u TntPon-exon boundary? 24. What are self-splicing introns, and why does their e
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u TntPon-exon boundary? 24. What are self-splicing introns, and why does their exis- ittation tence support the theory that RNA evolved before protein? before oe25. Antibiotics are drugs that selectively kill bacteria with out harming animals. Many antibiotics act by selectively binding to certain proteins that are critical for bacterial function. Explain why some of the most successful anti- biotics target bacterial RNA polymerase. hairpin 26. Describe four types of RNA that perform distinct y from functions. serting CHALLENGING PROBLEMS lowing 27. The following data represent the base compositions of double-stranded DNA from two different bacterial spe- cies and their RNA products obtained in experiments conducted in vitro: Species (A+T) (A+U (A+G) G+C) (G+C) (U+C) 1.30 0.98 h a Bacillus subrilis 1.36 1.00 1.02 0.80 E. coli apter and a. From these data, determine whether the RNA of these species is copied from a single strand or from both strands of the DNA. Draw a diagram to show how you solve this problem. b. How can you tell if the RNA itself is single stranded or double stranded? ra eta coli in 28. A human gene was initially identified as having three ex- ons and two introns. The exons are 456, 224, and 524 bp, whereas the introns are 2.3 kb and 4.6 kb. a. Draw this gene, showing the promoter, introns, exons, and transcription start and stop sites. b. Surprisingly, this gene is found to encode not one but two mRNAs that have only 224 nucleotides in common. The original mRNA is 1204 nucleotides, and the new mRNA is 2524 nucleotides. Use your drawing east wice rom e to rl ledExplanation / Answer
Ans 24
Self-Splicing introns are introns capable of carrying out splicing in the absence of proteins. They have discovered a no protein control in an experiment to identify proteins responsible for splicing.
Two kinds of self-splicing introns: groups I and II; Group 2 strongly resembles pre-mRNA splicing machinery considered previously except for the absence of proteins. Group 1 introns are fundamentally different. Rather than forming a lariat, the first transesterification reaction involves an exogenous guanine nucleotide.Group 2 self-splicing has the identical mechanism to pre-mRNA splicing save for the proteins.Group 1 self-splicing does not form a lariat. It uses an exogenous G OH to attack the 5' displacing 5' but not forming a lariat. Appears that it in addition initially assists in bending the mRNA to bring the splicing sites in proximity to one another.
Ans 26
The genomic DNA contains all the information for the structure and function of an organism.
In any cell, only some of the genes are expressed, that is, transcribed into RNA.(i) Messenger RNA (mRNA) (ii) Transfer RNA (tRNA) (iii) Ribosomal RNA (rRNA) (iv) sn RNA.
(i) Messenger RNA (mRNA): mRNA carries coded information for translation into polypeptide formation.Through reverse transcription, it can form compact genes which are used in genetic engineering. It is the blueprints DNA has provided to make the proteins, made by DNA polymerase, carries instructions from DNA to the cytoplasm.
(ii) Transfer RNA (tRNA):tRNA is adapter molecule which is meant for transferring amino acids to ribosomes for the synthesis of polypeptides They hold peptidyl chains over the mRNAs.
(iii) Ribosomal RNA (rRNA): made in the nucleolus, part of the ribosome.rRNAs bind protein molecules and give rise to ribosomes.
50S subunit of prokaryotic ribosome contains 23S rRNA, 5S rRNA, and some 32 protein molecules. 30S subunit of the prokaryotic ribosome has 16S rRNA and about 21 protein molecules.
60S subunit of eukaryotic ribosome contains 28S rRNA, 5S rRNA, 5.8S rRNA and about 50 protein molecules. 40S subunit of eukaryotic ribosome consists of 18S rRNA and some 33 protein molecules.
(iv) snRNA - Small nuclear RNA: With proteins, forms complexes that are used in RNA processing in eukaryotes. (Not found in prokaryotes.)
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