Molecular Biology and Genetics - GRE
Card 0 of 756
Which of the following is not true about transposable elements?
Which of the following is not true about transposable elements?
Transposable elements are portions of the DNA that are free to move around the genome and are generally considered non-coding DNA. This can be potentially dangerous, however. Transposable elements can insert themselves in the coding regions of genes, thus making them non-functional. This can lead to disease. Both eukaryotic and prokaryotic genomes contain transposable elements.
Transposable elements are portions of the DNA that are free to move around the genome and are generally considered non-coding DNA. This can be potentially dangerous, however. Transposable elements can insert themselves in the coding regions of genes, thus making them non-functional. This can lead to disease. Both eukaryotic and prokaryotic genomes contain transposable elements.
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Transposable elements, or transposons, are separated into two classes. Which of these categories of life have class I transposons in their genomes?
I. Bacteria
II. Yeast
III. Eukaryotes
Transposable elements, or transposons, are separated into two classes. Which of these categories of life have class I transposons in their genomes?
I. Bacteria
II. Yeast
III. Eukaryotes
Class I transposable elements are RNA-mediated elements of a single evolutionary origin, and are found in yeast, which only have class I elements, and in eukaryotes, which have both class I and class II elements. Bacteria only have class II elements, and hence are not included in the correct answer to this question.
Class I transposable elements are RNA-mediated elements of a single evolutionary origin, and are found in yeast, which only have class I elements, and in eukaryotes, which have both class I and class II elements. Bacteria only have class II elements, and hence are not included in the correct answer to this question.
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Barbara McClintock initially discovered transposons in her work on corn at Cold Spring Harbor Lab, which she called the Ac / Ds system. What were dissociators (Ds)?
Barbara McClintock initially discovered transposons in her work on corn at Cold Spring Harbor Lab, which she called the Ac / Ds system. What were dissociators (Ds)?
Barbara McClintock named the transposons that are defective, and serve as sites of chromosomal breakage where other transposons insert (the associator, Ac) the dissociators. These were likely transposons that lacked the transposase that catalyzes their movement.
Barbara McClintock named the transposons that are defective, and serve as sites of chromosomal breakage where other transposons insert (the associator, Ac) the dissociators. These were likely transposons that lacked the transposase that catalyzes their movement.
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Transposable elements can be significant factors in causing newly resistant bacterial strains. How do transposons cause resistance to develop?
Transposable elements can be significant factors in causing newly resistant bacterial strains. How do transposons cause resistance to develop?
Two transposons flanking an antibiotic resistance gene can easily move between bacteria and confer new resistance. A mix of transposons and new genes such as this is called a composite transposon. Recall that bacteria exchange genetic information via conjugation, transduction, and transformation.
Two transposons flanking an antibiotic resistance gene can easily move between bacteria and confer new resistance. A mix of transposons and new genes such as this is called a composite transposon. Recall that bacteria exchange genetic information via conjugation, transduction, and transformation.
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What makes an LTR retrotransposon unique among other transposons?
What makes an LTR retrotransposon unique among other transposons?
LTR stands for Long Terminal Repeats, which are 250-500 base pair repeats located on the ends of a transposon. These repeats encode a series of proteins, most significantly transposase. These are very likely to be early evolutionarily stages of retroviruses.
LTR stands for Long Terminal Repeats, which are 250-500 base pair repeats located on the ends of a transposon. These repeats encode a series of proteins, most significantly transposase. These are very likely to be early evolutionarily stages of retroviruses.
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How do non-LTR retrotransposons insert into the genome?
How do non-LTR retrotransposons insert into the genome?
Non-LTR retrotransposons use an endonuclease that nicks thymine-rich host DNA, which eventually leads to incorporation of the transposon by host DNA repair functions. These other methods are all associated with different specializations of transposon.
Non-LTR retrotransposons use an endonuclease that nicks thymine-rich host DNA, which eventually leads to incorporation of the transposon by host DNA repair functions. These other methods are all associated with different specializations of transposon.
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What differentiates a LTR retrotransposon and a retrovirus?
What differentiates a LTR retrotransposon and a retrovirus?
The only difference between most LTR retrotransposons and retroviruses are that retroviruses can encode an envelope protein. Phylogenetic analyses have shown that retrotransposons and retroviruses are extremely closely related, and may be direct ancestors of one another.
The only difference between most LTR retrotransposons and retroviruses are that retroviruses can encode an envelope protein. Phylogenetic analyses have shown that retrotransposons and retroviruses are extremely closely related, and may be direct ancestors of one another.
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The hybrid dysgenesis phenomenon was observed in Drosophila flies. It was determined that this was caused by a transposon no longer under control in wild type - lab strain crosses. What are transposons commonly controlled by in their hosts?
