Chapter 6

Question 1

What is a Virus

Answer 1

a cellular microorganism, consisting of proteins and genetic material (DNA or RNA), that can replicate itself by infecting a host cell

Question 2

What is a Prion

Answer 2

a cellular infectious particle consisting of just proteins that can cause progressive diseases in animals and humans

Question 3

What did D.Ivanoski find?

Answer 3

Found the Tobacco Mosaic Disease (TMD) caused by a filterable component (TMVirus)

Question 4

What is Bacteriophages?

Answer 4

Viruses that infect bacteria

Question 5

What are some of the causes of Viruses?

Answer 5

• Abnormal Growth of the Cell
• Cell Death
• Alter the Cell’s Genome
• Physiological Effect in the Cell

Question 6

What is the structure of Viruses?

Answer 6

Capsid: protein coat surrounding the genome of the virus

Capsomere: individual protein subunits that make up the capsid

Sheath: part of the tail on a bacteriophage that contracts to introduce the viral DNA into the bacterium

Naked Virus: Virus composed of a nucleic acid core, either DNA or RNA, surrounded by a capsid

Spike: Viral glycoprotein embedded within the viral capsid or envelope used for attachment to host cells.

Enveloped Virus: a virus formed with a nucleic-acid packed capsid surrounded by a lipid layer

Viral Envelope: Lipid membrane obtained from phospholipid membranes of the cell that surrounds the capsid

Question 7

Who classified Viruses?

Answer 7

David Baltimore

Question 8

Lytic Cycle

Answer 8

Virulent phages typically lead to the death of the cell through cell lysis

Question 9

Lysogenic Cycle

Answer 9

Temperate phages can become part of the host chromosome and are replicated with the cell genome until such time as they are induced to make newly assembled viruses/progeny viruses

Question 10

Process of the Lytic Cycle

Answer 10

Attachment: the phage attaches to the surface of the host through receptor

Penetration: Viral DNA enters host cell, tail sheath acts as needle & inject genome through cell wall & membrane

Biosynthesis: Phage DNA replicates and phage proteins are made, hijacks host cell to replicate. transcribe, and translate.

Maturation: New phage particles are assembled

Lysis: The cell lyses, releasing the newly made phages

Question 11

What does the Lysogenic Cycle do compared to Lytic Cycle

Answer 11

does not kill the host, phage genome integrates into the bacterial chromosome and becomes part of host

Question 12

Prophage (Lysogenic)

Answer 12

• Integrated phage genome

Question 13

Lysogen (Lysogenic)

Answer 13

• Bacterial host with a prophage

Question 14

Lysogeny (Lysogenic)

Answer 14

• The process in which bacterium is infected by a temperate phage

Question 15

Temperate Phages

Answer 15

• Remains latent (inactive). As the bacterium replicates chromosomes, also replicates the phages DNA and passes it on to new daughter cells during reproduction.

Question 16

Lysogenic/Phage Conversion

Answer 16

• The presence of the phage may alter the phenotype of the bacterium, since it can bring on extra genes.

Question 17

Generalized Transduction v.s Specialized Transduction

Answer 17

Generalized Transduction: A random piece of bacterial DNA is transferred by the phage during the lytic cycle

Specialized Transduction: At the end of the lysogenic cycle, when the prophage is excised and the bacteriophage enters the lytic cycle

Question 18

Life Cycle of the Flu (Influenza)

Answer 18

1. Influenza virus becomes attached to a target epithelial cells
2. The cell engulfs the virus by endocytosis
3. Fusion and uncoating: Viral RNA released
4. Viral RNA enters the nucleus where it is replicated by the viral RNA polymerase
5. Viral mRNA is used to make viral proteins
6. New viral particles are made and released into the extracellular fluid. The cell, which is not killed in the process, continues to make new virus.

Question 19

Life Cycle of HIV

Answer 19

1. HIV fuses with host cell
2. HIV RNA, reverse transcriptase, integrase, and other viral proteins enter the host cell.
3. Viral DNA is formed by reverse transcription
4. Viral DNA is transported across the nucleus and integrates into the host DNA
5. New viral RNA is used as genomic RNA and to make viral proteins.
6. New viral RNA and proteins move to the cell surface and a new immature HIV forms.
7. The virus matures when protease releases the proteins that form the mature HIV.

Question 20

Eclipse Phase (bacterial growth curve)

Answer 20

• Viruses bind and penetrate the cells with no virions detected into the medium

Question 21

Inoculation (bacterial growth curve)

Answer 21

• Inoculum of virus binds to the cells

Question 22

Burst (bacterial growth curve)

Answer 22

• Host cells release many viral particles

Question 23

Burst size (bacterial growth curve)

Answer 23

• Number of virions released per bacterium