During replication of dna the separated strands are prevented from recoiling by using

Considering Dual Enrollment? • Student Resources • BACK • • Degrees & Programs • Planning Your Degree • Information for Transfer Students • Dual Enrollment at WOU and Chemeketa • What do Chemistry Students Do With Their Degree? • Preparing for Professional and Graduate Programs • Course Descriptions • Online Chemistry Textbooks • Chemistry Corner • • • Need a Chemistry Tutor? • • • Placement Tests • Student Activities • BACK • • Chemistry Corner • Chemistry Majors • Internships and Scholarships • Research in Chemistry • Teaching Experiences in Chemistry • People • • Portal • Academics • Current Students • Employees • Give • Maps • Admission: • BACK • Admission • Apply • Get Info • Visit Us Considering Dual Enrollment? • Student Resources • Back • • Degrees & Programs • Planning Your Degree • Information for Transfer Students • Dual Enrollment at WOU and Chemeketa • What do Chemistry Students Do With Their Degree? • Preparing for Professional and Graduate Programs • Course Descriptions • Online Chemistry Textbooks • Chemistry Corner • • • 9.1 DNA Replication is Semiconservative The elucidation of the structure of the double helix by James Watson and Francis Crick in 1953 provided a hint as to how DNA is copied during the process of DNA replication. Separating the strands of the double helix would provide two templates for the synthesis of new complementary strands, but exactly how new DNA molecules were constructed was still unclear. In one model, semiconservative replicati...

\( \newcommand\) • • • • • Unwinding of the helix during DNA replication (by the action of helicase) results in supercoiling of the DNA ahead of the replication fork. • This supercoiling increases with the progression of the replication fork. • If the supercoiling is not relieved, it will physically prevent the movement of helicase. The topology of DNA can be described by three parameters: • Linking Number (L) An integer value. "Positive" is referenced as right-handed. • Twist (T) A real number (the "apparent" linkage number) • Writhe (W) A real number ("supercoils" in the DNA structure) Consider closed circular DNA: • Linking number is an integer value. • It refers to the number of times the two strands of the duplex make a complete 360 degree turn. For circularly closed DNA, like the E. coli genome, the linking number can only be changed if we do the following: • physically break the duplex • introduce (or remove) a 360 degree turn • ligate (covalently close) the break. Figure 1.6.1: Turns to change the linking number Rubber tubing "helix" experiment Cut two lengths of 1/8" rubber tubing, each about 20" long. Insert a smaller piece of tubing, or piece of pipette tip in the ends to allow the ends to be connected. These two pieces of rubber tubing represent each strand of a DNA duplex. DNA can be ligated, or joined, when we have 5' (phosphate) and 3' (hydroxyl) ends. So we need a way to keep track of which end is which for each piece of tubing. • You can either write "5" a...

13. During DNA replication, the reunion or recoiling of separated DNA strand is prevented by (A) Helix destabilizing protein (B) Single strnad binding protein (C) Rep protein (D) Both (A) and (B) Answer: (D) 14. The enzyme that cuts the bonds of DNA molecule at the origin of replication is (A) Endonuclease (B) DNA polymerase (C) DNA gyrase (D) DNA ligase Answer: (A) 15. Which of the following enzyme is required to release the tension imposed by uncoiling of strands? (A) Endonuclease (B) DNA ligase (C) DNA gyrase (D) DNA helicase

