Lecture 10/11: Viruses

Question 1

Virus notes

Answer 1

• Not considered “living”
• incapable of making ATP
• No metabolism
• Cannot replicate without host
• infectious agents, not organisms

Question 2

Virus

Answer 2

• Gene delivery system that contains genes encoding for structural components and facilitate it’s reproduction
• Viral surfaces are only compatible with the surfaces of certain types of cell

Question 3

Virus classifications

Answer 3

• Classified by the type of cell they infect: Eukaryotic or prokaryotic
• Bacteriophages: Infect prokaryotes, eats bacteria
• Classified by viral genome too: either DNA OR RNA, genome is linear OR circular, double OR single stranded

Question 4

Viral genome components

Answer 4

• DNA or RNA
• Single or Doubled stranded
• Capsid
• Some have envelope

Question 5

Capsid

Answer 5

Protective coating made out of protein that all viruses have AKA nucleocapsid if it has nucleus acid

• Carries enzymes
• Composed of identical subunits called capsomeres

Question 6

Envelope

Answer 6

Surrounds the capsid and is made of lipid and protein, only some viruses have this

Question 7

Viral reproduction

Answer 7

Viruses hijack ribosomes and polymerases to make copies of themselves

Question 8

Virus reproduction components

Answer 8

• Make more viral proteins like capsid

- Make viral genomes like DNA or RNA

Question 9

Virus characteristics

Answer 9

• Super small: 10 nanometers to 800 nanometers

- Smallest one is 10 nanometers with 10 genes

Question 10

Virion (viral particle)

Answer 10

• Virus without a host

- Has capsid, matrix proteins

Question 11

Enveloped virus

Answer 11

Have lipid bilayer envelope and mateix proteins between the nucleocapsid and envelope

Question 12

Non envelope (naked) viruses

Answer 12

Lack envelope

Question 13

Simplified viral life cycle

Answer 13

1) virus endocytose or fuses with cell
2) uncoats
3a) transcription of viral genes
3b) translation
3c) replication for more viral DNA
4) assembly of new viruses
5) leaves cell via budding or lyse

Question 14

Viral entry into cell

Answer 14

• Must be able to recognize and bind to cell’s surface
• Recognize membrane proteins of host cells
• Uses capsid or envelope for recognizing
• Viruses cannot infect all cells

Question 15

RNA viruses example

Answer 15

Rotaviruses, norovirus, polioviruses, rubella, hepatitus C

Question 16

Lyric phage infection w/ T4 phage

Answer 16

1) Attachment to cell wall
2) penetration via tail and leaves phage coating outside
3) transcription
4) Replication
5) Assembly
6) Release of viral particles

Question 17

General transduction

Answer 17

• Transfer of DNA from one cell to another via a virus

- Generalized transduction results from an error in DNA package

Question 18

Temperate phage infections w/ lambda

Answer 18

1) Virus binds to bacterium
2) Injects linear phage DNA that turns into circle
3) phage DNA enters lysogenic cycle
4a) phage DNA that is integrated into the bacterial chromosome and is called prophage
4b) Bacterial DNA with phage DNA is called lysogen
5) cell division and remains dormant until there are extreme conditions
6) phage DNA separates from bacterial DNA
7) phage DNA replicates
8) Lyses from host cell

Question 19

Lysogen

Answer 19

• Becomes immune to superinfection (cannot be infected by the same phage)
• Lysogenic conversion: lysogen’s phenotype changes due to prophage

Question 20

Microorganisms encoded by prophage EX

Answer 20

• Clostridium botulinum is encoded by botulinum toxic and causes botulism
• Corynebacterium diphtheriae is encoded by diphtheria and causes diphtheria

Question 21

Specialized transduction

Answer 21

• Transfer of DNA from one cell to another view of virus

- Specialized transduction results from an error in DNA excision of a prophage

Question 22

Bacterial defense against phages

Answer 22

• Bacteria produces proteins to cover surface proteins and prevents phage attachment
• Bacteria produce capsule or biofilm
• Restriction modification systems
• CRISPR system

Question 23

Restriction-modification systems

Answer 23

• Many bacteria encode restriction enzymes such as endonuclease
• Each restriction enzyme cuts a unique sequence EX if bacteria R. Enzyme scans GAATTC in a viral genome, it will cut it or degrade which means virus will degrade
• Modification: bacterial DNA protection from restriction enzyme

Question 24

Modification

Answer 24

Bacteria protects own bacterial DNA by either not containing the R. Enzyme-recognizing gene sequence or methylation of own DNA

Question 25

Methylation

Answer 25

Enzyme called methylase methylates host chromosome that has the R. Enzyme-recognized sequence

Question 26

CRISPR system

Answer 26

• Clusters of regularly Interspersed short palindromic repeats

Question 27

Studying bacteriophages

Answer 27

Melt agar
Inoculate with bacteria
Pour agar over tsa plate
Lawn of bacterial cells

Question 28

Animal virus enveloped virus

Answer 28

1) attachment
2) membrane fusion
3a) necleocapsid released
4a) in coating
3b) virus enters
4b) bacteria forms vesicles around virus
5) synthesis

Question 29

Animal virus synthesis

Answer 29

Expression of viral genes (transcription) to produce viral structure and catalytic proteins such as capsule proteins and enzymes required for replication

Question 30

Synthesis by (genome type)

Answer 30

DNA viruses
(+)ssRNA viruses
(-)ssRNA viruses
Reverse transcribing RNA viruses

Question 31

Double stranded DNA virus

Answer 31

1) viral gene
2) gene is transcribed from DNA into mRNA
3) ribosome translates mRNA into viral proteins

Question 32

Single stranded DNA virus

Answer 32

1) synthesis of complementary strand

2) normal DNA genome and protein synthesis

Question 33

Single stranded RNA virus

Answer 33

Viral proteins are made through translation

Viral genome is made by synthesizing the RNA