Microbiology Chapter 5

Identify the life forms that viruses have the ability to infect

- All forms--- bacterial cells, animal cells, etc.

Icosahedral viral capsids

- Capsomeres form an icosahedron, a 20-sided polygon containing 20 equilateral triangles - Looks like a sphere to the human eye

Helical viral capsids

- Capsomeres take a helical shape resulting in the appearance of a hollow tube - The capsomeres interact to form a structure that resembles a spiral staircase. - Looks like rods to human eye

Manner of entry for plant viruses

- Damage to plant cell wall and allows entry for virus - Examples of damage: insects, wind, hail, rain, fire, & human damage

Define lysogenic phage.

- Don't cause lyses immediately - A phage that incorporates its genome into the host genome - The combination of both is called a prophage. - The prophage is replicated and passed on to future generation - The prophage can be reactivated at a later point to produce new virion also.

Describe the basic structure of a virus

- Genome: RNA or DNA, never both - Capsid, protein covering, around the genome - Genome + Capside = NUCLEOCAPSID

Examples of enveloped viruses.

- Influenza virus - Human Immunodeficiency Virus (HIV)

Strategy used to cultivate animal viruses

- Involves tissue sample of host - Presence of virus is detected when there is CYTOPATHIC EFFECTS (CPE)--- structural changes in host due to virus Look for evidence of disease in healthy cells

Define receptor

- Located on the surface of the host cell - This is the protein that the viral attachment protein will bind to during ADHERENCE - Helps determine specificity of the virus

Phage vs. Animal virus entering host

- Phage viruses, the capsid does NOT enter the host - Animal virus, the capsid DOES enter the cell

Manner of entry for T4-bacteriophages

- T4 phage, the capsids NEVER GETS INTO THE HOST - The capsid INJECTS the genome into the host cell - Still specificity through viral attachment proteins and receptor interaction - Tail fibers of T4 will have viral attachment proteins on them - Tail fiber attachment proteins will attach to cell wall - T4 phage has conformational change when attachment occurs--- causes squatting - Genome moves through the core and it is released into the interior of the cell - THE CAPSID REMAINS ON THE OUTSIDE OF THE CELL - Phage capsids DO NOT GO INSIDE OF CELL

Strategy used to cultivate lytic phages

- The correct host bacterial cell can be grown in a liquid/broth culture. - The lytic phage can then be introduced into the culture. - As the bacterium grows the culture will get cloudy or turbid. - The phage, however, will kill the bacterium. - So as the phage replicates and infects more bacterial cells, the culture goes from cloudy to clear. - Filtration of the bacterial debris will leave you with isolated virion. Culture goes from clear to cloudy when bacteria cells are growing Phage gets introduced and infects host cells & replicate, the host cells lyse Culture goes from cloudy to clear because the host cells are dying

Why viruses are hard to grow/cultivate

- They're small - Only replicate within specific host cells

Examples of helical viruses

- Tobacco mosaic virus (TMV) - Rabies virus BOTH HAVE SINGLE STRANDED RNA GENOME THAT HAVE HELICAL CAPSIDS

List the steps in the replication cycle of a virus

1. Adherence 2. Penetration 3. Uncoating 4. Synthesis 5. Assembly 6. Exit

Steps in the replication cycle of a virus

1. Adherence - results in the virus adhering or sticking to a host cell membrane (usually using spikes (proteins) in the capsid or envelope) 2. Penetration - when the virus enters the host cell 3. Uncoating - when the viral genome is removed or released from the capsid 4. Synthesis - two events. (1) Replication of the viral genome and (2) translation of viral proteins--- to make capsid 5. Assembly - when the viral genome and capsomeres/other viral proteins are put together to form new viral particles 6. Exit - the process of the new viral particles leaving the host cell.

