Nucleotides and Nucleic Acids Quiz
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Questions and Answers

What is a primary function of nucleotides in biological systems?

  • Storage of genetic information
  • Processing of genetic information
  • Energy for metabolism (correct)
  • Transmission of genetic information

Which of the following bases is found only in RNA?

  • Cytosine
  • Adenine
  • Thymine
  • Uracil (correct)

Which type of bond connects the pentose in nucleotides to the nucleobase?

  • Hydrogen bond
  • Peptide bond
  • N-glycosidic bond (correct)
  • Phosphodiester bond

At neutral pH, what is the charge of the phosphate group in nucleotides?

<p>Negatively charged (B)</p> Signup and view all the answers

Which of the following is NOT a function of nucleic acids?

<p>Energy transfer (D)</p> Signup and view all the answers

What characteristic of nucleobases allows them to absorb UV light?

<p>Planar or almost planar structures (D)</p> Signup and view all the answers

What is the predominant form of nucleobases in solution at neutral pH due to tautomerism?

<p>Lactam form (C)</p> Signup and view all the answers

Which of the following is a purine base found in both DNA and RNA?

<p>Adenine (A)</p> Signup and view all the answers

Which carbon does the bond in β configuration of sugar attach to?

<p>Anomeric carbon (D)</p> Signup and view all the answers

What is the consequence of bond cleavage in nucleotides?

<p>It is catalyzed by acid. (B)</p> Signup and view all the answers

In a normal B-DNA structure, what conformation is primarily found around the N-glycosidic bond?

<p>Anti conformation (D)</p> Signup and view all the answers

Which element in nucleosides is typically methylated in eukaryotes?

<p>5-methylcytosine (A)</p> Signup and view all the answers

What modification occurs with inosine in tRNA?

<p>De-aminating adenosine (D)</p> Signup and view all the answers

What type of linkages form the covalent backbone of polynucleotides?

<p>Phosphodiester linkages (D)</p> Signup and view all the answers

Which of the following modifications is not found in eukaryotes?

<p>N6-Methyladenosine (C)</p> Signup and view all the answers

What angle corresponds to syn conformation around the N-glycosidic bond?

<p>0° (C)</p> Signup and view all the answers

What is the main reason that RNA degrades so quickly in cells?

<p>RNA is hydrolyzed by enzymes. (D)</p> Signup and view all the answers

Which of the following statements about RNA is true?

<p>RNA has directionality with a 5’ and a 3’ end. (C)</p> Signup and view all the answers

How does the action of S-RNase. found in plants, primarily function?

<p>To prevent inbreeding. (A)</p> Signup and view all the answers

What does Watson and Crick's discovery of the DNA structure emphasize?

<p>The importance of collaboration in scientific research. (A)</p> Signup and view all the answers

Which best describes the base pairing in double-stranded DNA?

<p>A pairs with T and C pairs with G. (C)</p> Signup and view all the answers

What mainly distinguishes RNA from DNA?

<p>RNA is a linear polymer without branching. (B)</p> Signup and view all the answers

What role does RNase P serve in cellular function?

<p>It processes tRNA precursors. (A)</p> Signup and view all the answers

What was a significant outcome of the study of the DNA structure?

<p>Recognition of base pairing rules. (D)</p> Signup and view all the answers

In the context of RNA hydrolysis, which enzyme cleaves double-stranded RNA?

<p>Dicer. (B)</p> Signup and view all the answers

Why is the discovery of the DNA double helix considered a pivotal point in biology?

<p>It helped in understanding heredity and genetic information. (C)</p> Signup and view all the answers

What major feature characterizes the Watson-Crick model of B-DNA?

<p>The two strands are complementary (D)</p> Signup and view all the answers

What is the role of DNA polymerases during DNA replication?

<p>To synthesize new DNA strands (D)</p> Signup and view all the answers

Which type of RNA is specifically involved in matching amino acids with the mRNA code?

<p>Transfer RNA (D)</p> Signup and view all the answers

What effect does high GC content have on the melting temperature (Tm) of DNA?

<p>It increases Tm (C)</p> Signup and view all the answers

How is DNA denaturation typically monitored?

<p>UV spectrophotometry at 260 nm (B)</p> Signup and view all the answers

What is the significance of palindromic sequences in DNA?

<p>They can form hairpins and cruciforms (B)</p> Signup and view all the answers

What happens during the deamination process in DNA?

<p>It converts cytosine to uracil (C)</p> Signup and view all the answers

What occurs when DNA is subjected to high temperatures during melting?

<p>Both strands dissociate (A)</p> Signup and view all the answers

Which of the following is true about the structure of mRNA compared to DNA?

<p>Contains uracil instead of thymine (B)</p> Signup and view all the answers

What is the basis for the polymerase chain reaction (PCR)?

<p>Reversible thermal denaturation and annealing (A)</p> Signup and view all the answers

Flashcards

What is a nucleotide?

A nucleotide consists of a nitrogenous base, a pentose sugar, and a phosphate group.

What is a nucleoside?

A nucleoside consists only of a nitrogenous base and a pentose sugar.

What is a nucleobase?

A nitrogenous base is a heterocyclic molecule containing nitrogen atoms.

What are the five nitrogenous bases?

Adenine, guanine, cytosine, thymine, and uracil are the five nitrogenous bases found in DNA and RNA.

