module 7 lec 2 Flashcards
Who cracked the genetic code in 1961?
Marshall Nirenberg and Heinrich Matthaei.
What codon did Nirenberg and Matthaei use to discover phenylalanine?
They used UUU, which codes for phenylalanine.
What other tools did Khorana use to further crack the code?
Khorana used polynucleotides like polydinucleotides, polytrinucleotides, and polytetranucleotides.
What was the outcome of using these polynucleotides?
Researchers could read amino acid sequences and deduce corresponding codons
Was the genetic code fully resolved?
No, there was still some ambiguity in the code.
Who helped Nirenberg resolve the ambiguities in the genetic code?
Philip Leder.
How did Nirenberg and Leder resolve the ambiguities of the genetic code?
hey used trinucleotide mRNAs of known sequence, tRNAs charged with radioactive amino acids, and ribosomes.
What was the role of tRNAs in Nirenberg and Leder’s experiment?
tRNAs were charged with radioactive amino acids to help identify which codons corresponded to which amino acids.
What are nonsense codons?
Nonsense codons are stop codons that signal the end of translation.
How many nonsense codons are there in the genetic code?
There are three nonsense codons: UAA, UAG, and UGA.
What is the role of nonsense codons in protein synthesis?
They terminate translation, causing the ribosome to release the newly synthesized polypeptide.
What do nonsense codons do?
Nonsense codons terminate the polypeptide chain during translation.
What are the three nonsense codons (stop codons)?
The three stop codons are UAA (ochre), UAG (amber), and UGA (opal).
What is another name for nonsense codons?
Nonsense codons are also called stop codons.
What does the 5’ to 3’ direction of mRNA correspond to in polypeptide synthesis?
It corresponds to the N-terminal to C-terminal direction of the polypeptide. and its the rna like strand
Which strand of DNA serves as the template for mRNA?
The template strand of DNA is used to synthesize mRNA.
What is the other strand of DNA called in relation to mRNA?
The other strand is the RNA-like strand, which has the same sequence as the mRNA (except for uracil replacing thymine).
Is the genetic code the same for all organisms?
Yes, the genetic code is almost universal for all living organisms.
Can mRNA from one organism be used to generate protein in another organism?
Yes, translational systems can use mRNA from one organism to generate protein in another.
What are some exceptions to the universal genetic code?
Exceptions include some mitochondrial genomes and certain ciliates.
Where are messenger RNAs made?
mRNAs are made in the nucleus.
Where do messenger RNAs travel after being made in the nucleus?
They travel to the cytoplasm.
What was the role of mRNA originally thought to be?
It was thought to transport DNA information from the nucleus to the cytoplasm as an intermediate molecule.
Where does protein synthesis take place?
Protein synthesis occurs in the cytoplasm.
What enzyme catalyzes transcription?
RNA polymerase catalyzes transcription.
What signals RNA polymerase where to begin transcription?
Promoters signal RNA polymerase where to start.
In which direction does RNA polymerase add nucleotides during transcription?
RNA polymerase adds nucleotides in the 5’ to 3’ direction.
What tells RNA polymerase when to stop transcription?
Terminator sequences signal when to stop transcription.
