Topic 3 Flashcards
Why is bacteria a could option to study genetics?
Simple one-celled organism, haploid, fast growing, asexual, easy to separate/select/store/mutate.
What is a major way we use bacteria?
Making insulin using E.Coli–>Cheaper
What is the best studied bacteria species?
E.Coli
Describe the growth of bacteria.
Exponential growth–> Stationary growth–> Death
What are the morphological differences in the bacteria during different times of growth?
Bacteria in stationary growth is thick and not permeable during this time. During exponential growth, the cell wall is thinner and more permeable to outside things. This stage is optimal to deliver foreign DNA into the bacterial cell.
How do you plate bacteria?
Take the suspension of bacterial cells and spread it on to a petri plate with agar gel. Incubate the plate for 1-2 days Visible colonies will appear of a clone corresponding to the single cell. (Colonies-many cells that are from a single cell and therefore have the same DNA content)
What does wild type mean?
A strain, gene, or characteristic that prevails among individuals in natural conditions, as distinct from an atypical mutant type.
Do bacteria cells typically have any essential amino acids?
No, because they can synthesize virtually any amino acid.
What happens when you have a mutant strand of bacteria?
Some amino acids can not be synthesized by the bacterial cells. Ex.) Arg A+ (wild type) Arg A- (mutant strand), His A-
-Could also be Lac- which would mean it does not have a lac operon therefore you should not give it lactose. So provide, Arginine, provide Histidine, but don’t provide lactose…provide glucose instead.
Exam question: What does Arg-, His-, Lac- mean?
Need to give bacteria arginine, histidine, but not lactose because no lac operon.
Describe mutant isolation using mutagens.
Bacterial cells are introduced to mutagens to induce mutations. They are then grown in conditional cultures and then you can select mutant colony.
How does the auxotrophic mutant selection work?
Colonies are placed in a rich medium which is treated with nutrients needed for the wild type to grow and has all kinds of amino acids that could be needed for mutant strands. Bacterial cells at this point have already been treated with mutants and probably already have gene mutations in the different colonies. The exact colonies are unknown though. Next you prepare two plates-1 that is minimum medium (only supports non-mutated bacteria) and the other is minimal plus arginine. Each prepared plate is stamped from the master plate. Colonies that present only in the Arg- strand are mutant strands. This is called conditional culture.
What are conditional lethal mutants?
They are mutants with a change in genetics material which kill the organism, but only when it faces certain environmental conditions. Otherwise, the organism survives and grows.
Give an example of conditional lethal mutants.
GroEL and GroES-If these are mutated, the bacteria can not grow in abnormally high temperatures.
Describe resistant mutant isolation.
Grow colonies in a master plate. Stamp the master plate on to a replica plate and a replica containing an antibiotic. Incubate the plates and in the replica plate without antibiotics, all colonies grow. The plate with antibiotics only has antibiotic resistant strands grow.
Describe bacterial DNA.
It is located in the nucloid (in the cytoplasm), anchored, & supercoiled to occupy less space.
problem Why is bacterial DNA circular?
Bacterial DNA does not have telomerase and therefore can not fix the end replication
What are the 3 ways bacteria exchange genetic material?
Transformation, transduction, conjugation
What was the Griffith experiment of transformation?
There is a R strand (rough) and S strand (smooth) form of Pneumococcus bacteria. The S strand was injected into the mouse and the mouse died. The R strand was injected and the mouse survived. He heat-fixed the S strand and the mouse survived. He then heat-fixed the S cells and mixed them with R cells. This killed the the mouse. This demonstrated transformation-The genetic material of one cell (frequently a dead cell) may enter another cell through the cell-cell contact, changing its phenotype.
How has the definition of transformation expanded?
Anytime a bacterial cell gains genetic information from outside of the cell, whether the other cell is dead or not, is from the environment, floating, etc. it is all transformation. Bacterial cells acquiring genetic info from the environment.
What type of genetic transfer is putting a plasmid into bacterial cell (Cell based DNA cloning)?
Transformation
Explain the experiment for the discovery of conjugation.
Bacterial cells labeled A & B and both requiring certain amino acids were grown and transferred into a minimal medium where they each died. They were then mixed together and transferred to a minimal medium where prototrophic colonies were created.
