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Questions and Answers
What is a primary function of nucleotides in biological systems?
What is a primary function of nucleotides in biological systems?
Which of the following bases is found only in RNA?
Which of the following bases is found only in RNA?
Which type of bond connects the pentose in nucleotides to the nucleobase?
Which type of bond connects the pentose in nucleotides to the nucleobase?
At neutral pH, what is the charge of the phosphate group in nucleotides?
At neutral pH, what is the charge of the phosphate group in nucleotides?
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Which of the following is NOT a function of nucleic acids?
Which of the following is NOT a function of nucleic acids?
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What characteristic of nucleobases allows them to absorb UV light?
What characteristic of nucleobases allows them to absorb UV light?
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What is the predominant form of nucleobases in solution at neutral pH due to tautomerism?
What is the predominant form of nucleobases in solution at neutral pH due to tautomerism?
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Which of the following is a purine base found in both DNA and RNA?
Which of the following is a purine base found in both DNA and RNA?
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Which carbon does the bond in β configuration of sugar attach to?
Which carbon does the bond in β configuration of sugar attach to?
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What is the consequence of bond cleavage in nucleotides?
What is the consequence of bond cleavage in nucleotides?
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In a normal B-DNA structure, what conformation is primarily found around the N-glycosidic bond?
In a normal B-DNA structure, what conformation is primarily found around the N-glycosidic bond?
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Which element in nucleosides is typically methylated in eukaryotes?
Which element in nucleosides is typically methylated in eukaryotes?
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What modification occurs with inosine in tRNA?
What modification occurs with inosine in tRNA?
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What type of linkages form the covalent backbone of polynucleotides?
What type of linkages form the covalent backbone of polynucleotides?
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Which of the following modifications is not found in eukaryotes?
Which of the following modifications is not found in eukaryotes?
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What angle corresponds to syn conformation around the N-glycosidic bond?
What angle corresponds to syn conformation around the N-glycosidic bond?
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What is the main reason that RNA degrades so quickly in cells?
What is the main reason that RNA degrades so quickly in cells?
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Which of the following statements about RNA is true?
Which of the following statements about RNA is true?
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How does the action of S-RNase. found in plants, primarily function?
How does the action of S-RNase. found in plants, primarily function?
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What does Watson and Crick's discovery of the DNA structure emphasize?
What does Watson and Crick's discovery of the DNA structure emphasize?
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Which best describes the base pairing in double-stranded DNA?
Which best describes the base pairing in double-stranded DNA?
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What mainly distinguishes RNA from DNA?
What mainly distinguishes RNA from DNA?
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What role does RNase P serve in cellular function?
What role does RNase P serve in cellular function?
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What was a significant outcome of the study of the DNA structure?
What was a significant outcome of the study of the DNA structure?
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In the context of RNA hydrolysis, which enzyme cleaves double-stranded RNA?
In the context of RNA hydrolysis, which enzyme cleaves double-stranded RNA?
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Why is the discovery of the DNA double helix considered a pivotal point in biology?
Why is the discovery of the DNA double helix considered a pivotal point in biology?
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What major feature characterizes the Watson-Crick model of B-DNA?
What major feature characterizes the Watson-Crick model of B-DNA?
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What is the role of DNA polymerases during DNA replication?
What is the role of DNA polymerases during DNA replication?
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Which type of RNA is specifically involved in matching amino acids with the mRNA code?
Which type of RNA is specifically involved in matching amino acids with the mRNA code?
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What effect does high GC content have on the melting temperature (Tm) of DNA?
What effect does high GC content have on the melting temperature (Tm) of DNA?
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How is DNA denaturation typically monitored?
How is DNA denaturation typically monitored?
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What is the significance of palindromic sequences in DNA?
What is the significance of palindromic sequences in DNA?
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What happens during the deamination process in DNA?
What happens during the deamination process in DNA?
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What occurs when DNA is subjected to high temperatures during melting?
What occurs when DNA is subjected to high temperatures during melting?
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Which of the following is true about the structure of mRNA compared to DNA?
Which of the following is true about the structure of mRNA compared to DNA?
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What is the basis for the polymerase chain reaction (PCR)?
What is the basis for the polymerase chain reaction (PCR)?
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Study Notes
Nucleotides and Nucleic Acids
- Nucleotides have biological functions in energy transfer (ATP), enzyme cofactors (NAD+), and signaling (cAMP).
- Nucleic acids function in storing genetic information (DNA), transmitting genetic information (mRNA), processing genetic information (ribozymes), and protein synthesis (tRNA and rRNA).
