20. Which of the following statements about alternative splicing is correct?
(A) Alternative splicing occurs only in protein-coding genes and excludes noncoding RNA genes.
(B) Alternative splicing is regulated by splice site selection influenced by RNAbinding proteins and cis-regulatory elements.
(C) All alternative splicing events result in functional protein isoforms.
(D) Alternative splicing is primarily limited to the removal of introns without any variation in exon usage.
(E) Alternative splicing is a rare event occurring in only a small fraction of eukaryotic genes.

16. Which of the following is the primary biological function of microRNAS (miRNAs) in eukaryotic cells? (A) To serve as templates for the synthesis of small interfering RNAs (siRNAS) during immune response. (B) To promote the splicing of pre-mRNA by recognizing intron-exon junctions. (C) To regulate gene expression by binding to complementary sequences on target mRNAs, leading to translational repression or mRNA degradation. (D) To act as ribozymes that catalyze peptide bond formation during protein synthesis. (E) To serve as direct messengers in the nucleus that enhance transcription by interacting with RNA polymerase II.

17. Which of the following statements correctly describes a key difference between microRNAs (miRNAs) and small interfering RNAs (siRNAs)? (A) miRNAs primarily regulate gene expression through translational repression, while siRNAs often induce mRNA cleavage when binding to their target. (B) miRNAs typically bind to perfectly complementary sequences on target mRNAs, while siRNAs bind to partially complementary sequences. (C) siRNAs are derived from endogenous transcripts, while miRNAs are always of exogenous origin. (D) Both miRNAs and siRNAs are loaded onto the RNA-induced silencing complex (RISC), but only siRNAs recruit the Argonaute protein. (E) miRNAs are processed in the cytoplasm by Dicer, while siRNAs are processed exclusively in the nucleus. 

18. What is the primary purpose of RNA polyadenylation in eukaryotic cells? (A) To prevent the formation of secondary structures in the coding region of the mRNA. (B) To enhance transcription elongation by stabilizing RNA polymerase on the DNA template. (C) To promote the export of mRNA from the nucleus and increase its stability and translational efficiency. (D) To remove introns from pre-mRNA during RNA splicing. (E) To initiate translation by providing a binding site for ribosomes at the 5' end of the mRNA.

19. Which of the following statements about RNA splicing is correct? (A) RNA splicing removes exons and joins introns to produce mature mRNA in eukaryotic cells. (B) The spliceosome removes introns and adds a polyA. tail to the 5' end of the RNA molecule. (C) RNA splicing is a process exclusive to prokaryotes. (D) Alternative splicing allows a single gene to produce multiple protein isoforms. (E) Splicing occurs in the cytoplasm after transcription is complete.

21. Which of the following statements about chromatin structure is correct? (A) Euchromatin is associated with active gene transcription and is less condensed compared to heterochromatin. (B) Heterochromatin is enriched with histone H3 lysine 4 methylation (H3K4me3), promoting transcriptional repression. (C) The nucleosome is composed of DNA wrapped around a complex of six histone proteins. (D) Chromatin structure is static and does not change in response to environmental or cellular signals. (E) Histone modifications, such as methylation and acetylation, do not influence chromatin accessibility or transcriptional activity.

複選題22. Which of the following statements accurately compares translational initiation between eukaryotes and bacteria? (A) Bacterial translation begins with N-formyl-methionine carried by tRNA, which differs from the tRNA carrying interior methionine. (B) Bacterial translation requires the Kozak sequence to guide ribosomes to the start codon. (C) Eukaryotic translation requires the Shine-Dalgarno sequence to guide ribosomes to the start codon. (D) Eukaryotic translation begins with methionine carried by tRNA, which is the same as the tRNA carrying interior methionine. (E) Bacterial mRNAs contain a 5' cap structure.

複選題23. What are the functions of IF3 in bacterial translation? (A) Binds the 50S ribosomal subunit. (B) Promotes reassociation of the 30S and 50S ribosomal subunits. (C) Facilitates the binding of fMet-tRNA to the 30S initiation complex. (D) Facilitates mRNA binding to the 30S initiation complex. (E) Helps align the Kozak sequence of mRNA with the 16S rRNA.

複選題24. Which of the following statements about poliovirus are correct? (A) Poliovirus directly degrades host mRNA. (B) Poliovirus protease degrades eIF4G. (C) Poliovirus RNA harbors a 5' cap structure. (D) The IRES element is present in most mRNAs. (E) eIF4E facilitates the translation of picornavirus mRNAs.

25. Which of the following molecules do NOT function as GTPases? (A) IF2 (B) EF-G (C) EF-T's (D) EF-Tu (E) RF-3

26. Which statements inaccurately describe base pairing between codon and anticodon? (A) The first two bases in a codon determine coding specificity by forming strong Watson-Crick base pairs with the anticodon. (B) Isoaccepting tRNAs bind different amino acids but recognize the same codon. (C) Wobble occurs when the third base of a codon forms a non-Watson-Crick base pair with the anticodon. (D) Wobble allows the same aminoacyl-tRNA to pair with multiple codons. (E) The super-wobble hypothesis suggests that a single tRNA with U in the first anticodon position (5' position of the anticodon) can recognize codons ending in any of the four bases under certain conditions.