Phages Flashcards
(38 cards)
Phages are considered _______ vector?
‘natural vectors’
What do phages transduce?
DNA from one cell to another
What is the advantages of phage vectors over plasmid vectors?
They infect cells more efficiently and readily than plasmids can transform cells.
They also produce a higher yield of clones.
What are the clones of cells produced by phages called? WHat are they called produced by plasmids?
Plaques.
Colonies.
How are plaques produced?
Plaques are formed when the phage clears a hole in the lawn of bacteria. Each plaque originates from a single phage that infects a cell, that in turn produces more phage, which in turn infects surrounding cells in the bacterial lawn. The plaque is an area of dead cells.
How were the first lambda phage vectors first created?
DNA was removed from the phage but the DNA coding for phage replication was left intact
What did the missing phage DNA allowed to occur?
It allowed for the foreign DNA to be inserted in its place.
What were the first lambda phage vectors called?
Charon phages also known as “replacement vectors”
When compared with plasmids, can lambda phage vectors hold more or less DNA? Give an example.
More DNA
For example, Charon 4 can accept approximately 20 KB of DNA.
What limits the amount of DNA accepted by the phage?
the size of the phage head
Lambda phages are commonly used int he construction of what?
genomic libraries
Lambda DNA has ends that are called what? And why?
Cos ends and they are called this because it means “cone size ends” referring to the shape of the DNA phage head.
What are cosmids?
Cosmids are vectors for cloning large DNA fragments. They act as both a phage and plasmid.
WHat specific parts does a cosmid contain of both a plasmid and a phage?
From a typical lambda phage the cosmid contains cos sites(sticky ends) that allows the DNA to be packaged into the phage heads.
From a plasmid the cosmid also contains a plasmid origin of replication.
Can the cosmid particles replicate as phages?
No because almost all of the phage DNA has been removed, but they do remain infectious
How do cosmids infect a bacterium?
They infect a bacterium by carrying in the foreign DNA to be cloned and replicated in the bacterium as a plasmid would replicate since they contain the plasmid origin of replication.
WHat are M13 phage vectors?
M13 is a long filamentous phage
WHat is the genome of the M13 phage composed of?
single stranded DNA
What is foreign DNA cloned into M13 received as? And how is this advantageous?
Single Stranded DNA. It is advantageous in site directed mutagenesis and in DNA sequencing.
When M13 infects bacterial cells its DNA is converted into what form of DNA and what is this form called?
It is converted into double stranded form of NDA and is called RF —> “replicated form” the form of M13 DNA used for cloning
What are phagemids?
Phagemids have both characteristics of phages and plasmids and are capable of producing single stranded DNA.
What is an often used phagemid?
pBluescript (pBS)
What characteristics does pBS have?
- an MCS inserted into the lacZ’ gene
2. Origin of replication of single stranded phage f1 which is related to M13
Why must pBS have and f1 helper phage?
Because the f1 helper phage supplies the needed single stranded DNA components
