QUIZ 5: BIO20A

Imagine that a mutant bacterial cell has a defective aminoacyl synthetase that attaches a lysine to tRNAs with the anticodon AAA (instead of a phenylalanine which is the amino acid that should be covalently attached to this tRNA). The consequence of this for the cell will be that A. Proteins in the cell will contain lysine instead of phenylalanine at amino acid positions specified by the codon UUU. B. None of the proteins in the cell will contain phenylalanine. C. The ribosome will skip a codon every time a UUU is encountered. D. None of the above will occur; the cell will recognize the error and destroy the tRNA

A. Proteins in the cell will contain lysine instead of phenylalanine at amino acid positions specified by the codon UUU.

A transcription unit in a gene that is 8,000 base pairs long may only use 1,200 bases to encode a protein consisting of 400 amino acids. This is best explained by the fact that A. There is redundancy and ambiguity in the genetic code. B. Many non protein coding bases are present in the mRNA C. There are termination exons near the beginning of mRNA. D. Nucleotides are degraded by nucleases during the transcription process.

B. Many non protein coding bases are present in the mRNA

A part of an mRNA molecule with the following sequence is being read by a ribosome: 5' CCG-ACG 3' (mRNA). The following charged transfer RNA molecules (with their anticodons shown in the 5' to 3' direction) are available. Two of them can correctly match the mRNA so that a dipeptide can form. tRNA Anticodon Amino Acid 5' CGG 3' Proline 5' UGC 3' Alanine 5' CGU 3' Threonine 5' GCC 3' Glycine 5' GCA 3' Cysteine 5' GGC 3' Alanine The dipeptide that will form will be A. Cysteine-alanine. B. Proline-threonine. C. Glycine-cysteine. D. Alanine-alanine.

B. Proline-threonine.

An extraterrestrial life form is discovered. It has a genetic code much like that organisms on Earth except that there are five different DNA bases instead of four and the base sequences are translated as doublets instead of triplets. How many different amino acids could be accommodated by this genetic code? A. 5 B. 10 C. 25 D. 32

C. 25

Which RNA was synthesized from the following DNA template strand? 5' AATGCCTTAGCG 3' A. 5' UUACGGUUACGC 3' B. 5' TTACGGAATCGC 3' C. 5' CGCUAAGGCAUU 3' D. 5' GCGUAAGGCUUA 3'

C. 5' CGCUAAGGCAUU 3'

A peptide has the sequence NH2-phe-pro-lys-gly-phe-pro-COOH. Which of the following sequences is the coding strand of the DNA (not the template strand, learn/google the difference!) that codes for this peptide? A. 3' UUU-CCC-AAA-GGG-UUU-CCC 5' B. 3' ATG-AAA-GGG-TTT-CCC-AAA-GGG 5' C. 5' TTT-CCC-AAA-GGG-TTT-CCC 3' D. 5' GGG-AAA-TTT-AAA-CCC-ACT-GGG 3' E. 5' ACT-TAC-CAT-AAA-CAT-TAC-UGA 3'

C. 5' TTT-CCC-AAA-GGG-TTT-CCC 3'

Translation is initiated at A. The origin of replication site on the DNA B. The promoter site on DNA C. The start codon on mRNA D. The transcription start site on mRNA

C. The start codon on mRNA

Eukaryotic RNAs cannot be transported to the cytoplasm unless A. They are modified at the 5' and 3' ends B. Internal sequences of the RNA are removed C. The 5' end is trimmed by endonculeases D. A & B E. B & C

D. A & B

Using RNA as a template for protein synthesis instead of translating proteins directly from the DNA is advantageous for the cell because A. RNA is much more stable than DNA. B. RNA acts as an expendable copy of the genetic material, allowing the DNA to serve as a permanent, pristine repository of the genetic material. C. Many mRNA molecules can be transcribed from a single gene, increasing the potential rate of gene expression. D. B & C E. All of the above

D. B & C

During translational initiation it is important to position the start codon in the correct site on the ribosome A. So that the codons will be read in the proper frame B. So that amino acids are linked together in the order specified by the gene sequence C. So that the introns are removed correctly and the protein that is synthesized will be functional D.A & B E. All of the above

D.A & B

Where is the information that directs protein synthesis found in DNA? A. The arrangement of phosphate groups B. The bonding types of the sugar molecules C. The twists in the coil of the DNA molecule D. The order of the amino acids. E. The order of nitrogenous bases

E. The order of nitrogenous bases