Nucleotides and Nucleic Acids (5D) - MCAT Chemical and Physical Foundations of Biological Systems
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Which bond forms the nucleic acid sugar-phosphate backbone?
Which bond forms the nucleic acid sugar-phosphate backbone?
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$3'$-$5'$ phosphodiester bond. Phosphodiester bonds link nucleotides, creating the directional backbone of DNA and RNA.
$3'$-$5'$ phosphodiester bond. Phosphodiester bonds link nucleotides, creating the directional backbone of DNA and RNA.
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Which functional groups are joined to form a $3'$-$5'$ phosphodiester bond?
Which functional groups are joined to form a $3'$-$5'$ phosphodiester bond?
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$3'$-$OH$ of one sugar to $5'$ phosphate of the next nucleotide. This linkage ensures the 5' to 3' polarity in nucleic acid strands.
$3'$-$OH$ of one sugar to $5'$ phosphate of the next nucleotide. This linkage ensures the 5' to 3' polarity in nucleic acid strands.
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Which bases are pyrimidines in nucleic acids?
Which bases are pyrimidines in nucleic acids?
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Cytosine, thymine, and uracil. Pyrimidines are single-ringed bases that pair with purines in nucleic acid duplexes.
Cytosine, thymine, and uracil. Pyrimidines are single-ringed bases that pair with purines in nucleic acid duplexes.
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What base is found in RNA but not in DNA?
What base is found in RNA but not in DNA?
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Uracil. RNA uses uracil instead of thymine to pair with adenine during transcription and translation.
Uracil. RNA uses uracil instead of thymine to pair with adenine during transcription and translation.
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How many hydrogen bonds are in a $G$-$C$ base pair in DNA?
How many hydrogen bonds are in a $G$-$C$ base pair in DNA?
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$3$ hydrogen bonds. Three hydrogen bonds between guanine and cytosine provide stronger pairing in DNA.
$3$ hydrogen bonds. Three hydrogen bonds between guanine and cytosine provide stronger pairing in DNA.
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What is the chemical difference between ribose and deoxyribose?
What is the chemical difference between ribose and deoxyribose?
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Deoxyribose has $H$ at $2'$; ribose has $OH$ at $2'$. The absence of the 2'-OH in deoxyribose enhances DNA stability by preventing hydrolysis.
Deoxyribose has $H$ at $2'$; ribose has $OH$ at $2'$. The absence of the 2'-OH in deoxyribose enhances DNA stability by preventing hydrolysis.
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Which atoms are connected by the N-glycosidic bond in nucleotides?
Which atoms are connected by the N-glycosidic bond in nucleotides?
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Sugar $1'$ carbon to base $N$ (purine $N^9$, pyrimidine $N^1$). The glycosidic bond connects the anomeric carbon of the sugar to the nitrogen of the base.
Sugar $1'$ carbon to base $N$ (purine $N^9$, pyrimidine $N^1$). The glycosidic bond connects the anomeric carbon of the sugar to the nitrogen of the base.
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What is the standard base-pairing rule in DNA?
What is the standard base-pairing rule in DNA?
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$A$ pairs with $T$; $G$ pairs with $C$. Complementary base pairing via hydrogen bonds stabilizes the DNA double helix.
$A$ pairs with $T$; $G$ pairs with $C$. Complementary base pairing via hydrogen bonds stabilizes the DNA double helix.
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What is the standard base-pairing rule in RNA?
What is the standard base-pairing rule in RNA?
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$A$ pairs with $U$; $G$ pairs with $C$. RNA uses uracil to pair with adenine, enabling specific interactions in RNA structures.
$A$ pairs with $U$; $G$ pairs with $C$. RNA uses uracil to pair with adenine, enabling specific interactions in RNA structures.
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How many hydrogen bonds are in an $A$-$T$ base pair in DNA?
How many hydrogen bonds are in an $A$-$T$ base pair in DNA?
