chapter 13 video 1 and 2

Divide with Binary fission? What about viruses? What about Rickettsias/Chlamydias? What about Typical bacteria?

(V) no (R/C) yes (T/B) yes

Are viruses obligate intracellular parasites? What about Rickettsias/Chlamydias? What about Typical bacteria?

(V)yes (R/C) yes (TB) no

HA spikes (hemagglutinin spikes) What does it bind? What does it mediate?

- Bind sialic acid on host cell membranes - Mediates fusion between virus and host cell membrane

NA spikes (neuraminidase spikes) What does it enable the virus to do? What is it the target of? what kind of drugs?

- Enable virus to be released from surface of host cell - Target of drugs like Tamiflu and Relenza

Capsid functions- 3

-Protection - Contains attachment sites - Proteins allow viral penetration of host cell

Filterability: Viruses can pass through bacterial filters, which typically have pore sizes of...

0.22 and 0.45 micrometers.

Our representative eukaryotic cell is a red blood cell, which has a diameter of about

10 micrometers

To be a suitable host for a virus, a cell needs two key characteristics: Internal Machinery for Replication:

A good host cell should possess the internal machinery necessary for replicating the virus. From the virus's perspective, a host cell is only suitable if it can support viral replication and the release of new viral particles.

What is a virion?

A virion is a complete, fully developed, infectious viral particle located outside a host cell

Small mutations in the virus's genome can result in minor changes in the proteins produced by mutated viral genes, especially in the HA or NA spikes. While these changes may be subtle, they can lead to a situation where pre-existing antibodies, designed to recognize the original HA and NA spikes, no longer bind effectively to these slightly altered spike proteins on the virus's surface. As a consequence, the immune system's ability to target and destroy the virus is compromised when antibodies can no longer recognize these modified spikes.

And so these small changes, these mutations, in the genome of the virus can lead to small changes in the protein products of the viral genes that are mutated. For example if those mutations occur in the HA or NA spikes of the virus. Those changes though relatively small may be significant enough such that existing defenses, so antibodies that were previously produced in response to HA version one spikes and the NA version one spikes no longer recognize these slightly altered spike proteins on the surface of the virus. And so if the antibodies no longer recognize, no longer are able to bind to those slightly changed HA and NA spikes. the ability of the immune system to then target those cells (should be viruses) for destruction will certainly be compromised.

The most commonly circulating human Type A influenza viruses include

H1N1, H1N2, and H3N2

Type A influenza viruses that circulate through bird populations

H5, H7, H7

Spikes What are 3 functions?

Means of attachment to host cells• Can provoke immune response• Can be used to characterize virus

So let's let's take a type A virus, H1N1. So what does this mean?

So all this means that this particular virus has version one of the HA spikes on its surface and it also has version one of the NA spikes on its surface as well.

Most animals viruses can infect only specific types of cells within the animal host.

So an animal virus may target an animal's respiratory system, but may not be able to infect cells present in other areas of that host.

so what makes a good host cell from the viruses point of view?

So the first thing is that a host cell has to have surface molecules, has to have receptors on its surface that the virus can recognize. If a particular cell doesn't have the right kind of receptor, then a particular virus isn't going to be able to infect that cell. And so these receptors might be somewhere on the cell surface. So if we're talking about a bacterial cell, maybe the receptors are on the cell wall. On the fimbriae or flagella. If this is a cell that's in an animal, maybe this receptor is located on the plasma membrane somewhere. So the second characteristic of a good host cell is that it has to have the internal machinery for replicating the virus. From the virus' point of view, a host cell isn't going to be a good host if it hasn't, if it can't support viral replication and release of more viral particles. So to recap, the host range of a virus ultimately comes down to the receptors that are present on the surface of the host cell and also the internal machinery.

So some viruses like influenza have evolved mechanisms for evading host defenses. So let's talk generally very generally about what a host defense might look like if say the H1N1 version of human influenza enters your body.

So the spikes on the surface of the virus. So the HA and NA spikes on the surface of the envelope are antigenic. They are going to be recognized by the individual's immune system as foreign. They don't belong here in the body. And as a consequence an immune response will be initiated. Part of that immune response will involve antibody production. So the antibodies that are produced are very specific for that virus. I said this was an H1N1 virus that infected the individual so the antibodies that are formed some of them will recognize and bind to the HA verson one spikes on the surface of the virus. Other antibodies that are produced will recognize and bind to the NA spikes version one on the surface of the virus. Once those antibodies bind to the surface of the virus they then recruit other what we call defensive cells and proteins to then actually perform the destruction of the virus.