Strategies used to name viruses

1. Appearance 2. Location of discovery 3. Organism they infect 4. Disease caused 5. Letter and number combinations (indicated different strains)

Strategies for the exit of new virions from a host cell

1. Budding - Virus push their way out - Take piece of host cell envelope with them as they exit cell Enveloped viruses will exit via budding 2. Lysing - Amount of virion builds up to where the host cannot contain - Host will burst or lyse releasing the virion into the environment This is how phages & non-enveloped viruses exit host

Characteristics ALL viruses must have

1. Genome 2. Capsid Genome + Capsid = NucleocapsidCE;

List morphologies of viral capsids

1. Helical 2. Icosahedral 3. Complex

Most virus particles studied to date fall into a range of ________ in diameter. - 10-100 nanometers - 10-100 millimeters - 1-10 micrometers - 10-100 micrometers

10-100 nanometers

Entry for enveloped viruses

2 ways to get into host cell BOTH WAS INVOLVE FUSION 1. Membrane fusion - Viral envelope fuses with the plasma membrane of the host - Conformational change - Membrane fusion - Nuclear capsid is released inside the cell and the capsids releases the viral genome Example: HIV 2. Endocytosis THEN fusion - Viral attachment protein binds to receptor - Endocytosis triggers - Endosome forms - Envelope fuses with the end-some membrane - Viral genome is released when endosome and viral envelope fuse Example: Influenza virus

What is the meaning of the term complex symmetry in relation to viruses? - Viral genetic information forms a symmetrical helical structure within the viral capsid - Capsid proteins associate with the genome and each other, twisting to form a tubelike coiled form - A combination of cylinder and sphere-like protein structures surrounds the viral genome - Capsid proteins form a closed sphere composed of multiple triangular faces around the viral genome

A combination of cylinder and sphere-like protein structures surrounds the viral genome.

Define virion

A complete viral particle - Genome - Capsid - Viral Envelope

Define viroid

A short piece of infectious RNA that infects plants

Define attachment protein

ALSO called viral attachment protein - Located in envelope OR capsid and they BIND to receptor - Allowing virus to bind to host cell - Attachment proteins are specific - Helps determine specificity of the virus

Identify the different types of viral genomes. - RNA or DNA. - Single or double stranded. - Circular or linear. - Single nucleic acid molecule or composed of several individual fragments. - All of these choices are correct.

All of these choices are correct.

Define viral envelope

All viruses MUST have - Genome - Capsid Some viruses have VIRAL ENVELOPE - viral envelope similar to cell membrane - When some viruses leave, they take plasma membrane of the host, the plasma membrane THEN BECOMES the viral envelope

Identify the eukaryal microbe that giant viruses usually infect

Amoeba

A proto-oncogene can be defined as - A gene involved in normal regulation of the cell cycle. - A not yet fully functional gene, still evolving. - An altered form of a gene that results in uncontrolled cell growth. - A gene that has become deleted from the sequence over time.

An altered form of a gene that results in uncontrolled cell growth.

Identify potential functions of a viral envelope

An envelope may be used by a virus for attachment and entry into a host cell. It may also allow a virus to evade a hosts immune defenses

Identify the correct sequence of events from start to finish in a general viral replication cycle. - Attachment, entry/uncoating, gene expression, genome replication, assembly/exit - Entry/uncoating, gene expression, genome replication, attachment, assembly/exit - Entry/uncoating, attachment, genome replication, gene expression, assembly/exit - Attachment, genome replication, entry/uncoating, gene expression, assembly/exit

Attachment, entry/uncoating, gene expression, genome replication, assembly/exit

Describe the size range of viruses

Between 10 and 100 nanometers. Take home point...they are the smallest of the microbes in size. Smaller than eukaryotic microbes, bacteria, and archaea Viruses are the SMALLEST of the microbes

What is the first step to any virus infection? - Fusion of the envelope with the host membrane - Entry of the genome - Binding of the virus particle with specific host proteins - Replication of the viral genome

Binding of the virus particle with specific host proteins

Oncolytic viruses

Can be used to destroy cancerous cells

What are the characteristics of a satellite virus? - Only protein, no genome - Only naked RNA, no capsid - Cannot replicate without a helper virus - Can replicate independently

Cannot replicate without a helper virus

What are capsids made of

Capsomeres

Capsomere of icosahedral virus

Capsomeres form a icosahedron 20 equilateral triangles put together that make 20 sided polygon

Oncoviruses

Cause cancer

What is the viral envelope similar to?

