Molecular Biology: Nucleic Acids Quiz
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Questions and Answers

What provides nucleic acids with their acidic properties?

  • The free –OH group from phosphate groups (correct)
  • The nitrogen bases in nucleic acids
  • The double-helix structure
  • The 3′,5′-phosphodiester linkage

    • Which of the following is NOT a characteristic shared between nucleic acids and proteins?

  • Both exhibit directionality
  • Both exhibit primary structure
  • Both have backbones with a constant structure
  • Both have variable types of linkage (correct)

    • What discovery did Watson and Crick make regarding the structure of DNA in 1953?

  • DNA has a double helix structure (correct)
  • DNA has a triple-helix structure
  • DNA is composed of unequal proportions of nitrogen bases
  • DNA consists of a single strand of nucleotides

    • What aspect of nucleic acids demonstrates directionality?

    <p>The presence of the 5′ and 3′ ends</p> Signup and view all the answers

    What equal ratios in DNA were used to determine its three-dimensional structure?

    <p>%A = %T, %C = %G</p> Signup and view all the answers

    Which scientists provided key X-ray diffraction studies that helped define DNA structure?

    <p>Rosalind Franklin and Maurice Wilkens</p> Signup and view all the answers

    Which of the following statements about nucleic acids is false?

    <p>Nucleic acids lack any acidic properties</p> Signup and view all the answers

    What is the role of the nitrogen bases in nucleic acids?

    <p>They distinguish one nucleic acid from another</p> Signup and view all the answers

    What occurs during the elongation phase of transcription?

    <p>RNA polymerase synthesizes RNA by reading exposed DNA bases.</p> Signup and view all the answers

    Which property distinguishes ribonucleotides from deoxyribonucleotides in RNA synthesis?

    <p>Ribonucleotides utilize uracil instead of thymine.</p> Signup and view all the answers

    What is the primary function of the 5′-methylated cap in eukaryotic mRNA?

    <p>To enhance ribosome attachment for translation.</p> Signup and view all the answers

    In eukaryotic cells, what occurs to the primary transcript before it is exported for translation?

    <p>It undergoes several post-transcriptional modifications.</p> Signup and view all the answers

    What happens when RNA polymerase encounters a termination sequence?

    <p>It releases both the RNA transcript and the DNA strands.</p> Signup and view all the answers

    What role does the poly(A) tail serve in mRNA?

    <p>It protects the RNA from degradation.</p> Signup and view all the answers

    Which statement correctly describes the structure of the RNA nucleic acid backbone?

    <p>It includes ribose sugar and phosphate groups.</p> Signup and view all the answers

    How many primary post-transcriptional modifications do eukaryotic transcripts typically undergo?

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

    What is the primary mechanism by which semiconservative replication occurs?

    <p>An enzyme reads one strand and synthesizes a complementary strand.</p> Signup and view all the answers

    During the experiment by Meselson and Stahl, how was the parental DNA distinguished from the daughter DNA?

    <p>By the heavy and light isotopes of nitrogen.</p> Signup and view all the answers

    What role does the enzyme helicase play in DNA replication?

    <p>It unwinds the DNA double helix at the replication fork.</p> Signup and view all the answers

    What distinguishes the leading strand from the lagging strand during DNA replication?

    <p>The leading strand is synthesized continuously while the lagging strand is built in Okazaki fragments.</p> Signup and view all the answers

    What occurs during the termination phase of DNA replication?

    <p>All RNA primers are removed and replaced with DNA bases by an enzyme.</p> Signup and view all the answers

    Which of the following is a key function of primase in DNA replication?

    <p>To generate RNA primers that initiate DNA synthesis.</p> Signup and view all the answers

    How does chromatin disassembly facilitate DNA replication in eukaryotic cells?

    <p>It allows easier access of replication enzymes to the DNA.</p> Signup and view all the answers

    What is the outcome of growing E. coli cells in a medium with only 15NH4+ before transferring to 14NH4+?

    <p>Daughter DNA consists of one heavy and one light strand.</p> Signup and view all the answers

    What is the primary function of telomeres in eukaryotic chromosomes?

    <p>To protect important genes from being deleted during DNA replication</p> Signup and view all the answers

    What happens to the lagging strand after multiple rounds of DNA replication?

    <p>It becomes shorter than its template strand</p> Signup and view all the answers

    What is the role of Ribonuclease H (RNAse H) during DNA replication?

    <p>To remove the RNA primer from newly synthesized DNA</p> Signup and view all the answers

    What is the composition of a typical chromosome by mass?

    <p>15% DNA and 85% protein</p> Signup and view all the answers

    What mechanism protects telomeres from DNA repair systems?

    <p>The formation of protective loops by single-stranded overhangs</p> Signup and view all the answers

    What occurs after a certain number of replications regarding telomeres?

    <p>They shorten to a point that leads to replicative cell senescence or apoptosis</p> Signup and view all the answers

    What is the primary component that forms the structural unit called chromosomes when DNA interacts with proteins?

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

    What is the function of the Shelterin protein complex in relation to telomeres?

