Bacterial transformation. the genetic code is universal. All living things use the same genetic code Each codon corresponds to a specific amino acid, regardless of the species
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All living things use the same genetic code
Each codon corresponds to a specific amino acid, regardless of the species
We can take a gene from one species and insert it into a different one and still get the same protein (same amino acid sequence)
A plasmid is a small, circular piece of double-stranded DNA
In addition to the nucleoid DNA, E. coli bacteria contain small circles of DNA called plasmids;
Plasmid DNA contains coding sequences (genes) which are expressed by the bacterium (the bacterium produces the corresponding proteins ;
Often, the genes carried in plasmids provide bacteria with genetic advantages, such as antibiotic resistance.
The cell that receives the piece of DNA (plasmid) is called transformed cell
Transformation rarely occurs naturally;
By subjecting bacteria to certain artificial conditions, we can enable many of them to take up DNA;
When bacterial cells are in a state in which they are able to take up DNA, they are referred to as competent
Color marker gene
When a bacterium divides, all of the plasmids contained within the cell are copied;
Each daughter cell receives a copy of each plasmid;
This gene is useful to “select” the transformed cells (cells that contain the plasmid)
In the presence of antibiotic ……..
Bacterium without plasmid
(plasmids contain gene for antibiotic resistance)
In the presence of antibiotic ……..
Bacterium with plasmid
Transformed cells contain the plasmid with ampicillin resistance gene
Non-transformed cells do not contain the plasmid
Ampicillin is a member of the penicillin family of antibiotics;
Like other antibiotics, it works by keeping a bacterium from building a cell wall;
Without the cell wall, the bacterium cannot live (the membrane bursts)
Ampicillin (like other penicillin antibiotics) contains a chemical group called a beta-lactam ring;
Bacteria build cell walls by linking molecules together: beta-lactams block this process.
The ampicillin-resistance gene encodes for a protein called beta-lactamase;
This is an enzyme that destroys the activity of ampicillin by breaking down the beta-lactam ring.
Thus, bacteria expressing beta lactamase gene can resist the effects of ampicillin and other beta-lactam antibiotics (penicillin);
These bacteria can grow in the presence of ampicillin
galactose + glucose
The beta-galactosidasegene (sometimes called lacZgene) encodes a protein, called beta-galactosidase;
This is an enzyme that normally cleaves the disaccharide sugar lactose into its two constituent sugars, galactoseand glucose.
Color marker gene = beta-galactosidase
However, beta-galactosidasecan also cleave a synthetic analog of lactosecalled X-gal;
X-gal is colorless, but when it is cleaved by beta-galactosidase, one of the products is dark blue;
When bacteria expressing beta-galactosidaseare grown on a agar plate containing X-gal, the enzyme digests X-gal and produces a blue compound;
The colonies will bebright blue
If the bacteria do not produce beta-galactosidase, the colonies will be white