Biology: Nucleotides and Nucleic Acids
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Questions and Answers

What is one of the primary roles of nucleotides in living organisms?

  • To store and transfer genetic information (correct)
  • To act as structural components of proteins
  • To catalyze biochemical reactions
  • To serve as the main constituents of cellular membranes

    • Which of the following is a property required for nucleotides to fulfill their biological roles?

  • Highly reactive under physiological conditions
  • Stable under diverse environmental conditions (correct)
  • Active in all metabolic processes
  • Insoluble in water

    • How many hydrogen bonds exist between adenine and thymine in DNA?

  • 2 (correct)
  • 4
  • 1
  • 3

    • Why is DNA more stable than RNA?

    <p>Because DNA's structure lacks 2’-OH groups</p> Signup and view all the answers

    What type of bond connects nucleotides in a nucleic acid chain?

    <p>Phosphodiester bonds</p> Signup and view all the answers

    What is the melting temperature (tm) related to in the context of DNA?

    <p>The temperature at which helical nature is lost</p> Signup and view all the answers

    What kind of structures can nucleotides form due to their recognition features?

    <p>Self-assembling complexes</p> Signup and view all the answers

    Which nucleoside is produced from ribose and adenine?

    <p>Adenosine</p> Signup and view all the answers

    What role does tRNA play in cellular processes?

    <p>Acts as an adapter molecule in protein synthesis</p> Signup and view all the answers

    Which of the following describes the unusual base pairs that can form in RNA?

    <p>Guanine and uracil can pair non-Watson-Crick</p> Signup and view all the answers

    What constitutes the backbone of nucleic acids?

    <p>The sugar and phosphate groups</p> Signup and view all the answers

    What defines the unusual DNA structures involving three or four strands?

    <p>Involvement of Hoogsteen pairing</p> Signup and view all the answers

    What is the significance of the presence of π electrons in nucleotides?

    <p>They contribute to the aromaticity and stability of bases</p> Signup and view all the answers

    In what manner are nucleotides categorized based on their nitrogen bases?

    <p>Into purines and pyrimidines</p> Signup and view all the answers

    What occurs more frequently due to hydrolysis in purines compared to pyrimidines?

    <p>Loss of nucleotides</p> Signup and view all the answers

    What is the role of S-adenosyl methionine in DNA methylation?

    <p>It serves as a donor of methyl groups.</p> Signup and view all the answers

    Which of the following best describes the consequences of excessive DNA methylation?

    <p>Mutations and potential cancer development</p> Signup and view all the answers

    How do alkylating agents affect cancer cells?

    <p>They cause DNA damage leading to cell death.</p> Signup and view all the answers

    What occurs as a result of the intercalating action of drugs like doxorubicin?

    <p>It blocks RNA polymerase from transcribing DNA.</p> Signup and view all the answers

    Which of the following is a consequence of UV radiation on DNA?

    <p>Chemical changes through photochemical reactions.</p> Signup and view all the answers

    What is the significance of xeroderma pigmentosum in relation to DNA repair?

    <p>It results from a deficiency in UV-specific endonuclease.</p> Signup and view all the answers

    What type of agents are used to induce DNA damage in cancer treatment?

    <p>Alkylating agents</p> Signup and view all the answers

    Which of the following can result from the interaction between alkylating agents and DNA?

    <p>Formation of cross-linked DNA chains</p> Signup and view all the answers

    What is a potential effect of acidic pH on nucleotide reactions?

    <p>Accelerates purine hydrolysis</p> Signup and view all the answers

    What is the primary role of methylation of DNA in vivo?

    <p>To control gene expression</p> Signup and view all the answers

    Which statement accurately describes the nature of alkylating agents?

    <p>They are toxic and some act as antineoplastics.</p> Signup and view all the answers

    Which of the following is a false statement regarding non-enzymatic reactions of nucleotides?

    <p>Alkylation enhances DNA repair.</p> Signup and view all the answers

    What is a key structural requirement for nucleotides to perform their roles effectively?

    <p>Presence of recognition features for self-assembly</p> Signup and view all the answers

    Which of the following describes a structural characteristic of nucleotides?

    <p>They consist of three main structural elements</p> Signup and view all the answers

    What is one significant advantage of DNA over RNA in terms of stability?

    <p>Resistance to alkaline hydrolysis</p> Signup and view all the answers

    Which type of bond primarily connects nucleotides in a nucleic acid chain?

    <p>Phosphodiester bonds</p> Signup and view all the answers

    What role does the secondary structure of RNA play?

    <p>Enables self-complementary sequences to create complex structures</p> Signup and view all the answers

    Nucleotides are categorized into purines and pyrimidines based on what characteristic?

    <p>Shape and structure</p> Signup and view all the answers

    Which of the following best describes an unusual structure formed by DNA?

    <p>Triplex DNA involving Hoogsteen pairing</p> Signup and view all the answers

    What determines the melting temperature (tm) of DNA?

    <p>The number of hydrogen bonds in base pairs</p> Signup and view all the answers

    What type of pairing occurs between guanine and uracil in RNA?

    <p>G-U wobble pairing</p> Signup and view all the answers

    What is a consequence of the presence of π electrons in the nitrogenous bases of nucleotides?

