Question

Define the following terms as they pertain to translation (see diagram in back)  

a. mRNA b. anticodon c. polysome d. ribosomal subunits e. rRNA f. Start and stop codons g. tRNA 

Answer 1

(a)

Messenger RNA (mRNA) is a subtype of RNA. An mRNA molecule carries a portion of the DNA code to other parts of the cell for processing. mRNA is created during transcription. During the transcription process, a single strand of DNA is decoded by RNA polymerase, and mRNA is synthesized. Physically, mRNA is a strand of nucleotides known as ribonucleic acid, and is single-stranded.

In translation mRNA sequence is used as a template to assemble—in order—the chain of amino acids that form a protein.

(B)Anticodons are sequences of nucleotides that are complementary to codons. They are found in tRNAs, and allow the tRNAs to bring the correct amino acid in line with an mRNA during protein production.

(C)polysome- a cluster of ribosomes that held together by a strand of messanger RNA which each is translating.

More than one ribosome can translate mRNA at. One time making it possible to produce many polypeptides simultaneously from single mRNA

(D)A ribosome is made up of two basic pieces: a large and a small subunit. During translation, the two subunits come together around a mRNA molecule, forming a complete ribosome. The ribosome moves forward on the mRNA, codon by codon, as it is read and translated into a polypeptide . Then, once translation is finished, the two pieces come apart again and can be reused.

(F) Start codon -The codon AUG is called the START codon as it the first codon in the transcribed mRNA that undergoes translation. AUG is the most common START codon and it codes for the amino acid methionine in eukaryotes and formyl methionine in prokaryotes. During protein synthesis, the tRNA recognizes the START codon AUG with the help of some initiation factors and starts translation of mRNA.

Stop codon -

There are 3 STOP codons in the genetic code - UAG, UAA, and UGA. These codons signal the end of the polypeptide chain during translation. These codons are also known as nonsense codons or termination codons as they do not code for an amino acid.

The three STOP codons have been named as amber (UAG), opal or umber (UGA) and ochre (UAA)