DNA Structure and Replication Quiz
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Questions and Answers

What distinguishes the semi-conservative model of DNA replication from the conservative and dispersive models?

  • Each new DNA molecule consists of one old strand and one new strand. (correct)
  • DNA replication occurs without the involvement of histones.
  • DNA is replicated in fragments throughout the entire molecule.
  • DNA strands remain completely intact without mixing.

Which observation supported the semi-conservative model of DNA replication by Meselson and Stahl?

  • Molecules of both ¹⁴N DNA and hybrid molecules appeared after two rounds. (correct)
  • Only hybrid molecules were formed after the second round of replication.
  • All DNA molecules remained entirely of ¹⁴N after two rounds.
  • Density gradient centrifugation failed to differentiate between DNA types.

What role do nucleosomes play in eukaryotic DNA organization during replication?

  • They help compact DNA, preventing damage during replication. (correct)
  • They act as stabilizers that prevent DNA unwinding.
  • They serve as templates for the synthesis of new DNA strands.
  • They facilitate the recruitment of polymerase enzymes.

Which component is essential for initiating DNA replication in prokaryotes?

<p>Specific nucleotide sequences known as origins of replication. (B)</p> Signup and view all the answers

Which of the following describes how DNA replication proceeds in prokaryotic cells?

<p>Bidirectionally from a single origin of replication. (B)</p> Signup and view all the answers

What is the role of single-strand-binding proteins during DNA replication?

<p>They stabilize unwound DNA strands to prevent re-annealing. (C)</p> Signup and view all the answers

Which process occurs immediately after the initiator proteins bind to the DNA during replication?

<p>Formation of the replication fork. (C)</p> Signup and view all the answers

Which statement correctly characterizes the structure of eukaryotic DNA?

<p>It is organized into linear chromosomes within the nucleus. (B)</p> Signup and view all the answers

What initiates the process of transcription in the synthesis of RNA?

<p>Separation of DNA strands at the promoter region (B)</p> Signup and view all the answers

Which statement correctly describes the role of spliceosomes during RNA processing?

<p>They splice out introns and join exons together. (B)</p> Signup and view all the answers

What occurs during the elongation phase of translation?

<p>A polypeptide chain is synthesized codon by codon. (B)</p> Signup and view all the answers

How does termination occur in translation?

<p>Through hydrolysis of the bond between polypeptide and tRNA. (C)</p> Signup and view all the answers

What is the primary function of the TATA box in the transcription process?

<p>It acts as a promoter region for the binding of RNA polymerase. (A)</p> Signup and view all the answers

Which of the following components is NOT part of a nucleotide?

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

What does Chargaff's Rule indicate about the relationship between adenine and thymine?

<p>Their amounts are equal (A)</p> Signup and view all the answers

Which scientist is credited with proposing the double helix structure of DNA?

<p>James Watson and Francis Crick (A)</p> Signup and view all the answers

What primary mechanism allows supercoiling in prokaryotic DNA?

<p>Enzymatic activity of topoisomerase (C)</p> Signup and view all the answers

Which of the following is a characteristic of eukaryotic DNA organization?

<p>Linear chromosomes (B)</p> Signup and view all the answers

What is NOT a feature of prokaryotic DNA structure?

<p>Association with histones (D)</p> Signup and view all the answers

What do plasmids typically contain in prokaryotic cells?

<p>Non-essential genes (D)</p> Signup and view all the answers

Which type of cells primarily possess a haploid genome?

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

In the context of DNA structure, which pairing reflects the presence of purines and pyrimidines according to Chargaff's findings?

<p>A equals T, C equals G (B)</p> Signup and view all the answers

What structure in eukaryotic cells allows for further compaction of DNA?

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

Which process is used to synthesize RNA primers during DNA replication?

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

What are the short DNA fragments synthesized on the lagging strand known as?

<p>Okazaki fragments (B)</p> Signup and view all the answers

Which enzyme is primarily responsible for adding new nucleotides to the leading strand during DNA replication?

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

What happens to errors that remain after DNA polymerase proofreading and mismatch repair?

<p>They become permanent mutations (C)</p> Signup and view all the answers

What direction does the leading strand of DNA synthesize?

<p>5′ to 3′ (B)</p> Signup and view all the answers

What is the error rate during DNA replication in human cells?

<p>1 in 1 billion nucleotide pairs (B)</p> Signup and view all the answers

What is the role of mismatch repair proteins in DNA replication?

<p>To identify and correct mispaired bases (A)</p> Signup and view all the answers

What is the central dogma of genetics?

<p>DNA → RNA → Protein (B)</p> Signup and view all the answers

Which of the following describes the termination phase of DNA replication?

<p>Synthesis of new DNA strands is completed (C)</p> Signup and view all the answers

What common mutation can occur due to errors in DNA replication?

<p>All of the above (D)</p> Signup and view all the answers

Which type of bacteria did Frederick Griffith use in his experiments to demonstrate DNA as hereditary material?

