Viruses

Question 1

A virus is an obligate intracellular parasite meaning

Answer 1

Only able to reproduce within the cell

Outside cell; has no activity

Therefore is not a cell or living organism; has no ability to do anything on its own

Question 2

Structure of all viruses

Answer 2

Nucleic acid genome packed in a protein shell

Question 3

Once in a cell, the virus

Answer 3

Virus genome directs the production of new copies of the genome and of the protein packing needed to produce more viruses

Question 4

What form does viruses genomes come in?

Answer 4

ALL forms (double or single stranded, DNA or RNA, linear or circular)

Question 5

If a given virus has an unequal amount of thymine to adenine in its genome, what can be said about the virus?

Answer 5

It is not double stranded

Question 6

Limiting factor of all viral genomes: (2)

Answer 6

Size
-Much smaller than the host they infect
Protein coat
-Rigid: unable to accommodate a larger genome

Question 7

Adaptations found in viral genomes to accommodate their limitations

Answer 7

Carries few genes, relies on host-encoded proteins for translation, transcription and replication

Encode more than one protein in a given length of genome, more than one reading frame so genes can overlap

Question 8

The protein coat surrounding the genome in a virus is called the ___ which is made from ___ and used to:

Answer 8

Capsid
Repeating pattern of a few protein building blocks
Classify viruses

Question 9

Helical capsids

Answer 9

Rod shaped

Question 10

Polyhedral capsids

Answer 10

Multiple-sided geometric figures with regular surfaces

Question 11

E. Coli

Genome is located within the ____
___ and ___ attach to the surface of the host cell
____ contracts using ATP to inject the genome into the host

Answer 11

Capsid head
Tail fibers and base plate
Sheath

Question 12

Why does a bacteriophage inject its DNA while animal viruses do not?

Answer 12

Because bacteriophage must penetrate a cell wall while animal viruses can enter the cell as a whole

Question 13

Viruses have ____ which surrounds the capsid, which is:

Answer 13

Envelope

Membrane on the exterior of the virus made from the membrane of the host cell

Question 14

Enveloped versus acquire their covering by

Answer 14

Budding through the host cell membrane

Question 15

Naked Viruses

Answer 15

Enveloped viruses fuse with plasma membrane of host and leave the de-enveloped capsid inside the host cell

Question 16

What kinds of viruses are always naked?

Answer 16

All phages and plant viruses because they affect cells with cell walls

Question 17

Is viral infection a specific process?

Answer 17

Yes the virus must bind to a receptor on the cell membrane, which explains why only certain cells are exposed to viruses

Question 18

How do viruses reproduce since they are incapable of doing anything on their own?

Answer 18

They inject their genome into the host, modifying it to produce more viruses

Question 19

Attachment / Absorption

Answer 19

First step in redirecting host genome to reproduce the virus

Question 20

Penetration / Eclipse

Answer 20

2nd step in redirecting host genome to reproduce virus

Injection of the viral genome into the host cell

Question 21

After attachment and penetration the phage follows one of two paths:

Answer 21

Lytic cycle or the Lysogenic cycle

Question 22

Hydrolase

Answer 22

Hydrolytic enzyme that degrades the entire host genome

One of the first enzymes transcribed from the virus upon entering the host genome

Question 23

Hydrolase is an example of an early gene, one that:

Answer 23

Is expressed immediately after infections and which includes any special enzymes requires to express viral genes

Question 24

Lysozyme, an example of a late gene, functions to

Answer 24

Destroy the bacterial cell wall, and the host bacterium bursts, releasing more viruses to repeat the cycle

Question 25

Lytic cycle of phages:

1. Attachment of phage and injection of phage chromosome
2. ____________ by phage-specific enzyme
3. ____________ using bacterial materials and phage enzymes
4. ____________ to produce phage structural components
5. ___________ progeny phage particles
6. Release of progeny phage by __________

Answer 25

Lytic cycle of phages:

1. Attachment of phage and injection of phage chromosome
2. Breakdown of bacterial chromosome by phage-specific enzyme
3. Replication of phage chromosome using bacterial materials and phage enzymes
4. Expression of phage genes to produce phage structural components
5. Assembly of progeny phage particles
6. Release of progeny phage by lysis of bacterial wall

Question 26

Lytic cycle is effective in giving virus a way to rapidly increase in number but it is problematic in the sense that

Some viruses are clever and instead go into the

Answer 26

All host cells are destroyed

Lysogenic cycle

Question 27

Lysogenic Cycle: Upon infection the phage genome is incorporated into the bacterial genome and is to referred to as the ___ and the host is now referred to as the ___

Answer 27

Prophage

Lysogen

Question 28

In the lysogenic cycle, when the host cell reproduces:

