the similarities and differences between a bacterial chromosome and a plasmid.
Bacterial chromosomes and plasmids are similar in that they are both circular DNA molecules. However, bacterial chromosomes are usually much longer than plasmids and carry many more genes. Also, bacterial chromosomes tend to be more compacted due to the formation of loop domains and DNA supercoiling.
What are the 4 different categories as to why plasmids exist?
- Resistance plasmids, also known as R factors, contain genes that confer resistance against antibiotics and other types of toxins.
- Degradative plasmids carry genes that enable the bacterium to digest and utilize an unusual substance. For example, a degradative plasmid may carry genes that allow a bacterium to digest an organic solvent such as toluene.
- Virulence plasmids carry genes that turn a bacterium into a pathogenic strain.
- Fertility plasmids, also known as F factors, allow bacteria to transfer genes to each other.
What is also termed episomes?
On occasion, a plasmid may integrate into the bacterial chromosome. Such plasmids, which can integrate or remain independent of the chromosome, are also termed episomes.
How often can E. coli divide and replicate?
Every 20-30 minutes
What is a clone of genetically identical cells formed from a single bacterium by repeated cell divisions?
Bacterial colony
Starting with a single cell that is invisible to the unaided eye, a visible bacterial colony containing 10–100 million cells forms in less than a day!
Suppose a bacterial strain divides every 30 minutes. If a single cell is placed on a plate, how many cells will be in the colony after 16 hours?
In 16 hours, there will be 32 doublings. So, 232 = 4,294,967,296. (The actual number would be much less because the cells would deplete the growth media and grow more slowly than the maximal rate.)
What is the process of cell division in bacteria and archaea in which on cell divides into two cells?
Binary fission
What is evolutionarily related to the proteins, FtsA and FtsZ, which are required in most bacterial species for binary fission?
Eukaryotic Actin and Tubulin proteins, respectively.
These proteins assemble in a ring at the site where a septum will be formed that separates the daughter cells.
While the mechanism by which Fts proteins promote septum formation is not well understood, their role is thought to involve the binding of other proteins that are needed in the process. For example, FtsZ proteins attract enzymes that are involved with synthesizing peptidoglycan. Researchers have proposed that FtsZ proteins may guide the insertion of new cell wall by building smaller and smaller rings of peptidoglycan to eventually divide the cell into two daughter cells. Some archaea also use Fts proteins during cell division, but others utilize different mechanisms.
Which of the following statements best describes bacteria?
Multiple choice question.
Unicellular and found only in certain locations
Multicellular and found only in certain locations
Multicellular and widespread on Earth
Unicellular and widespread on Earth
Unicellular and widespread on Earth
A bacterium typically has ______ identical copies of its chromosome.
Multiple choice question.
4-10
1-4
10-15
1-10
1-4
Which of the following statements about prions and viroids is TRUE?
Multiple choice question.
Viroids are composed solely of protein, and prions are composed solely of RNA.
Both viroids and prions are composed solely of RNA.
Viroids are composed solely of RNA, and prions are composed solely of protein.
Both viroids and prions are composed solely of proteins.
Viroids are composed solely of RNA, and prions are composed solely of protein.
The region of a bacterial cell where the chromosome is tightly packed is known as the ___________ region.
nucleoid
Viroids infect ______ cells.
Multiple choice question.
bacterial
plant
animal
protozoan
plant
Unlike the eukaryotic nucleus, the bacterial nucleoid region is not a separate cellular compartment bounded by a(n) __________
membrane
Individual bacterial cells may exist as single units or remain associated with each other after cell division to form higher arrangements. These include which of the following?
Multiple choice question.
Pairs and chains
Pairs, chains, and clumps
Chains and clumps
Pairs and clumps
Pairs, chains, and clumps
The genome of a typical bacterium consists of a ______ chromosome that carries a few ______ genes.
Multiple choice question.
linear ; hundred
circular ; million
circular ; thousand
circular ; hundred
linear ; thousand
circular ; thousand
Select all that apply
By studying plasmids in many different species, researchers have discovered that most plasmids fall into four categories. What are they?
Multiple select question.
Fertility
Transposition
Degradative
Virulence
Resistance
Anabolic
Fertility
Degradative
Virulence
Resistance
When placed on a solid growth medium in a petri dish, an E. coli cell and its daughter cells undergo repeated cellular divisions and form a clone of genetically identical cells called a ______.
