Biology Chapter: DNA and RNA Structures

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Questions and Answers

Which of the following is NOT a type of RNA?

  • transfer RNA (tRNA)
  • protein RNA (pRNA) (correct)
  • ribosomal RNA (rRNA)
  • messenger RNA (mRNA)

What is the role of messenger RNA (mRNA) in protein synthesis?

  • mRNA helps to assemble amino acids into proteins.
  • mRNA carries genetic information from DNA to the ribosomes. (correct)
  • mRNA provides structural support for ribosomes.
  • mRNA carries amino acids to the ribosomes.

According to Chargaff's rules, which of the following base pairings is always true in DNA?

  • Adenine pairs with Guanine.
  • Guanine pairs with Uracil.
  • Adenine pairs with Thymine. (correct)
  • Cytosine pairs with Thymine.

What does the term 'transforming molecule' refer to in the context of DNA and inheritance?

<p>A molecule that can change the physical characteristics of an organism. (B)</p> Signup and view all the answers

What was the significance of Photo 51 in the discovery of DNA's structure?

<p>Photo 51 revealed the double helix structure of DNA. (B)</p> Signup and view all the answers

What is the function of the 3’→5’ exonuclease activity of DNA polymerase I?

<p>To proofread the newly synthesized DNA (B)</p> Signup and view all the answers

Which DNA polymerase activity is responsible for removing RNA primers?

<p>DNA polymerase I 5’→3’ exonuclease activity (A)</p> Signup and view all the answers

What is the role of DNA polymerase III in DNA replication?

<p>Synthesizing DNA in the 5’→3’ direction (A)</p> Signup and view all the answers

When does DNA polymerase I become involved in DNA replication?

<p>When DNA polymerase III encounters an RNA primer (D)</p> Signup and view all the answers

Which of the following activities is NOT present in DNA polymerase III?

<p>5’→3’ exonuclease activity (C)</p> Signup and view all the answers

Which of the following statements regarding DNA polymerase I is TRUE?

<p>It is essential for the removal of RNA primers. (A)</p> Signup and view all the answers

How does the 3’→5’ exonuclease activity of DNA polymerase I contribute to the accuracy of DNA replication?

<p>By removing incorrectly incorporated nucleotides (D)</p> Signup and view all the answers

What is the primary function of DNA polymerase III's 3' to 5' exonuclease activity?

<p>To proofread the newly synthesized DNA strand, removing any mismatched nucleotides. (A)</p> Signup and view all the answers

Which of the following scenarios best illustrates the concept of "proofreading" during DNA replication?

<p>The DNA polymerase III removing a mismatched nucleotide and replacing it with the correct one. (A)</p> Signup and view all the answers

What is the purpose of the 5'→3' exonuclease activity of DNA polymerase I?

<p>To remove RNA primers from the lagging strand (A)</p> Signup and view all the answers

Which of the following enzymes is responsible for joining the two stretches of DNA synthesized by DNA polymerase III and DNA polymerase I?

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

What is the primary function of nucleotide analogues in DNA replication?

<p>To block DNA replication by interfering with the process of nucleotide addition. (C)</p> Signup and view all the answers

How does the 5'→3' exonuclease activity differ from the 3'→5' exonuclease activity?

<p>The 5'→3' exonuclease activity is used only by DNA polymerase I, while the 3'→5' exonuclease activity is used by both DNA polymerase I and DNA polymerase III. (C)</p> Signup and view all the answers

What is the consequence of misreading the template sequence during DNA replication?

<p>Deleterious mutations may be introduced in the DNA sequence. (D)</p> Signup and view all the answers

What is the function of DNA polymerase α?

<p>To lay down primers on the lagging strand (A)</p> Signup and view all the answers

Which of the following best describes the function of DNA helicase in DNA replication?

<p>To unwind the DNA double helix, separating the two strands. (C)</p> Signup and view all the answers

What is the main reason why it is crucial for the survival of an organism that DNA replication is highly accurate?

<p>To minimize the risk of introducing mutations that could lead to disease or dysfunction. (A)</p> Signup and view all the answers

Which of the following statements about DNA polymerase III is TRUE?

<p>It is responsible for the majority of DNA synthesis on the leading strand. (D)</p> Signup and view all the answers

What is the source of energy used for joining the two DNA fragments synthesized by DNA polymerase III and DNA polymerase I?

<p>ATP hydrolysis to AMP and PPi (A)</p> Signup and view all the answers

Why is the leading strand synthesized continuously while the lagging strand is synthesized discontinuously?

<p>DNA polymerase III can only add nucleotides to the 3’ end of the growing strand, and the strands run in opposite directions. (C)</p> Signup and view all the answers

What is the role of DNA polymerase Î’?

