Lecture 31 Transcription notes

Lecture 31 Transcription notes - Lecture 31 Transcription...

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Lecture 31 Transcription and RNA Processing Campbell 6 th Ed. 304-313; 7 th Ed. 311-319. Fig. from Chap 19 on Alternative RNA splicing (Fig. 19.8, 7 th ed.) & the relevant text paragraph RNA You remember that RNA is similar to one strand of DNA, except that it has ribose instead of deoxyribose as its sugar, and the base uracil (U) instead of T. Importantly, DNA is always (except in unusual cases such as in some viruses) double-stranded, and forms a double helix. In contrast, though RNA can base-pair, it does NOT form a double helix. There are several different types of RNA, with different functions. The three most familiar are mRNA (messenger RNA), (discussed later in the lecture), tRNA (transfer RNA), and rRNA (ribosomal RNA) (both discussed next lecture). However, cells also contain other types of RNA. In many cases, RNA is present in large complexes, together with protein molecules. Ribosomes are an example. Another example is telomerase (discussed last time). We’ll see another example (snRNPs and the spliceosome) later in the lecture. The functions of several types of RNA (including those in telomerase and the spliceosome) have only been discovered in the last 20-30 years. As an extreme example microRNAs , very short RNA molecules that regulate gene expression, were only discovered in 1998. However, it is already clear that they are extremely important. In fact, this year’s Nobel Prize in Medicine was awarded for the discovery of microRNA. All RNAs are made by the same mechanism, called transcription , that we’ll discuss today. Transcription Transcription is synthesis of RNA by inserting ribonucleotide triphosphates (abbreviated NTPs) into a growing chain, by base-pairing them with a strand of DNA that's used as a template. (U in RNA base-pairs with A in DNA). The enzyme that does this is called RNA polymerase . There are several different RNA polymerases, but you don’t need to know that for this course. I’ll just refer to “RNA polymerase”, meaning all of them. The mechanism of transcription is very similar to that of DNA synthesis. However, there’s an important difference. Each RNA molecule comes from transcription of ONE GENE. Furthermore, not all genes are transcribed at once. This is very different from DNA replication, where the entire DNA molecule is copied. Instead, we pick and choose which genes to transcribe at any time. To choose which genes to transcribe, we use a promoter . A promoter is a DNA sequence close to a gene. Each gene has its own promoter. Binding of RNA polymerase and other proteins called
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This note was uploaded on 09/19/2009 for the course BIO 202 taught by Professor Dean during the Spring '08 term at SUNY Stony Brook.

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Lecture 31 Transcription notes - Lecture 31 Transcription...

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