GENET 270: Lec 4 - Plasmids

What is a plasmid?

It is extrachromosomal circular dsDNA

Is a plasmid necessary for the survival of a cell? why?

No

• Doesn’t contain essential genes

True Or False: All bacteria only have 1 plasmid

False

• sometimes they have more than 1 type plasmid in 1 cell

***What are 2 things that Plasmids are Critical for in the cell?

1. Adaptation

2. Evolution

****Do plasmids resemble gDNA? Why or Why not?

Yes

• So that the same machinery can work on it

True or False: Plasmids are always significantly smaller than gDNA making it easy to differ?

FALSE

• They vary greatly in size = sometimes difficult to determine which is Chromosome + which is plasmid

How can you differ between plasmid + chromosome

Plasmid does not contain any essential genes

****What does things do Plasmids normally encode? Give an example.

Proteins + RNAs that often BENEFIT bacterium in specific environment

• Eg. Antibiotic resistance (what led to discovery of plasmids)

What does the F plasmid do?

Fertility plasmid 

= conjugation: Infect recipient cells with F plasmid DNA

What is characteristic of plasmids?

Extra genes 

• not necessary but beneficial

How were plasmids initially named? As an example: What is plasmid called for antibiotic resistance

After the functions encoded

• eg. R plasmid = antibiotic resistance

• eg. F plasmid = feritlity

Now How are plasmids named (standardized)

pTR1

• p = plasmid

• TR = initials of creator'

• 1 = version

****True or false: Plasmids are normally circular dsDNA but can sometimes be Linear or ssDNA

True

****In what scenarios would plasmids be linear or ssDNA?

If the chromosomal DNA in cell was linear or ssDNA

• Structure of Plasmid DNA = REFLECTS gDNA of cell

*****What type of supercoiling do Plasmids have?

NEGATIVE supercoiled

Fill in the blank: Supercoil stress is relieved by ____ _____ and used to facilitate _____ eg. ______ + _____

Supercoil stress is relieved by Protein binding and used to facilitate reactions (eg. Replication + transcription

What technique is used to purify/isolate plasmids? How does it work

Mini prep (solutions 1-3 + centrifuge + alcohol)

• How: Small size of plasmid allows for selective precipitation

****True or false: Plasmids are replicated alongside chromosomes?

False

• Plasmids must replicate independently of chromosome

True or False: Plasmid = Replisome Define the word.

TRUE

• Replisome = any DNA molecule (chromosome, plasmid, or viral genome) that can replicate independently because it has its own origin and control system.

***Do plasmids require a origin of replication? If yes, what is the origin of replication called? (eg. in DNA = OriC)

Yes

• OriV

***OriV vs. OriT what is the difference?

Ori V = origin of replication

Ori T = used in conjugation

• origin of transfer site on a conjugative plasmid.

Fill in the blank: Many plasmids encode ____ protein required for ____ _____

Encode ONE PROTEIN for INITIATION of REPLICATION

Where is this ONE PROTEINS required for initiation of replication LOCATED on the plasmid?

encoded very to Ori V

• eg. repE

****What is the only region of plasmid required for replication?

The one protein used for INITIATION of Replication (eg, repE)

*****If the plasmid only encode one protein for replication, where do the remaining required proteins come from?

Borrow from host bacterium