Replication errors and DNA damage are actually happening in the cells of our bodies all the time. In most cases, however, they don’t cause cancer, or even mutations. That’s because they are usually detected and fixed by DNA proofreading and repair mechanisms. Or, if the damage cannot be fixed, the cell will undergo programmed cell death ( DNA polymerases are the enzymes that build DNA in cells. During DNA replication (copying), most DNA polymerases can “check their work” with each base that they add. This process is called proofreading. If the polymerase detects that a wrong (incorrectly paired) nucleotide has been added, it will remove and replace the nucleotide right away, before continuing with DNA synthesis 1 ^1 1 start superscript, 1, end superscript . Many errors are corrected by proofreading, but a few slip through. Mismatch repair happens right after new DNA has been made, and its job is to remove and replace mis-paired bases (ones that were not fixed during proofreading). Mismatch repair can also detect and correct small insertions and deletions that happen when the polymerases "slips," losing its footing on the template 2 ^2 2 squared . How does mismatch repair work? First, a protein complex (group of proteins) recognizes and binds to the mispaired base. A second complex cuts the DNA near the mismatch, and more enzymes chop out the incorrect nucleotide and a surrounding patch of DNA. A DNA polymerase then replaces the missing section with correct nucleotides, and...

Term Meaning DNA (deoxyribonucleic acid) Nucleic acid that transmits genetic information from parent to offspring and codes for the production of proteins Nucleotide Building block of nucleic acids Double helix Structure of two strands, intertwining around an axis like a twisted ladder DNA replication Process during which a double-stranded DNA molecule is copied to produce two identical DNA molecules Base pairing Principle in which the nitrogenous bases of the DNA molecules bond with one another Image of a DNA double helix, illustrating its right-handed structure. The major groove is a wider gap that spirals up the length of the molecule, while the minor groove is a smaller gap that runs in parallel to the major groove. The base pairs are found in the center of the helix, while the sugar-phosphate backbones run along the outside. Some people think that in the leading strand, DNA is synthesized in the 5’ to 3’ direction, while in lagging strand, DNA is synthesized in the 3’ to 5’ direction. This is not the case. DNA polymerase only synthesizes DNA in the 5’ to 3’ direction only. The difference between the leading and lagging strands is that the leading strand is formed towards replication fork, while the lagging strand is formed away from replication fork. The replication fork is the branched (forked) DNA at either end of the replication bubble. The replication complex is the group of proteins that help synthesize the new DNA strands. A replication unit is any chunk of DNA ...

[ "article:topic", "DNA ligase", "primase", "origin of replication", "authorname:openstax", "semiconservative", "initiation of replication", "supercoiled", "DNA gyrase", "helicase", "single-stranded binding protein", "primer", "DNA polymerase III", "elongation", "leading strand", "lagging strand", "Okazaki fragments", "DNA polymerase I", "Telomeres", "telomerase", "Rolling circle replication", "showtoc:no", "license:ccby", "licenseversion:40", "source@https://openstax.org/details/books/microbiology" ] \( \newcommand\) • • • • • • • • Learning Objectives • Explain the meaning of semiconservative DNA replication • Explain why DNA replication is bidirectional and includes both a leading and lagging strand • Explain why Okazaki fragments are formed • Describe the process of DNA replication and the functions of the enzymes involved • Identify the differences between DNA replication in bacteria and eukaryotes • Explain the process of rolling circle replication The elucidation of the structure of the double helix by James Watson and Francis Crick in 1953 provided a hint as to how DNA is copied during the process of replication. Separating the strands of the double helix would provide two templates for the synthesis of new complementary strands, but exactly how new DNA molecules were constructed was still unclear. In one model, semiconservative replication, the two strands of the double helix separate during DNA replication, and each strand serves as a template from which the new ...