<p>To proofread and repair DNA (B)</p> Signup and view all the answers

What is the role of Okazaki fragments in DNA replication?

<p>They are short segments of DNA synthesized on the lagging strand. (C)</p> Signup and view all the answers

Which DNA polymerase is unique to mitochondria?

<p>DNA polymerase Υ (D)</p> Signup and view all the answers

What is the function of the type I DNA topoisomerase enzyme?

<p>To unwind the DNA helix by breaking and resealing a single strand of DNA, without requiring ATP. (B)</p> Signup and view all the answers

Which of the following describes the orientation of the two newly synthesized nucleotide chains during DNA replication?

<p>One grows in the 5' → 3' direction towards the replication fork, and the other grows in the 5' → 3' direction away from the replication fork. (D)</p> Signup and view all the answers

What is the role of the SSB (single-stranded binding) protein in DNA replication?

<p>It prevents the single-stranded DNA from re-forming a double helix, keeping the strands separated. (B)</p> Signup and view all the answers

Which enzyme is responsible for adding nucleotides to the growing DNA strand during replication?

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

How does type II DNA topoisomerase (DNA gyrase) contribute to DNA replication?

<p>It removes supercoils in the DNA, making it easier to unwind. (D)</p> Signup and view all the answers

Which of the following enzymes is involved in the removal of RNA primers from the newly synthesized DNA strand?

<p>DNA polymerase I (A)</p> Signup and view all the answers

During DNA replication, how do the two new DNA strands differ in their synthesis?

<p>One strand is synthesized continuously, while the other is synthesized discontinuously in short fragments. (A)</p> Signup and view all the answers

What is the primary role of the enzyme primase in DNA replication?

<p>To synthesize short RNA primers that provide a starting point for DNA polymerase. (A)</p> Signup and view all the answers

What is the primary function of helix destabilizing proteins (HD proteins) during DNA replication?

<p>To unwind the DNA helix ahead of the replication fork. (C)</p> Signup and view all the answers

Which of the following is NOT a characteristic of helix destabilizing proteins (HD proteins)?

<p>They are enzymes that catalyze DNA unwinding. (D)</p> Signup and view all the answers

Why is the separation of parental strands necessary for DNA replication?

<p>To provide a template for DNA polymerases. (C)</p> Signup and view all the answers

What is the role of single-stranded DNA binding proteins (SSB) in DNA replication?

<p>They help to keep the separated strands of DNA from re-annealing. (A)</p> Signup and view all the answers

How do HD proteins (SSB) shift the equilibrium of DNA towards single-stranded DNA?

<p>They bind cooperatively to the DNA helix, destabilizing it. (D)</p> Signup and view all the answers

Which of the following would most likely be the consequence of a deficiency in HD proteins?

<p>Increased susceptibility to DNA damage. (B)</p> Signup and view all the answers

What is the significance of the 'V'-shaped region formed during DNA replication?

<p>It is the site where the two strands of DNA separate. (A)</p> Signup and view all the answers

What is the role of DNA topoisomerases in DNA replication?

<p>To prevent the formation of supercoils in the DNA helix. (B)</p> Signup and view all the answers

Flashcards

Structure of DNA

DNA has a double helix structure made of nucleotides containing deoxyribose sugar, phosphate, and nitrogenous bases (A, T, C, G).

Chargaff's Rules

  1. Base pairing rule: %G = %C and %A = %T in DNA. 2. DNA composition varies between species, but remains constant within an organism.

Types of RNA

mRNA carries genetic information, rRNA is a structural component of ribosomes, tRNA transfers amino acids during protein synthesis.

Photo 51

An X-ray diffraction image of DNA, key to discovering its double helix structure, taken by Rosalind Franklin.

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RNA polymerase

An enzyme that synthesizes RNA from a DNA template, crucial for producing mRNA and other RNA types.

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Strand Separation

The process of separating DNA strands for replication at the replication fork.

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Helix Destabilizing Proteins

Proteins that prevent the re-annealing of separated DNA strands during replication.

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Replication Fork

The Y-shaped region where DNA splits and replication occurs.

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Leading Strand

The strand of DNA that is replicated continuously toward the replication fork.

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Lagging Strand

The strand of DNA that is replicated in fragments away from the replication fork.

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Excision

The process of removing incorrectly paired or damaged DNA segments.

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RNA Primer

A short RNA segment that serves as a starting point for DNA synthesis.

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DNA helicases

Enzymes that unwind DNA by separating strands at the replication fork using ATP energy.

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SSB protein

Single-strand binding protein that stabilizes unwound DNA during replication.

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DNA polymerase III

Main enzyme that synthesizes a new DNA strand in the 5’ to 3’ direction during replication.

