Nucleic Acids Overview
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Questions and Answers

Which sugar is found in RNA, contributing to its structure?

  • Glucose
  • Ribose (correct)
  • Fructose
  • Deoxyribose

What type of bond connects the heterocyclic base to the sugar in nucleotides?

  • Glycosidic bond (correct)
  • Peptide bond
  • Hydrogen bond
  • Phosphodiester bond

Which base is unique to DNA and not present in RNA?

  • Thymine (correct)
  • Adenine
  • Cytosine
  • Uracil

What structural feature do RNA and DNA share regarding their bases?

<p>They share three common bases. (D)</p> Signup and view all the answers

What is the primary reason nucleic acids are heteropolymers?

<p>They are made up of different kinds of nucleotides. (A)</p> Signup and view all the answers

What characterizes the B-form of DNA compared to the A-form?

<p>The bases are more closely packed in the B-form. (A), B-form is commonly found under high humidity conditions. (C)</p> Signup and view all the answers

Which of the following statements about RNA and DNA-RNA hybrid structures is accurate?

<p>They always take on the A structure. (C)</p> Signup and view all the answers

What is a distinguishing structural feature of the A-form of DNA compared to the B-form?

<p>Base tilting is more pronounced in the A-form. (B)</p> Signup and view all the answers

How does the stability of both A and B forms of DNA contribute to biochemical processes?

<p>Moderate stability aids in opening the double helix for replication. (A)</p> Signup and view all the answers

What is true regarding the replicative hybrid structure of DNA?

<p>It has one strand of parental DNA and one strand of newly synthesized DNA. (D)</p> Signup and view all the answers

Which statement accurately describes a form of DNA replication?

<p>It occurs in a semiconservative manner. (C)</p> Signup and view all the answers

What is the primary type of topoisomerase responsible for introducing supercoiling in DNA?

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

Which of the following structures is formed by the interaction of polynucleotides?

<p>H-DNA (B)</p> Signup and view all the answers

What relationship do the terms twist (T), writhe (W), and linking number (L) hold in DNA structure?

<p>L = T + W (B)</p> Signup and view all the answers

In which condition is DNA melting most easily observed?

<p>Regions rich in A-T pairs (C)</p> Signup and view all the answers

What was primarily recognized by 1952 regarding DNA's role in genetics?

<p>DNA must be the genetic substance. (B)</p> Signup and view all the answers

Which of the following pairs are correctly complementary according to DNA base pairing rules?

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

What aspect of the Watson-Crick model contributes to the stability of the DNA structure?

<p>Hydrogen bonding between base pairs on opposite strands. (B)</p> Signup and view all the answers

Which grooves in the DNA double helix provide direct access to the bases?

<p>Major groove only (D)</p> Signup and view all the answers

What is the significance of the semiconservative nature of DNA replication?

<p>It ensures that one strand is conserved in each new DNA molecule. (B)</p> Signup and view all the answers

What type of structure is described as the secondary structure of DNA?

<p>The double helix formed by two strands. (D)</p> Signup and view all the answers

What information was revealed by Rosalind Franklin's X-ray diffraction studies?

<p>DNA has a regular, repetitive three-dimensional structure. (A)</p> Signup and view all the answers

What role do the 1' carbons of the deoxyribose moieties play in DNA structure?

<p>They maintain a consistent distance in base pairing. (B)</p> Signup and view all the answers

What primarily contributes to the stability of the double helix structure in DNA?

<p>Hydrogen bonds between base pairs and van der Waals interactions (B)</p> Signup and view all the answers

Which factor is NOT associated with the denaturation of DNA?

<p>Increased hydrogen bonding (D)</p> Signup and view all the answers

What is the significance of superhelical stress in DNA?

<p>It promotes local melting and formation of H-DNA regions (C)</p> Signup and view all the answers

In terms of free energy change, which condition ensures stability of the double helix?

<p>AH must be large enough to make AG positive (B)</p> Signup and view all the answers

What type of nucleic acid contains ribose as its sugar component?

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

What is the correct pairing of bases in the DNA structure as elucidated by Watson and Crick?

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

What characteristic of DNA's phosphodiester linkage affects its stability?

<p>It is inherently unstable and hydrolyzes slowly in absence of catalysts (B)</p> Signup and view all the answers

What is the relationship between superhelical density and free energy stored in supercoiling?

<p>It is directly proportional to the square of the superhelical density (C)</p> Signup and view all the answers

What is the primary role of nucleic acids in biological systems?

<p>Storage and transmission of biological information (B)</p> Signup and view all the answers

Which of the following accurately describes the composition of nucleic acids?

<p>Organic nitrogenous bases, a pentose sugar, phosphate (B)</p> Signup and view all the answers

What distinguishes DNA from RNA?

<p>DNA contains thymine while RNA does not (A)</p> Signup and view all the answers

In what way do nucleic acids participate in protein synthesis?

<p>They provide the instructions for protein synthesis through transcription and translation (D)</p> Signup and view all the answers

What is the significance of the phosphodiester link in nucleic acids?