Cell/Plasma Membrane

A prophage is an immature virus particle just prior to assembly. True False

False

Prophage

Genetic material of a bacteriophag

What is a nucleocapsid

Genome (RNA or DNA) + Capside ( protein covering genome) = Nucleocapsid

Describe the contribution of Walter Reed to the field of virology

He discovered that yellow fever was caused by a virus and transmitted via mosquitoes Learned that mosquitoes are vector for virus

Describe common morphologies that viral capsids have

Helical - Capsomeres take a helical shape resulting in the appearance of a hollow tube - The capsomeres interact to form a structure that resembles a spiral staircase. Icosahedral - capsomeres form an icosahedron, a 20-sided polygon containing 20 equilateral triangles Looks like a sphere to the human eye Complex viruses - There are viruses that don't demonstrate just helical or icosahedral symmetry. - Some, like the T-4 bacteriophage have both--- an icosahedral head and a helical tail - Still others have complex morphologies that don't fit either category (like poxviruses). - This is referred to usually as complex symmetry

Capsomeres of helical virus

Helical shape that looks like hallow tube Capsomeres come together to make spiral staircase structure

Which viral quantification method utilizes a phenomenon where viruses will cause red blood cells to clump together? - Direct count by electron microscopy - Endpoint assay - Hemagglutination - Plaque assay

Hemagglutination

Example satellite virus

Hepatitis D virus

Budding

How enveloped viruses exit the host Budding - Virus push their way out - Take piece of host cell envelope with them as they exit cell Enveloped viruses will exit via budding

Lysing

How phage and non-enveloped viruses exit host Lysing - Amount of virion builds up to where the host cannot contain - Host will burst or lyse releasing the virion into the environment

strategy used to quantify viruses

How to COUNT viruses Hemagglutination assay - How red blood cells stick together - Adding virus to RBS you can determine the amount of virus present - Through this you can tell the amount of virus needed to cause agglutination

How big are most viruses compared to the cells they infect? - Much smaller - between 10-100nm - Smaller- between 100nm and 1µm - About the same - Larger- greater than 10µm

Much smaller - between 10-100nm

In which way are viruses most similar to living cells? - Most viruses contain both DNA and RNA. - Mutations in virus genomes are inherited by the next generation. - Viruses can reproduce independently. - Viruses have a simple cellular organization.

Mutations in virus genomes are inherited by the next generation.

Entry for non-enveloped viruses

Non-enveloped viruses enter a cell via receptor-mediated endocytosis. This requires their attachment proteins to bind to a receptor in the membrane of the host cell. From there the host cell would endocytose the virion---- Endosome forms Nuclear capsids escapes endosome Viral genome enters the cytoplasm where synthesis happens A shape change follows that allows the viral genome to escape the capsid and enter the cytoplasm of the host cell

Process of viral synthesis and assembly

Once the viral genome is in a host cell, the host is forced to synthesize copies of viral proteins and viral genome. These are the components that will become new virions. Assembly occurs when these components are put together. Assembly happens without energy input

some influences of virology and viruses in medicine today

Oncoviruses - cause cancer Oncolytic viruses - can be used to destroy cancerous cells Viruses can be used to introduce new genes into host cells during gene therapy

Hemagglutination assay

One way of quantifying/counting virus - How red blood cells stick together - Adding virus to RBS you can determine the amount of virus present - Through this you can tell the amount of virus needed to cause agglutination

: What occurred when T4 heads were exposed to large DNA fragments (e.g., 48.5 kbp)? A Partial T4 heads packaged the large DNA fragments B Full T4 heads were able to incorporate some of the larger DNA fragments C Full T4 heads were able to incorporate all of the large DNA fragments D Partial T4 heads packaged less than 10% of the large DNA fragments

Partial T4 heads packaged the large DNA fragments

Define lytic phage

Phages that will lyse the host cell upon exit

Identify the life form viroids cause infections in.

Plants

Define prion

Proteinaceous infectious particles proteins that cause disease Only affect mammals and the target the nervous system Cause TSE

Satellite viruses and RNAs are different from viroids because the former two A : Are replicated with host cell DNA polymerase B : Replicate outside of host cells C : Require a helper virus to replicate D : Lack a protein coat surrounding their genome

Require a helper virus to replicate

Example of an icosahedral virus

Rhinovirus (causes the common cold HAS ICOSAHEDRAL CAPSID

Hepatitis D virus

Satellite virus

Define satellite virus

Satellite viruses need a helper virus to allow for replication. Both viruses have to be present in order for the satellite virus to replicate BASICALLY: need another virus to infect the host FIRST

Genome usually associated with helical viruses

Single stranded RNA

Define virus

Small, subcellular particles that can replicate only within a host cell Another way to describe a virus is a "obligate intracellular parasite" Viruses are NOT living because they CANNOT REPRODUCE ON THEIR OWN, outside host they are inactive

