MCDB1A2010-Dr._Feinstein-Part_3

MCDB1A2010-Dr._Feinstein-Part_3 - Big question #2: How does...

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Big question #2: How does DNA direct the synthesis of proteins? 1. How is the information in DNA accessed to direct protein synthesis? 2. How does protein synthesis proceed? Are there any clues from structure, such as helped us to understand replication?
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"A genetic material must ...... duplicate itself, and it must exert a highly specific influence on the cell. Our model for DNA suggests a simple mechanism for the first process, but at the moment we cannot see how it carries out the second one. We believe, however, that its specificity is expressed by the precise sequence of the pairs of bases. The backbone of our model is highly regular, and the sequence is the only feature which can carry the genetic information. Dr. James Watson shortly after the 1953 Nature paper
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RNA is very similar to DNA, except: 1. Uracil replaces thymine 3. Ribose replaces deoxyribose 4. RNA is single stranded instead of double stranded 5. RNA chains can be of varying lengths, ranging from ~10 bases long to many thousands of bases long 5. RNA can fold up on itself into precise 3D structures much like proteins forming A=U and C=G base pairs 6. There are 3 kinds of RNA ribosomal RNA (rRNA; ~95% of total) structural component of ribosomes transfer RNA (tRNA; ~3% of total) messenger RNA (mRNA’ ~2% of total)
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Three kinds of RNA molecules
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Francis Crick’s “Central Dogma” RNA is the intermediate between DNA and proteins
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Figure 14-2 From gene to protein
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Figure 14-4 DNA is transcribed into RNA (note “promoter”)
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Figure 14-4 DNA is transcribed into RNA (note terminator)
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A few key points: 1. RNA synthesis is 5’ to 3’, just like DNA synthesis; 2. RIBOnucleotide triphosphates are monomer is precursors; U in RNA replaces T in DNA 3. Several RNA polymerases can be on a given gene at the same time; 4. Different genes can transcribe off different strands of DNA; Next key question: How does the mRNA direct the synthesis of its protein?
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How do we begin to address the question? We can make synthetic RNA molecules by organic chemistry; how about making polyA, polyC, polyG and polyU mix with cell extracts and see what gets made?
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Figure 14-5 Deciphering the genetic code
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Doublets: ACACACACACACACACACAC get: thr-his-thr-his-thr-his……. CUCUCUCUCUCUCUCUCUC get: leu-ser-leu-ser-leu-ser……. Triplets:
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MCDB1A2010-Dr._Feinstein-Part_3 - Big question #2: How does...

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