from RNA to protein: protein synthesis

from RNA to protein:

protein synthesis

Genetic Code

• there are 20 amino acids found in proteins

• the order of amino acids in a protein is determined by the order of nucleotides in

DNA

each amino acid is encoded by

three-nucleotide sequences on DNA called codons

• in total, there are 64 codons (genetic code)

• 61 codons represent amino acids and 3 codons cause the termination of translation

(stop codons)

The Nobel Prize in Physiology or Medicine 1968

"for their interpretation of the genetic code and its function in protein synthesis"

Robert W. Holley Har Gobind Khorana Marshall W. Nirenberg

1/3 of the prize 1/3 of the prize 1/3 of the prize

USA USA USA

Cornell University

Ithaca, NY, USA University of Wisconsin

Madison, WI, USA

National Institutes of Health

Bethesda, MD, USA b. 1922

d. 1993 b. 1922

d. 2011 b. 1927

d. 2010

• the same amino acid may be encoded by multiple codons (except methionine and tryptophan)

degeneracy of the genetic code

• codons specifying the same amino acids are called

“synonymous” codons

• in synonymous codons, generally the first two nucleotides are the same but the third nucleotide

differs

• genetic code lacks punctuation

the code is read sequencially three bases at a time

• genetic code is non-overlapping

Open Reading Frame ORF

a DNA sequence consisting of codons that can be translated into amino acids starting with an initiation codon and ending with a termination

codon

genetic code is universal

Aminoacyl-tRNA synthetases

enzymes that attach amino acids to tRNAs each tRNA synthetase is specific for a

single amino acid

translation

• initiation

• elongation

• termination

RF1

• UAA

• UAG

RF2

• UAA

• UGA

in prokaryotes, translation can start before the termination of transcription