TRANSLATION

Building a Protein

Central Dogma of Molecular Biology

mRNA translated to polypeptide/protein

Central Dogma of Molecular Biology

mRNA translated to polypeptide/protein

nucleotide sequence

amino acid sequence

The Genetic Code

The Genetic Code- Triplet

CODON

3 bases specify 1 amino acid

- Non-overlapping

each base is only part of one codon

e.g. AUCAGUCUA AUC, AGU, CUA

not AUC, UCA, CAG, AGU, GUC, UCU, CUA

The Genetic Code- Continuous

not punctuated no additional chemical groups designate the start or end of a codon

However, it contains directions for starting or stopping translation:

AUG (Start) UAA (Stop)UAG (Stop)UGA (Stop)

The Genetic Code- Universal

All organisms use the same genetic code.

All life on earth evolved from a common ancestor.

Recombinant DNA Technology Green Fluorescent Mice!!!

The Genetic Code- Redundant…

Some amino acids were specified by more than one codon.

… But not ambiguous

No two amino acids are coded for by the same codon.

- Degenerate (WOBBLE EFFECT)Different codons coding for the same amino acid

differ only by the base in the 3rd position.

protection vs. mutation

TRANSLATION

mRNA

tRNA (carrying amino acids)

ribosomes

+ ATP

TRANSLATION

Stages:

1) INITIATION

2) ELONGATION

3) TERMINATION

TRANSLATION: Initiation

- mRNA binds to rRNA in the small ribosomal unit

- AUG (Start) attracts initiator tRNA carrying fmet

INITIATION COMPLEX

TRANSLATION: Elongation

- large ribosomal sub-unit attaches to the initiation complex

- next codon bonds to its complementary anticodon

- enzyme joins two amino acids together in a peptide bond

- first tRNA is releases as ribosome moves on to the next codon

TRANSLATION: Termination- elongation halts when “Stop” codon is reached

binding of release factor- last tRNA released- mRNA & polypeptide released & ribosomal sub-units

separate

Polyribosomes

mRNA can be translated by several ribosomes at a time.

Time for practice…

- From which labeled structure is structure D made? Identify.- Identify structure F. What does it specify?- What is structure E? What does it specify?

- What would happen to structure F if structure C were deleted?- What effect would the deletion of structure C have on the

process that occurs in step Y?