Lecture 4

Question 0

When 50s subunit combines with 30s subunit what happens with tRNA?

Answer 0

fMet tRNA starts off in p site of ribosome

Question 1

Translation steps

Answer 1

1. fMet tRNA finds AUG
2. 16s rRNA on 30s subunit finds SD sequence
3. 50s comes into contact with 30s and forms complete 70s ribosome
4. Translation begins and continues until stop codon reached

Question 2

A site

Answer 2

Accepts incoming charged tRNAs

Question 3

P site

Answer 3

Peptide site; growing protein

Question 4

E site

Answer 4

Exit site where uncharged tRNAs exit ribosome

Question 5

Translation continues until

Answer 5

Stop codon is in the A site

Question 6

What is needed to form the peptide bonds to attach 1 amino acid to another?

Answer 6

ATP

Question 7

What do stop codons code for?

Answer 7

Not an amino acid so the ribosome A site sits empty, ribosome stalls and dissociates

Question 8

Function of 16s rRNA gene

Answer 8

• shine delgarno sequence flags ribosome and it has a complimentary sequence to the conserved region in 16s rRNA
• part of the 30s subunit of ribosome
• conserved regions involved in recognizing and binding to SD sequence at the 5’ end of mRNA that is coming off of transcription

Question 9

Genetic exchange

Answer 9

• conjugation: direct cell to cell contact via sex pilus; exchanges plasmid DNA
• transformation: cells pickup naked DNA from enviro.
• transduction: viruses serve as vehicle for introduction of DNA into cell

Question 10

DNA binding proteins

Answer 10

DNA transport protein to bring DNA into the cell

DNA is brought into the cell as ssDNA and bound to single-stranded binding proteins to protect it

Question 11

Rec A

Answer 11

binds ssDNA and incorporates it into chromosomes of the cell

Question 12

F plasmid

Answer 12

• plasmids containing tra genes

- contains genes for variety of functions eg. antibiotic resistance

Question 13

Tra genes

Answer 13

code for the enzymes used in formation of sex pilus

Question 14

F+

Answer 14

donor; has F plasmid and tra genes

Question 15

F-

Answer 15

recipient; no F plasmid and no tra genes

Question 16

Can conjugation occur between 2 donors?

Answer 16

No

Question 17

Conjugation steps

Answer 17

• pilus forms
• pilus retracts slightly
• F plasmid nicked in one strand
• transfer of one strand from F+ to F-; F plasmid simultaneously replicated in F+
• synthesis of complimentary strand in recipient cell
• completion of DNA transfer and synthesis; cells separate

Question 18

Phage

Answer 18

bacterial virus

Question 19

Viral DNA codes for…

Answer 19

nuclease designed to destroy host chromosome and replication of itself

Question 20

How is transducing virus created?

Answer 20

host cell packages DNA in capsid but puts piece of host chromosome in instead of viral NA

Question 21

How does transducing virus DNA get inserted into chromosome?

Answer 21

Rec A proteins

Question 22

Viruses

Answer 22

• redirect host metabolism and resources to create more virus
• no metabolism themselves
• every known organism/cell type has viruses that infect it

Question 23

Morphology/structure of virus

Answer 23

• 0.02-0.3 um diameter (TEM best to view)
• RNA or DNA genomes or hybrid
• Variable genome structure (dsRNA, dsDNA, dsRNA:RNA, ssRNA, etc. linear, circular, segmented, etc.)
• viral genome replication occurs independently of host cell/genome replication
• capsid

Question 24

Capsid

Answer 24

- protein coat/structure designed to protect genetic material and recognition of infection of host cell - helical - icosahedral - complex

Question 25

helical capsid

Answer 25

- individual protein subunits come together to form helix, subunits wrap around a ss genome - pushes genome into host cell via unwinding genome throuhg cell layers - eg. tobacco mosaic virus

Question 26

icosahedral capsid

Answer 26

- flat surfaces and corners, highly stable structure - spontaneously forms inside host cells - capsid docks on host cell and experiences protein conformation change that push viral genome into host cell - can have membrane or cell wall degrading enzymes attached to introduce holes which the genome can enter through

Question 27

complex capsid

Answer 27

- tail fibers find appropriate receptor on host cell surface, change conformation to contract tail, syringe protein pushed through cell layers to release viral genome into cytoplasm

Question 28

envelope

Answer 28

- some viruses have envelopes - made out of host cell membrane - picked up as virus buds out - envelope is not metabolically maintained - short half-life outside of host cell - susceptible to degredation - w/o envelope virus no longer infective - masks virus to evade immune system

Question 29

Some viruses carry around enzymes in capsid

Answer 29

- HIV - reverse transcriptase RNA --> DNA --> RNA - other viruses: RNA --> RNA RNA-dependent RNA polymerase - seen with genomes that otherwise cannot be replicated by host cell machinery - can include enzymes for entry or exit from host: - neuraminidases - enzymes that breakdown membranes - lysozyme - enzyme that degrades cell walls

Question 30

Viral replication cycle

Answer 30

1. recognition and attachment to host cell 2. penetration 3. replication 4. assembly and packaging 5. release of virus from host cell

Question 31

recognition and attachment to host cell

Answer 31

- protein: protein biding between virus and host - host cell proteins are not virus specific, carry out normal function for host - irreversible connection

Question 32

Penetration

Answer 32

viral capsid or envelope facilitates delivery of viral genome into host cell

Question 33

replication (viral)

Answer 33

1. early replication: viral nucleic acid alter host cell machinery; shuts down host cell processes 2. late replication: active viral genome replication and capsid synthesis, and synthesis of viral enzymes

Question 34

assembly and packaging

Answer 34

packaging of viral NA into capsids

Question 35

Release of virus from host cell

Answer 35

- eg. envelope viruses bud out of host cell - eg. some viruses degrade membrane/cell wall - eg. some viruses cause host cell lysis (host cell is too full)

Question 36

Burst size

Answer 36

number of viruses released by an infected host cell; varies from virus to virus and host cell to host cell - larger burst size = higher number of viruses made by host cell

Question 37

latent, lysogenic, temperate viruses

Answer 37

- can enter state of lysogeny where viral NA is not being expressed (no early replication) - at some point in lysogeny become activated and enter lytic state (active viral infection) - viral genome will get copied by host cell as host cell replicates

Question 38

Polio

Answer 38

- non-enveloped icosahedral virus - infects CNS cells - also infects GI cells - spread via fecal:oral route - RNA genome virus: RNA --> RNA - RNA dependent RNA polymerase - genome = VpG 5' ssRNA - one of first proteins translated by host ribosome is 2A protease and it looks for 7mg 5' and cuts it off, rendering euk. mRNA unrecognizable to ribosomes - once host cell stopped from translating own mRNA, only get viral synthesis