Protein Synthesis - Biochemistry
Card 0 of 104
Which of the following is false about ribosomal binding sites?
Which of the following is false about ribosomal binding sites?
There are three tRNA binding sites -- A, P, and E (for Aminoacyl, Peptidyl, and Exit) -- but only one mRNA binding site. The enzyme which bonds amino acids carried by tRNAs at A and P is indeed called peptidyl transferase. tRNA is held at A and P when its anticodon matches the codon of the mRNA to be translated. Because each codon is three codons long, per amino acid, the mRNA is indeed shifted three nucleotides' length through the ribosome, each time an amino acid is added to the growing chain.
There are three tRNA binding sites -- A, P, and E (for Aminoacyl, Peptidyl, and Exit) -- but only one mRNA binding site. The enzyme which bonds amino acids carried by tRNAs at A and P is indeed called peptidyl transferase. tRNA is held at A and P when its anticodon matches the codon of the mRNA to be translated. Because each codon is three codons long, per amino acid, the mRNA is indeed shifted three nucleotides' length through the ribosome, each time an amino acid is added to the growing chain.
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Which of the following amino acids has only one possible codon that codes for it?
Which of the following amino acids has only one possible codon that codes for it?
Among the amino acids, there are two which only have one codon that code for them: tryptophan (UGG), and methionine. Methionine, is, of course, special among them, because the same codon is also the start codon -- AUG. Aspartic acid, asparagine, tyrosine, and phenylalanine all each have two possible corresponding codons (respectively: GAC/GAU, AAC/AAU, UAC/UAU, and UUC/UUU).
Among the amino acids, there are two which only have one codon that code for them: tryptophan (UGG), and methionine. Methionine, is, of course, special among them, because the same codon is also the start codon -- AUG. Aspartic acid, asparagine, tyrosine, and phenylalanine all each have two possible corresponding codons (respectively: GAC/GAU, AAC/AAU, UAC/UAU, and UUC/UUU).
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Which of the following translation initiation factors is incorrectly matched with its function?
Which of the following translation initiation factors is incorrectly matched with its function?
eIF2B is a GEF (guanine nucleotide exchange factor) for eIF1 eIF2.
eIF2B is a GEF (guanine nucleotide exchange factor) for eIF1 eIF2.
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Which of the following eukaryotic elongation factors promotes translocation through GTP binding and hydrolysis?
Which of the following eukaryotic elongation factors promotes translocation through GTP binding and hydrolysis?
eEF1A first binds to the aminoacyl-tRNA and has GTPase activity. eEF1B is a GEF for eEF1A. eEF2 has the elongation role similar to EF-G in prokaryotes. Neither Ran-GTP nor IP3 are elongation factors.
eEF1A first binds to the aminoacyl-tRNA and has GTPase activity. eEF1B is a GEF for eEF1A. eEF2 has the elongation role similar to EF-G in prokaryotes. Neither Ran-GTP nor IP3 are elongation factors.
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__________ are 21-23 nucleotide long strands of duplex double stranded RNA with symmetric 2-3 nucleotide overhangs that trigger mRNA degradation.
__________ are 21-23 nucleotide long strands of duplex double stranded RNA with symmetric 2-3 nucleotide overhangs that trigger mRNA degradation.
All are part of RNA interference.
siRNA = short interfering RNA
miRNA = micro RNA
pri-miRNA = primary miRNA
piRNA = piwi interacting RNA
All are part of RNA interference.
siRNA = short interfering RNA
miRNA = micro RNA
pri-miRNA = primary miRNA
piRNA = piwi interacting RNA
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During translation, which enzyme attaches the appropriate amino acid onto its tRNA?
During translation, which enzyme attaches the appropriate amino acid onto its tRNA?
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.
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.
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Which of the following codons is neither a stop nor a start codon?
Which of the following codons is neither a stop nor a start codon?
AUG is the universal start codon. The stop codons are UGA, UAG, and UAA.
AUG is the universal start codon. The stop codons are UGA, UAG, and UAA.