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What are the pentose sugars in DNA and RNA?

The pentose sugar in DNA is 2'-deoxyribose and in RNA is ribose.

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Where is the phosphate group attached in nucleotides?

The phosphate group in nucleotides is typically attached to the 5' position of the pentose sugar.

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What is the structure of DNA?

DNA is a double-stranded helix, with two complementary strands held together by hydrogen bonds between the nitrogenous bases.

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What is the structure of RNA?

RNA is typically single-stranded and can fold into complex three-dimensional structures.

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N-Glycosidic Bond

The bond formed between the sugar and the nitrogenous base in nucleotides.

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Nucleoside

A purine or pyrimidine ring system attached to a pentose sugar.

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Syn Conformation

The conformation where the nitrogenous base is on the same side of the sugar as the C5' atom.

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Anti Conformation

The conformation where the nitrogenous base is on the opposite side of the sugar from the C5' atom.

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Chi Conformation

The angle around the N-glycosidic bond that determines the conformation.

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Minor Nucleosides in DNA

Modified nucleosides found in DNA that play a role in DNA recognition and epigenetic regulation.

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Minor Nucleosides in RNA

Modified nucleosides found in RNA that play a role in structure and function, like in tRNA and rRNA.

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Phosphodiester Linkage

A covalent bond linking nucleotides together to form a polynucleotide chain.

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Why is RNA less stable than DNA?

RNA is more prone to degradation than DNA, particularly in cellular environments. This is because RNA is more reactive and susceptible to hydrolysis.

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What enzymes break down RNA?

RNA is typically broken down by enzymes known as RNases. These enzymes are present in cells and in the environment.

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What are ribozymes?

Ribozymes, such as RNase P, are RNA molecules that can act as enzymes. They are involved in various cellular processes, such as processing tRNAs.

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Describe how DNA bases pair.

The structure of DNA allows for specific pairing of bases. Adenine (A) binds with Thymine (T), and Guanine (G) binds with Cytosine (C). This is known as Watson-Crick base pairing.

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Why is the discovery of DNA's structure significant?

The discovery of DNA's structure revolutionized understanding of inheritance and genetic information. It is considered a pivotal moment in biological research.

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How did Watson and Crick determine DNA's structure?

Watson and Crick used X-ray diffraction data, gathered by Franklin and Wilkins, to deduce the double-helix structure of DNA. This was a collaborative effort with significant contributions from multiple researchers.

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Describe the structure of DNA.

The double helix structure of DNA features two strands with complementary base pairs held together by hydrogen bonds. This allows for accurate replication and transfer of genetic information.

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How does DNA differ from RNA in structure?

DNA differs from RNA in its sugar component. DNA uses deoxyribose, while RNA uses ribose. This structural difference contributes to the different properties of the two molecules.

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What is the function of DNA?

The sequence of nucleotides in DNA encodes genetic information. Each gene is a specific sequence of DNA that determines the production of a protein.

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What is the Watson-Crick model of DNA?

The Watson-Crick model describes the structure of DNA as a double helix with two antiparallel strands. Each strand is made up of a sugar-phosphate backbone with nitrogenous bases projecting inwards, forming hydrogen bonds with complementary bases on the opposite strand. The two strands are twisted around each other to form a helix.

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How do the bases in DNA pair?

Adenine (A) forms two hydrogen bonds with thymine (T), while guanine (G) forms three hydrogen bonds with cytosine (C). This complementary pairing ensures that the two strands of DNA are held together by strong hydrogen bonds.

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Why are the two strands of DNA antiparallel?

This means one strand runs from 5' to 3' and the other runs from 3' to 5'. This antiparallel orientation is crucial for DNA replication and transcription.

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How does DNA replication occur?

Replication is the process of creating an exact copy of a DNA molecule. It starts with the separation of the two DNA strands, with each strand serving as a template for the synthesis of a new complementary strand.

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What is the role of DNA polymerases in replication?

DNA polymerases are enzymes that catalyze the addition of nucleotides to the newly synthesized DNA strand. They use the existing strand as a template and ensure that the new strand is complementary to the template.

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What is the semi-conservative nature of DNA replication?

The newly formed DNA molecule contains one original (parent) strand and one newly synthesized (daughter) strand. This semi-conservative mechanism ensures accuracy and continuity of genetic information.

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What are palindromic sequences in DNA?

A palindromic sequence is a DNA sequence that reads the same backwards and forwards. Such sequences can form hairpin or cruciform structures, which are important for DNA regulation and protein binding.

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What is Messenger RNA (mRNA)?

Messenger RNA (mRNA) is a type of RNA that carries genetic information from DNA to ribosomes, where proteins are synthesized. mRNA is synthesized using DNA as a template and contains the code for the sequence of amino acids in a protein.

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What is Transfer RNA (tRNA)?

Transfer RNA (tRNA) is a type of RNA that carries amino acids to the ribosome during protein synthesis. Each tRNA molecule has a specific anticodon that recognizes a codon on the mRNA, ensuring the correct amino acid is added to the growing protein chain.

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What is DNA denaturation?

Denaturation is the process of breaking the hydrogen bonds that hold the two strands of DNA together, resulting in the separation of the strands. Denaturation can be induced by high temperatures, changes in pH, or chemicals.

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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.

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