Processing Key BB - Questions and solutions PDF

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1. Which of the following statements correctly describes the facts about introns and exons? a. b. c. d. e.

The number of introns is always less than the number of exons in a gene. Introns are degraded in the cytoplasm. All eukaryotic genes contain an intron. Mitochondrial and chloroplast genes do not contain introns. Introns do not contain sequence-specific information.

2. In 1958, Francis Crick proposed that genes and their corresponding polypeptides are “colinear.” Which of the following statements concerning the concept of colinearity is incorrect? a. Colinearity means that the linear nucleotide sequence of a given gene corresponds directly to the linear amino acid sequence in the corresponding polypeptide. b. The number of nucleotides in a gene should be precisely proportional to the number of amino acids present in the corresponding polypeptide. c. Colinearity generally holds true for the coding regions of prokaryotic viral genes. d. The vast majority of eukaryotic genes also follow the concept of coliniarity although the size of genes may be larger. e. The exception to colinearity between genes and polypeptides is the presence of untranslated sequences (UTRs). 3. The 5′ and 3′ untranslated regions (UTRs) of processed mRNA molecules are derived from a. b. c. d. e.

exons. introns. promoter. terminator. protein-coding region.

4. Which of the following best explains why only pre-mRNA is recognized and receives a 5′ cap? a. The enzyme that initiates the capping step is known to associate with RNA polymerase II, which generate mRNAs. b. Only pre-mRNAs contain proper sequence for the cap to be added on. c. The tail of the pre-mRNA can recruit the right combination of enzymes for capping. d. Nuclear pore complex only recognize pre-mRNA to be allowed out to the cytoplasm for capping process to begin. e. rRNA and tRNAs do not exit the nucleus to receive the cap via enzyme sin the cytoplasm.

5. The human gene encoding for calcitonin contains six exons and five introns and is located on chromosome 11. The pre-mRNA transcript from this gene can generate either calcitonin or calcitonin gene related peptide (CGRP) in a tissue-specific manner. Calcitonin produced from the thyroid gland is 32 amino acids long and functions to regulate the calcium while CGRP, which contains 37 amino acids, is produced by the brain cells and involved in transmission of pain. Which of the following processes makes production of two functionally and structurally different proteins from the same gene possible? a. Self-spicing introns b. Differential trnascription c. Alternative replication d. 5′ capping and polyadenylation e. Alternative RNA processing 6. Which of the following elements would not be found on an mRNA molecule? a. b. c. d. e.

Protein-coding region 3′ untranslated region 5′ untranslated region Promoter Start and stop codons

7. Which of the following is found on the primary product of transcription but not on a mature mRNA molecule? a. b. c. d. e.

Start codon Promoter Exons Introns Stop codon

8. The 5′ cap on an mRNA is important for all the processes listed below except for the _________ of an mRNA molecule. a. b. c. d. e.

transcription intron removal stability initiation of translation ribosomal interaction

9. A key modification in the 3′ end of eukaryotic mRNA is the addition of 50 to 250 adenine nucleotides at the 3′ end, forming a poly(A) tail. Which of the following statements is not a salient feature of this polyadenylation reaction? a. b. c. d. e.

The stability of mRNA transcripts in the cytoplasm is affected by poly(A) tail. Poly(A) tail facilitates the attachment of the ribosomes to the mRNA. Proper poly(A) tail is important for proper nuclear export of mRNA. Poly(A) tail at the 3′ end translates to a long stretch of repeated amino acids. Multiple proteins will recognize and bind to poly(A) tail in the cytoplasm.

10. During the post transcriptional processing of pre-mRNA, a 5′ cap is added to an mRNA in step by step manner. Which of the following reason prevents the possibility of 5′ capping process involving methylation occurring on a DNA strand? a. b. c. d. e.

Lack of OH group on 2′ carbon of the deoxyribose Lack of OH group on 3′ carbon of the deoxyribose Lack of uracil nitrogenous base on the DNA strand Lack of GTP hydrolysis associated with DNA transcription Lack of H on 4′ carbon of the deoxyribose

11. Which of the following correctly describes the concept of alternative splicing? a. Eukaryotic gene and protein sequences are precisely colinear. b. With the rare exception of RNA editing, every nucleotide contained in a processed mRNA molecule is derived from exon sequences. c. Every other intron is removed in alternate manner to generate functional mRNA transcript. d. Only a subset the same mRNA transcripts are specifically selected for splicing in the nucleus. e. Multiple protein products are often produced from single eukaryotic genes. 12. Which of the following choices does not support the notion that the gene is much more than DNA sequences that are transcribed into a single RNA molecule that encodes a single polypeptide? a. Alternative splicing—a single gene can yield multiple mRNA and protein products. b. A single ribosomal RNA transcripts can liberate several RNA molecules via further processing c. RNAs can be the functional product of a gene without being translated into protein product d. Protein coding region—each codon represents specific amino acid that will be linked to form a polypeptide e. Regulatory elements are part of a gene that regulate timing, degree, and specificity of gene expression but are not transcribed....