    <p>To protect telomeres from DNA repair mechanisms</p> Signup and view all the answers

    What is the primary function of transfer RNA (tRNA) in protein synthesis?

    <p>To decode the genetic message and bind specific amino acids</p> Signup and view all the answers

    Which of the following statements accurately describes the composition of the ribosomal subunits?

    <p>The small subunit contains one rRNA molecule and thirty-three proteins</p> Signup and view all the answers

    What happens during the translocation step of translation?

    <p>The first tRNA exits the ribosome and a new tRNA enters</p> Signup and view all the answers

    Which step in protein synthesis involves the synthesis of mRNA from DNA?

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

    How is the correct amino acid attached to tRNA during protein synthesis?

    <p>By tRNA synthetase during tRNA activation</p> Signup and view all the answers

    What occurs when the ribosome encounters a stop codon during translation?

    <p>The protein chain is released and translation stops</p> Signup and view all the answers

    Which function does NOT describe the role of tRNA in protein synthesis?

    <p>Synthesis of mRNA from DNA</p> Signup and view all the answers

    Why is methionine often removed from the beginning of the newly formed protein chain?

    <p>It is not necessary for protein structure</p> Signup and view all the answers

    What primarily determines the compatibility of base pairings in DNA?

    <p>The physical dimensions of the DNA double helix interior</p> Signup and view all the answers

    Which of the following statements accurately describes the orientation of DNA strands?

    <p>One strand runs in the 5′-to-3′ direction while the other runs 3′-to-5′</p> Signup and view all the answers

    What is the function of hydrogen bonds in DNA?

    <p>They stabilize the double helix structure</p> Signup and view all the answers

    What is the primary reason for the stability of the DNA double helix?

    <p>The hydrophobic nature of purine and pyrimidine bases</p> Signup and view all the answers

    How many nucleotides are found in each strand per complete 360° turn of the DNA helix?

    <p>10.0 nucleotides</p> Signup and view all the answers

    Which type of bonding is most favorable for A-T and G-C pairings in DNA?

    <p>Hydrogen bonding</p> Signup and view all the answers

    What is the result of the antiparallel orientation of DNA strands?

    <p>Strands can be replicated in opposing directions</p> Signup and view all the answers

    What type of base pair interaction occurs between a pyrimidine and a purine?

    <p>Hydrogen bonding</p> Signup and view all the answers

    Study Notes

    Nucleic Acids

    • Nucleic acids are unbranched polymers containing monomer units called nucleotides.
    • Two types of nucleic acids exist: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
    • DNA is primarily found within the cell nucleus, its function is storing and transferring genetic information, passed from existing cells to new cells during cell division.
    • RNA occurs in all parts of a cell and functions primarily in protein synthesis.

    Types of Nucleic Acids

    • Deoxyribonucleic acid (DNA)
      • Found primarily in the nucleus
      • Stores genetic information
      • Passed from existing cells to new cells during cell division.
    • Ribonucleic acid (RNA)
      • Occurs in all parts of a cell
      • Functions in protein synthesis

    Chemical Composition of DNA and RNA

    • Components:
      • Five-carbon (pentose) sugar
      • Phosphate
      • Nitrogenous bases (four types)

    Nucleotides: Structural Building Blocks

    • A nucleotide is a three-subunit molecule.
    • A sugar (ribose or deoxyribose) is bonded to both a phosphate group and a nitrogenous base.
    • Nucleosides are formed by combining a sugar (ribose or deoxyribose) with a purine or pyrimidine base.
    • Nucleotides are produced from nucleosides by adding a phosphate group.

    Nucleotides: Pentose Sugar

    • The sugar unit of a nucleotide is either ribose or 2'-deoxyribose.
    • The only structural difference between these sugars is at carbon 2'.
    • Ribose has an -OH group at carbon 2', while deoxyribose has an -H atom.

    Nucleotides: Nitrogen-Containing Heterocyclic Bases

    • Two types of nitrogenous bases: Purines (Adenine, Guanine) and Pyrimidines (Cytosine, Thymine, Uracil).
    • Purines have two rings, while pyrimidines have one.
    • DNA contains Adenine, Guanine, Cytosine, and Thymine.
    • RNA contains Adenine, Guanine, Cytosine, and Uracil.

    Nucleotides: Phosphate

    • Phosphate is derived from phosphoric acid (H3PO4).
    • Under cellular pH conditions, phosphoric acid loses two hydrogen atoms to form a hydrogen phosphate ion (HPO42-).

    Nucleotides: Structural Building Blocks

    • Nucleosides consist of a sugar and a base
    • Nucleotides consist of a nucleoside and a phosphate group

    Nucleotide Formation

    • Nucleotide formation occurs in two steps.
    • First, a pentose sugar and a nitrogenous base react to form a nucleoside.
    • Second, the nucleoside reacts with a phosphate group to form a nucleotide.

    Nucleoside Formation & Important Characteristics

    • The nitrogenous base is always attached to carbon 1' of the sugar.
    • For purines, the attachment is through N-9; for pyrimidines, the attachment is through N-1.
    • The bond connecting the sugar and base is a β-N-glycosidic linkage.
    • A molecule of water is formed

    Naming of Nucleosides

    • Pyrimidine bases are named with the suffix -idine (cytidine, thymidine, uridine).
    • Purine bases are named with the suffix -osine (adenosine, guanosine).
    • The prefix deoxy- is used for deoxyribonucleosides.

