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DNA structure and replication: fill in the blank

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20 Questions

Cells make two kinds of polynucleotides or nucleic acids: ______ and DNA.

RNA

DNA is a polymer of the four nucleotides A, C, G and ______ with the sugar deoxyribose.

T

RNA is a polymer of the four nucleotides A, C, G and ______ with the sugar ribose.

U

Nucleotides can be either ______ (A and G), which have a double ring base.

purines

The Watson-Crick Model of DNA has four main features: ______ with sugar-phosphate backbone outside.

Double helix

The Watson-Crick Model of DNA has four main features: Strict ______ of nucleotides (A:T; C:G).

base-pairing

DNA is copied using ______ replication - each parental strand from a double helix is used as a template to make a daughter strand along its entire length.

semi-conservative

This results in two double helices, each one having an “old” DNA strand paired with a “new” DNA ______.

strand

DNA replication involves a number of ______ that are required to unwind the double helix and make new, complementary strands.

proteins

Purines (A and G) have a ______ ring base.

double

Helicase breaks the ______ bonds between bases

hydrogen

Topoisomerase relieves the ______ caused by helicase

strain

Single Strand Binding Protein prevents DNA strands from ______ back together

winding

DNA polymerase III extends the 3' end of the ______ to make a new DNA strand

primer

DNA pol I removes the ______ primer and replaces it with DNA nucleotides

RNA

Ligase links two DNA fragments together with a ______ bond

covalent

DNA replication starts at an ______ of replication

origin

A replication bubble consists of two ______ that move away from each other in opposite directions

replication forks

Primase makes a short ______ primer to provide a pre-existing 3'-end

RNA

DNA polymerase 3 follows ______ and makes one long daughter strand on the leading strand

helicase

Study Notes

Molecular Composition of Nucleic Acids

  • Nucleic acids are composed of two types: DNA (Deoxyribose Nucleic Acid) and RNA (Ribose Nucleic Acid)
  • DNA is a polymer of four nucleotides: A, C, G, and T with sugar deoxyribose
  • RNA is a polymer of four nucleotides: A, C, G, and U with sugar ribose

Nucleotide Structure

  • Nucleotides can be classified into two types: purines and pyrimidines
  • Purines (A and G) have a double ring base
  • Pyrimidines (C, T, and U) have a single ring base

Watson-Crick Model of DNA

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

DNA Replication

  • Semi-conservative replication: each parental strand serves as a template for a new daughter strand
  • Two double helices are formed, each with an "old" DNA strand paired with a "new" DNA strand
  • Process involves several proteins: helicase, topoisomerase, single strand binding protein, primase, DNA polymerase III, DNA pol I, and ligase

DNA Replication Proteins

  • Helicase: breaks hydrogen bonds between bases, unwinding the double helix
  • Topoisomerase: relieves strain caused by helicase, cutting and repairing the DNA
  • Single Strand Binding Protein: prevents DNA strands from winding back together
  • Primase: makes an RNA primer, providing a 3' end for DNA synthesis
  • DNA polymerase III: extends the 3' end of the primer, making a new DNA strand
  • DNA pol I: removes the RNA primer, replacing it with DNA nucleotides
  • Ligase: links two DNA fragments together with a covalent bond

Replication Fork

  • Origin of replication: where DNA strands are separated and replication begins
  • Replication bubble: two replication forks moving away from each other, unwinding the parental DNA
  • Helicase and topoisomerase work together to unwind the DNA, exposing new single-stranded DNA

Leading Strand Synthesis

  • 3' end of the daughter DNA is towards the fork, allowing DNA polymerase III to synthesize a long, continuous strand

Lagging Strand Synthesis

  • 3' end of the daughter DNA is away from the fork, resulting in the synthesis of short, discontinuous fragments
  • Primase, DNA polymerase III, and DNA pol I work together to synthesize these fragments, which are later linked by ligase

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