    <p>Enhanced hydrogen bonding capabilities</p> Signup and view all the answers

    What occurs at an accelerated rate due to acidic pH in purines?

    <p>Hydrolysis</p> Signup and view all the answers

    Which of the following best describes the role of S-adenosyl methionine in DNA methylation?

    <p>It acts as a methyl donor</p> Signup and view all the answers

    What is a possible consequence of excessive DNA methylation?

    <p>Mutations and cancer</p> Signup and view all the answers

    Which type of agent is used to damage the DNA of cancer cells?

    <p>Alkylating agents</p> Signup and view all the answers

    What mechanism does the anticancer agent doxorubicin use to block RNA transcription?

    <p>Intercalation between base pairs</p> Signup and view all the answers

    What repair mechanism is deficient in individuals with xeroderma pigmentosum?

    <p>UV-specific endonuclease</p> Signup and view all the answers

    Which statement accurately reflects the nature of nitrogen mustards as alkylating agents?

    <p>They can form cross-linked DNA chains.</p> Signup and view all the answers

    What can result from the hydrolysis of purines?

    <p>Loss of base pairs</p> Signup and view all the answers

    Which type of radiations is believed to cause about 10% of total DNA damage?

    <p>UV radiation</p> Signup and view all the answers

    Which of the following statements is true regarding the spontaneous deamination of cytosine?

    <p>It leads to the formation of thymine.</p> Signup and view all the answers

    Study Notes

    Nucleotides: Structure and Function

    • Nucleotides are essential building blocks of life, playing critical roles in DNA and RNA, energy storage and release, and cellular signaling.
    • Nucleotides are composed of three main components: a nitrogen-containing base (purines or pyrimidines), a five-carbon sugar (ribose or deoxyribose), and a phosphate group.
    • Purines, like adenine (A) and guanine (G), consist of a double-ring structure. Pyrimidines, like cytosine (C), thymine (T) and uracil (U), have a single-ring structure.
    • Adenine (A) pairs with thymine (T) in DNA and uracil (U) in RNA, forming two hydrogen bonds. Guanine (G) pairs with cytosine (C) in both DNA and RNA, forming three hydrogen bonds.
    • The sugar components in nucleotides are either ribose (in RNA) or deoxyribose (in DNA). The presence of 2'-OH group in ribose makes RNA more susceptible to alkaline hydrolysis compared to DNA.
    • Nucleotides are linked through phosphodiester bonds, which form the backbone of DNA and RNA molecules.
    • Sequences of nucleotides are read from the 5' end to the 3' end, with the phosphate group at the 5' end and a hydroxyl group at the 3' end.
    • DNA has a higher melting temperature (Tm) than RNA due to the presence of three hydrogen bonds between G-C base pairs, compared to two hydrogen bonds between A-T base pairs.
    • The stability of DNA allows it to preserve genetic information for longer periods, making it a suitable molecule for storing genetic information. RNA, despite its less stable nature, plays diverse roles in protein synthesis and other cellular processes.

    DNA Structures

    • There are different forms of DNA, including the standard double-stranded helix (Watson-Crick form) and alternative forms like Z-DNA, which are influenced by sequence and environmental conditions.
    • Palindromic DNA sequences can form alternative structures with intra-strand base pairing, creating hairpin loops or other unique shapes.
    • Some unusual DNA structures involve three or four DNA strands, like triplex DNA which forms through Hoogsteen pairing.

    RNA Structures

    • RNA exhibits a diverse range of secondary and tertiary structures due to its flexible backbone and ability to form non-canonical base pairs like G-U pairs.
    • Transfer RNA (tRNA) plays a crucial role in translation, carrying specific amino acids to the ribosome and facilitating protein synthesis.

    DNA Damage and Repair

    • DNA can undergo spontaneous deamination (conversion of cytosine to uracil by a process called hydrolysis), hydrolysis of purines (adenine and guanine), and alkylation (addition of methyl groups).
    • Alkylation of DNA can occur both naturally (through metabolic processes) and through exposure to chemical alkylating agents.
    • Excessive methylation can cause mutations and cancer, while controlled methylation plays a role in gene regulation
    • Alkylation of DNA by agents like nitrogen mustard can damage DNA and ultimately lead to cell death, making these agents useful in chemotherapy.

    DNA Inhibition and Damage

    • Drugs like doxorubicin inhibit DNA transcription by intercalating between GC base pairs in DNA, blocking RNA polymerase activity.
    • UV radiation can damage DNA by causing photochemical reactions, leading to the formation of thymine dimers.
    • Lack of UV-specific endonuclease, an enzyme that repairs thymine dimers, is responsible for the genetic disease Xeroderma pigmentosum, characterized by severe sun sensitivity.

    Other Functions of Nucleotides

    • They are involved in coenzyme synthesis, as in the synthesis of NAD+, NADP+, FAD and CoA.
    • They are precursors of signal molecules, such as cyclic AMP, which are involved in cellular signaling pathways.

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    Nucleotides Quiz PDF

    Description

    Test your knowledge on the essential roles of nucleotides in living organisms and their structural properties. This quiz covers topics ranging from the stability of DNA to the functions of tRNA in cellular processes. Challenge yourself with questions about hydrogen bonds, melting temperature, and unusual base pairs in RNA.

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