Biology Lecture - 37 - Second Step: Translation -from RNA transcript=mRNA

IV. Several ribosomes are often attached to and translating the same mRNA.

A. As soon as the initial portion of mRNA has been translated by one ribosome, and the ribosome has begun to move down the mRNA, another ribosome attaches to the mRNA. B. The entire complex is called a polyribosome and greatly increases the efficiency of translation.

B. Elongation - is the protein synthesis step in which a polypeptide increases in length one amino acid at a time

A. Elongation requires elongation factors, which facilitate the binding of tRNA anticodons to mRNA codons at a ribosome. B. tRNA come in and leave and keep going which make it longer

III. Function of a Ribosome

A. Join one amino acid to another amino acid as a polypeptide

A. Initiation - is the step that brings all the translation components together.

A. Proteins called initiation factors are required 1. a small ribosomal subunit attaches to the mRNA in the vicinity of the start codon (AUG). 2. The first or initiator tRNA pairs with this codon. Then, a large ribosomal subunit joins to the small subunit B. A ribosome has three binding sites for tRNAs. 1.E (for exit) site - initiator tRNA leaves 2.second is the P (for peptide) site - initiator tRNA comes 3.the third is the A (for amino acid) site. - for the next tRNA

II. The Role of Ribosomal RNA -

A. Ribosomal RNA (rRNA) is produced from a DNA template in the nucleolus of a nucleus B.The rRNA is packaged with a variety of proteins into two ribosomal subunits, one of which is larger than the other. C. Then the subunits move separately through nuclear envelope pores into the cytoplasm, where they combine when translation begins. D. Ribosomes can remain in the cytoplasm, or they can become attached to endoplasmic reticulum.

C. Termination

A. Termination of polypeptide synthesis occurs at a stop codon—that is, a codon that does not code for an amino acid. B. Termination requires a protein called a release factor, which can bind to a stop codon and also cleave the polypeptide from the last tRNA. 1.After this occurs, the polypeptide is set free and begins to take on its three-dimensional shape

I. Codon(mRNA) and Anti-codon(tRNA)

A. The opposite end of the molecule contains an anticodon, 1.a group of three bases that is complementary to a specific mRNA codon. *The opposite of tRNA(anti-codon) links to mRNA codon 1.aminoacyl-tRNA synthetases helps it attach correctly

V. Translation Requires Three Steps 1. Initiation, elongation and termination

A.Initiation B.Elongation C.termination

Translation - The ribosome(tRNA) interpreting the RNA(mRNA) message into the exact sequence of amino acids and assembling(rRNA) them into a protein

I. Codon and Anti-codon II. The Role of Ribosomal RNA III. Function of a Ribosome