Bio 99 Lecture 3 + Reading 3

What is a gene?

"All the stuff required for the end product"

Genes result in the end production of polypeptides.

Gene ---> pre-mRNA (unprocessed) ---> mRNA (spliced) during mRNA processing

What is an auxotroph?

An auxotroph is a mutant that is defective in the ability to synthesize a specific compound needed for growth.

Example: Arginine auxotroph

Give a rough outline of how genome sequencing first occurred.

Griffith Experiment:

Revealed that a "transformation principle" was possible---a nonlethal strain could be transformed in the presence of a lethal one.

---transformation would be confirmed by experiments done by Avery, McLeod, McCarty, and Avery & Chase

Avery's Transformation Experiment

Nuclease: cuts DNA---treating with nuclease would result in the mouse living, as the lethal DNA is degraded

Ribonuclease: Dies, lethal DNA is still present

Protease: Dies --- lethal DNA is still present

Destroyed specific cellular components to help confirm DNA as component involved in transformation.

Hershey & Chase Experiment

-Confirms that DNA is the genetic material, rather than protein.

Viruses made of two components: Protein outer shell and DNA.

Individual components are radioactively tagged, then allowed to infect bacteria.

Since the radioactive phosphorus was detected in the pellet instead of the sulfur, DNA was passed on and is the genetic material.

Transformation

Incorporation of foreign DNA from outside the cell.

George Beadle, Edward Tatum

"One gene, one polypeptide"

Looked at auxotrophs to come to the conclusion of "one gene, one enzyme" (which is not necessarily 100% true, see new phrase at top)

---Looking at when auxotroph is deficient of product, but buildup of precursor. Specific block, so specific gene responsible for production of enzyme (more correctly, polypeptide)

Genotype vs Phenotype

URA3: involved in uracil synthesis

LEU2: involved in leucine synthesis

Knock out URA3 or LEU2, then grow on media lacking uracil or leucine.

- would die

Knock out LEU2, then grow on media WITH leucine?

-lives

Just like in research, fam.

Genotype vs Phenotypes:

What is a selection marker?

Used to distinguish between cells that have gene of interest vs those without. Especially useful for looking at transformation.

ex: antibiotic resistance genes such as NeoR (which results in the ability to break down Neomycin, an antibiotic)

You decide to knock out LEU2 by replacing it with NeoR. What type of media will you plate your teast on to obtain the leu2 strain? Neomycin is an antibiotic.

You will need media with leucine present (LEU2 was knocked out, so yeast cannot produce leucine) and neomycin in order to select for those that specifically and successfully picked up the selection marker, NeoR (antibiotic resistance).

Components of a Gene

Exons

Protein Coding DNA

Promoter

Introns

3' UTR (Downstream region)

What is a genome?

The sequences that constitute an organism.

-chromosomal

-could be RNA or DNA

-contains protein/RNA coding sequences as well as non-coding sequences.