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DNA Replication and its Importance in Cell Growth

This text explains the process of DNA replication, including the role of enzymes and the formation of new DNA strands. It also highlights the significance of DNA replication in the cell cycle and the growth of organisms.

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DNA Replication and its Importance in Cell Growth

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  1. The student is expected to:3E evaluate models according to their limitations in representing biological objects or events; 5A describe the stages of the cell cycle, includingdeoxyribonucleic acid (DNA)replication and mitosis, and the importance of the cell cycle to the growth of organisms; 9C identify and investigate the role of enzymes

  2. KEY CONCEPT DNA replication copies the genetic information of a cell.

  3. Replication copies the genetic information. • A single strand of DNA serves as a template for a new strand. • The rules of base pairing directreplication. • DNA is replicated during theS (synthesis) stage of thecell cycle. • Each body cell gets acomplete set ofidentical DNA.

  4. During DNA replication: the DNA is unwound and unzipped by the enzyme Helicase. The strands are held apart by single-stranded binding proteins (also known as ssbps)

  5. 2. each original DNA strand is used as a template (or model) to make a new DNA strand with base pairing New DNA strand New DNA strand

  6. 3. The enzyme Primase lays down an RNA Primer a few base pairs long to which the new DNA can be added.

  7. 4. Another enzyme, called DNA Polymerase, adds new nucleotides to the RNA Primer. It always reads 3’ to 5’ and synthesizes the new strand from 5’ to 3’. This occurs in the direction following Helicase opening up the “replication fork”. For this reason, the new strand is called the leading strand.

  8. 5. Another DNA Polymerase also “proofreads” the new DNA to check for errors. 6. Meanwhile, on the other strand, known as the lagging strand, Primase and DNA Polymerase synthesize DNA from 5’ to 3’ away from the replication fork. These small spurts of replication form what are known as Okazaki fragments.

  9. ** DNA Polymerase only works in one direction. One strand is read and synthesized continuously while the other is synthesized in fragments. Original strand New strand DNA polymerase Growth DNA polymerase Growth Replication fork Replication fork Nitrogenous bases New strand Original strand

  10. 7. The Okazaki fragments are joined together by the enzyme Ligase. 8. On both strands, the RNA Primer is replaced with DNA nucleotides by the enzyme DNA Polymerase.

  11. When replication is complete, each DNA molecule is made of one old strand and one new strand. This is described as the semi-conservative model of replication. 9. The new DNA molecules are rewound by the enzyme Gyrase. Original DNA New DNA (one old strand, one new strand)

  12. There are many origins of replication in eukaryotic chromosomes. Replication is fast and accurate. • DNA replication starts at many points in eukaryotic chromosomes. • DNA polymerases can find and correct errors.

  13. new strand original strand Two molecules of DNA • Two new molecules of DNA are formed, each with an original strand and a newly formed strand. • DNA replication is semiconservative.

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