Lecture 31 Transcription Notes

Lecture 31 Transcription Notes - Lecture 31 Transcription....

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Lecture 31 Transcription. 6 th Ed. 304-313; 7 th Ed. 311-319; 368; 8 th Ed. 325-336; 362-363. 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, the 2006 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 . Bacteria have only 1 RNA polymerase, while eukaryotes have at least 3 different ones, for making different kinds of RNA. We’ll focus on the one that makes mRNA, called RNA polymerase II. 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 Transcription Factors to a promoter starts transcription of that gene. These proteins bind to a promoter only if the associated gene is to be transcribed. We call the direction of transcription “downstream”, and the opposite direction “upstream”. That is, a promoter is upstream of its gene, and RNA polymerase moves in a downstream direction along the DNA during transcription. In bacteria, RNA polymerase binds directly to the promoter.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 09/04/2009 for the course SBU 101 taught by Professor Debag during the Spring '09 term at SUNY Stony Brook.

Page1 / 3

Lecture 31 Transcription Notes - Lecture 31 Transcription....

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online