Multiple choice question.
bacterial plaque
bacterial lawn
bacterial colony
bacterial complex
bacterial colony
Select all that apply
Characteristics of a typical bacterial genome include which of the following?
Multiple select question.
Several hundred genes
Tens of thousands of genes
Several thousand genes
Circular chromosomes
Linear chromosomes
Several thousand genes
Circular chromosomes
What refers to a given species, a lineage that has genetic differences compared to another lineage?
Strain
How does genetic diversity arise in an asexual species?
First, mutations occur that alter the bacterial genome and affect the traits of bacterial cells.
Second, diversity arises from gene transfer, in which genetic material is transferred from one bacterial cell to another.
Through gene transfer, genetic variation that arises in one bacterium can be spread to other strains and even to other species. For example, an antibiotic-resistance gene may be transferred from a resistant strain to a sensitive strain.
What are the three ways that gene transfer occurs?
Conjugation, transformation, and transduction.
Which mode of gene transfer requires bacterial cells to physically contact where one bacterium acts as a donor and transfers DNA to a recipient cell?
Conjugation
What act of gene transfer involves DNA being RELEASED into the environment and taken up by another bacterial cell?
Transformation
What process occurs when a bacteriophage infects a bacterium and the newly made bacteriophage transfers some of that cell’s DNA to another bacterium?
Transduction
What did American microbiologists Joshua and Esther Lederberg, Irish physician William Hayes, and Italian geneticist Luca Cavalli-Sforza independently discover when it came to conjugation?
Only certain bacterial strains can donate genetic material during conjugation.
For example, about 5% of E. coli strains found in nature act as donor strains. Further research showed that a strain that is incapable of acting as a donor can acquire this ability after being mixed with a donor strain.
What did Hayes correctly propose about the type of plasmid that donor strains contain?
A plasmid called a fertility factor, or F factor, that can be transferred to recipient strains.
If a donor cell has only one F factor, explain how the donor and recipient cell both contain one F factor following the transfer of an F factor during conjugation.
During conjugation, only one strand of the DNA from an F factor is transferred from the donor to the recipient cell. The single-stranded DNA in both cells is then used as a template to create double-stranded F factor DNA in both cells.
What are hairlike structures made by bacterial F+ cells that bind specifically to F- cells?
Sex pili
They are so named because conjugation has been called bacterial mating. However, this term is a bit misleading because the process does not involve equal genetic contributions from two gametes and it does not produce offspring.
Describe the conjugation process with sex pili between an F+ cell and an F- cell.
n E. coli and some other species, F+ cells make very long pili that attempt to make contact with nearby F– cells. Once contact is made, the pili shorten, drawing the donor and recipient cells closer together.
After the pili have shortened, contact between donor and recipient cell stimulates the donor cell to begin the transfer process. First, a conjugation bridge is formed that provides a direct passageway for DNA transfer. One strand of F factor DNA is cut at the origin of transfer and then travels through the conjugation bridge into the recipient cell.
The other strand remains in the donor cell, and the complementary strand is synthesized, thereby restoring the F factor DNA to its original double-stranded condition.
In the recipient cell, the two ends of the newly acquired F factor DNA strand are joined to form a circular molecule, and its complementary strand is synthesized to produce a double-stranded F factor. If conjugation is successful, the end result is that the recipient cell has acquired an F factor, converting it from an F– to an F+ cell. The genetic composition of the donor strain has not been changed.
In what strains of bacteria did Frederick Griffith first discover the process of transformation which does not rely on direct physical contact to donate bacterial DNA?
Streptococcus pneumoniae
How does a bacterial cell become transformed?
First, it imports a strand of DNA from the environment. This DNA strand, which is typically derived from a dead bacterial cell, may then insert or recombine into the bacterial chromosome. The live bacterium then carries genes from the dead bacterium—the live bacterium has been transformed.
How are bacteria described who have the ability to “take up” DNA from its environment and what proteins do they encode to complete the process?
Competent and they make proteins called competence factors.
What do competence factor proteins accomplish in transformation?
Competence factors facilitate the binding of DNA fragments to the bacterial cell surface, the uptake of DNA into the cytoplasm, and the incorporation of the imported DNA into the bacterial chromosome.
