A scientist identifies a cell line derived from muscle with reduced expression of several muscle-specific proteins including -actin and myosin.
Further investigation shows that while mRNA specific to these proteins is transcribed and polyadenylated at normal rates, the half-life of the mRNAs is significantly lower. What would be a likely explanation?
A. There is a mutation in RNA polymerase II.
B. There is an increase in RNA-editing terminal uridylyltransferase (TUTase) activity.
C. There is amutation in poly(A) binding protein (PABP).
D. There is amutation in polyadenylate polymerase (PAP).
E.There is an increase in number of processing bodies.
Which of the following is true of the structure of the TPP riboswitch only when bound to thiamine pyrophosphate?
A. The conformation of the riboswitch allows the ribosome to access the Shine-Dalgarno sequence.
B. The riboswitch folding creates a binding site for the ribosome.
C. The riboswitch RNA becomes catalytically active to cleave mRNA.
D. The riboswitch is less susceptible to cleavage by ribonuclease.
Recombination between homologous chromosomes:
A. can lead to a gene conversion event if the region between the two Holliday intermediates contains base pair differences.
B. uses extended synthesis-dependent strand annealing (ESDSA) rather than synthesis-dependent strand annealing (SDSA).
C. can occur at completely random sites on the chromosome; there is no apparent regulation of the process.
D. occurs between sister chromatids and nonsister chromatids with equal frequency.
E. None of the choices given is true.
Through an electron microscope, chromatin will have the appearance of beads on a string. What protein(s) will tighten the beads to create a pronounced zigzag appearance?
A. scaffolding proteins
B. NAP-1
C. H1 histone
D. Sp1
E. bromodomain proteins
Which of the following is a possible reason why DNA uses thymine instead of uracil?
A. Thymine is more stable than uracil.
B. Cytidine is deaminated to uracil so it would be difficult for any repair mechanism to differentiate between uracil that belongs in the sequence and uracil that resulted from deamination.
C. Adenine is deaminated to uracil so it would be difficult for any repair mechanism to differentiate between uracil that belongs in the sequence and uracil that resulted from deamination.
D. When uracil is bound to a deoxyribose it will become more reactive, forming covalent bonds with other bases.
E. None of these choicesis correct.
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