DNA and RNA Composition and Structure
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Questions and Answers

Which of the following nitrogenous bases are purines found in DNA?

  • Cytosine
  • Guanine (correct)
  • Adenine (correct)
  • Thymine

What is the main structural difference between a nucleoside and a nucleotide?

  • Nucleotides are larger than nucleosides due to additional nitrogenous bases.
  • Nucleotide sugar can only be ribose, while nucleosides contain deoxyribose.
  • Nucleosides contain a sugar and a nitrogenous base, while nucleotides contain a sugar, a nitrogenous base, and a phosphate group. (correct)
  • Nucleosides include a phosphate group, and nucleotides do not.

Which sugar is included in DNA nucleotides?

  • Glucose
  • Fructose
  • Ribose
  • Deoxyribose (correct)

What is the primary function of the phosphate group in nucleotides?

<p>To stabilize the structure of nucleic acids (C)</p> Signup and view all the answers

What type of sugar is found in DNA nucleotides?

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

Which of the following statements is true regarding the nitrogenous bases in DNA?

<p>The nitrogenous bases are weakly basic and can form positive charges. (D)</p> Signup and view all the answers

Which nitrogenous base is found in RNA but not in DNA?

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

What type of bond connects nucleotides in a DNA polynucleotide chain?

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

What is contained in a nucleoside?

<p>A sugar and a nitrogenous base (B)</p> Signup and view all the answers

Which nucleotide pairing has the stronger bond in DNA?

<p>Cytosine and Guanine (D)</p> Signup and view all the answers

What type of nitrogenous bases are cytosine and thymine classified as?

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

What is the overall charge of DNA and why?

<p>Negative due to the phosphate group (D)</p> Signup and view all the answers

In which direction do the two strands of DNA run?

<p>Antiparallel, one 5' to 3', the other 3' to 5' (D)</p> Signup and view all the answers

What is the structural shape of DNA?

<p>Double helix (D)</p> Signup and view all the answers

What is the role of nucleoside analogs like AZT in viral infections?

<p>Inhibiting viral DNA synthesis (C)</p> Signup and view all the answers

Which pairing of bases occurs in DNA?

<p>Thymine pairs with Adenine (D)</p> Signup and view all the answers

Which of these best describes the role of histones in DNA packaging?

<p>They provide structural support by winding DNA to form nucleosomes. (B)</p> Signup and view all the answers

How does the presence of uracil in RNA differ from thymine's role in DNA?

<p>Uracil replaces thymine as a pyrimidine base in RNA. (A)</p> Signup and view all the answers

What is the key distinction between heterochromatin and euchromatin concerning gene expression?

<p>Euchromatin is more accessible to transcription machinery, therefore more actively transcribed, whereas heterochromatin is tightly packed and less transcribed. (D)</p> Signup and view all the answers

If a strand of DNA includes the sequence 5’-GCTAT-3’, what would be its complementary strand?

<p>3’-CGATA-5’ (D)</p> Signup and view all the answers

How do nucleoside analogs like AZT interfere with viral replication?

<p>They become incorporated into the viral genome, causing chain termination. (C)</p> Signup and view all the answers

Transcription describes the process by which a DNA sequence is used to synthesize which type of molecule?

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

The process where tRNA interacts with mRNA to build a specific amino acid chain is typically called

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

What role does acetylation of histones play in gene expression?

<p>It opens up the chromatin structure, promoting gene expression. (B)</p> Signup and view all the answers

Which of the following best describes the relationship between a nucleoside and a nucleotide?

<p>A nucleotide is a nucleoside with an added phosphate group. (A)</p> Signup and view all the answers

How many hydrogen bonds are formed between guanine and cytosine in a DNA molecule?

<p>3 (A)</p> Signup and view all the answers

If a segment of DNA has the sequence 5'-ATGC-3' on one strand, what would be the sequence of the complementary strand?

<p>3'-CGTA-5' (C)</p> Signup and view all the answers

What is the primary role of histone proteins in DNA packaging?

<p>To compact and organize DNA into nucleosomes (D)</p> Signup and view all the answers

What is the primary function of histone proteins within a cell?

<p>To compact and organize DNA. (D)</p> Signup and view all the answers

Which of the following best describes heterochromatin?

<p>Highly condensed DNA, transcriptionally inactive (D)</p> Signup and view all the answers

Which structural feature stabilizes the double helix of DNA, in addition to hydrogen bonds?

<p>Van der Waals interactions and hydrophobic properties of the bases (A)</p> Signup and view all the answers

Why are nucleoside analogs used in antiviral treatments such as AZT and acyclovir?