How is viral envelope formed

Some viruses take part of the host's plasma membrane when they leave The plasma membrane then BECOMES the viral envelope

Adherence

Step 1 of 6 in virus replication Results in the virus adhering or sticking to a host cell membrane (usually using spikes (proteins) in the capsid or envelope)

Penetration

Step 2 of 6 in virus replication When the virus enters the host cell

Uncoating

Step 3 of 6 in virus replication When the viral genome is removed or released from the capsid

Synthesis

Step 4 of 6 in virus replication Two events. 1. Replication of the viral genome 2. translation of viral proteins

Assembly

Step 5 of 6 in virus replication When the viral genome and capsomeres/other viral proteins are put together to form new viral particles

Exit

Step 6 of 6 in virus replication The process of the new viral particles leaving the host cell.

Example of an complex virus

T-4 bacteriophage An icosahedral head and a helical tail

What determines the specificity of the virus

The attachment protein and receptor

Icosahedron

The shape that capsomeres of icosahedral virus form 20 equilateral triangles put together that make 20 sided polygon

Define virology

The study of viruses

Define capsomeres

The subunits that form a viral capsid What makes up capsid are small, individual capsomeres

Describe what is meant by "obligate intracellular parasite"

This means that they must invade a host and when they do, they do damage to the host in some way in order to replicate (produce more virus). When virus enters host, they force the host to make more virus MUST ABSOLUTELY BE INSIDE HOST TO REPLICATE

Type of diseases associated with prions

Transmissible spongiform encephalopathies (TSE's). Only affect mammals and the target the nervous system

Within the viral world, there is a spectrum of genome complexity, including some viruses which cannot fully direct synthesis of all of their own components. - True - False

True

Describe viral genomes

Viral genomes show great variability. - DNA or RNA - Single or Double Strand - Linear or circular - Separated or segmented - Genomes are small

Which of the following would make the most effective target for immunization against enveloped animal viruses? - Viral proteins embedded in the envelope. - Nucleic acids. - Host proteins embedded in the envelope. - Capsomeres.

Viral proteins embedded in the envelope.

Non-developed virus

Virus that does NOT have a viral envelope

Define enveloped viruses

Viruses that contain a cell-membrane derived covering called a viral envelope. These viruses usually take a piece of the host cell membrane as they exit the host cell. Many animal viruses contain an viral envelope VIRAL ENVELOPE IS USED TO HELP ANIMAL VIRUS GET INTO A HOST CELL

Define non-enveloped or naked virus

Viruses that don't have an envelope.

Define bacteriophages (aka phages)

Viruses that infect bacteria

Complex viruses

Viruses whose capsid shape is NOT helical OR icosahedral - There are viruses that don't demonstrate just helical or icosahedral symmetry - Some, like the T-4 bacteriophage (see fig. 5.8) have both (an icosahedral head and a helical tail) - Still others have complex morphologies that don't fit either category (like poxviruses) - This is referred to usually as complex symmetry

Identify if exceptions to the size range and genome size exist within viruses

YES. They do. Many of these are referred to giant viruses Giant viruses affect eukaryotic cells - Have large genome for virus Giant viruses affect amoeba's

Which of the following is NOT a strategy used to name viruses? - after the organelle they attack - after other physical characteristics - after their morphology - after the location where they were first noticed - after the disease they cause

after the organelle they attack

A prion is - a subcellular infectious agent with a naked RNA genome - a subcellular infectious agent with a protein coated RNA genome - an abnormally shaped protein - an abnormally shaped RNA molecule

an abnormally shaped protein.

The most common type of infectious agent in the world is: - animal viruses. - prions. - viroids. - bacteriophage.

bacteriophage

Viruses obtain the following from their host cells EXCEPT: - ribosomes. - capsid protein genes. - amino acids and nucleotides. - energy for building macromolecules.

capsid protein genes.

What do researchers use as a sign of viral infection? cytopathic effect dead cells death of host formation of new viral particles

cytopathic effect structural changes in the host cell

Example of disease associated with prions

mad cow disease

Which of the following is not a subcellular, infectious agent? - viroid - mycoplasma - satellite virus - prion

mycoplasma

What are the characteristics of a prion? - Only protein, no genome - Cannot replicate without a helper virus - Can replicate independently - Only naked RNA, no capsid

only protein, no genome