Eventually, the prophage becomes

Answer 28

So does the prophage

Activated and removes itself via excision to enter the lytic cycle

Question 29

One potential consequence of the lysogenic cycle

Answer 29

When the prophage excises itself from the host, it may take some of the host genome with it possibly inducing traits in other cells the prophage infects that were not previously there

Question 30

Transduction

Answer 30

When a prophage takes a part of a host cells DNA and infects another host cell, expressing a trait that was not previously encoded for in the new host cell

Question 31

Lysogenic Cycle

1. Phage binds to bacterium
2. Phage __________
3. Phage DNA integrates and becomes _________
4. Chromosome with integrated prophage ________
5. In rare cases, the prophage may ________________

Answer 31

Lysogenic Cycle

1. Phage binds to bacterium
2. Phage enters the host cell
3. Phage DNA integrates and becomes a non-infective prophage
4. Chromosome with integrated prophage replicates
5. In rare cases, the prophage may separate and the cells will be induced to lyse

Question 32

Animal cell infection: Getting the genome in the cell

1. Virus binds to proteins on the animal cell’s ________
2. Virus undergoes penetration into the cell via _______
3. Once inside, the viral genome is _____ (_______)

OR

The virus ________

Answer 32

Animal cell infection: Getting the genome in the cell

1. Virus binds to proteins on the animal cells plasma membrane
2. Virus undergoes penetration into the cell via endocytosis
3. Once inside, the viral genome is uncoated (released from the capsid)

OR

The virus fuses with the plasma membrane and injects virus into the cytoplasm

Question 33

After the virus enters its genome into the animal cell, it:

Answer 33

Enters the:

Lytic cycle / productive cycle / lysogenic cycle

Question 34

Lytic cycle in animal cells is

Answer 34

Same as in phages

Question 35

Productive cycle in animal cells

Answer 35

Similar to lytic cycle but does not destroy the cell. Instead the virus exits via budding through the host cell membrane, and the membrane can reseal as the virus level

Question 36

In the animal virus, the lysogenic cycle’s inactive form of the viral genome is called the

Answer 36

Provirus (analogous to the prophage)

Question 37

(+) RNA virus genome

Answer 37

Must ENCODE RNA-dependent RNA poly but don’t have to carry it

As soon as it is in the cell, the host translates it (acts directly as mRNA)

Question 38

Infective virus

Answer 38

Injecting the virus into the host will result in the production of the virus

RNA virus genome

Question 39

(+) RNA viruses cause ___, ___ and __

Answer 39

common cold, rubella and polio

Question 40

(-) RNA viruses genome

Answer 40

must CARRY RNA-dependent RNA poly

• RNA is complementary to the RNA that encodes viral proteins meaning it is the template for mRNA production

Entering cell: create (+) strand first

Question 41

(-) RNA viruses produce ___, ___, ___ and ___

Answer 41

Rabies, measles, mumps and influenza

Question 42

Retroviruses genome

Answer 42

Must ENCODE reverse transcriptase (aka RNA-dependent DNA polymerase)

Integrate as proviruses, so they must be turned into DNA from RNA to integrate into the host genome for replication

Question 43

Retroviruses cause ___, ___ and ___

Answer 43

HIV, AIDS and HTLV (human t-cell leukemia virus)

Question 44

Double stranded DNA viruses genome

Answer 44

ENCODE enzymes required for dNTP synthesis and DNA replication

Large genomes with genes for enzymes involved in DNA synthesis and replication so that it can reproduce without having to wait for the cell to do so

Question 45

Subviral particles

Answer 45

Infection agents that are smaller and simpler than viruses

Question 46

Two categories of sub viral particles:

Answer 46

Prions and viroids

Question 47

Prions: what are they and how do they replicate?

Answer 47

Mis-folded version of a protein that already exists that are self replicating (violate central dogma)

Question 48

When the normal protein comes in contact with the prion:

Answer 48

The prion acts as a template and the normal protein alters into an infectious form

Question 49

Prions are responsible for transmissible spongiform encephalopathies (TSEs) which are responsible for:

Answer 49

Degeneration of the nervous system

Question 50

Prion diseases are transmitted via: (2)

Answer 50

Ingesting tissue containing the abnormally folded proteins

OR

Genetically via mutations in the gene encoding for the prion protein

Question 51

Viroids structure:

Answer 51

Short, circular single stranded RNA with extensive self complementarity (can base pair with itself to create some double stranded regions)

Question 52

Viroids lack capsids and do NOT

Answer 52

Code for proteins

Question 53

Some viroids are ____ while others ____

Answer 53

Catalytic enzymes while others silence gene expression

Question 54

Viroids share similarity to replication of

Answer 54

RNA viruses

Question 55

Most diseases caused by viroids are found in ____

The only one found in humans is

Answer 55

Plants

Hepatitis B