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What amino acid is synthesized as a part of the initiation signal for translation with the mRNA code, UAG?
What amino acid is synthesized as a part of the initiation signal for translation with the mRNA code, UAG?
Protein translation begins by recognizing an initiation signal on the mRNA - the codon UAG. The amino acid that coded for by UAG is 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.
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Which of the following is not necessary in order for a protein to be transcribed and translated?
Which of the following is not necessary in order for a protein to be transcribed and translated?
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.
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.
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Which of the following correctly describes the formation of the 80S initiation complex that begins translation?
Which of the following correctly describes the formation of the 80S initiation complex that begins translation?
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.
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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Where does the pentose phosphate pathway primarily take place?
Where does the pentose phosphate pathway primarily take place?
The pentose phosphate pathway (also known as the hexose monophosphate shunt or HMS), which mainly serves to produce 
for anabolic reduction reactions and ribose-5-phosphate for nucleic acid production, takes place in the cytosol of hepatic cells.
The pentose phosphate pathway (also known as the hexose monophosphate shunt or HMS), which mainly serves to produce
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Which of the following statements is false about the human genome?
Which of the following statements is false about the human genome?
Scientists have indeed counted about 20,000 proteins coded for by the genome. Coding sequences are only about 2% or less of the genome. The definition of paralogs is genes related by duplication within a genome. Within the genome, not about 5%, but rather about 50%, of DNA sequences are repeated.
Scientists have indeed counted about 20,000 proteins coded for by the genome. Coding sequences are only about 2% or less of the genome. The definition of paralogs is genes related by duplication within a genome. Within the genome, not about 5%, but rather about 50%, of DNA sequences are repeated.
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Which of the following amino acids can be created from the carbon skeleton of oxaloacetate?
Which of the following amino acids can be created from the carbon skeleton of oxaloacetate?
From the carbon skeleton of oxaloacetate, methionine can be created. However, glutamine comes from alpha ketoglutarate, valine and leucine come from pyruvate, and histidine comes from ribose-5-phosphate.
From the carbon skeleton of oxaloacetate, methionine can be created. However, glutamine comes from alpha ketoglutarate, valine and leucine come from pyruvate, and histidine comes from ribose-5-phosphate.
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Which of the following molecules is not necessary to create glutamate from alpha-ketoglutarate?
Which of the following molecules is not necessary to create glutamate from alpha-ketoglutarate?
The reaction for the conversion of glutamine into glutamate is:
As seen in the reaction above, carbon dioxide is uninvolved.
The reaction for the conversion of glutamine into glutamate is:
As seen in the reaction above, carbon dioxide is uninvolved.
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Which of the following correctly lists the severity of damage done by mutations in DNA from most severe to least?
Which of the following correctly lists the severity of damage done by mutations in DNA from most severe to least?
When a change results in an early stop codon, nonsense mutation occurs and the protein is done being read early, often resulting in a nonfunctional protein. When a base change results into a different amino acid, this is a missense mutation. When a base change occurs but results in the same amino acid being read, this is considered a silent mutation.
When a change results in an early stop codon, nonsense mutation occurs and the protein is done being read early, often resulting in a nonfunctional protein. When a base change results into a different amino acid, this is a missense mutation. When a base change occurs but results in the same amino acid being read, this is considered a silent mutation.
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Which of of the following are the termination signals for translation?
Which of of the following are the termination signals for translation?
Just as there is an initiation codon regulating translation, there are termination codons that code for the end of translation. The three termination codons are UAA, UAG, and UGA.
A helpful mnemonic for these are the phrases:
You are annoying (UAA)
You are gross (UAG)
You go away (UGA)
Just as there is an initiation codon regulating translation, there are termination codons that code for the end of translation. The three termination codons are UAA, UAG, and UGA.
A helpful mnemonic for these are the phrases:
You are annoying (UAA)
You are gross (UAG)
You go away (UGA)
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Which of the following correctly describes the function of a signal sequence with respect to proteins?