<p>They replace natural nucleosides, causing chain termination. (C)</p> Signup and view all the answers

What is the effect of histone acetylation on DNA?

<p>It decreases the electrostatic attraction between histones and DNA, leading to increased gene expression (D)</p> Signup and view all the answers

How does the structure of a DNA molecule contribute to its function in storing genetic information?

<p>The specific base pairing and the double helical structure. (C)</p> Signup and view all the answers

What is the role of histone deacetylases?

<p>To remove acetyl groups from histones, which decreases gene expression (C)</p> Signup and view all the answers

What are the repeating units that comprise chromatin?

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

Which nitrogenous base is present in RNA but not in DNA?

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

What is a key structural difference between RNA and DNA?

<p>RNA has a ribose sugar, while DNA has a deoxyribose sugar (C)</p> Signup and view all the answers

How does the phosphate group contribute to the function of a nucleotide?

<p>It gives the nucleotide a negative charge important for stability and function. (D)</p> Signup and view all the answers

What distinguishes Z-DNA from B-DNA?

<p>Z-DNA is a left-handed helix, while B-DNA is right-handed. (A)</p> Signup and view all the answers

The formation of what type of structures are primarily responsible for the three-dimensional folding of RNA?

<p>Secondary structure (B)</p> Signup and view all the answers

Where does the process of DNA compaction using histones and nucleosome formation primarily occur?

<p>Cell nucleus (D)</p> Signup and view all the answers

Which of the following best describes the role of messenger RNA (mRNA)?

<p>To carry the genetic code for proteins, to the cytoplasm (A)</p> Signup and view all the answers

What type of bond connects nucleotides along a strand of DNA?

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

Which type of RNA is a component of ribosomes?

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

Which of the following statements best describes the antiparallel nature of the DNA double helix?

<p>One strand is oriented 5' to 3' while the complementary strand is 3' to 5'. (C)</p> Signup and view all the answers

What is the function of transfer RNA (tRNA)?

<p>To carry amino acids to the ribosome during translation (C)</p> Signup and view all the answers

What is the anticodon region of tRNA responsible for?

<p>Binding to specific mRNA codons. (A)</p> Signup and view all the answers

What is the role of supercoiling in DNA packaging?

<p>To help minimize the space occupied by the DNA (B)</p> Signup and view all the answers

Why is the ratio of A to T and G to C consistent within a DNA molecule?

<p>Because hydrogen bonding only occurs between those specific pairs. (A)</p> Signup and view all the answers

Which of the following is a direct result of the removal of acetyl groups from lysine residues of histones?

<p>A more compact chromatin structure. (A)</p> Signup and view all the answers

What is the role of aminoacyl-tRNA synthetase enzymes?

<p>To attach specific amino acids to their corresponding tRNA molecules (A)</p> Signup and view all the answers

Which of the following is NOT a function of the RNA molecule?

<p>To permanently store the genetic information of the cell. (C)</p> Signup and view all the answers

In the context of RNA structure, what are hairpin loops, stem-loops, bulges, and internal loops?

<p>Structural features formed due to base pairing within the RNA molecule. (D)</p> Signup and view all the answers

Flashcards

Pyrimidine

A heterocyclic aromatic organic compound containing two nitrogen atoms in the ring structure, found in DNA, including cytosine and thymine.

Purine

A heterocyclic aromatic organic compound consisting of a pyrimidine ring fused to an imidazole ring, found in DNA, including adenine and guanine.

Nucleoside

The basic building block of nucleic acids, consisting of a nitrogenous base and a sugar molecule (deoxyribose or ribose).

Cytosine

A type of nitrogenous base found in DNA, which is a pyrimidine.

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Thymine

A type of nitrogenous base found in DNA, which is a pyrimidine.

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Adenine

A type of nitrogenous base found in DNA, which is a purine.

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Guanine

A type of nitrogenous base found in DNA, which is a purine.

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Nucleotide

The basic structural and functional unit of nucleic acids ( DNA and RNA), consisting of a nitrogenous base, a sugar molecule, and a phosphate group.

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What is a nucleotide?

A nucleotide is composed of three parts: a nitrogenous base (adenine, guanine, cytosine, or thymine in DNA; adenine, guanine, cytosine, or uracil in RNA), a sugar molecule (deoxyribose in DNA, ribose in RNA), and a phosphate group.

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How does DNA store genetic information?

The specific sequence of nucleotides in a DNA molecule determines the genetic information it carries. This sequence is read from the 5' end to the 3' end.