    Nucleotide Formation: (c) Phosphate

    • Phosphate, the third component of nucleotide, is derived from phosphoric acid (H3PO4).
    • Under cellular pH conditions, the phosphoric acid loses two hydrogen atoms to form a hydrogen phosphate ion (HPO42-).

    Nucleotides: Structural Building Blocks

    • Nucleotides are the building blocks for nucleic acids, composed of a sugar, a nitrogenous base, and a phosphate group.
    • DNA contains deoxyribose sugar, while RNA contains ribose.
    • DNA has A, T, G, C, and RNA has A, U, G, C.

    Primary Structure of Nucleic Acids

    • The primary structure of nucleic acids (DNA and RNA) is linear sequences of nucleotides.
    • Nucleotides are linked together by phosphodiester bonds.
    • The sequence of bases determines the unique properties of each nucleic acid.

    DNA Structure: Double Helix

    • DNA's double helix is made of two polynucleotide chains wound around each other.
    • The sugar-phosphate backbone forms the outer edges of the helix.
    • Nitrogen bases pair in the interior, forming hydrogen bonds (A-T, G-C).

    DNA Structure: Base Pairing

    • A-T base pairs form two hydrogen bonds.
    • G-C base pairs form three hydrogen bonds.
    • Base pairing ensures complementary strands.

    DNA Structure: Chromosomes

    • Chromosomes are organized structures of DNA.
    • They contain the genetic information encoded for a particular organism.
    • Chromosomes contain a combination of DNA and proteins called chromatin.

    DNA Replication

    • DNA replication is the process through which DNA molecules produce exact duplicates of themselves.
    • Crucial for genetic information to be passed on to daughter cells accurately.
    • Mistakes during DNA replication can lead to mutations.

    DNA Replication: Overview

    • Chromatin disassembly (eukaryotes).
    • DNA double helix unwinding.
    • Primer binding.
    • Elongation.
    • Termination.

    Telomeres

    • Telomeres protect the ends of linear chromosomes, preventing deletion of important genes.
    • Telomeres consist of repetitive sequences (TTAGGG in humans).
    • They act as protective caps.

    Karyotype

    • Karyotype is a laboratory-produced image of an individual's complete set of chromosomes.
    • Used to look for chromosomal abnormalities.

    Human Genetic Disorders

    • Some human genetic disorders are characterized by unusual chromosome numbers.
    • Examples include Down syndrome, Edward syndrome, and Klinefelter syndrome.

    Anti-metabolites (Anticancer Drugs)

    • These drugs inhibit DNA synthesis by mimicking the chemical structure of normal molecules needed for DNA replication.
    • They are used in cancer treatment to inhibit the rapid cell division in tumors.

    Information Flow in Biological Systems

    • The central dogma of molecular biology describes the flow of genetic information in cells.
    • It illustrates how genetic information flows from DNA to RNA to protein.
    • Transcription converts a DNA sequence into an hnRNA/mRNA sequence.
    • Translation converts an mRNA sequence into a polypeptide (protein) sequence.

    Types of RNA

    • Types of RNA include hnRNA, mRNA, snRNA, rRNA, and tRNA.
    • Each type has a specific role in the process of protein synthesis and gene expression.

    RNA Synthesis (Transcription)

    • Transcription is the process of copying a DNA sequence into a complementary RNA sequence.
    • It involves three major steps: initiation, elongation, and termination.
    • RNA polymerase is the main enzyme involved in the transcription process.

    RNA Splicing

    • RNA splicing is the process of removing introns (non-coding regions) and joining exons (coding regions) in a hnRNA molecule.
    • It converts the hnRNA into a mature mRNA molecule.

    The Genetic Code

    • The genetic code is a set of rules that translates a sequence of nucleotides in mRNA into a amino acid sequence in a polypeptide (protein).
    • It consists of three-nucleotide codons.
    • The genetic code is universal (nearly identical) in most organisms.

    Translation: Protein Synthesis

    • Translation is the process of converting the mRNA sequence into a protein sequence.
    • Ribosomes, composed of rRNA and proteins, are the sites of translation.
    • tRNA molecules bring amino acids to the ribosome, guided by the mRNA. This process involves initiation, elongation, and termination steps.

    Post-Translation Processing

    • Post-translation processes modify the newly synthesized protein into its functional form.
    • This often involves the removal of initial amino acids, disulfide bridge formation, and protein folding.

    Efficiency of mRNA Utilization

    • mRNA molecules can be translated by multiple ribosomes simultaneously.
    • This process is called polyribosome or polysome formation, ensuring that many proteins are generated from one mRNA molecule.

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    Chapter 5 - Nucleic Acids PDF

    Description

    Test your knowledge on nucleic acids' structure and function with this quiz. Explore key concepts such as DNA and RNA characteristics, transcription processes, and the discoveries that shaped our understanding of molecular biology. Perfect for students studying molecular genetics or biology.

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