Temperature, ionic conditions, and the availability of nutrients affect whether or not a bacterium will be competent to take up genetic material.
[Quiz Start]
In our case study, we learned about a type of antibiotic that inhibits cell wall formation by binding to enzymes necessary for making the peptidoglycan cross-linkages.
Question 1 options:
Sulfonamides
Erythromycin
Streptomycin
Ciprofloxacin
Penicillin
Penicillin
The incorporation of methicillin resistance genes that are picked up by a bacterium directly from the environment outside the cell is an example of
Question 2 options:
conduction.
conjugation.
transformation.
sexual reproduction.
transduction.
transformation.
In our case study, we learned about a type of antibiotic that prevents folic acid synthesis which then inhibits growth and reproduction of bacteria.
Question 3 options:
Erythromycin
Ciprofloxacin
Penicillin
Sulfonamides
Streptomycin
Sulfonamides
A naturally competent bacterium can
Question 4 options:
form a sex pilus.
reproduce via genetic exchange with other bacteria.
resist antibiotics.
reproduce sexually.
bind and take up DNA fragments.
bind and take up DNA fragments.
In our case study, we learned about a type of antibiotic that binds to the 50s subunit of bacterial ribosomes and interferes with protein synthesis.
Question 5 options:
Sulfonamides
Ciprofloxacin
Penicillin
Erythromycin
Streptomycin
Erythromycin
The _____ is the protein coat of a virus that surrounds the genetic material.
Question 6 options:
viroid
envelope
capsid
host
prion
capsid
During _____, direct contact is made between bacterial cells, whereas during _____, genetic material is taken up directly from the surrounding environment.
Question 7 options:
transduction; conjugation
transformation; transduction
conjugation; transduction
conjugation; transformation
transformation, conjugation
conjugation; transformation
Bacterial cells always contain one copy of a circular chromosome.
Question 8 options:
True
False
False
Bacterial infections have become much more of a threat to human health due to which of the following?
Question 9 options:
the increased use of antibiotics
horizontal transfer of pathogenicity
an increased use of antibiotics coupled with an increase in acquired antibiotic resistance by innocuous strains
an increased use of antibiotics, horizontal transfer of pathogenicity, and an increase in acquired antibiotic resistance by innocuous strains
an increase in acquired antibiotic resistance by innocuous strains
an increased use of antibiotics, horizontal transfer of pathogenicity, and an increase in acquired antibiotic resistance by innocuous strains
Bacterial plasmids
Question 10 options:
are artificially created by humans and are present in bacteria only because humans put them there.
are essential for growth.
are essential for cellular respiration.
are essential for chromosome replication and binary fission.
can provide genes that allow the bacteria to grow and thrive in the presence of potential toxins.
can provide genes that allow the bacteria to grow and thrive in the presence of potential toxins.
A bacterial species that becomes resistant to certain antibiotics may have acquired the resistance genes from another bacterial species. The phenomenon of acquiring genes from another organism without being the offspring of that organism is known as
Question 11 options:
competence.
hybridization.
vertical gene transfer.
integration.
horizontal gene transfer.
horizontal gene transfer.
During the lysogenic cycle, viral particles are actively being manufactured and assembled.
Question 12 options:
False
True
False
Which of the following is found in all viruses?
Question 13 options:
capsid
DNA
glycoproteins
RNA
envelope
capsid
Integration occurs when
Question 14 options:
the virus binds to the surface of the host cell.
the viral genes are packaged into newly constructed viral capsids.
the virus uncoats and enters a host cell.
the viral genes are incorporated into the host cell’s genome.
the viral genes direct the synthesis of viral polypeptides.
the viral genes are incorporated into the host cell’s genome.
The influenza virus is typical of many animal viruses in that is has an envelope composed of lipids and glycoproteins. Which of the following statements about the envelope is ACCURATE?
Question 15 options:
The envelope is obtained from the host cell upon entry into the cell.
The envelope glycoproteins are encoded by genes found in the host genome.
The envelope is formed via the action of integrase.
The envelope is obtained from the host cell when the virus buds from the plasma membrane.
The envelope is inside the capsid.
The envelope is obtained from the host cell when the virus buds from the plasma membrane.
