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DNA structure and replication

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BeneficialSupernova
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20 Questions

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

Deoxyribose has a single ring structure, while ribose has a double ring structure

Which of the following nucleotides is NOT a pyrimidine?

A

What is the primary function of the proteins involved in DNA replication?

To unwind the double helix and make new, complementary strands

What is the term for the process by which DNA is copied, resulting in two double helices, each with one 'old' and one 'new' strand?

Semi-conservative replication

Which of the following is NOT a feature of the Watson-Crick Model of DNA?

Helical structure with sugar-phosphate backbone inside

What is the term for the nucleotides that have a double ring base?

Purines

What is the result of DNA replication?

Two new double helices, each with one 'old' and one 'new' strand

What is the base-pairing rule for DNA, according to the Watson-Crick Model?

A:T; C:G

What is the purpose of the sugar-phosphate backbone in DNA?

To provide structural support for the double helix

What is the term for the process by which new nucleotides are synthesized?

Nucleotide synthesis

What is the primary function of topoisomerase during DNA replication?

To relieve the strain caused by the unwinding of the double helix

What is the role of Primase in the process of DNA replication?

To make a short RNA primer to provide a pre-existing 3'-end

What is the characteristic of the leading strand during DNA replication?

The 3'-end of the daughter DNA is towards the fork

What is the reason for lagging strand synthesis during DNA replication?

The 3'-end of the daughter DNA is away from the fork

What is the function of Ligase in DNA replication?

To link two DNA fragments together with a covalent bond

What is the result of the activity of Primase during DNA replication?

The formation of multiple short DNA fragments

What is the function of DNA polymerase III during DNA replication?

To extend the 3'-end of the primer to make a new DNA strand

What is the role of Helicase during DNA replication?

To break the hydrogen bonds between nucleotides at the replication fork

What is the characteristic of the replication fork during DNA replication?

It consists of two replication forks that move away from each other in opposite directions

What is the function of DNA polymerase I during DNA replication?

To remove the RNA primer and replace it with DNA nucleotides

Study Notes

Nucleic Acids

  • Cells produce two types of polynucleotides: RNA and DNA
  • DNA is a polymer of nucleotides A, C, G, and T with the sugar deoxyribose
  • RNA is a polymer of nucleotides A, C, G, and U with the sugar ribose

Nucleotides

  • Nucleotides can be either purines (A and G) with a double ring base or pyrimidines (C, T, and U) with a single ring base

Watson-Crick Model of DNA

  • Double helix with sugar-phosphate backbone outside
  • Antiparallel strands
  • Strict base-pairing of nucleotides (A:T; C:G)
  • Two strands held together by hydrogen bonding between bases

DNA Replication

  • Semi-conservative replication: each parental strand is used as a template to make a daughter strand along its entire length
  • Results in two double helices, each with an “old” DNA strand paired with a “new” DNA strand

Proteins Involved in DNA Replication

  • Helicase: breaks hydrogen bonds between bases
  • Topoisomerase: relieves strain caused by helicase (overwound DNA)
  • Single Strand Binding Protein: prevents DNA strands from winding back together
  • Primase: makes an RNA primer
  • DNA polymerase III: extends the 3' end of the primer to make a new DNA strand
  • DNA pol I: removes the RNA primer and replaces it with DNA nucleotides
  • Ligase: links two DNA fragments together with a covalent bond

DNA Replication Process

  • Starts at an origin of replication, where origin recognition proteins bind and separate the DNA strands
  • A replication bubble consists of two replication forks that move away from each other in opposite directions
  • Helicase breaks hydrogen bonds between nucleotides at the fork, making the bubble bigger and exposing new single-stranded DNA
  • Topoisomerase relieves strain created by helicase by cutting and repairing the double helix
  • Primase makes a short RNA primer to provide a pre-existing 3'-end
  • DNA polymerase III extends each primer by adding DNA nucleotides to the 3'-end
  • DNA polymerase I removes the RNA primer and replaces it with DNA nucleotides
  • Ligase adds a phosphodiester bond between the 3'- and 5'-ends of two fragments, making a single daughter strand

Leading and Lagging Strands

  • On the leading strand, the 3'-end of the daughter DNA is towards the fork, so DNA polymerase III follows helicase and makes one long daughter strand
  • On the lagging strand, the 3'-end of the daughter DNA is away from the fork, so DNA polymerase III goes the "wrong way" and creates DNA fragments

Test your understanding of the molecular structure of DNA and RNA, including the composition of nucleotides, sugar molecules, and the Watson-Crick Model of DNA. Learn about the differences between purines and pyrimidines, and how they come together to form these essential biomolecules.

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