Drugs like Tamiflu and Relenza interfere with the neuraminidase activity... how

So they inhibit the action of this enzyme which means that the sialic acids on the surface of the host cell releasing the viruses, those sialic assets are still in place. So that means that when the viruses are released from the cell they typically stick to its surface. And if you have a lot of viruses stuck to the surface of that same host cell that is definitely going to limit or slow down the spread of the virus to additional cells.

Viruses- they are filterable, might seem confusing. What does that even mean?

So what that means is that viruses can pass through the pores of most bacterial filters. So common bacterial filter pore sizes are 0.22 micrometers, another common size is 0.45 micrometers.

If we consider these swine type A viruses that most commonly circulate again we have

Swine flu- The main swine influenza viruses circulating in US recently are swine trH1N1, trH3N2, trH1N2

Chlamydia trachomatis-Symptoms for both men and women include

Symptoms for both men and women include discharge from the vagina or penis and burning with urination. Most men don't have serious long term effects. Women, on the other hand, can, if this infection remains untreated, may develop pelvic inflammatory disease, may struggle with infertility, and this type of infection, especially if untreated, can increase the risk of ectopic pregnancy as.

Influenza has two types of glycoprotein spikes

The haemagglutinin or HA spikes and the neuraminidase or NA spikes.

The haemagglutinin (HA) spikes of the virus play a crucial role in attaching to host cells by binding to sialic acid receptors on the cell membranes. Sialic acid is a sugar commonly located at the end of glycoproteins. This binding allows the virus to enter the host cell, initiating the infection process.

The haemagglutinin spikes, the HA spikes, mediate attachment between the virus and host cells. It is going to be these HA spikes that bind to receptors on the surface of animal cell membranes, host cell membranes. The specific receptor that is recognized by the HA spikes is sialic acid. This is a sugar that is typically found on the terminal end of glycoproteins. And once the HA spikes attached to these sialic acids on the surface of the host's cells that attachment will ultimately facilitate the uptake of the virus into the host cell.

To be a suitable host for a virus, a cell needs two key characteristics: Surface Receptors:

The host cell must have specific surface molecules or receptors that the virus can recognize. These receptors may be located on the cell wall, fimbriae, flagella (for bacterial cells), or the plasma membrane (for animal cells). If a cell lacks the right receptors, it cannot be infected by a particular virus.

Neuraminidase (NA) spikes have a different role: they facilitate the release of the virus from host cells. When host cells produce many influenza virus particles, the NA cleaves the sialic acids on the cell's surface, allowing the viruses to attach to sialic acids on neighboring cells, including the releasing host cell. This prevents the viruses from sticking to the cell that produced them and promotes their spread to other cells.

The neuraminidase spikes, NA spikes, on the other hand seem to be more important for promoting the release of virus from host cells. So once a host cell makes lots and lots of influenza viral particles the viruses are released from the host cell and they can then bind to sialic acids on surrounding cells. Including the target cell, the host cell that just released them. So what neuraminidase does is it cleaves the sialic acids on the surface of the host cell that's releasing the influenza viruses such that the viruses will go and attach to sialic acids on neighboring cells rather than stick to the same cell that produced them.

trH1N1, trH3N2, trH1N2

These are triple reassortment viruses. So these are viruses that contain genes not only from swine influenza viruses but also human and avian viruses as well.

Viruses do not indiscriminately infect cells. Why? give an example..

They only have a limited number of cells in which they will infect. So if you consider a particular type of bacteriophage, remember, these are bacterial viruses, a particular type of bacteriophage is only capable of usually infecting a single species or maybe even just a strain within a species of bacteria.

T or F- Nucleic acid may be segmented

True

T or F- These type A influenza viruses also contribute to influenza pandemics.

True

Able to pass through bacteriological filters? What about viruses? What about Rickettsias/Chlamydias? What about Typical bacteria?

V- yes R/C- no/yes TB- no

Do they possess both DNA and RNA? What about viruses? What about Rickettsias/Chlamydias? What about Typical bacteria?

V-No R/C-yes TB- yes

Ribosomes- What about viruses? What about Rickettsias/Chlamydias? What about Typical bacteria?

V-no R/C- yes TB-yes

Sensitive to antibiotics? What about viruses? What about Rickettsias/Chlamydias? What about Typical bacteria?

V-no R/C- yes TB-yes

ATP-generating metabolism- What about viruses? What about Rickettsias/Chlamydias? What about Typical bacteria?

V-no R/C- yes/no TB- Yes

Sensitive to interferon? What about viruses? What about Rickettsias/Chlamydias? What about Typical bacteria?