<p>It connects monomer units in a nucleic acid chain (A)</p> Signup and view all the answers

What characteristic of nucleic acids allows them to have the potential for self-duplication?

<p>The specific sequence of nitrogenous bases (B)</p> Signup and view all the answers

Which statement regarding the discovery of DNA is correct?

<p>It was first identified in animal tissues in the 19th century (B)</p> Signup and view all the answers

What role do nitrogenous bases play in nucleic acids?

<p>They provide genetic coding information (B)</p> Signup and view all the answers

What is the function of the phosphate group in the structure of nucleic acids?

<p>To connect nucleotides by forming phosphodiester bonds (C)</p> Signup and view all the answers

Which of the following is a unique feature of deoxyribonucleic acid (DNA) compared to ribonucleic acid (RNA)?

<p>DNA has thymine, whereas RNA has uracil (A)</p> Signup and view all the answers

Flashcards

Nucleotides

The building blocks of DNA and RNA, composed of a phosphate group, a pentose sugar, and a nitrogenous base.

Deoxyribose

The sugar molecule found in DNA, lacking a hydroxyl group at the 2' carbon.

Ribose

The sugar molecule found in RNA, containing a hydroxyl group at the 2' carbon.

Phosphodiester linkage

The covalent bond that links nucleotides together in a nucleic acid chain. Formed between the phosphate group of one nucleotide and the hydroxyl group of the next.

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Nitrogenous bases

Organic molecules found in nucleic acids that contribute to their unique properties. They can be adenine (A), guanine (G), cytosine (C), thymine (T) or uracil (U).

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DNA replication

The process by which a cell creates a copy of its DNA, ensuring that each daughter cell receives a complete set of genetic information.

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Transcription

The process by which a cell reads the genetic code in DNA and creates a messenger RNA (mRNA) copy of it.

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Translation

The process by which a cell uses the mRNA copy of its DNA to build proteins. This involves the ribosomes interpreting the genetic instructions.

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DNA (deoxyribonucleic acid)

The primary form of nucleic acid in which genetic information is stored. It's a double-stranded helix with complementary base pairing (A-T and G-C).

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RNA (ribonucleic acid)

A nucleic acid molecule involved in protein synthesis. RNA serves as a temporary copy of genetic information from DNA and is used to direct protein assembly.

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Nucleic acid chain

A long chain of repeating units, often containing hundreds of millions of units, that makes up DNA and RNA.

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Nucleic acid backbone

The repeated sugar-phosphate backbone of a nucleic acid. It provides structural support and doesn't directly encode genetic information.

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Nucleoside 5'-monophosphate

A sugar-base adduct (nucleoside) with a phosphate group attached to its 5' carbon.

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DNA secondary structure

The three-dimensional arrangement of DNA molecules, characterized by a regular, repetitive structure.

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DNA primary structure

The linear sequence of nucleotides in a DNA molecule.

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Complementary base pairing

The specific pairing of adenine (A) with thymine (T), and guanine (G) with cytosine (C) in DNA.

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Antiparallel DNA strands

The two strands of DNA run in opposite directions.

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Chargaff's rule

The observation that adenine (A) and thymine (T) are present in equal amounts in DNA, as are guanine (G) and cytosine (C).

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Major groove

A deep groove in the DNA double helix that allows access to the bases.

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Minor groove

A shallow groove in the DNA double helix that faces the sugar backbone.

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What is the B-form of DNA?

A form of DNA found in cells, most common in cells under conditions of high humidity.

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What are DNA and RNA conformations?

DNA or RNA molecules can take on different shapes. These are called conformations.

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What is the A-form of DNA?

A form of DNA found in cells, observed in fibers under conditions of low humidity. It's also the structure of RNA molecules.

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How does the A-form of DNA differ from the B-form?

This structure lies further out from the helix axis and has a distinct surface based on the major and minor grooves

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How does the B-form of DNA differ from the A-form?

This structure is the most common in cells, found in conditions of high humidity, has bases perpendicular to the helix axis, and has a large major groove.

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DNA Structure

Most DNA is double-stranded, meaning it consists of two polynucleotide chains that are complementary and antiparallel.

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Circular DNA

Circular DNA can exist in different forms, including relaxed, supercoiled (tightly wound), and various topologies.

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RNA Structure

RNA is predominantly single-stranded, but can fold back on itself to form complex three-dimensional structures.

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DNA Denaturation

The process of a double-stranded DNA helix unfolding into two single strands due to the breaking of hydrogen bonds between base pairs.

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Superhelical Stress

The force that arises from the twisting or coiling of DNA, causing it to be either underwound or overwound.

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Superhelical Density (σ)

The measure of how much a circular DNA molecule is over- or underwound compared to a relaxed DNA molecule.

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Stability of DNA Helix

The stability of DNA is favored by a large positive enthalpy change (ΔH).

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Unfolding Reaction

The process of converting a double-stranded DNA helix into a single-stranded form.

