Question

The difference between a pre-mRNA and a mature eukaryotic mRNA is __________.

a. the 5' and 3' ends have been modified in mRNA

b. the removal of the leader sequence from the pre-mRNA

c. the fact that all introns have been spliced out in the mRNA

d. Both a and c

Which of the following statement is TRUE about transcription?

a. Transcription in prokaryotes does not differ from transcription in eukaryotes. b. Prokaryotes carry out transcription in the cytosol, whereas eukaryotes carry out transcription in the nucleus. c. Eukaryotes use RNA polymerase and prokaryotes do not. d. Prokaryotes synthesize double stranded RNA and eukaryotes do not

Which of the following statement concerning structural genes is FALSE?

a. Most structural genes code for a single polypeptide.

b. Coding regions always contain introns.

c. There may be noncoding regions at the end of the gene.

d. A single DNA sequence can sometimes code for more than one polypeptide

Which of the following is NOT true about exons?

a. They are retained sequences in the final RNA product.

b. They have a 5 and a 3 end.

c. They are removed when the primary transcript is processed. d. Their sequences are in the same order in the gene and in the RNA.

Answer 1

Pre-mRNA are synthesized from DNA in the process of transcription. This pre-mRNA has to undergo certain processing steps making it ready for being translated. The Processing steps include removal of introns and addition of methylated caps and poly A tail at the 5'end and 3' end respectively.

Ans. (d) Both a and c.

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Transcription is a process in which a complementary RNA molecule is synthesized from a DNA sequence. The transcription and translation are coupled together and is carried out in the cytoplasm in the prokaryotes. While transcription takes place in the nucleus. Both have RNA polymerase for synthesis of RNA molecules. Unlike DNA, RNA molecules are always single stranded.

Ans. (d) Prokaryotes synthesize double stranded RNA and eukaryotes do not.

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Structural genes are genes that are responsible for coding of proteins or RNA molecules other than regulatory proteins. They are responsible to encode for specific polypeptides. The genes are composed of exons and Introns are scattered in the region. It has noncoding regions in the gene structure.

Ans. (d) A single DNA sequence can sometimes code for more than one polypeptide.

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Exons are nucleotide sequences and are coding regions of RNA transcripts. Exons do have a 5' and 3'end. Their sequences are retained in the final RNA product. Their sequences are in the same order in the gene and in the RNA.

Ans. (c) They are removed when the primary transcript is processed.