Conjugation

Question 1

Conjugation Basics 101

Answer 1

-involves CELL-to-CELL CONTACT sometimes called MATING

Question 2

Conjugation 1-Plasmid

Answer 2

-DONOR cell contains a PLASMID (autonomously replicating, extrachromosomal molecule of circular, dbl-stranded DNA)
-CONJUGAL PLASMID because it has all the genes for conjugation
(RECIPIENT does NOT carry the conjugal plasmid)
-EXCONJUGANT-official title of recipient once recipient receives plasmid
-In this process never have nakey DNA because it goes from cell to cell and is not exposed to proteins

Question 3

Conjugation 2-Clinical Relevance (A)

Answer 3

• R plasmids=conjugal plasmids with important AB resistance determinants
  
  • most R’s carry more than oneAB resistance gene (those that encode resistance to:
    - chloramphenicol
    - streptomycin
    - ampicillin
    - kanamycin
    - neomycin
  • R’s mediate conjugation amongst E coli AND between E coli and its RELATIVES
• RAPID DISSEMINATION of drug resistance via R’s or conjugal transposons
• normal flora act as resistance reservoirs (non pathogenic guys)

Question 4

Conjugation 3-Gram-NEG Bacterium E. coli

Answer 4

Q. Why can R be passed onto both daughter cells during cell division?

A. R plasmid consists of circular dble-stranded DNA that can replicate autonomously

Question 5

Conjugation 4-Genes carried by R plasmid

Answer 5

Encode a sex pilus

• LONGER and THICKER than the commoner pilus
• facilitates capture of the recipient cell to form a MATING PAIR
• sexytime pilus RETRACTED brings the pair CLOSER TOGETHER

Question 6

Conjugation 5-Conjugation Bridge

Answer 6

Bridge forms between the two cells through which DNA passes

-DNA transfer occurs through a special form of replication: TRANSFER REPLICATION

Question 7

Conjugation 6-Where does Replication initiate/procedural mechanism

Answer 7

at the ORIGIN of TRANSFER (oriT) DNA is nicked

• located on the R plasmid
• proceeds by the ROLLING CIRCLE MECHANISM

Question 8

Conjugation 7-Steps of Rolling Circle Mechanism + Following Steps

Answer 8

1. one of the DNA strands breaks
2. BROKEN strand is pulled away from its complement through the CONJUGATION BRIDGE (tube).
3. Strand left behind on donor is replicated, REFORMS the dbl-stranded R plasmid. yayy.
4. (Entry and Replication) TRANSFERRED strand RECIRCULARIZES and REPLICATES into a dbl-stranded R plasmid
5. ## Cells DETACHFINAL: BOTH donor AND recipient cells possess a COMPLETE COPY of the R plasmid. EACH can go on to mate with other R-RECIPIENTS

Question 9

Cojugation 8-Take Note

Answer 9

• cells must remain in contact during DNA transfer
• PHYSICAL DISRUPTION can break contact. DETERGENTS canNOT.
• DNA is never nakey, it is NOT destroyed by extracellular nucleases

Question 10

Exconjugant

Answer 10

aka transconjugant