10/4/2023 0 Comments Transcription translation steps![]() ![]() A DNA molecule in a human chromosome can be up to 250 million nucleotide-pairs long in contrast, most RNAs are no more than a few thousand nucleotides long, and many are considerably shorter. In addition, because they are copied from only a limited region of the DNA, RNA molecules are much shorter than DNA molecules. Thus, the RNA molecules produced by transcription are released from the DNA template as single strands. Instead, just behind the region where the ribonucleotides are being added, the RNA chain is displaced and the DNA helix re-forms. Unlike a newly formed DNA strand, the RNA strand does not remain hydrogen-bonded to the DNA template strand. Transcription, however, differs from DNA replication in several crucial ways. It is not uncommon, however, to find other types of base pairs in RNA: for example, G pairing with U occasionally.ĭNA transcription produces a single-stranded RNA molecule that is complementary to one strand of DNA. ![]() Since U, like T, can base-pair by hydrogen-bonding with A ( Figure 6-5), the complementary base-pairing properties described for DNA in Chapters 4 and 5 apply also to RNA (in RNA, G pairs with C, and A pairs with U). It differs from DNA chemically in two respects: (1) the nucleotides in RNA are ribonucleotides-that is, they contain the sugar ribose (hence the name ribo nucleic acid) rather than deoxyribose (2) although, like DNA, RNA contains the bases adenine (A), guanine ( G), and cytosine (C), it contains the base uracil (U) instead of the thymine (T) in DNA. Like DNA, RNA is a linear polymer made of four different types of nucleotide subunits linked together by phosphodiester bonds ( Figure 6-4). The information in RNA, although copied into another chemical form, is still written in essentially the same language as it is in DNA-the language of a nucleotide sequence. The first step a cell takes in reading out a needed part of its genetic instructions is to copy a particular portion of its DNA nucleotide sequence-a gene-into an RNA nucleotide sequence. Portions of DNA Sequence Are Transcribed into RNA ![]()
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