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

What was the main conclusion drawn from Avery, MacLeod, and McCarty's experiment regarding the different enzymes used?

<p>DNA is the only molecule that affects transformation. (C)</p> Signup and view all the answers

What radioactive atoms did Hershey and Chase use to label bacteriophage DNA and proteins, respectively?

<p>Phosphorus-32 for DNA and Sulfur-35 for proteins (D)</p> Signup and view all the answers

What characteristic of the S-strain bacteria was crucial for Frederick Griffith's transformation experiments?

<p>It was virulent or pathogenic. (C)</p> Signup and view all the answers

In the Griffith experiment, what did the injection of heat-killed S-strain and living R-strain demonstrate?

<p>R-strain can become virulent due to transformation. (C)</p> Signup and view all the answers

What encompasses the structural basis of DNA in eukaryotic cells?

<p>Nucleotides, which create chromosomes. (B)</p> Signup and view all the answers

Which of the following statements correctly reflects the outcome of Hershey and Chase's study on bacteriophages?

<p>DNA alone entered the bacteria and produced new bacteriophages. (D)</p> Signup and view all the answers

Which molecular components were used to treat the heat-killed S-strain extracts in Avery's experiment?

<p>Protease, RNase, and DNase (D)</p> Signup and view all the answers

What term describes the ability of dead S-strain cells to confer virulence to live R-strain cells in Griffith's experiment?

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

In what year did Oswald Avery and his team conduct their transformative experiment regarding DNA?

<p>1944 (C)</p> Signup and view all the answers

Flashcards

Eukaryotic DNA structure

Double-stranded, linear DNA molecules organized within the nucleus.

Nucleosome

DNA wrapped around histone proteins.

Telomeres

Protective structures at chromosome ends, preventing damage.

Semi-conservative Replication

Each new DNA molecule has one old and one new strand.

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Prokaryotic DNA Replication

Starts at a single origin, moves in two directions. (circular).

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Replication Origin

Specific sequence where DNA replication begins in a chromosome.

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Replication Bubble/Fork

Unzipped section of DNA where replication happens.

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Meselson-Stahl Experiment

Used density gradient centrifugation to prove semi-conservative DNA replication.

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Leading Strand Synthesis

Continuous DNA synthesis in the 5' to 3' direction from the parent strand during DNA replication.

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Lagging Strand Synthesis

Discontinuous DNA synthesis in short segments (Okazaki fragments) away from the replication fork during DNA replication.

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DNA Replication Termination

The final stage of DNA replication where the new DNA strands separate, and the replication machinery breaks down.

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DNA Replication Error Rate

The frequency of errors during DNA replication in human cells, approximately 1 in 1 billion nucleotide pairs.

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DNA Polymerase (Proofreading)

Enzyme that identifies and corrects errors in newly synthesized DNA.

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Mismatch Repair

A process that identifies and fixes mispaired bases in newly synthesized DNA.

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Genetic Code (Triplet)

A sequence of three DNA bases that codes for a specific amino acid.

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Central Dogma

The flow of genetic information: DNA to RNA to protein.

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Okazaki fragments

Short DNA fragments synthesized during lagging strand replication.

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Mutation

A permanent change in DNA sequence.

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Genetic Material

The substance responsible for carrying and transmitting hereditary information from one generation to the next.

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Griffith's Experiment

Demonstrated that a 'transforming principle' could transfer virulence from heat-killed pathogenic bacteria to live non-pathogenic bacteria.

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Avery, MacLeod, McCarty

Identified DNA as the transforming principle by using enzymes to isolate the responsible molecule in Griffith's experiment.

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Hershey-Chase Experiment

Used bacteriophages, viruses that infect bacteria, to confirm DNA as the genetic material.

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Nucleotides

Building blocks of DNA, composed of a sugar (deoxyribose), a phosphate group, and one of four nitrogenous bases (adenine, guanine, cytosine, thymine).

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Double Helix

The structural shape of DNA, consisting of two complementary strands of nucleotides linked by hydrogen bonds.

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Base Pairing Rules

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

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Chromosomes

Highly organized structures made of DNA and proteins that carry genetic information in eukaryotic cells.

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DNA Replication

The process by which DNA makes an exact copy of itself before cell division, ensuring identical copies are passed to new cells.

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Nucleotide Structure

A nucleotide is made up of a 5-carbon sugar (deoxyribose), a phosphate group, and a nitrogenous base (adenine, thymine, guanine, or cytosine).

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Chargaff's Rule

The amount of adenine (A) always equals thymine (T), and the amount of cytosine (C) always equals guanine (G) in DNA.

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DNA Structure

DNA is a double helix structure, with two strands running in opposite directions (antiparallel) and held together by base pairs (A-T, C-G).

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Gene

A specific sequence of DNA that codes for a protein or RNA molecule.