The hybrid dysgenesis phenomenon was observed in Drosophila flies. It was determined that this was caused by a transposon no longer under control in wild type - lab strain crosses. What are transposons commonly controlled by in their hosts?
Movement of transposons is very commonly controlled by RNA interference. The RNAi system cuts up problematic RNAs, and uses these small pieces to target transposons for destruction.
Movement of transposons is very commonly controlled by RNA interference. The RNAi system cuts up problematic RNAs, and uses these small pieces to target transposons for destruction.
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How do transposons rapidly propogate through and between species?
How do transposons rapidly propogate through and between species?
It is hypothesized that transposons can rapidly move through populations and species by horizontal transfer, most likely through viruses.
It is hypothesized that transposons can rapidly move through populations and species by horizontal transfer, most likely through viruses.
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Which of the following types of RNA have been shown to regulate protein synthesis?
I. lncRNA
II. miRNA
III. tRNA
Which of the following types of RNA have been shown to regulate protein synthesis?
I. lncRNA
II. miRNA
III. tRNA
Protein synthesis can be directly affected by molecules involved in translation, or indirectly by molecules involved in the transcription of mRNA templates.
Transfer RNA (tRNA) is involved in translation and serves the function of bringing amino acids to ribosomes. Due to its important function in translation tRNA, is capable of globally controlling translation and, therefore, is involved in protein regulation.
Long non-coding RNA (lncRNA) has been shown to regulate transcription in a number of ways. One of the most prominent is the existence of a lncRNA (Xist) that inactivates the majority of the extra X-chromosome in human females.
Micro RNA (miRNA) is involved in a process known as RNAi and is capable of controlling the translation of targeted molecules of mRNA.
Protein synthesis can be directly affected by molecules involved in translation, or indirectly by molecules involved in the transcription of mRNA templates.
Transfer RNA (tRNA) is involved in translation and serves the function of bringing amino acids to ribosomes. Due to its important function in translation tRNA, is capable of globally controlling translation and, therefore, is involved in protein regulation.
Long non-coding RNA (lncRNA) has been shown to regulate transcription in a number of ways. One of the most prominent is the existence of a lncRNA (Xist) that inactivates the majority of the extra X-chromosome in human females.
Micro RNA (miRNA) is involved in a process known as RNAi and is capable of controlling the translation of targeted molecules of mRNA.
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X-chromosome inactivation occurs in females in which one X-chromosome is silenced and transcriptionally inactivated. The X-inactive specific transcript (Xist) gene is responsible for mediating this inactivation.
What does Xist encode?
X-chromosome inactivation occurs in females in which one X-chromosome is silenced and transcriptionally inactivated. The X-inactive specific transcript (Xist) gene is responsible for mediating this inactivation.
What does Xist encode?
The correct answer is long non-coding (lnc) RNA. Xist lncRNA coats the X-chromosome from which it is transcribed, effectively silencing that X-chromosome. MicroRNAs are small RNAs (~20 base pairs (bp)) and play a role in RNA silencing and post-transcriptional regulation of gene expression. Short interfering RNAs are double-stranded (20-25 bp) and play a role in post-transcriptional gene silencing. Piwi-interacting RNAs are small non-coding RNAs that interact with piwi proteins in epigenetic and post-transcriptional silencing of genetic elements such as retroposons. While MicroRNAs, siRNAs and Piwi-interacting RNAs all silence genes, the mechanism of X-chromosome inactivation requires Xist lncRNA.
The correct answer is long non-coding (lnc) RNA. Xist lncRNA coats the X-chromosome from which it is transcribed, effectively silencing that X-chromosome. MicroRNAs are small RNAs (~20 base pairs (bp)) and play a role in RNA silencing and post-transcriptional regulation of gene expression. Short interfering RNAs are double-stranded (20-25 bp) and play a role in post-transcriptional gene silencing. Piwi-interacting RNAs are small non-coding RNAs that interact with piwi proteins in epigenetic and post-transcriptional silencing of genetic elements such as retroposons. While MicroRNAs, siRNAs and Piwi-interacting RNAs all silence genes, the mechanism of X-chromosome inactivation requires Xist lncRNA.
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Which comparisons between eukaryotic and prokaryotic genomes are true?
Which comparisons between eukaryotic and prokaryotic genomes are true?
The only true comparison of those listed is that eukaryotic genes are not often present in operons, like prokaryotes often have (think the frequently studied lac operon). Eukaryotes, not prokaryotes, have many transposable elements (a contributing factor to why our genomes are so large). Prokaryotes do not have large spacer regions between their genes, their genomes are often extremely compact. Prokaryotic cells lack nuclei, thus, DNA replication occurs in the cytosol.