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Entropy Change (ΔS)

The relative entropy change (ΔS) of a system in a particular process. A positive ΔS indicates that the system is becoming more disordered.

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Supercoiling Free Energy (AGS)

The change in free energy (ΔG) associated with the supercoiling of DNA.

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Supercoil-Favored DNA Structures

DNA structures that are more stable when supercoiled. These structures include Z-DNA, H-DNA, and cruciform extensions.

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Study Notes

Nucleic Acids

  • Nucleic acids are fundamental biological molecules responsible for information storage and transmission.
  • They are polymers composed of monomeric constituents joined by hydrolyzable chemical bonds.
  • Nucleic acids are likely to be the earliest forms of life, possessing the potential for self-duplication.
  • The blueprint for an organism's development and function is encoded in its nucleic acid.

The Nature of Nucleic Acids

  • Nucleic acids are crucial for storing and transferring biological information.
  • DNA, a type of nucleic acid, was discovered in 1869 by Friedrich Miescher.
  • Nucleic acids consist of organic nitrogenous bases, a pentose sugar, and phosphate.
  • There are two major types of nucleic acids: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).
  • The structures of DNA and RNA monomers are different; DNA has deoxyribose and RNA has ribose.

Two Types of Nucleic Acid: DNA and RNA

  • DNA and RNA are polynucleotides.
  • DNA contains deoxyribose sugar, and RNA contains ribose sugar.
  • Nucleic acid bases are classified as purines (adenine, guanine) and pyrimidines (cytosine, thymine, uracil).
  • RNA uses uracil, while DNA uses thymine.
  • RNA monomers are connected by phosphodiester links.
  • DNA and RNA have negatively charged phosphate groups at physiological pH.
  • The sugar-phosphate backbone forms the structural core of nucleic acid molecules.
  • Heterocyclic bases are linked to the 1' carbon of the sugar.

Properties of the Nucleotides

  • Nucleotides are strong acids with a primary phosphate ionization pKa of roughly 1.
  • Secondary ionization of the phosphate and protonation/deprotonation of base amino groups occur near neutral pH values.
  • Bases exist in tautomeric forms, important for specific base interactions.
  • Bases and their derivatives absorb light strongly in the UV region.
  • This absorbance permits quantitative measurement of nucleic acid concentrations.
  • UV light can damage DNA, causing health issues.

Stability and Formation of the Phosphodiester Linkage

  • Polynucleotides form via dehydration reactions.
  • The free energy change of this reaction is positive.
  • Formation of phosphodiester bonds requires energy from nucleoside triphosphates (e.g., ATP, deoxyATP).
  • Hydrolysis (breaking down) of polynucleotides to nucleotides is favored.
  • Nucleases catalyze the hydrolysis of phosphodiester bonds in RNA and DNA.

Primary Structure of Nucleic Acids

  • Nucleic acids have a defined directionality.
  • The 5' carbon of one monomer and the 3' carbon of the next are bonded.
  • The nucleotide sequence dictates the primary structure.
  • Notation for DNA sequences utilize single-letter abbreviations for bases (A, C, G, T). The 5' end is written to the left and 3' to the right.
  • Genetic information is encoded in the primary structure of DNA.

DNA as the Genetic Substance: Early Evidence

  • Discovery of DNA's role as the genetic material was the result of various experiments.
  • Oswald Avery and colleagues showed DNA from pathogenic strains of bacteria can transform non-pathogenic strains.
  • Hershey and Chase experiments confirmed that phage DNA, not protein, enters bacterial cells, directing phage production.
  • Watson and Crick proposed a double helix structure, explaining DNA replication and other biological functions.

Secondary and Tertiary Structure of Nucleic Acids

  • Secondary structure refers to regular folding patterns in polymers.
  • DNA exists as a double helix with two antiparallel strands.
  • Complementary bases pair (A-T and G-C).
  • 10 base pairs per turn.
  • Hydrogen bonds stabilize the double helix.
  • DNA can exist in different forms (e.g., B-form, A-form, Z-form).
  • Most DNA molecules in cells are in the B-form.
  • Double-stranded circular DNA can be supercoiled.
  • Supercoiling refers to extra twists around the axis of a circular DNA molecule.

Replication

  • Replication is the copying of both strands of a duplex DNA to produce two identical DNA duplexes.
  • Enzyme complexes, or replisomes, centered on proteins called DNA polymerase, carry out DNA replication.
  • The process is accurate but errors can occur leading to mutations.

Transcription

  • Transcription is the copying of a DNA strand into a complementary RNA molecule.
  • This process uses ribonucleotide triphosphates and RNA polymerases.
  • Only one DNA strand serves as the template for RNA synthesis.

Translation

  • Translation is the decoding of an RNA sequence to produce a specific amino acid sequence, creating a protein.
  • Uses the genetic code which relates nucleic acid codons to amino acids.
  • Messenger RNA (mRNA) carries information from DNA to the ribosomes.

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