mRNA Chapter 5

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Fig. 5.16 •Poly(A) is a stretch of ~200 bases of adenylic acid that is added to the 3′ end of mRNA following its synthesis.
i Only o after the completion of all modification and processing events can the n mRNA be exported from the nucleus to the cytoplasm. The average delay in leaving for the cytoplasm is ~20 minutes. Once the mRNA has entered o the cytoplasm, it is recognized by ribosomes and translated. Figure 5.17 shows that the life cycle of eukaryotic mRNA is f more protracted than that of bacterial mRNA. Transcription in animal cells occurs at about the same speed as in bacteria, ~40 nucleotides per second. Many eukaryotic genes are large; m R N A a gene of 10,000 bp takes ~5 minutes to transcribe. Transcription of mRNA is not terminated by the release of enzyme from the DNA; instead the enzyme continues past the end of the gene. A coordinated series of events generates the 3′ end of the mRNA by cleavage, and adds a length of poly(A) to the newly generated 3′ end. i s Eukaryotic mRNA constitutes only a small proportion of the total cellular RNA (~3% of the mass). Half-lives are relatively short in yeast, ranging from 1-60 minutes. There is a substantial increase in stability in higher eukaryotes; animal cell mRNA is relatively stable, with half-lives ranging from 4- n o t 24 hours. Eukaryotic polysomes are reasonably stable. The modifications at both ends of the mRNA contribute to the stability.
Page 1 and 2: mRNA Chapter 5 By Rasul Chaudhry
Page 3 and 4: The coding function of mRNA is uniq
Page 5 and 6: • Transfer RNA (tRNA) is the inte
Page 7 and 8: • The acceptor arm consists of a
Page 9 and 10: • The base paired double-helical
Page 11 and 12: A polyribosome (Polysome) is an mRN
Page 14 and 15: The 20,000 or so ribosomes account
Page 16 and 17: •Bacterial transcription and tran
Page 20 and 21: A cap is the structure at the 5′
Page 22 and 23: • The first methylation occurs in
Page 24 and 25: 3’-Adenylation • poly(A)+ mRNA
Page 26 and 27: • RNAase E is the key enzyme in i
Page 28 and 29: • A common feature in some unstab
Page 30: • RNA is transported through a me

mRNA Chapter 5

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