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What is the role of the phosphate group in DNA?

In DNA, the phosphate groups are linked to the sugar molecules, forming a backbone that gives DNA its negative charge.

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What are the base pairing rules in DNA?

Adenine always pairs with thymine (A-T), and cytosine always pairs with guanine (C-G).

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What is meant by antiparallel strands in DNA?

The two strands of DNA run in opposite directions, with one strand going from 5' to 3' and the other from 3' to 5'.

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What stabilizes the double helix structure of DNA?

The double helix structure is stabilized by hydrogen bonds between the base pairs, along with van der Waals interactions and hydrophobic properties of the bases.

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What is the role of nucleoside analogs in antiviral treatment?

Some drugs, like AZT and acyclovir, are designed to mimic natural nucleosides and inhibit viral DNA synthesis. This is because they stop the DNA chain from being properly extended.

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How does the number of hydrogen bonds influence DNA stability?

The stability of the DNA double helix is influenced by the number of hydrogen bonds between base pairs. A-T pairs have two hydrogen bonds, while C-G pairs have three, leading to a stronger interaction.

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What are the three components of a nucleotide?

A nitrogenous base, a five-carbon sugar (deoxyribose in DNA, ribose in RNA), and a phosphate group.

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What does "antiparallel" mean in relation to DNA strands?

The two strands of DNA run in opposite directions, with one strand going from 5' to 3' and the other from 3' to 5'.

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What is the difference in the sugar molecules between DNA and RNA?

The sugar in DNA is deoxyribose, while the sugar in RNA is ribose.

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What is euchromatin?

It is a less condensed form of chromatin that allows for gene expression to occur.

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What is heterochromatin?

It is a more condensed form of chromatin that inhibits gene expression.

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What are histones?

Proteins that DNA wraps around in the nucleus to form nucleosomes.

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How do nucleoside analogs work as antiviral drugs?

They are molecules that mimic natural nucleosides, blocking viral DNA replication by causing chain termination.

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What are the components of a nucleotide?

A nitrogenous base, a sugar molecule (deoxyribose or ribose), and a phosphate group.

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What does it mean for DNA strands to be antiparallel?

The two strands run in opposite directions, with one strand going from 5' to 3' and the other from 3' to 5'.

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How do nucleoside analogs work in antiviral treatment?

Drugs like AZT and acyclovir mimic natural nucleosides and inhibit viral DNA synthesis by stopping the DNA chain from being properly extended.

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What are histones and how do they contribute to DNA packaging?

The DNA wraps around these small, positively charged proteins to create nucleosomes, the basic units of chromatin.

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What are nucleosomes, and how do they condense DNA?

These units then pack together into higher-order structures called solenoids, further condensing the DNA.

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Why is DNA packaging necessary?

DNA molecules are very long and must be packaged to fit inside the cell nucleus.

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How does supercoiling contribute to DNA packaging?

In addition to wrapping around histones and forming higher-order chromatin structures, DNA can also coil upon itself, creating supercoiled configurations that further condense the genetic material.

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What is the significance of the phosphate group in DNA?

The phosphate group gives DNA an overall negative charge, which is crucial in many biological processes.

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How are DNA nucleotides linked together?

DNA nucleotides are linked through a phosphate backbone via phosphodiester bonds.

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What does the term 'antiparallel' mean in the context of DNA?

The two strands of a double-stranded DNA molecule are antiparallel, with one strand in the 5' to 3' direction and the other in the 3' to 5' direction.

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Describe the structure of DNA.

DNA forms a double helix structure, stabilized by van der Waals interactions, hydrophobic properties of the bases, and hydrogen bonds between the base pairs.

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Heterochromatin

A state of highly condensed chromatin that is usually associated with regions of the genome that are inactive for gene transcription.

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Euchromatin

A less condensed form of chromatin, allowing for easier access to the DNA by transcription factors. It is often associated with actively transcribed genes.

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Histone Acetyltransferases (HATs)

Enzymes that add acetyl groups to lysine residues on histone proteins, which weakens the bond between DNA and histones.

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Histone Deacetylases (HDACs)

Enzymes that remove acetyl groups from lysine residues on histone proteins, which strengthens the bond between DNA and histones.

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Messenger RNA (mRNA)

A type of RNA that serves as a messenger molecule carrying genetic information from DNA to ribosomes, where proteins are made.

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Ribosomal RNA (rRNA)

A type of RNA that forms a structural component of ribosomes, essential for protein synthesis.