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Prokaryotic DNA

Prokaryotes, like bacteria, have a single, circular DNA molecule that is tightly packed and supercoiled.

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Supercoiling

The process of DNA twisting upon itself, creating additional coils for compaction.

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Topoisomerases

Enzymes that control DNA supercoiling, preventing tangling and enabling proper DNA replication.

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Plasmids

Small, circular or linear DNA molecules in some prokaryotes, often carrying non-essential genes.

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Haploid Prokaryotes

Most prokaryotes have a single copy of each gene, meaning they are haploid.

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Regulatory Sequences

DNA sections that control when and how genes are activated.

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Transcription

The process of copying genetic information from DNA to RNA. It's like making a photocopy of a recipe so you can cook without the original.

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RNA Processing

The maturation of pre-RNA molecules, where non-coding regions (introns) are removed, and the remaining coding regions (exons) are joined together.

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Translation

The process of converting the genetic code in RNA into a sequence of amino acids, forming a protein. It's like using a codebook to translate RNA into protein.

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Initiation (Translation)

The beginning of protein synthesis, where mRNA, a tRNA with the first amino acid, and ribosomal subunits come together. It's like assembling a puzzle's first pieces.

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Elongation (Translation)

The process of adding amino acids to a growing polypeptide chain, one by one. It's like extending a chain, adding links one at a time.

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Study Notes

DNA Structure and Function

  • DNA is a nucleic acid composed of nucleotides.
  • Each nucleotide comprises a 5-carbon sugar (deoxyribose), a phosphate group, and a nitrogenous base (adenine, thymine, cytosine, or guanine).
  • DNA is a double helix with antiparallel strands.
  • Complementary bases (adenine with thymine, and guanine with cytosine) pair together.
  • Chargaff's rule: The amount of adenine equals thymine, and the amount of cytosine equals guanine.

DNA Replication

  • DNA replication produces two identical DNA molecules.
  • Three proposed models of DNA replication: semi-conservative, conservative, and dispersive.
  • The semi-conservative model was correct
  • Meselson-Stahl experiment confirmed DNA replication is semi-conservative.
  • Replication starts at a single origin on a circular DNA molecule.
  • Replication proceeds bidirectionally around the chromosome.
  • DNA replication is a replicon.

Steps of DNA Replication

  • Initiation:

    • Unwinding begins at a specific origin of replication.
    • Initiator proteins attach to the DNA and initiate unwinding.
    • Helicase enzymes break hydrogen bonds between complementary base pairs.
    • Single-strand-binding (SSB) proteins stabilize the unwound strands, and DNA gyrase relieves strain ahead of the replication fork.

  • Elongation (Leading strand):

    • DNA polymerase III adds new nucleotides to the 3' end of the growing strand continuously in the 5' to 3' direction.
    • The strand synthesized continuously is called the leading strand.

  • Elongation (Lagging strand):

    • Formed in short segments (Okazaki fragments) away from the replication fork.
    • Requires primase to synthesize an RNA primer.
    • DNA polymerase III extends the strand.
    • DNA polymerase I removes RNA primers and fills in the gaps.
    • DNA ligase joins Okazaki fragments.

  • Termination:

    • Takes place once the synthesis of new DNA strands is complete.
    • The two new DNA molecules separate.

Errors During Replication & Correction

  • Errors naturally occur during DNA replication.
  • Base mispairing and strand slippage cause nucleotide insertions or deletions.
  • DNA polymerase has proofreading capabilities to correct errors.
  • Mismatch repair fixes deformities.
  • Errors that remain become mutations.

Transcription

  • Synthesis of RNA molecules using DNA strands as templates.
  • Begins at the promoter region (e.g., TATA box) and ends at the terminator region.
  • RNA polymerase separates DNA strands and links RNA nucleotides.
  • The pre-RNA molecule is released when transcription is complete.

RNA Processing

  • Maturation of pre-RNA molecules occurs in the nucleus.
  • Introns are spliced out by spliceosomes, and exons are joined together.
  • Mature RNA molecule leaves the nucleus for the cytoplasm.
  • Introns are non-coding DNA sequences between exons.

Translation

  • Initiation: mRNA, tRNA (methionine), and ribosomal subunits assemble.
  • Elongation: The ribosome moves along the mRNA, adding amino acids to the growing polypeptide chain.
  • Termination: Stop codon signals the end of translation.

Applications of DNA Technology

  • Medicine: Diagnosis of infectious diseases, genetic disorders, human gene therapy.
  • Forensics: DNA fingerprinting.
  • Environmental: Genetically engineered organisms.
  • Agricultural: Transgenic organisms, "pharm" animals, crops.
  • Molecular Biology: Polymerase Chain Reaction (PCR).

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DNA Structure and Function PDF 2024-2025

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Test your knowledge on the structure and function of DNA, including its unique double helix configuration and base pairing rules. Additionally, explore the processes involved in DNA replication, examining the models and steps for creating identical DNA molecules.

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