Protein and Translation

Central Dogma of Biology

• _____________________________________:- Transcription: The decoding of DNA into

mRNA- Translation: The decoding of an mRNA

message into a polypeptide chain

Proteins

• Proteins are made of: ____________________• A few ___________ joined together are called

polypeptide chain:- Each poly peptide contains a combination of

any or all of the 20 different amino acids- The property of the protein is determined by

the order of the amino acids

Translation

• The “language” of the mRNA instruction is called the genetic code

• How can a code with just 4 letter (A,U,C,G) carry instruction for 20 amino acid?

- The genetic code is read 3 letters at a time- Eg. UCGCACGGUThis sequence would be read 3 bases at a time:

UCG-CAC-GGU

Translation• Each 3 letter “word” in mRNA is know as a

codon:- A codon consist of 3 consecutive nucleotides

that specify a single amino acid- eg. Using codons, the sequence

UCG-CAC-GGU would be translated into:

Serine – Histidine – Glysine

Problems

• Transcribe the following DNA sequence into mRNA:

T A C A A G G G T C A C A T C

• Translate the above mRNA into protein:

Codons• Some amino acids can be specified by more than one

codone.g. 6 different codons specify the amino acid

leucine • One codon can only code for one amino acid

e.g. the codon CAG can only code for the amino acid Glutamine• The codon AUG, code for ____________, serves as the

start codon• There are 3 “Stop” codon that do not code for any

amino acid

Ribosome

• Before transformation can occur, mRNA must be transcribed from DNA in the nucleus and released into the cytoplasm

• Translation happens in the ribosomes in the cytoplasm

tRNA• tRNA: transporting specific amino

acid to the ribosome to be added on the growing polypeptide chain

• Each tRNA has:- An amino acid attach to one end- A region of 3 unpaired bases at

the other end (anticodon): the bases on the anticodon are complementary to the mRNA codons

E.g. the anticodon base for AUG would be UAC

Translation

• The ribosome joins the two amino acids on the two adjacent tRNA and moves along the mRNA binding more amino acids to the peptide chain