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Transfer RNA (tRNA)

A small RNA molecule that acts as an adaptor in protein synthesis, bringing specific amino acids to the ribosome based on the mRNA codons.

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Anticodon

A region on a tRNA molecule that contains three nucleotides that recognize and bind to a specific codon on mRNA.

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Codon

A three-nucleotide sequence on mRNA that codes for a specific amino acid during protein synthesis.

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Translation

The process of converting the genetic information encoded in mRNA into a sequence of amino acids, resulting in the synthesis of a protein.

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Transcription

The process of using DNA as a template to produce a complementary copy of RNA.

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RNA (Ribonucleic acid)

A single-stranded nucleic acid that plays a crucial role in protein synthesis and other cellular processes.

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Ribose

The sugar molecule found in RNA, which differs from the deoxyribose sugar found in DNA by having an additional hydroxyl group.

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Uracil

A nitrogenous base found in RNA but not in DNA, replacing thymine. It pairs with adenine.

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Protein Synthesis

The process by which the amino acid sequence encoded by mRNA is used to construct a functional protein.

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Study Notes

DNA and RNA Composition and Structure

  • Nitrogenous Bases: DNA contains two groups:
    • Pyrimidines: Cytosine, Thymine; aromatic molecules with two nitrogens in the ring.
    • Purines: Adenine, Guanine; aromatic, with a pyrimidine ring fused to an imidazole ring.
    • These bases are weakly basic.
  • Nucleotide Structure:
    • Nucleoside: A nitrogenous base and a sugar (no phosphate).
      • Sugar is deoxyribose in DNA and ribose in RNA.
      • This combination forms the nucleoside; building blocks of nucleic acids.
    • Nucleotide: A nucleoside with a phosphate group.
      • The phosphate group gives the nucleotide a negative charge.
      • Essential structural and functional unit of nucleic acids (DNA and RNA).
  • DNA Polynucleotide Chain: DNA nucleotides are linked by phosphodiester bonds, forming a phosphate backbone.
    • This arrangement gives DNA an overall negative charge.
  • Nucleotide Base Pairing:
    • Adenine pairs with Thymine via two hydrogen bonds (A-T).
    • Guanine pairs with Cytosine via three hydrogen bonds (G-C).
    • The specificity of these pairings maintains the DNA's double-stranded nature.
  • Double-Stranded DNA: The two DNA strands run antiparallel (5' to 3' and 3' to 5').
  • Double Helix: DNA forms a double helix, stabilized by:
    • Hydrogen bonds between base pairs.
    • Van der Waals interactions.
    • Hydrophobic interactions among the bases.
    • This arrangement can occur in different forms (e.g., B-DNA, A-DNA, Z-DNA).
  • Nucleoside Analogs: Some analogs, like AZT and acyclovir, can block viral DNA synthesis by substituting natural nucleosides and causing chain termination.

DNA Packaging and Chromatin

  • DNA Packaging in the Nucleus: DNA is packaged by winding around histone proteins to form nucleosomes.
    • Nucleosomes are further compacted into solenoids and chromatin structures.
    • Histones are small, positively charged proteins involved in DNA compaction.
  • Histones and Chromatin: Nucleosomes consist of DNA wrapped around histone protein cores.
    • Chromatin exists in two forms:
      • Heterochromatin: Highly condensed, transcriptionally inactive.
      • Euchromatin: Less condensed, more gene expression.
  • Histone Modifications:
    • Acetylation: Weakening the bond between histones and DNA, leading to higher gene expression.
    • Deacetylation: Increasing the bond between histones and DNA, leading to lower gene expression.

RNA Types and Functions

  • RNA Types:
    • mRNA (messenger RNA): Encodes proteins, contains the nucleotide sequence for translation.
    • rRNA (ribosomal RNA): Structural component of ribosomes, involved in protein synthesis.
    • tRNA (transfer RNA): Delivers amino acids for protein synthesis; anticodon region recognizes mRNA codons, amino acid attachment site.
    • Other RNAs: RNA primers, small nuclear RNAs, microRNAs, also have regulatory roles.
    • Eukaryotic ribosomes contain four types of rRNA (18S, 28S, 5S, 5.8S) packaged with proteins into two subunits (60S and 40S).
    • RNA typically exists as a single-stranded molecule that can fold on itself.

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Description

This quiz explores the intricate composition and structure of DNA and RNA, focusing on nitrogenous bases, nucleotides, and polynucleotide chains. Test your knowledge on base pairing and the unique properties of these essential biomolecules.

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