Translation is the process that takes the information passed from DNA as messenger RNA and turns it into a series of amino acids bound together with peptide bonds. It is essentially a translation from one code nucleotide sequence to another code amino acid sequence. The ribosome matches the base sequence on the mRNA in sets of three bases called codons to tRNA molecules that have the three complementary bases in their anticodon regions.
Those mRNA letters are called a codon, and each codon codes for a different amino acid. And eventually those amino acids are all joined together to assemble a protein. Christopher P. Austin, M. DNA polymerases have proofreading activity, and a DNA repair enzymes have evolved to correct these mistakes. Occasionally, mispairs survive and are incorporated into the genome in the next round of replication.
These mutations may have no consequence, they may result in the death of the organism, they may result in a genetic disease or cancer; or they may give the organism a competitive advantage over its neighbours, which leads to evolution by natural selection. Transcription is the process by which DNA is copied transcribed to mRNA, which carries the information needed for protein synthesis.
Transcription takes place in two broad steps. The mechanism of transcription has parallels in that of DNA replication. As with DNA replication, partial unwinding of the double helix must occur before transcription can take place, and it is the RNA polymerase enzymes that catalyze this process.
Unlike DNA replication, in which both strands are copied, only one strand is transcribed. The strand that contains the gene is called the sense strand, while the complementary strand is the antisense strand.
The mRNA produced in transcription is a copy of the sense strand, but it is the antisense strand that is transcribed. The DNA molecule re-winds to re-form the double helix. The pre-messenger RNA thus formed contains introns which are not required for protein synthesis. In alternative splicing, individual exons are either spliced or included, giving rise to several different possible mRNA products.
Each mRNA product codes for a different protein isoform; these protein isoforms differ in their peptide sequence and therefore their biological activity. Several different mechanisms of alternative splicing are known, two of which are illustrated in Figure 6. Alternative splicing contributes to protein diversity - a single gene transcript RNA can have thousands of different splicing patterns, and will therefore code for thousands of different proteins: a diverse proteome is generated from a relatively limited genome.
Splicing is important in genetic regulation alteration of the splicing pattern in response to cellular conditions changes protein expression. Perhaps not surprisingly, abnormal splicing patterns can lead to disease states including cancer.
This process, catalyzed by reverse transcriptase enzymes, allows retroviruses, including the human immunodeficiency virus HIV , to use RNA as their genetic material. The mRNA formed in transcription is transported out of the nucleus, into the cytoplasm, to the ribosome the cell's protein synthesis factory. Here, it directs protein synthesis. The ribosome is a very large complex of RNA and protein molecules.
Figure 7: The ribosome and translation. A ribosome is composed of two subunits: large and small. Figure 8: The major steps of translation. Cellular DNA contains instructions for building the various proteins the cell needs to survive. In order for a cell to manufacture these proteins, specific genes within its DNA must first be transcribed into molecules of mRNA; then, these transcripts must be translated into chains of amino acids, which later fold into fully functional proteins.
Although all of the cells in a multicellular organism contain the same set of genetic information, the transcriptomes of different cells vary depending on the cells' structure and function in the organism. Cell Biology for Seminars, Unit 2. Topic rooms within Cell Biology Close. No topic rooms are there. Or Browse Visually. Student Voices. Creature Cast. Simply Science. Green Screen. Green Science. Bio 2.
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