The only true comparison of those listed is that eukaryotic genes are not often present in operons, like prokaryotes often have (think the frequently studied lac operon). Eukaryotes, not prokaryotes, have many transposable elements (a contributing factor to why our genomes are so large). Prokaryotes do not have large spacer regions between their genes, their genomes are often extremely compact. Prokaryotic cells lack nuclei, thus, DNA replication occurs in the cytosol.
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Which comparisons between eukaryotic and prokaryotic genomes are true?
Which comparisons between eukaryotic and prokaryotic genomes are true?
The only true comparison of those listed is that eukaryotic genes are not often present in operons, like prokaryotes often have (think the frequently studied lac operon). Eukaryotes, not prokaryotes, have many transposable elements (a contributing factor to why our genomes are so large). Prokaryotes do not have large spacer regions between their genes, their genomes are often extremely compact. Prokaryotic cells lack nuclei, thus, DNA replication occurs in the cytosol.
The only true comparison of those listed is that eukaryotic genes are not often present in operons, like prokaryotes often have (think the frequently studied lac operon). Eukaryotes, not prokaryotes, have many transposable elements (a contributing factor to why our genomes are so large). Prokaryotes do not have large spacer regions between their genes, their genomes are often extremely compact. Prokaryotic cells lack nuclei, thus, DNA replication occurs in the cytosol.
Compare your answer with the correct one above
Which of the following types of RNA have been shown to regulate protein synthesis?
I. lncRNA
II. miRNA
III. tRNA
Which of the following types of RNA have been shown to regulate protein synthesis?
I. lncRNA
II. miRNA
III. tRNA
Protein synthesis can be directly affected by molecules involved in translation, or indirectly by molecules involved in the transcription of mRNA templates.
Transfer RNA (tRNA) is involved in translation and serves the function of bringing amino acids to ribosomes. Due to its important function in translation tRNA, is capable of globally controlling translation and, therefore, is involved in protein regulation.
Long non-coding RNA (lncRNA) has been shown to regulate transcription in a number of ways. One of the most prominent is the existence of a lncRNA (Xist) that inactivates the majority of the extra X-chromosome in human females.
Micro RNA (miRNA) is involved in a process known as RNAi and is capable of controlling the translation of targeted molecules of mRNA.
Protein synthesis can be directly affected by molecules involved in translation, or indirectly by molecules involved in the transcription of mRNA templates.
Transfer RNA (tRNA) is involved in translation and serves the function of bringing amino acids to ribosomes. Due to its important function in translation tRNA, is capable of globally controlling translation and, therefore, is involved in protein regulation.
Long non-coding RNA (lncRNA) has been shown to regulate transcription in a number of ways. One of the most prominent is the existence of a lncRNA (Xist) that inactivates the majority of the extra X-chromosome in human females.
Micro RNA (miRNA) is involved in a process known as RNAi and is capable of controlling the translation of targeted molecules of mRNA.
Compare your answer with the correct one above
X-chromosome inactivation occurs in females in which one X-chromosome is silenced and transcriptionally inactivated. The X-inactive specific transcript (Xist) gene is responsible for mediating this inactivation.
What does Xist encode?
X-chromosome inactivation occurs in females in which one X-chromosome is silenced and transcriptionally inactivated. The X-inactive specific transcript (Xist) gene is responsible for mediating this inactivation.
What does Xist encode?
The correct answer is long non-coding (lnc) RNA. Xist lncRNA coats the X-chromosome from which it is transcribed, effectively silencing that X-chromosome. MicroRNAs are small RNAs (~20 base pairs (bp)) and play a role in RNA silencing and post-transcriptional regulation of gene expression. Short interfering RNAs are double-stranded (20-25 bp) and play a role in post-transcriptional gene silencing. Piwi-interacting RNAs are small non-coding RNAs that interact with piwi proteins in epigenetic and post-transcriptional silencing of genetic elements such as retroposons. While MicroRNAs, siRNAs and Piwi-interacting RNAs all silence genes, the mechanism of X-chromosome inactivation requires Xist lncRNA.
The correct answer is long non-coding (lnc) RNA. Xist lncRNA coats the X-chromosome from which it is transcribed, effectively silencing that X-chromosome. MicroRNAs are small RNAs (~20 base pairs (bp)) and play a role in RNA silencing and post-transcriptional regulation of gene expression. Short interfering RNAs are double-stranded (20-25 bp) and play a role in post-transcriptional gene silencing. Piwi-interacting RNAs are small non-coding RNAs that interact with piwi proteins in epigenetic and post-transcriptional silencing of genetic elements such as retroposons. While MicroRNAs, siRNAs and Piwi-interacting RNAs all silence genes, the mechanism of X-chromosome inactivation requires Xist lncRNA.
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Which of the following is not a phase in translation?
Which of the following is not a phase in translation?