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$2$ hydrogen bonds. Two hydrogen bonds form between adenine and thymine, contributing to DNA stability.
$2$ hydrogen bonds. Two hydrogen bonds form between adenine and thymine, contributing to DNA stability.
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Which bases are purines in nucleic acids?
Which bases are purines in nucleic acids?
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Adenine and guanine. Purines are double-ringed bases essential for DNA and RNA structure and function.
Adenine and guanine. Purines are double-ringed bases essential for DNA and RNA structure and function.
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What is the structural difference between a nucleoside and a nucleotide?
What is the structural difference between a nucleoside and a nucleotide?
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Nucleoside lacks phosphate; nucleotide includes phosphate. Nucleosides are precursors to nucleotides, with the phosphate addition enabling polymerization into nucleic acids.
Nucleoside lacks phosphate; nucleotide includes phosphate. Nucleosides are precursors to nucleotides, with the phosphate addition enabling polymerization into nucleic acids.
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What are the three components of a nucleotide?
What are the three components of a nucleotide?
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Nitrogenous base + pentose sugar + phosphate group. Nucleotides form the building blocks of nucleic acids, combining these components via covalent bonds.
Nitrogenous base + pentose sugar + phosphate group. Nucleotides form the building blocks of nucleic acids, combining these components via covalent bonds.
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Which end of a nucleic acid strand typically has the free hydroxyl group?
Which end of a nucleic acid strand typically has the free hydroxyl group?
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The $3'$ end. The 3' end hydroxyl is the site for chain elongation during nucleic acid synthesis.
The $3'$ end. The 3' end hydroxyl is the site for chain elongation during nucleic acid synthesis.
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Which end of a nucleic acid strand typically has the free phosphate group?
Which end of a nucleic acid strand typically has the free phosphate group?
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The $5'$ end. The 5' end phosphate is where synthesis begins and caps or modifications often occur.
The $5'$ end. The 5' end phosphate is where synthesis begins and caps or modifications often occur.
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Which DNA base pair is expected to increase duplex melting temperature ($T_m$)?
Which DNA base pair is expected to increase duplex melting temperature ($T_m$)?
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Higher $G$-$C$ content. G-C pairs form three hydrogen bonds, increasing stability and thus raising the melting temperature.
Higher $G$-$C$ content. G-C pairs form three hydrogen bonds, increasing stability and thus raising the melting temperature.
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What is the major chemical reason RNA is less stable than DNA in base?
What is the major chemical reason RNA is less stable than DNA in base?
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RNA has a $2'$-$OH$ that promotes backbone hydrolysis. The 2'-OH in RNA enables nucleophilic attack on the phosphodiester bond in alkaline conditions.
RNA has a $2'$-$OH$ that promotes backbone hydrolysis. The 2'-OH in RNA enables nucleophilic attack on the phosphodiester bond in alkaline conditions.
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Which nitrogenous bases are aromatic and therefore absorb UV light near $260,\text{nm}$?
Which nitrogenous bases are aromatic and therefore absorb UV light near $260,\text{nm}$?
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All nucleobases (purines and pyrimidines) are aromatic. Aromaticity confers planarity and UV absorbance, useful for quantifying nucleic acids.
All nucleobases (purines and pyrimidines) are aromatic. Aromaticity confers planarity and UV absorbance, useful for quantifying nucleic acids.
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What is the key structural difference between purines and pyrimidines?
What is the key structural difference between purines and pyrimidines?
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Purines have two rings; pyrimidines have one ring. The ring structure affects base pairing and stacking interactions in nucleic acids.
Purines have two rings; pyrimidines have one ring. The ring structure affects base pairing and stacking interactions in nucleic acids.
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What base is found in DNA but not in RNA?
What base is found in DNA but not in RNA?
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Thymine. DNA incorporates thymine for greater stability against cytosine deamination compared to uracil.
Thymine. DNA incorporates thymine for greater stability against cytosine deamination compared to uracil.
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