Transcription and Translation:  Codons

An auxotroph is a nutritional mutant unable to synthesize certain essential molecules from minimal ingredient.

The Theory

Theory:	One gene-One enzyme          One gene-One protein        One gene-One polypeptide
Explanation:	A gene transcribes an enzymeA gene transcribes a proteinA gene transcribes a polypeptide

Comparison of Prokaryotic and Eukaryotic methods of Transcription and Translation

Prokaryotes	Eukaryotes
transcription and translation are grouped together:  as messenger RNA (mRNA) is produced ribosomes start coding at the leading strand	transcription is in the nucleus and translation is in the cytoplasm thus allowing RNA processing

The Triplet Code is comprised of 3 mRNA nucleotides in sequential order are called codons.  Sixty-four codons code for 20 amines.

DNA: Template strand

For each gene, only one of the 2 DNA strands is transcribed, the template.  mRNA is complementary to the template.

DNA: Other strand provides instructions for making a new template strand during DNA replication.

DNA: Important

A given DNA strand can be a template in some regions of the DNA molecule; in other regions, the complementary strand may function as the template.

The Reading frame is the correct non-overlapping sequence and grouping of mRNA to form the correct codons.

UAA and UAG are the codons that stop transcription in humans (exceptions in chloroplasts and mitochondria; codes for glutamine in the paramecium)

Transcription unit

This is all the DNA that was transcribed between initiation and termination.  In eukarotes it is the equivalent of a single gene.  In prokaryotes it can be several genes coding for proteins with similar functions.

Next:  "RNA Polymerase."