2nd Semester BOW #1 (transcription, translation, protein synthesis)

BOW 1
Get a picture of transcription, translation or protein synthesis
Explain in as much detail as you can what is happening.




Transcription:    
Transcription may be broken into three major steps: 1) The DNA unwinds and unzips in the area of the gene. Enzymes match RNA nucleotides to the unzipped nitrogen bases of the gene, forming a single strand of mRNA.  2) The strand of mRNA detaches from the gene and goes out of the nucleus through one of the pores in the nuclear envelope. The DNA zips back together and winds back up.  3) The mRNA finds a ribosome where protein synthesis will happen.

Translation  :  Translation involves taking the message that's in the messenger RNA and in a sense decoding the message from the language of nucleic acids to the language of proteins or polypeptides. For translation to happen, the messenger RNA goes to the cytoplasm where it is attached to a cellular structure called a ribosome. Ribosomes are two part molecular assemblies consisting of various proteins plus a special kind of RNA called ribosomal RNA. Ribosomal RNA is involved in catalyzing some of the chemical reactions of translation.
In addition to the ribosome, another kind of RNA called tRNA carries amino acids to the mRNA when it is attached to a particular part of the ribosome's small subunit, called a binding site. A critical feature of mRNA and how it is translated is the fact that each three nucleotides in the mRNA is called a codon and it is the codon that is translated. Thus the sequence of codons corresponds to the sequence of amino acids in the polypeptide. You will see that the tRNA molecules have a set of three nucleotide bases at one end that are complementary to a corresponding codon. The bases on the tRNA are called the anti codon. This is critical because the anti codons make the connection between the codons and the correct amino acids that go with each codon.

Protein synthesis:  The first step in protein synthesis is the transcription of mRNA from a DNA gene in the nucleus. At some other prior time, the various other types of RNA have been synthesized using the appropriate DNA. The RNAs migrate from the nucleus into the cytoplasm.   In the cytoplasm, protein synthesis is actually initiated by the AUG codon on mRNA. The AUG codon signals both the interaction of the ribosome with m-RNA and also the tRNA with the anticodons (UAC). The tRNA which initiates the protein synthesis has N-formyl-methionine attached. The formyl group is really formic acid converted to an amide using the -NH₂group on methionine.