HW%207%20F%202008%20solution

HW%207%20F%202008%20solution - Prof. Wood CHEN 651/471...

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Prof. Wood CHEN 651/471 Homework #7 Due 10-30-08 Ch. 4 Shuler, Problems 4.2, 4.3, 4.4, 4.6, 4.7, 4.9, 4.11, 4.12 Ch. 8 Shuler, Problems 8.1, 8.3, 8.7, 8.10
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Prof. Wood Solution 4.2 Why is m-RNA so unstable in most bacteria (half-life of about 1 min)? In many higher organisms, m-RNA half-lives are much longer (> 1h). Why Solution: In prokaryotic cells, there is no physical separation of the chromosome from the cytoplasm and ribosomes. Often an m-RNA will bind to a ribosome and begin translation immediately, even while part of it is still being transcribed. m-RNA is also not designed to be stable so that the bacterium may respond to different environmental conditions (if mRNA stayed around forever, the bacterium could not make new enzymes to respond to different environmental conditions since the old enzymes would continuously be made). In eukaryotes, where the nuclear membrane separates chromosomes and ribosomes, the m-RNA is often subject to processing before translation, so the m-RNA is more stable. In addition, two modifications occurred in eukaryotic cells are also increase m-RNA stability. One is RNA capping, in which 5’ end is modified by the addition of a guanine nucleotide with a methyl group attached. The other one is polyadenylation, in which a string of adenine nucleotides are added to the 3’ end. 4.3 What would be the consequence of one base deletion at the beginning of the message for a protein? The deletion of one base would cause the wrong reading frame on the m-RNA, so all of the following message will be misread. As a result, some different or nonsense protein will be produced in which all of the amino acids are wrong. 4.4 How many ribosomes are actively synthesizing proteins at any instant in an E.coli cell growing with a 45-min doubling time? The birth size of E. coli is 1- μ m diameter and 2- μ m length. The water content is 75%. About 60% of the dry material is protein, and the rate of amino acid addition per ribosome is 20 amino acids per second. The average molecular weight of free amino acids in E. coli is 126. Solution: Assume E. coli is a cylinder, sec min 20 min 10 023 . 6 1000 1 126 min sec 60 min 45 25 . 0 6 . 0 10 2 ) 10 5 . 0 ( 10 1 23 6 2 6 3 3 × × × × × × × × × × × × × ribosome oacide a mol oacid a mol kmol kmol protein kg wetcells kg l drymateria kg l drymateria kg protein kg m m m wetcells kg π ribosomes 4 10 08 . 2 × = Note: 126 is the average molecular weight of free amino acids as showing up in the question , lkmol/1000mol is the way to change unit from kmol to mol. 1*10 3 is the density of E. coli. 4.6 For the m-RNA nucleotide code below: (a) Deduce the corresponding sequence of amino acids.
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HW%207%20F%202008%20solution - Prof. Wood CHEN 651/471...

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