Which of the following correctly describes the function of a signal sequence with respect to proteins?
To answer this question, it's essential to have an understanding of what a signal sequence is.
A signal sequence (also sometimes called a signal peptide) is a specific sequence of amino acids on a polypeptide that appears near the beginning of translation. When this signal sequence is present, it causes a temporary halt in the translation process. Meanwhile, another protein called a signal recognition particle (SRP) comes along and binds to the ribosome that is translating the polypeptide. Together, this polypeptide-ribosome-SRP complex is transferred from the cytosol to the surface of the endoplasmic reticulum (ER). Once there, the complex allows the polypeptide to resume synthesis, but in doing so, causes it to be synthesized into the inner lumen of the endoplasmic reticulum. Consequently, this polypeptide will go on to be modified within the ER and also the Golgi apparatus. Afterwards, it will be sent off within a vesicle, where is will either be A) secreted outside of the cell or B) incorporated into the endomembrane system of the cell (in other words, the peptide will be inserted into a membrane such as the plasma membrane, ER membrane, Golgi membrane, etc.). Lastly, it is the nuclear localization sequence (NLS) that, when added to a protein, allows it to enter the nucleus through the nuclear membrane.
To answer this question, it's essential to have an understanding of what a signal sequence is.
A signal sequence (also sometimes called a signal peptide) is a specific sequence of amino acids on a polypeptide that appears near the beginning of translation. When this signal sequence is present, it causes a temporary halt in the translation process. Meanwhile, another protein called a signal recognition particle (SRP) comes along and binds to the ribosome that is translating the polypeptide. Together, this polypeptide-ribosome-SRP complex is transferred from the cytosol to the surface of the endoplasmic reticulum (ER). Once there, the complex allows the polypeptide to resume synthesis, but in doing so, causes it to be synthesized into the inner lumen of the endoplasmic reticulum. Consequently, this polypeptide will go on to be modified within the ER and also the Golgi apparatus. Afterwards, it will be sent off within a vesicle, where is will either be A) secreted outside of the cell or B) incorporated into the endomembrane system of the cell (in other words, the peptide will be inserted into a membrane such as the plasma membrane, ER membrane, Golgi membrane, etc.). Lastly, it is the nuclear localization sequence (NLS) that, when added to a protein, allows it to enter the nucleus through the nuclear membrane.
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What are some post-translational modifications collagen goes thru before attaining its final structure?
I. The precursor collagen molecule undergoes hydroxylation of selected proline and lysine amino acids.
II. The procollagen precursor is glycosylated by the addition of galactose and glucose.
III. Procollagen has amino and carboxy procollagen extension propeptides that make it soluble.
IV. Procollagen proteinases remove extension peptides from the ends of the molecule to form collagen.
What are some post-translational modifications collagen goes thru before attaining its final structure?
I. The precursor collagen molecule undergoes hydroxylation of selected proline and lysine amino acids.
II. The procollagen precursor is glycosylated by the addition of galactose and glucose.
III. Procollagen has amino and carboxy procollagen extension propeptides that make it soluble.
IV. Procollagen proteinases remove extension peptides from the ends of the molecule to form collagen.
Procollagen has amino and carboxy procollagen extension propeptides that make it soluble. The preprocollagen undergoes both hydroxylation and glycosylation at specific aminoacid residues to form procollagen. Once secreted extracellularly, proteinases remove the extension peptides from procollagen to form the final collagen molecule.
Procollagen has amino and carboxy procollagen extension propeptides that make it soluble. The preprocollagen undergoes both hydroxylation and glycosylation at specific aminoacid residues to form procollagen. Once secreted extracellularly, proteinases remove the extension peptides from procollagen to form the final collagen molecule.
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Which of the following enzyme cofactors transfer methyl groups?
Which of the following enzyme cofactors transfer methyl groups?
Biotin moves carboxyl groups in the enzyme acetyl-CoA carboxylase. Tetrahydrofolate and S-adenylosyl methionine move methyl groups in amino acid synthesis and post-translational modifications such as DNA methylation. B12 cobalamin is a cofactor in the reactions producing succinyl-CoA and methionine, where it transfers methyl groups to complete the products.
