1. 8.3 DNA Replication TEKS 3E, 5A, 9C 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, including deoxyribonucleic 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. 8.3 DNA Replication TEKS 3E, 5A, 9C KEY CONCEPT DNA replication copies the genetic information of a cell.

3. 8.3 DNA Replication TEKS 3E, 5A, 9C Replication copies the genetic information. A single strand of DNA serves as a template for a new strand. The rules of base pairing direct replication. DNA is replicated during the S (synthesis) stage of the cell cycle. Each body cell gets a complete set of identical DNA.

4. 8.3 DNA Replication TEKS 3E, 5A, 9C During DNA replication: 1.the DNA is unwound and unzipped by the enzyme Helicase. The strands are held apart by single-stranded binding proteins (also known as ssbps)The strands are held apart by single-stranded binding proteins (also known as ssbps)

5. 8.3 DNA Replication TEKS 3E, 5A, 9C 2. each original DNA strand is used as a template (or model) to make a new DNA strand with base pairing New DNA strand

6. 8.3 DNA Replication TEKS 3E, 5A, 9C 3. The enzyme Primase lays down an RNA Primer a few base pairs long to which the new DNA can be added.

7. 8.3 DNA Replication TEKS 3E, 5A, 9C 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. 8.3 DNA Replication TEKS 3E, 5A, 9C 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.These small spurts of replication form what are known as Okazaki fragments.

9. 8.3 DNA Replication TEKS 3E, 5A, 9C ** DNA Polymerase only works in one direction. One strand is read and synthesized continuously while the other is synthesized in fragments. Growth Replication fork DNA polymerase New strand Original strand DNA polymerase Nitrogenous bases Replication fork Original strand New strand

10. 8.3 DNA Replication TEKS 3E, 5A, 9C 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. 8.3 DNA Replication TEKS 3E, 5A, 9C 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.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. 8.3 DNA Replication TEKS 3E, 5A, 9C

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

14. 8.3 DNA Replication TEKS 3E, 5A, 9C DNA replication is semiconservative. original strand new strand Two molecules of DNA Two new molecules of DNA are formed, each with an original strand and a newly formed strand.