Biochemistry : Protein Synthesis
Study concepts, example questions & explanations for Biochemistry
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Example Questions
Example Question #21 : Anabolic Pathways And Synthesis
__________ are 21-23 nucleotide long strands of duplex double stranded RNA with symmetric 2-3 nucleotide overhangs that trigger mRNA degradation.
pri-miRNAs
piRNAs
miRNAs
None of these
siRNAs
siRNAs
All are part of RNA interference.
siRNA = short interfering RNA
miRNA = micro RNA
pri-miRNA = primary miRNA
piRNA = piwi interacting RNA
Example Question #22 : Anabolic Pathways And Synthesis
During translation, which enzyme attaches the appropriate amino acid onto its tRNA?
DNA polymerases
DNA helicase
RNA polymerase
Aminoacyl-tRNA synthetase
Aminoacyl-tRNA synthetase
Aminoacyl-tRNA synthetases are important enzymes in translation. Their function is to match the specific amino acid to its tRNA. DNA polymerases, RNA polymerase, and DNA helicase are not involved in this process. DNA polymerases are enzymes involved in DNA replication; they create DNA molecules by assembling nucleotides. RNA polymerase produces RNA and has nothing to do with the translation process. Lastly, DNA helicase unwinds DNA during DNA replication, allowing the strands to be copied.
Example Question #23 : Anabolic Pathways And Synthesis
Which of the following is not necessary in order for a protein to be transcribed and translated?
rRNA
tRNA
DNA
mRNA
miRNA
miRNA
For this question, we're asked to identify an answer choice that contains something that is not needed for transcription and translation.
To begin, let's define these two terms. Transcription is the production of mRNA from DNA. The subsequent coding of a polypeptide from this mRNA is known as translation. During translation, tRNA serves as the carriers of amino acids. In doing so, these tRNA's bring certain amino acids to the ribosome-mRNA complex, depending on the codon sequence of the mRNA. Furthermore, the ribosome itself is composed of rRNA as well as protein. So in total, DNA, mRNA, rRNA, and tRNA are needed for transcription and, subsequently, translation.
But what about miRNA? This type of RNA, together with another class of RNA called siRNA, are both involved in a process called RNA interference. In this process, either miRNA or siRNA acts to inhibit gene expression by inhibiting certain key steps at the level of transcription and translation. Therefore, miRNA is not required for proper transcription and translation to occur because it acts to inhibit these processes.
Example Question #14 : Translation
Which of the following codons is neither a stop nor a start codon?
AUG
UGA
UAA
TAG
UAG
TAG
AUG is the universal start codon. The stop codons are UGA, UAG, and UAA.
Example Question #15 : Translation
What amino acid is synthesized as a part of the initiation signal for translation with the mRNA code, UAG?
Methionine
Leucine
Glycine
Lysine
Threonine
Methionine
Protein translation begins by recognizing an initiation signal on the mRNA - the codon UAG. The amino acid that coded for by UAG is methionine.
Example Question #24 : Anabolic Pathways And Synthesis
Which of the following correctly describes the formation of the 80S initiation complex that begins translation?
A tRNA that pairs with the UAG start codon on mRNA will begin translation after ribosome 40S and 60S assemble.
A tRNA that matches AUG on the mRNA will bind in the A site of the newly formed ribosome.
The initiator tRNA with its alanine will bind in the P site of the ribosome.
Complementary mRNA strands for the start codon will bind in the P site of a ribosome.
A tRNA with methionine will match with the mRNA start codon in the P site of the newly formed ribosome.
A tRNA with methionine will match with the mRNA start codon in the P site of the newly formed ribosome.
The initiation complex of a ribosome to start translation begins with the tRNA carrying methionine, matching the start codon AUG on mRNA, binding with the 40S and 60S ribosomal subunits, to form an 80S ribosomal subunit with the initiation tRNA in the P site.
The next tRNA that matches the following codon will then come into the A site to continue translation.
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