3.5 Transcription Translation 7.4 Translation Part 2

Genes and Polypeptides

Polypeptides are long chains of amino acids. This chain consists of 20 different types of amino acids. In order to create this sequence a specific polypeptide must be linked in in a precise order. The information to create these chains are stored in coded form. This coded form is decoded during the process. The two stages in this process are called transcription and translation.

Differences Between DNA and RNA

Both structures are long chains of nucleotides, which consists of a sugar, a base and a phosphate. The DNA, however has two strands crewing a double helix, whereas the RNA only has one strand. The sugar in each nucleotide is also different. In DNA the sugar is called deoxyribose and in RNA the sugar is called ribose. In addition the bases are different. The bases in DNA are A, C, G and T. In RNA the bases are A, C, G and U.

Transcription

In this process a copy of one of the DNA strands is made. This copy is called RNA. The RNA transfers the information to make a polypeptide out into the cytoplasm making it called mRNA. This copying of the base order of a gene by using RNA is called transcription. Since RNA is used uracil paris with adenine because RNA does not have thymine.

The image above shows the three steps of transcription initiation, elongation and termination.In initiation the DNA polymerase begins to separate the two DNA strands. In elongation the mRNA is produced and in termination the mRNA is released.

Translation

In translation both the mRNA and tRNA are used. The genetic code that is being translated comes in triplets, three codes = one amino acid.

The image above shows the steps of translation. First the tRNA that is charged attaches to the mRNA where the small ribosomes subunit is already attached. The tRNA becomes charged because it was attached earlier to an enzyme where it was assembled with its amino acid. Then the larger subunit comes over the tRNA so that it is in the P (middle) position in the ribosome. In the strand below the next tRNA is entering the large subunit. It enters into the A (entry) position and the amino acids are transfered to the next tRNA. Then the old tRNA moves into the E (exit) position and is released and the new tRNA moves into the P position. The old tRNA has just gone through the cycle EBME (enter, bond, move, exit). This process continues until the there is a stop codon, which is shown in the last portion of the image. The stop codon enters and the large, small subunit and polypeptide are released, ending the process.