How does dna unwind during transcription

Nature Milestones in Gene Expression 8 Lee, J. Methods in Molecular Biology , 23—37 Logan, J. A poly A addition site and a downstream termination region are required for efficient cessation of transcription by RNA polymerase II in the mouse beta maj-globin gene. Proceedings of the National Academy of Sciences 23 , — Nabavi, S. Restriction Enzymes. Genetic Mutation. Functions and Utility of Alu Jumping Genes. Transposons: The Jumping Genes. DNA Transcription. What is a Gene? Colinearity and Transcription Units.

Copy Number Variation. Copy Number Variation and Genetic Disease. Copy Number Variation and Human Disease. Tandem Repeats and Morphological Variation.

Chemical Structure of RNA. Eukaryotic Genome Complexity. RNA Functions. Citation: Clancy, S. Nature Education 1 1 If DNA is a book, then how is it read? Aa Aa Aa. The genetic code is frequently referred to as a "blueprint" because it contains the instructions a cell requires in order to sustain itself. We now know that there is more to these instructions than simply the sequence of letters in the nucleotide code, however. For example, vast amounts of evidence demonstrate that this code is the basis for the production of various molecules, including RNA and protein.

Research has also shown that the instructions stored within DNA are "read" in two steps: transcription and translation. In some cases, the RNA molecule itself is a "finished product" that serves some important function within the cell. Often, however, transcription of an RNA molecule is followed by a translation step, which ultimately results in the production of a protein molecule.

Visualizing Transcription. Figure 1. The Transcription Process. Transcription Initiation. Figure 3. Triplets are groups of three successive nucleotide bases in DNA. Codons are complementary groups of bases in mRNA. Transcription takes place in three steps: initiation, elongation, and termination. The steps are illustrated in Figure 2. Figure 2. Transcription occurs in the three steps—initiation, elongation, and termination—all shown here. Like DNA replication, transcription proceeds in the 5' to 3' direction ie the old polymer is read in the 3' to 5' direction and the new, complementary fragments are generated in the 5' to 3' direction.

Transcription is divided into 3 stages: initiation, elongation and termination. Your Account. Author Profile. Show caption. 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. Each three-base stretch of mRNA triplet is known as a codon , and one codon contains the information for a specific amino acid.

This tRNA molecule carries an amino acid at its 3'-terminus, which is incorporated into the growing protein chain. The tRNA is then expelled from the ribosome. Figure 7 shows the steps involved in protein synthesis. Transfer RNA adopts a well defined tertiary structure which is normally represented in two dimensions as a cloverleaf shape, as in Figure 7.

The structure of tRNA is shown in more detail in Figure 8. The reaction of esters with amines is generally favourable but the rate of reaction is increased greatly in the ribosome.