Introduction to Viruses

Question 1

How many viruses are there compared to other microorganisms on Earth?

Answer 1

There are more viruses than any other microorganism on this Earth.

Question 2

How old are viruses estimated to be?

Answer 2

Viruses are at least 4 billion years old.

Question 3

Are all viruses harmful?

Answer 3

Not all viruses are bad.

Question 4

What type of DNA do humans have more of compared to eukaryotic DNA?

Answer 4

Humans are made of more viral DNA than eukaryotic DNA.

Question 5

Define a virus.

Answer 5

Genetic element that can multiply only in a living host cell.

Question 6

What characterizes a virus in terms of its living status?

Answer 6

Not living, can’t reproduce independently.

Question 7

What is an obligate intracellular parasite?

Answer 7

A parasite that needs a host cell for energy, metabolic intermediates, and protein synthesis.

Question 8

What is a virion?

Answer 8

Virus particle, extracellular form of a virus, exist outside host and facilitates transmission from one host cell to another

Question 9

Virion

Answer 9

-Replication/reproduction occurs only upon infection (entry to host cell)
-Contain nucleic acid : DNA or RNA
-No cytoplasmic membrane or organelles

Question 10

What types of nucleic acids can viruses contain?

Answer 10

DNA or RNA.

Question 11

What is the structure of a virion?

Answer 11

Capsid surrounding nucleic acid; some have a phospholipid envelope.

Question 12

What is the nucleocapsid?

Answer 12

Capsid + nucleic acid.

Question 13

What is an envelope in the context of viruses?

Answer 13

Phospholipid bilayer from host cell membrane + viral protein.

Question 14

envelop of virus

Answer 14

-phospholipid bilayer from host cell membrane + viral protein

-many posses glycoproteins (spikes) : recognize, bind receptors of host cell

-outermost layer provides protection and recognition site for host cell

Question 15

2 types of viruses based on envelop

Answer 15

Naked virus: nucleocapsid
Enveloped virus: nucleocapsid + envelope (phospholipid) + may have spikes (glycoprotein)

Question 16

What happens to the capsid during the intracellular state of a virus?

Answer 16

Capsid is removed; virus exists as nucleic acid.

Question 17

Who showed that tobacco mosaic disease was transmissible from disease plant to healthy plant?

Answer 17

Chemist Adolf Mayer in 1886.

Question 18

What significant discovery did Dimitri Iwanowski make?

Answer 18

He found that an infectious agent smaller than bacteria passed through a porcelain filter.

He filter the sap of diseased plant through porcelain filter that designed to retain bacteria.

Question 19

What did Wendell Stanley do?

Answer 19

Isolation, characterization, and crystallization of TMV.

Question 20

Who said some viruses can lead to cancer

Answer 20

Sarah Stewart

Question 21

What hypotheses exist about the origins of viruses?

Answer 21

1. Viruses arose prior to or from cells ~4 billion years ago
2. Viruses require host cell→ evolved after cells appeared
3. Viruses existed in a precellular era (RNA-World), free living

Question 22

Viruses have mechanism to quickly move genes, they enrich gene diversity of hosts by facilitating gene transfer (How)

Answer 22

1.horizontal gene trensfer (prokaryotic cells)

2.earliest viruses co-existed with host cells: a lot of gene transformation → Later evolved killing host cells

3.viruses as part of the RNA world played a role in RNA to DNA transition?
-Some RNA viruses evolved DNA genomes to protect their genomes from cellular ribonucleases
-DNA is more stable than RNA
-Use of the host cell machinery to replicate

Question 23

virus comprise ~ % of the nucleic-acid-containing particles, but due to its small size, viruses only comprise ~ % ef the biomass on Earth.

Answer 23

94%
5%

Question 24

What is the size range of most viruses?

Answer 24

require electron microscopy

20–1000 nm in length

20–300 nm, with giant viruses about 500 nm in diameter

Question 25

What is a giant virus, and when was the first one discovered?

Answer 25

The first giant virus, Mimivirus, was discovered in 2003, first seen in its amoebae host

Question 26

Giant virus

Answer 26

-first one discovered in 2003, named Mimivirus, first seen in its amoebae host -large capsid of ~ 400 nm with protein filaments extending ~ 100 nm from the suface -large genome encode ~1000 genes (DNA genome) -Nucleocytoplasmic Lange DNA viruses (NLDV): replicate in both the host's cell nucleus and cytoplasm -only infect eukaryotic unicellular hosts ex. amoebas, algae, and other protists -their genomes are large and very diverse.

Question 27

What is a virophage?

Answer 27

Small DNA viruses that replicate only in cells co-infected with a giant virus.

Question 28

What is an example of a virophage?

Answer 28

Sputnik, which replicates only in Mimivirus infected amoeba cells.

Question 29

Fill in the blank: Viruses control bacterial populations and influence the evolution and diversity of their host organisms, known as _______.

Answer 29

Bacteriophages (phages).

Question 30

What impact does climate change have on viruses?

Answer 30

Increases the risk of new infectious diseases.

Question 31

Hypothesis of giant virus

Answer 31

1.they may have been small viruses, but they steal genes from their host 2.they originated from bacteria, archaea and even other viruses. acquired genes by **lateral transfer** from bacteria or viruses with an intra-amoebal life style

Question 32

What have played a significant role in evolution of eukaryotes through gene exchange

Answer 32

Giant viruses

Question 33

Giant viruses have their own viral parasites: Virophages

Answer 33

-virophages: small DNA viruses that replicate only in cells co-infected with a giant viruses -they use the viral replication factory established by the giant virus -parasitic relationship with the co-infecting giant virus Ex.Sputnik: first virophage discovered, replicates only in Mimivirus infected amoeba cells, decrease the Mimivirus replication by ~70% -virophages may improve survival of the host ex. by preventing cell lysis by the giant virus

Question 34

Most viruses are not pathogenic, many co-exist with us, many play a crucial role in many ecosystems.

Question 35

What help control bacterial populations and influence the evolution and diversity of their host organisms

Answer 35

Bacteriophages

Question 36

Bacteriophages (phages)

Answer 36

viruses that infect and kill bacteria

Question 37

possible alternations for antibiotics

Answer 37

phage therapy to combat bacterial infection in human

Question 38

Viruses can infect nearly all organisms