Download Neuraspora crassa


Transcription – DNA
making RNA

Translation – RNA
making Protein; (aka
protein synthesis)
Archibald Garrod (1909) –
determined that genes
dictate phenotype
through enzymes
 His ideas stem from his
observations of an
inherited disease –
Alkaptonuria where
affected individuals have
a defective enzyme that
does not break down two
amino acids as aresult the
produce Alkapton which
makes their urine to turn
black




George Beadle and
Edward Tatum (1940’s) –
American geneticists
working with bread mold
(Neuraspora crassa)
Strains of nutritional
mutants helped them
prove that specific
enzymes were need to at
specific steps in metabolic
pathways
“One Gene/One Enzyme”





DNA making RNA
Takes place in the
nucleus
One main enzyme –
RNA Polymerase
RNA is transcribed in
a 5’ to 3’ direction
Only ONE strand of
DNA is transcribed at
a time
Initiation – DNA separates and ONE strand serves as a
template for the RNA; RNA polymerase binds to the
promotor region of DNA
Elongation -RNA elongates as complementary RNA
nucleotides match up with DNA
nucleotides are added in a 5’ to 3’ direction; U is
substituted for T
As RNA polymerase moves forward, RNA releases from
DNA; and DNA rewinds
Termination – RNA polymerase reaches the terminator
sequence & releases the DNA and RNA; DNA rewinds;
RNA is ready for the next step





Promoter – specific nucleotide sequence in
DNA, located @ the start of a gene; binding
site for RNA polymerase; where transcription
begins
Transcription region – segment of DNA that
is made into RNA; the gene
Terminator – sequence of nucleotides in
DNA that marks the end of a gene. It
signals
Sense Strand – the strand of DNA that is
transcribed into DNA
Nonsense Strand – the strand of DNA this in
not transcribed
Universal – shared by all organisms; the
set of rules giving the correspondence
between nucleotide triplets (codons)
and amino acids in proteins
 Codes for Amino acids –

› Building blocks of a proteins
› 20 different amino acids
› Coded for by groups of three nucleotide
bases - codons

Codons – groups of three consecutive
nucletides in mRNA that specifies a particular
amino acid or a polypeptide termination
signal
› AUG – start codon; indicates the starting point for
translation; also codes for methionine
› Stop codons – don’t code for an amino acid instead
it signals the end of translation