There are four phases in translation: activation, initiation, elongation, and termination. Activation is the process that joins the correct amino acid to the correct tRNA. When the tRNA has an amino acid bound to it, it is "charged." Initiation occurs when the small ribosomal subunit binds the 5' end of mRNA, with the help of initiation factors and other proteins. The structure then recruits a methionine tRNA to the start codon to begin the elongation process. Elongation occurs as charged tRNA molecules transfer their amino acids to the growing polypeptide. Termination results when a stop codon is recognized by release factors and the completed protein is released from the ribosome.
Modification of the transcript occurs after translation has been completed.
There are four phases in translation: activation, initiation, elongation, and termination. Activation is the process that joins the correct amino acid to the correct tRNA. When the tRNA has an amino acid bound to it, it is "charged." Initiation occurs when the small ribosomal subunit binds the 5' end of mRNA, with the help of initiation factors and other proteins. The structure then recruits a methionine tRNA to the start codon to begin the elongation process. Elongation occurs as charged tRNA molecules transfer their amino acids to the growing polypeptide. Termination results when a stop codon is recognized by release factors and the completed protein is released from the ribosome.
Modification of the transcript occurs after translation has been completed.
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Which of the following is not a type of modification that can occur after translation?
Which of the following is not a type of modification that can occur after translation?
Post-translational modifications that may occur after a protein is translated include numerous processes to alter the structure or function of the protein. Trimming modification involves removal of the N- or C - terminal propeptides from zymogens to generate mature proteins. Covalent alterations, including phosphorylation, glycosylation and hydroxylation, are frequently used to modify the structure or energy state of a protein. Proteasomal degradation requires the attachment of ubiquitin to defective proteins to tag them for degradation and digestion. Amino acids from degraded proteins can often be recycled to generate new molecules.
5' capping occurs in the nucleus after transcription and is required for transport of RNA out of the nucleus prior to translation.
Post-translational modifications that may occur after a protein is translated include numerous processes to alter the structure or function of the protein. Trimming modification involves removal of the N- or C - terminal propeptides from zymogens to generate mature proteins. Covalent alterations, including phosphorylation, glycosylation and hydroxylation, are frequently used to modify the structure or energy state of a protein. Proteasomal degradation requires the attachment of ubiquitin to defective proteins to tag them for degradation and digestion. Amino acids from degraded proteins can often be recycled to generate new molecules.
5' capping occurs in the nucleus after transcription and is required for transport of RNA out of the nucleus prior to translation.
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Which of the following ensures that viral gene translation occurs even when host translation is inhibited?
Which of the following ensures that viral gene translation occurs even when host translation is inhibited?
Viruses utilize IRES to allow translation to occur in a 5' cap-independent manner. Translational machinery (ribosomes) are located to the IRES so that translation can occur. 5' guanine cap and 3' poly-A tails are mRNA modifications that are normally necessary to initiate translation, but are cap-dependent. The promoter regulates genes expression on the level of transcription, whereas the 5' UTR regulates translation.
Viruses utilize IRES to allow translation to occur in a 5' cap-independent manner. Translational machinery (ribosomes) are located to the IRES so that translation can occur. 5' guanine cap and 3' poly-A tails are mRNA modifications that are normally necessary to initiate translation, but are cap-dependent. The promoter regulates genes expression on the level of transcription, whereas the 5' UTR regulates translation.
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Most translation occurs by a mRNA cap-dependent mechanism, however, translation can occur by cap-independent initiation. One mechanism by which eukaryotic cells can initiate cap-independent translation is by which of the following approaches?
Most translation occurs by a mRNA cap-dependent mechanism, however, translation can occur by cap-independent initiation. One mechanism by which eukaryotic cells can initiate cap-independent translation is by which of the following approaches?
The correct answer is the internal ribosome entry site. This site is a specific nucleotide sequence that allows for translation initiation in the middle of a mRNA sequence, rather than at the 5' end, and does not require the cap-dependent elF4F initiation complex or the 5'cap. The poly(A)-binding protein complexes with the 3' end of mRNA strands during translation initiation via the cap-dependent mechanism.
The correct answer is the internal ribosome entry site. This site is a specific nucleotide sequence that allows for translation initiation in the middle of a mRNA sequence, rather than at the 5' end, and does not require the cap-dependent elF4F initiation complex or the 5'cap. The poly(A)-binding protein complexes with the 3' end of mRNA strands during translation initiation via the cap-dependent mechanism.
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Which amino acid is the "start" amino acid in a peptide chain?
Which amino acid is the "start" amino acid in a peptide chain?
The correct answer is methionine. The ATG codon triplet in a mRNA strand codes for the start of the peptide, and this first amino acid that is coded by ATG is methionine.
The correct answer is methionine. The ATG codon triplet in a mRNA strand codes for the start of the peptide, and this first amino acid that is coded by ATG is methionine.
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