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DNA replication is the biological process of producing two identical copies of DNA from one original DNA molecule. It occurs in all living organisms and is essential for inheritance, growth, repair and reproduction1


Steps of DNA replication


DNA replication involves the following steps:


  1. Replication fork formation: An enzyme called DNA helicase unwinds the double-stranded DNA molecule and breaks the hydrogen bonds between the complementary base pairs (A-T and C-G). This creates a Y-shaped structure called the replication fork, where the two single strands of DNA serve as templates for new synthesis
  2. Elongation: An enzyme called DNA polymerase adds new nucleotides to the 3’ end of the growing strand, following the base-pairing rules (A with T and C with G). However, DNA polymerase can only work in one direction, from 5’ to 3’. This means that one strand, called the leading strand, can be synthesized continuously, while the other strand, called the lagging strand, has to be synthesized in short fragments called Okazaki fragments. Another enzyme called DNA ligase joins these fragments together
  3. Termination: The process of DNA replication ends when the entire DNA molecule has been copied and two identical daughter molecules are formed. Each daughter molecule consists of one original (parental) strand and one newly synthesized (daughter) strand. This is called semi-conservative replication because half of the original molecule is conserved in each daughter molecule

Enzymes and proteins involved in DNA replication

DNA replication requires the coordinated action of several enzymes and proteins that work together to ensure the accuracy and fidelity of DNA synthesis. Some of these are:


  • DNA helicase: Unwinds and separates the double-stranded DNA molecule into single strands.
  • DNA polymerase: Adds new nucleotides to the end of the growing strand, following the base-pairing rules.
  • DNA ligase: Joins the Okazaki fragments on the lagging strand into a continuous strand.
  • Primase: Synthesizes short RNA sequences called primers that provide a starting point for DNA polymerase to begin synthesis.
  • Single-strand binding proteins: Bind to the single-stranded DNA and prevent them from reannealing or forming secondary structures.
  • Topoisomerase: Relieves the tension and supercoiling caused by DNA unwinding at the replication fork.
  • Telomerase: Extends the ends of linear chromosomes (called telomeres) that tend to shorten during replication.



Science

DNA Replication Worksheet

DNA replication is the biological process of producing two identical copies of DNA from one original DNA molecule. It occurs in all living organisms and is essential for inheritance, growth, repair and reproduction1


Steps of DNA replication


DNA replication involves the following steps:


  1. Replication fork formation: An enzyme called DNA helicase unwinds the double-stranded DNA molecule and breaks the hydrogen bonds between the complementary base pairs (A-T and C-G). This creates a Y-shaped structure called the replication fork, where the two single strands of DNA serve as templates for new synthesis
  2. Elongation: An enzyme called DNA polymerase adds new nucleotides to the 3’ end of the growing strand, following the base-pairing rules (A with T and C with G). However, DNA polymerase can only work in one direction, from 5’ to 3’. This means that one strand, called the leading strand, can be synthesized continuously, while the other strand, called the lagging strand, has to be synthesized in short fragments called Okazaki fragments. Another enzyme called DNA ligase joins these fragments together
  3. Termination: The process of DNA replication ends when the entire DNA molecule has been copied and two identical daughter molecules are formed. Each daughter molecule consists of one original (parental) strand and one newly synthesized (daughter) strand. This is called semi-conservative replication because half of the original molecule is conserved in each daughter molecule

Enzymes and proteins involved in DNA replication

DNA replication requires the coordinated action of several enzymes and proteins that work together to ensure the accuracy and fidelity of DNA synthesis. Some of these are:


  • DNA helicase: Unwinds and separates the double-stranded DNA molecule into single strands.
  • DNA polymerase: Adds new nucleotides to the end of the growing strand, following the base-pairing rules.
  • DNA ligase: Joins the Okazaki fragments on the lagging strand into a continuous strand.
  • Primase: Synthesizes short RNA sequences called primers that provide a starting point for DNA polymerase to begin synthesis.
  • Single-strand binding proteins: Bind to the single-stranded DNA and prevent them from reannealing or forming secondary structures.
  • Topoisomerase: Relieves the tension and supercoiling caused by DNA unwinding at the replication fork.
  • Telomerase: Extends the ends of linear chromosomes (called telomeres) that tend to shorten during replication.



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