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1
Q

how is genetic code deciphered?

A

DNA -> transcription -> mRNA -> translation -> polypeptide

2
Q

DNA (and RNA) notation

A
  • the sequence of one strand of DNA dictates the sequence of the other strand
  • if only one strand is show, 5’ is to the left unless otherwise noted
  • if only one strand is shown the DNA is assumed to be double stranded unless otherwise noted
3
Q

translation

A

proteins are synthesized by ‘reading’ mRNA

-tRNAs, guided by mRNA, align amino acids for peptide bond formation in the ribosome

4
Q

DNA is collinear with encoded protein

A

approach:

  • isolate many mutants of one gene
  • map the mutants to establish position within gene
  • isolate mutant proteins, determine amino acid sequence
  • linear order of DNA mutations correlates with linear order of amino acid changes
5
Q

how many different amino acids could be specified by a two letter code?

A

16; 4^2

6
Q

codons are triplets

A
  • use Phage T4 rll mutants to define the size of a codon
  • many ‘frameshift’ mutants were isolated
  • combining 3 different mutations with the same sign (+ or -) can yield rll+
7
Q

deciphering the genetic code

A

basic approach:

  • synthesize RNA of known sequence
  • translate the RNA into protein (in vitro)
  • determine the sequence or composition of protein
8
Q

nonsense codons

A

“stop” codons, ends a sequence of amino acids

  • UAA
  • UAG
  • UGA
  • amber mutants
  • truncated proteins end before an amino acid whose codon differs from UAG at one position
9
Q

combination of +1 and -1 mutants

A

yield wildtype