class notes Chap7 part 1

class notes Chap7 part 1 - Biology 302 Cell and Molecular...

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Biology 302 Cell and Molecular Biology Chapter 7 part1 FROM DNA to RNA- Transcription Remember the central dogma- genetic information flows from DNA to RNA to protein (occasionally, it flows from RNA to DNA but not usually). Coined by Francis Crick in the mid- 1950’s Now, we move to the question of how the cell decodes the information held in the DNA. Today, we’ll talk about the first step in this process Transcription. - we’ve got DNA with just four bases or letters- and this has the instructions to make many proteins that make a human a human and a worm a worm. - We know how to decode DNA – effectively, we know how to read the language. The DNA sequence exactly specifies the sequence of amino acids in proteins DNA to RNA (Transcription) (Figure 7-1) RNA to protein (Translation) Together – these are called Gene Expression Transcription - many identical RNA’s can be made from a single DNA sequence in a cell- so there’s in effect an amplification of the info in the DNA – to form many RNAs. - The cell can control when an RNA is made and how much of that RNA is made. - So some RNA’s may be very abundant at times and very low at others- regulation - In general, some may be very abundant and some may be very rare. This is important, because cells need lots of certain proteins and tiny amts. of others. And, having too much or too little of a particular protein can be bad. ( Figure 7-2) - Efficiency of transcription Transcription- copying of one strand of DNA into a complementary RNA sequence by the enzyme RNA polymerase. All of the DNA on a chromosome is not transcribed (or used to produced RNA) - the cell copys just a portion of the DNA corresponding to genes into RNA - the process is called transcription because although the information is copied into another chemical form- its in essentially the same language- nucleotides 1
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We’ve talked about a couple of the differences between DNA and RNA – let’s over them in more detail now. Major differences: 1. DNA uses the sugar deoxyribose; RNA uses ribose ( Figure 7-3A) difference is OH a position 2 in RNA (hence ribonucleic acid and ribonucleotides instead of deoxyribonucleic acid 2. Instead of the pyrimidine thymine (DNA), RNA contains uracil (uracil is missing the methyl group found in thymine ( Figure 7-3B) Uracil forms two hydrogen bonds with adenine (like thymine) ( Figure 7-4) . RNA (like DNA ) contains C, A and G -the nucleotides in RNA are linked as they are in DNA – through the 5’phosphate and the 3’OH group. 3. Overall structure of RNA is dramatically different from the structure of DNA in cells:
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class notes Chap7 part 1 - Biology 302 Cell and Molecular...

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