3.A.1 DNA and RNA Part IV:Translation

DNA, and in some cases RNA, is the primary source of heritable information. DNA, and in

some cases RNA, is the primary source of heritable information.

The Central Dogma of molecular biology states that the flow of genetic information

in a cell is from DNA to RNA to protein.

Beadle and Tatum developed the “one gene–one enzyme hypothesis,” which states that

the function of a gene is to dictate the production of a specific enzyme. We now call

this the “one gene–one polypeptide hypothesis.”

A gene can also code for RNA molecules that are never transcribed into proteins,

such as ribozymes or tRNA.

Genetic information is encoded as a sequence of nonoverlapping base

triplets, or codons.

Many amino acids have more than one codon (redundancy).

Codons must be read in the correct reading frame for the specified

polypeptide to be produced.

The genetic code is nearly universal, shared by organisms from the simplest bacteria to the most complex animals.

There are many types of RNA. mRNA transcripts carry the genetic information

from the DNA in the nucleus to ribosomes in the cytoplasm.

tRNA molecules bind specific amino acids.

tRNA molecules allow information in the mRNA to be translated to a linear

peptide sequence.

rRNA molecules are the functional building blocks of ribosomes.

Genetic information flows from a sequence of nucleotides in a gene to a sequence of amino acids in a protein.

Translation of the mRNA occurs in the cytoplasm on the ribosomes.

In prokaryotes, there is no nucleus. Transcription and translation occur

together.

Translation is the RNA-directed synthesis of a polypeptide.

The correct amino acid is covalently bonded to the correct transfer RNA (tRNA) with the correct anticodon.

The ribosome has three binding sites:

• The P site• The A site• The E site

Another tRNA brings the next amino acid into the A-site of the ribosome.

A peptide bond forms between the first two amino acids. The tRNA is then

moved from the A-site to P-site and the ribosome moves over one codon.

The first tRNA is released from the E site.

The amino acid is transferred to the growing peptide chain.

The process continues along the mRNA until a “stop” codon is reached.

The process terminates by release of the newly synthesized peptide/protein.