Genetic Code and Translation

mRNA is the code (recipe?) for making a protein

Enzyme called the ribosome reads the base sequence of RNA, makes a protein

Protein

-          polymer made of amino acids linked together (20 common amino acids)

-          has two distinct ends

o       N (amino terminal) end

o       C (carboxy terminal) end

-          Ribosome reads mRNA 5’ to 3’ and produces protein from N end to C end

By radioactivity in the 50s, researchers found that proteins are synthesized in the nucleus and that some RNAs (mRNAs) travel from nucleus to cytoplasm.  So mRNAs convey info from nucleus to cytoplasm.

The Genetic Code

-          somehow a sequence of nucleotides specifies a sequence of amino acids in a protein

-          how many nucleotides/amino acid?

o       If 1nt, could only specify 1aa

o       If 2nt, could only specify 4²=16 amino acids

o       If 3nt, can specify 4³ = 64 different combinations

-          What sequence of nt specifies what amino acid?

o       Nirenberg experiment UUU=Phe

§         In vitro translation system

o       Khorana exps Fig.8.7

-          The Genetic code (Fig.8.3)

o       Universal (almost!)

o       Triplet codons

o       Nonoverlapping

o       Degenerate

o       initiation codon

o       Stop codons

o       Open reading frame

Frameshifting

-          insertions or deletions of 1nt, 2nt, or any number that isn’t a multiple of 3nt causes this

Point mutations

Nonsense mutations

Study Questions

I, 3,4,56,7,11,13,15a,