Biochem section J Tophat Q's

Which component is NOT part of a deoxyribonucleotide?

ribose

Which of the following bases is found in DNA but not in RNA?

thymine

• purine bases:- adenine (A) = in DNA and RNA- guanine (G) = in DNA and RNA

• pyrimidine bases:- cytosine (C) = in DNA and RNA- thymine (T) = only in DNA- uracil (U) = only in RNA6

In a sample of DNA isolated from an unidentified species ofbacteria, adenine makes up 28% of the total bases. Whichstatement is false about the relative proportions of the bases inthe DNA sample?

The DNA must contain 28% C.

Explanation: For any double-helical DNA, A = T and G = C. The DNAfrom the unidentified bacteria has 28% A and thereforemust contain 28% T. A and T bases account for 56% of thebases and leaves 44% as G and C pairs: 22% G and 22% C.Together, C, T, and G bases account for 72% of the bases.

Which statement is true about the three-dimensional structureof DNA?

The offset pairing of the two strands creates a major groove and a minor groove on the surface of the duplex.

Which one of the following statements about DNA replication is false?

Synthesis of leading and lagging strands is independent and uncoordinated.

Which statement does NOT describe a fundamental feature of DNA replication?

It involves polymerizing deoxyribonucleotides only.

Which enzyme relieves the topological stress introduced by strandseparation during DNA replication?

DNA Gyrase

Which drug inserts into DNA duplex to hinder DNA replication incancer?

Doxorubicin

During transcription, the α-phosphate group of an incoming ribonucleotide triphosphate is added to which moiety of the growing RNA polymer?

ribose at the 3' end

Other than having U in the RNA in place of T in the DNA, the base sequence of transcribed RNA:

is identical to the nontemplate DNA strand sequence.

Which sequence correctly reflects the steps involved in the initiation of transcription after E. coli RNA polymerase binds to a promoter?

closed and then open complex formation, RNA synthesis,promoter clearance.

Which compound CANNOT be used to inhibit bacterial RNA polymerase?

α-amanitin

Which of the following enzymes is NOT a component of the 5'-cap synthesizingcomplex for eukaryotic mRNAs?

Polyadenylate polymerase

What is removed from the RNA primary transcript in order to produce mRNA?

Introns

Which of the following processes involves the formation of a lariatstructure? Select all that apply.

splicing of group II introns and splicing of spliceosome introns

Different mRNA transcripts are encoded by one gene when:

spliceosome remove some of the exons along with all the introns.

Why is the genetic code said to be "degenerate"?

Certain amino acid can be specified by more than one codon.

What is explained by the 'wobble' hypothesis?

one tRNA molecule may recognize to more than one codon

Mature tRNAs:

All have very similar three-dimensional structures.

Which statement regarding aminoacyl-tRNA synthetases is NOT true?

These enzymes hydrolyze ATP to ADP and Pi.

What is a significant difference between bacteria and eukaryotes in initiation of translation?

in bacteria, base-pairing between the mRNA and arRNA determines which start codon to use; ineukaryotes, the small subunit begins scanning themRNA at the 5′ cap until it reaches the first start codon.

What reaction mechanism provides a role in bacterial cellproofreading during elongation, ensuring the correctaminoacyl-tRNA is added to the A-site?

GTP hydrolysis

Given the initiation and elongation phases of protein synthesis,how many nucleoside triphosphates (or their equivalents) arehydrolyzed to nucleoside diphosphates in order to make onepeptide bond?

at least 4

Which antibiotic or toxin mechanism is INCORRECT?

Puromycin blocks the P site of bacterial ribosomes.