Biotin moves carboxyl groups in the enzyme acetyl-CoA carboxylase. Tetrahydrofolate and S-adenylosyl methionine move methyl groups in amino acid synthesis and post-translational modifications such as DNA methylation. B12 cobalamin is a cofactor in the reactions producing succinyl-CoA and methionine, where it transfers methyl groups to complete the products.
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Which of the following is a true statement regarding translation in eukaryotes?
Which of the following is a true statement regarding translation in eukaryotes?
Translation is a process by which polypeptides are synthesized from a mRNA transcript, which was previously synthesized from the process of transcription. During this process, tRNA acts as a carrier by bringing with it specific amino acids to the ribosome, which are then incorporated into a growing polypeptide chain.
Eukaryotic translation differs in quite a few ways from prokaryotic translation. For one thing, prokaryotic mRNA contains a Shine-Delgarno sequence, which serves as a binding site for prokaryotic ribosomes to assemble on the mRNA. This binding, in turn, helps to initiate translation in prokaryotic cells. Eukaryotic cells do not contain a Shine-Delgarno sequence.
Furthermore, in eukaryotes, translation always begins with the assembly of ribosomal subunits on mRNA in the cytosol. Therefore, translation always begins on free ribosomes in the cytosol! Sometimes, translation will also finish on free ribosomes if the resulting protein is destined to stay within the cytosol where it will serve its function. Alternatively, if the first few amino acids of the polypeptide consists of a specific "signal sequence," translation will be temporarily paused. During this time, the entire ribosome-mRNA-polypeptide complex will be translocated to the rough endoplasmic reticulum. Once attached, polypeptide synthesis will resume and the polypeptide will thread its way into the endoplasmic reticulum. As it does so, additional folding and post-translational modifications are usually done to the polypeptide for it to carry out its proper function. Generally, polypeptides that make their way through the endoplasmic reticulum are destined either to be secreted out of the cell, or to become incorporated into the endomembrane system of the cell. And finally, as polypeptides are synthesized on a ribosome, whether it is free or bound, the amino terminus (aka N-terminus) side of the polypeptide is synthesized first and the carboxy terminus (aka C-terminus) is synthesized last.
Translation is a process by which polypeptides are synthesized from a mRNA transcript, which was previously synthesized from the process of transcription. During this process, tRNA acts as a carrier by bringing with it specific amino acids to the ribosome, which are then incorporated into a growing polypeptide chain.
Eukaryotic translation differs in quite a few ways from prokaryotic translation. For one thing, prokaryotic mRNA contains a Shine-Delgarno sequence, which serves as a binding site for prokaryotic ribosomes to assemble on the mRNA. This binding, in turn, helps to initiate translation in prokaryotic cells. Eukaryotic cells do not contain a Shine-Delgarno sequence.
Furthermore, in eukaryotes, translation always begins with the assembly of ribosomal subunits on mRNA in the cytosol. Therefore, translation always begins on free ribosomes in the cytosol! Sometimes, translation will also finish on free ribosomes if the resulting protein is destined to stay within the cytosol where it will serve its function. Alternatively, if the first few amino acids of the polypeptide consists of a specific "signal sequence," translation will be temporarily paused. During this time, the entire ribosome-mRNA-polypeptide complex will be translocated to the rough endoplasmic reticulum. Once attached, polypeptide synthesis will resume and the polypeptide will thread its way into the endoplasmic reticulum. As it does so, additional folding and post-translational modifications are usually done to the polypeptide for it to carry out its proper function. Generally, polypeptides that make their way through the endoplasmic reticulum are destined either to be secreted out of the cell, or to become incorporated into the endomembrane system of the cell. And finally, as polypeptides are synthesized on a ribosome, whether it is free or bound, the amino terminus (aka N-terminus) side of the polypeptide is synthesized first and the carboxy terminus (aka C-terminus) is synthesized last.
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