Nucleotides and Nucleosides
- A nucleotide is composed of a nitrogenous base, a pentose sugar, and a phosphate group.
- A nucleoside is composed of a nitrogenous base and a pentose sugar.
- A nucleobase is simply a nitrogenous base.
Phosphate Group
- The phosphate group is negatively charged at neutral pH.
- Common attachment point is the 5' position in nucleic acids.
- Typically found as 5'-triphosphates during nucleic acid synthesis.
- A single phosphate moiety is found per nucleotide in nucleic acids.
Pentose in Nucleotides
- RNA contains β-D-ribofuranose.
- DNA contains β-2'-deoxy-D-ribofuranose.
- Different puckered conformations of the sugar ring are possible.
Nucleobases
- Derivatives of purines or pyrimidines
- Nitrogen-containing heteroaromatic molecules.
- Planar or nearly planar structures.
- Absorb UV light around 250-270 nm.
- Examples: Adenine, Guanine, Cytosine, Thymine, Uracil
N-Glycosidic Bond
- The pentose ring attaches to the nucleobase via an N-glycosidic bond.
- Formed to position N1 in pyrimidines.
- Formed to position N9 in purines.
- Generally quite stable.
- Cleavage is catalyzed by acid.
Deamination
- A very slow reaction, involving the loss of an amino group.
- In mammalian cells, a significant number of cytosine residues are deaminated to uracil; many mechanism for repairing.
- Loss of an amino group also occurs in 5-methylcytosine residues. This can cause mutations but is typically repaired through the methyl group.
- Significance for purines: 10,000 purines lost/day in a mammalian cell.
Depurination
- N-glycosidic bond hydrolysis removes purines.
- A significant amount of purines are lost daily (10,000 in mammalian cells); repaired.
Oxidative Damage
- Hydroxylation of guanine is a common form of oxidative damage.
- Mitochondrial DNA is particularly vulnerable to oxidative damage.
- Chemical alkylation is also a form of chemical damage, including methylation of guanine.
- Cells have mechanisms to repair these modifications.
UV Light and Ionizing Radiation
- UV light induces pyrimidine dimerization, a primary cause of skin cancer.
- Ionizing radiation (X-rays, γ-rays) cause DNA ring opening and strand breakage. These are difficult to fix.
DNA Denaturation and Renaturation
- Covalent bonds remain intact during denaturation; the genetic code remains intact.
- Hydrogen bonds are broken, causing the two strands to separate.
- Base stacking is lost causing increased UV absorbance.
- Denaturation may be reversible (annealing).
- This process is important for techniques such as PCR.
Factors Affecting DNA Denaturation
- Midpoint of melting (Tm) depends on base composition (high CG content increases Tm).
- Tm depends on DNA length (longer DNA has a higher Tm).
- Tm depends on pH and ionic strength (high salt increases Tm).
Nomenclature of Nucleotides
- Both ribo and deoxyribo-specific nucleotides are included in the generic terms nucleoside and nucleotide.
- Specific names such as "adenosine" and "deoxyadenosine" are used.
Other Forms of DNA Structure
- DNA exists in multiple structural forms, including A form, B form and Z form. These forms differ slightly in helical parameters.
mRNA
- Messenger RNA (mRNA) is synthesized using a DNA template.
- It contains ribose instead of deoxyribose and uracil instead of thymine.
- One mRNA sequence may code for multiple proteins (polycistronic).
tRNA
- Transfer RNA (tRNA) molecules have specialized structures for matching amino acids to the mRNA code..
Types of DNA
- DNA is in different forms such as monocistronic and polycistronic.
Palindromic Sequences
- Palindromic sequences are sequences that read the same forwards and backwards.
- They can form hairpin structures in single-stranded DNA or RNA and cruciforms in double-stranded DNA.
Two Near-Complementary DNA Strands
- Complementary DNA sequences can hybridize and hybridized DNA can be detected through multiple methods (e.g. fluorescent probes, radioactive probes, etc.)
Molecular Mechanisms of Mutagenesis
- Mechanisms causing DNA mutations were covered including deamination, depurination and alkylation (oxidative modifications of DNA by chemical agents).
- DNA is damaged through physical (UV, radiation) and chemical agents that break or modify the structure.
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Description
Test your knowledge of the crucial functions of nucleotides and the structures of nucleic acids. This quiz covers key concepts, including the types of bonds involved, the characteristics of bases, and modifications in DNA and RNA. Perfect for biology students looking to deepen their understanding of nucleotides.