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Primase

Enzyme that synthesizes RNA primers needed to start DNA synthesis.

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Type I topoisomerases

Cut one DNA strand to relieve supercoiling, then reseal it without requiring ATP.

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Type II topoisomerases

Make breaks in both DNA strands, requiring ATP, and introduce negative supercoils.

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Direction of DNA synthesis

DNA is synthesized in the 5’ to 3’ direction, meaning strands grow opposite at the fork.

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Antiparallel strands

The orientation of the two DNA strands; one runs 5’ to 3’ and the other 3’ to 5’ during replication.

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3'→5' exonuclease activity

Activity that degrades improperly paired nucleotides from the end of a DNA strand.

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5'→3' polymerase activity

The function that synthesizes DNA in the 5' to 3' direction.

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5'→3' exonuclease activity

Activity responsible for removing RNA primers during DNA synthesis.

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Nucleotide analogues

Modified nucleotides that block DNA replication.

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5’→3’ polymerase activity

The ability of DNA polymerase III to add nucleotides from 5' to 3' direction.

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3’→5’ exonuclease activity

The proofreading activity of DNA polymerase III that removes mispaired nucleotides.

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Replication fidelity

The accuracy of DNA replication, minimizing errors.

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Mutations

Errors in the DNA sequence that can have harmful effects.

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DNA ligase

An enzyme that catalyzes the final joining of DNA strands.

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DNA polymerase α (alpha)

Enzyme that lays down RNA primers on the lagging strand.

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DNA polymerase β (beta)

Enzyme involved in editing and repairing DNA.

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Energy source for ligase

Provided by the cleavage of ATP to AMP and PPi during DNA joining.

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Study Notes

DNA Structure and Function

  • DNA is a double helix, formed by two strands running antiparallel.
  • The strands are held together by hydrogen bonds between base pairs (A-T, C-G).
  • The diameter of the helix is consistent at 20 angstroms.
  • The bases are stacked 3.4 angstroms apart along the axis.
  • The helix completes one turn every 34 angstroms.

RNA Structure and Function

  • RNA is a single-stranded molecule.
  • It differs structurally from DNA by having a ribose sugar instead of deoxyribose.
  • Uracil replaces thymine as a base in RNA.
  • Involved in protein synthesis (mRNA), ribosomal structure (rRNA), and transportation of amino acids (tRNA)

Erwin Chargaff's Rules

  • The percentage of adenine equals the percentage of thymine in DNA.
  • The percentage of guanine equals the percentage of cytosine in DNA.
  • The percentages of A/T and G/C bases vary among species.

Oswald Avery

  • Discovered that DNA is the genetic material

DNA Replication

  • DNA replication is semiconservative, meaning each new DNA molecule contains one original strand and one newly synthesized strand.
  • Enzymes like Helicase unwind the DNA double helix, creating replication forks.
  • DNA polymerase III synthesizes new DNA strands using the existing strands as templates.
  • Leading strand is synthesized continuously while lagging strand is synthesized in short fragments (Okazaki fragments).
  • DNA polymerase I removes RNA primers and replaces them with DNA.
  • DNA ligase joins the Okazaki fragments together.

DNA Replication Proteins

  • Helicase unwinds the DNA double helix
  • Single-stranded binding proteins (SSBs) stabilize the unwound strands.
  • Topoisomerases relieve the tension ahead of the replication fork.
  • DNA polymerase III synthesizes new DNA strands.
  • DNA polymerase I removes RNA primers and replaces them with DNA.
  • DNA ligase joins Okazaki fragments.

DNA Replication Steps

  • Strand separation
  • Primer formation
  • Chain elongation
  • Excision
  • Joining

DNA Polymerases

  • DNA polymerase III is the main enzyme responsible for DNA synthesis during replication
  • DNA polymerase I replaces the RNA primers with DNA.
  • DNA polymerase has a proofreading mechanism to reduce replication errors.
  • Different types of DNA polymerases exist in eukaryotes.

RNA Primer

  • RNA primer is a short RNA sequence that DNA polymerase uses as a starting point for DNA synthesis.

Chain elongation

  • DNA chain elongation involves the addition of nucleotides to the growing DNA chain by DNA polymerase.

Excision

  • Excision involves the removal and replacement of RNA primers with DNA.

Ligase

  • Ligase joins the Okazaki fragments together.

DNA Topoisomerases

  • DNA topoisomerases resolve the knots and tangles in the DNA molecule during DNA replication.

Types of DNA Topoisomerases

  • Type I topoisomerases: break and rejoin one of the two DNA strands.
  • Type II topoisomerases (DNA gyrase): breaks and rejoins both DNA strands.

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