Virus Structure

Question 1

Light microscope can be used to view viruses. True or false?

Answer 1

False.

Only the poxvirus can be seen with a light microscope but you cannot view it efficiently.

Question 2

What are the 3 kinds of electron microscopy studies used to examine viruses? What is the difference between all three?

Answer 2

Transmission EM: uses a beam of electrons that goes through and around the viral structure
Cryo EM : uses low temperature of -160 degrees celsius liquid nitrogen to rapid freeze and analyze the viral structure
Scanning EM: looks at the surface properties of infected viral cells

Question 3

When using electron microscopy, you use some type of contrast that is produced by the use of what?

Answer 3

heavy metals such as tungsten or uranium
you place them in a solution –> phosphotungstic acid or uranyl acetate

when an e- beam strikes a heavy metal they bounce off them but they penetrate the virus particle, which are much more transparent to the beam of e- compared to the heavy metals

Question 4

You can evaluated stool specimens from patients with gastroenteritis for viruses such as?

Answer 4

rotavirus, astroviruses, adenoviruses, noroviruses

Question 5

Herpesvirus, poxvirus, and Ebola virus have unique discernable characteristics that are easily identified by?

Answer 5

electron microscopy.

Question 6

Electron microscopy can be used for the detection of viral particles when viral culture conditions or reagants are not readily available. One such example is?

Answer 6

SARS= Severe Acute Respiratory Syndrome

Question 7

HIV has what shape type capsid?

Answer 7

conical shape

Question 8

What is a limitation for using electron microscopy? What is another technique that can be used to offset this limitation?

Answer 8

There is not a high resolution when you’re trying to understand subtle features of some viruses.

So Cryo-electron microscopy was developed. There is no staining or fixation is needed. You freeze virus particles in -160 degrees celsius and take the frozen structure and place them in an electron microscope that is engineered so that the temp is maintained at -160 C. The electron beam creates a 3D structure with 1-2 nm (very high resolution). Information is received by applying fourier transforms to generate waveforms that will be converted into an image.

Question 9

Viral capsids are made of ____________protein subunits. Capsids are self-___________-.
Proteins and nucleic acids are held together via what type of bonds?
Most virus capsids are of what symmetry?

Answer 9

repeated
self-assembled
non-covalent
helical or icosahedral

Question 10

Enzymatic reactions occur for the assembly of viral capsids. True or false?

Answer 10

FALLLSSEEE!!!!
There is no enzymatic reaction required. These viral proteins for the capsid are able to assemble themselves into beautiful structures. Nature is amazing!

Question 11

Basic nucleocapsid structures include helical, cubic, and irregular. What is the difference between the three and what are some examples of viruses that fit into these structural categories?

Answer 11

Helical: rod-shaped with varying widths; NO THEORETICAL LIMIT to the amount of nucleic acid that can be packaged; RNA virus: influenza; open structure

Cubic AKA icosahedral: spherical, amount of nucleic acid that can be packaged IS LIMITED; mirrors a closed dome with the viral genome within; DNA viruses: adenovirus, parvovirus, warts virus; RNA viruses: rotavirus; closed structure

Irregular: without clear symmetry; Poxvirus

Question 12

What are the 3 kinds of symmetry with icosahedral viruses?

Answer 12

5 fold axis
3 fold axis
2 fold axis

Question 13

Caspar and Klug used what that helped to give a clue as to how viral capsids are made?

Answer 13

the Fuller geodesic

Question 14

Helical viruses like the influenza virus is organized around a _________axis. They allow flexibility (bending). The protein making up the capsid called__________ is in intimate contact with the nucleic acid genome.

Answer 14

a single axis

capsomere

Question 15

The spikes in the capsid of the influenza particle refer to what?

Answer 15

hemagglutinin and neuraminidase

Question 16

What are the viruses that have negative sense RNA, are enveloped, and have helical capsids?

Answer 16

Influenza- orthomyxovirus

Paramyxovirus: measles virus, mumps virus, RSV
Rhabdovirus: rabies virus
Filovirus: Ebola virus, Marburg virus
Arenavirus: lymphocytic choriomeningitis
Bunyavirus: California encephalitis virus, hantavirus
Deltavirus: Hepatitis D virus

Question 17

Matrix proteins in icosahedral capids are found between the capsid and envelope of viruses such as?

Answer 17

flavivirus and togavirus

Question 18

Viruses _______ encode enzymes that are required to make the membrane as it parasitizes the cell in which it grows as a source of its enveloped structures.

Answer 18

do not

Question 19

Adenovirus structure is so striking as it contains fibers that function as what?

Answer 19

the fibers function as the viral attachment proteins which come in contact with the receptors of target cells

Question 20

All viruses encode their own structural protein except for? Why is this important?

Answer 20

Deltavirus is a defective virus as it borrows its viral attachment protein from Hepatitis B. It explains why we can differentiate viruses from each other based on antigenic differences.

Question 21

If the genome of a given virus is unique, it follows that the amino acid composition of the structural protein will be unique to that virus.

Answer 21

We can differentiate polyomavirus from papillomavirus. on the surface they may look alike but they are not alike because of their genetic differences. Their surface capsid proteins are different. That’s why its so striking that each virus encodes its own structural protein which drives the need for mRNA productivity so that these proteins can be made. Viruses are either DNA or RNA. Whichever mechanism the virus uses to encode its structural proteins must be expressed.

Question 22

Poliovirus structure consists of what?

Answer 22

a small icosahedral with capsid of 4 different proteins: 5 copies of VP1, variable copies of VP2 andVP3, and VP4 insid

In picarnovirus family:
Poliovirus
Rhinovirus
Hepatitis A virus

No envelope
Capsid icosahedral
ss linear nonsegmented
Positive polarity

Question 23

This virus is intensely studied in the lab as it is very safe to use and that it is in the same family as the rabies virus. Thus it has what type of structural shape? What is this virus?

Answer 23

Vesicular stomatitis virus

bullet shape

Question 24

This virus has a conical capsid shape that is conferred by geometric rules about 5-fold defects.

Answer 24

HIV-1

Question 25

Viral budding, a process deals with viral release, occurs when?

Answer 25

at the end of viral replication

Question 26

Viral glycoproteins of virus such as the influenza virus are what?

Answer 26

hemagglutinin and neuraminidase

Question 27

How do viruses become enveloped?

Answer 27

Viral glycoproteins, nucleocapsid proteins, and matrix proteins push the cell membrane (budding) until it eventually forms an envelope.

Question 28

When the budding process is complete, what happens to the virus?

Answer 28

the virus is released

Question 29

This is a technique in which you add RBCs to infected cells to detect the presence of the virus in infected cells. The RBCs will adhere to the viral proteins, specifically hemagglutinin, and thus infected cells will be surrounded with RBCs.

Answer 29

Hemadsorption

Question 30

Negative sense RNA viruses carry what specific type of RNA polymerase?

Answer 30

RNA-dependent RNA polymerase

Question 31

Analysis of viral structure require physical and mathematical methods which are?

Answer 31

microscopy and Fourier transform

Question 32

What is the purpose of viral capsids?

Answer 32

They protect the viruses and allow them to enter the cells and replicate.

Question 33

What strategies do viruses use to enter and exit the cell?

Answer 33

enter: fusion or endocytosis
exit: budding or lysis