V-yes R/C-no TB- no

viruses are a- cellular.

Viruses are acellular, meaning they are biological entities that do not have a cellular structure. They therefore lack most of the components of cells, such as organelles, ribosomes, and the plasma membrane.

Can viruses replicate outside the host cell?

Viruses cannot replicate outside of a host cell.

Why don't viruses have a plasma membrane like bacterial cells?

Viruses lack a plasma membrane because they are not cellular in nature.

What do viruses do when they need enzymes for replication?

Viruses produce very few, if any, enzymes. When they require enzymes for replication, they repurpose enzymes already present within host cells.

The definition of an epidemic is

a disease acquired by many hosts in a given area in a short period of time.

Why are viruses not refer to a microbes?

because microbes or microorganisms are terms that we reserve for living things and viruses are not considered living

Nucleic acid can be double stranded or single stranded? *DNA

both

What do viruses have DNA or RNA?

both

in viruses is the nucleic acid/ genome circular or linear?

both

What is the name of the protein coat that surrounds the nucleic acid on viruses?

capsid

Protein subunits of capsid are called...

capsomeres

Chlamydia trachomatis is the etiological agent of.. how is it passed down?

chlamydia, which is a sexually transmitted disease.

Rhinoviruses are a common cause of the

common cold

Enveloped viruses do

do have an envelope

Type B viruses also contribute to the nearly yearly flu epidemics that are seen but the type B influenza viruses do or do not cause pandemics?

do not.

A pandemic is an

epidemic of infectious disease, so in this case influenza, that spreads through human populations across large regions, so large regions that include multiple continents or perhaps even worldwide.

What is a segmented genome?

genome found in multiple pieces

Influenza classification- A What does it infect?

infects humans and several types of animals (i.e. birds, horses, swine)

What does influenza use to replicate its genome?

influenza uses RNA polymerases to replicate its genome.

What is an example of an enveloped virus with Spikes on the surface?

influenza virus

What are interferons? they are chemicals what what do they do to viruses?

interferons are just proteins that really limit the spread of viral multiplication within the host. They limit the spread of the virus.

Nonenveloped viruses lack a

lack an envelope

Envelopes usually consist of some combination of...

lipids, proteins, and/or CHOs - Often a result of extrusion from host cell - May contain viral proteins

some viruses have oncolytic tendencies, meaning..

meaning that some viruses naturally or through laboratory manipulation can treat cancer.

Adenoviruses are respiratory viruses that cause generally mild

mild cold- like and flu-like symptoms.

Does Swine Flu normally infect humans?

no

Do they have a Plasma membrane? What about viruses? What about Rickettsias/Chlamydias? What about Typical bacteria?

no yes yes

So what kind of cells do viruses invade? Can they invade just any old cell?

no.

What are viruses composed of?

nucleic acid

Viruses are obligate intracellular parasites, what does this mean?

so they parasitize the host cells for whatever they need. So they will use host cell amino acids to make viral proteins. They will use host cell lipids to make viral envelopes and use host cell nucleotides to make viral genomes.

Type A viruses are classified into subtypes based on that

that particular combination of HA and NA spikes that are present on the surface of these individual viruses.

What determines the shape of a capsid?

the shape of that capsid is really dependent on the viral genome

What are bacteriophages? What do they target

they are bacterial viruses, they only target bacterial cells

So RNA polymerases are very poor proofreaders which means that

they make a lot of mistakes when they copy the viral genome such that mistakes or mutations are going to occur with every round of replication.

typical bacterial cell. This is from E. coli and it has a length of only about

three micrometers.

Capsid-So a big function of the capsid is to-

to protect the viral genome from nucleases that may be present in host cells or in host fluids.

Characteristics of viruses -small or big? -what can they only be visualized with?

very small electron microscopes

They will use host cell lipids to make

viral envelopes

use host cell nucleotides to make

viral genomes.

So they will use host cell amino acids to make

viral proteins

Can a viruses reproduce by binary fission?

viruses do not reproduce by binary fission like bacteria do

Are viruses always considered small?

what you should notice is that the viruses generally are considerably smaller, even when compared with bacterial cells. So viruses are tiny, tiny infectious particles or infectious agents.

typical bacteria

which would be like the bacteria that you've been using in the laboratory, E. coli, Staph aureus, etc.

Do some viruses have an envelope/ lipid layer surrounding the capsid?

yes

Why do we care about viruses? - -They causes illness and disease and sometimes death Can viruses be used to treat diseases?

yes, potentially treat disease.