Replication errors and DNA damage are actually happening in the cells of our bodies all the time. In most cases, however, they don’t cause cancer, or even mutations. That’s because they are usually detected and fixed by DNA proofreading and repair mechanisms. Or, if the damage cannot be fixed, the cell will undergo programmed cell death ( DNA polymerases are the enzymes that build DNA in cells. During DNA replication (copying), most DNA polymerases can “check their work” with each base that they add. This process is called proofreading. If the polymerase detects that a wrong (incorrectly paired) nucleotide has been added, it will remove and replace the nucleotide right away, before continuing with DNA synthesis 1 ^1 1 start superscript, 1, end superscript . Many errors are corrected by proofreading, but a few slip through. Mismatch repair happens right after new DNA has been made, and its job is to remove and replace mis-paired bases (ones that were not fixed during proofreading). Mismatch repair can also detect and correct small insertions and deletions that happen when the polymerases "slips," losing its footing on the template 2 ^2 2 squared . How does mismatch repair work? First, a protein complex (group of proteins) recognizes and binds to the mispaired base. A second complex cuts the DNA near the mismatch, and more enzymes chop out the incorrect nucleotide and a surrounding patch of DNA. A DNA polymerase then replaces the missing section with correct nucleotides, and...

\( \newcommand\) • • • • • Unwinding of the helix during DNA replication (by the action of helicase) results in supercoiling of the DNA ahead of the replication fork. • This supercoiling increases with the progression of the replication fork. • If the supercoiling is not relieved, it will physically prevent the movement of helicase. The topology of DNA can be described by three parameters: • Linking Number (L) An integer value. "Positive" is referenced as right-handed. • Twist (T) A real number (the "apparent" linkage number) • Writhe (W) A real number ("supercoils" in the DNA structure) Consider closed circular DNA: • Linking number is an integer value. • It refers to the number of times the two strands of the duplex make a complete 360 degree turn. For circularly closed DNA, like the E. coli genome, the linking number can only be changed if we do the following: • physically break the duplex • introduce (or remove) a 360 degree turn • ligate (covalently close) the break. Figure 1.6.1: Turns to change the linking number Rubber tubing "helix" experiment Cut two lengths of 1/8" rubber tubing, each about 20" long. Insert a smaller piece of tubing, or piece of pipette tip in the ends to allow the ends to be connected. These two pieces of rubber tubing represent each strand of a DNA duplex. DNA can be ligated, or joined, when we have 5' (phosphate) and 3' (hydroxyl) ends. So we need a way to keep track of which end is which for each piece of tubing. • You can either write "5" a...

13. During DNA replication, the reunion or recoiling of separated DNA strand is prevented by (A) Helix destabilizing protein (B) Single strnad binding protein (C) Rep protein (D) Both (A) and (B) Answer: (D) 14. The enzyme that cuts the bonds of DNA molecule at the origin of replication is (A) Endonuclease (B) DNA polymerase (C) DNA gyrase (D) DNA ligase Answer: (A) 15. Which of the following enzyme is required to release the tension imposed by uncoiling of strands? (A) Endonuclease (B) DNA ligase (C) DNA gyrase (D) DNA helicase

Considering Dual Enrollment? • Student Resources • BACK • • Degrees & Programs • Planning Your Degree • Information for Transfer Students • Dual Enrollment at WOU and Chemeketa • What do Chemistry Students Do With Their Degree? • Preparing for Professional and Graduate Programs • Course Descriptions • Online Chemistry Textbooks • Chemistry Corner • • • Need a Chemistry Tutor? • • • Placement Tests • Student Activities • BACK • • Chemistry Corner • Chemistry Majors • Internships and Scholarships • Research in Chemistry • Teaching Experiences in Chemistry • People • • Portal • Academics • Current Students • Employees • Give • Maps • Admission: • BACK • Admission • Apply • Get Info • Visit Us Considering Dual Enrollment? • Student Resources • Back • • Degrees & Programs • Planning Your Degree • Information for Transfer Students • Dual Enrollment at WOU and Chemeketa • What do Chemistry Students Do With Their Degree? • Preparing for Professional and Graduate Programs • Course Descriptions • Online Chemistry Textbooks • Chemistry Corner • • • 9.1 DNA Replication is Semiconservative The elucidation of the structure of the double helix by James Watson and Francis Crick in 1953 provided a hint as to how DNA is copied during the process of DNA replication. Separating the strands of the double helix would provide two templates for the synthesis of new complementary strands, but exactly how new DNA molecules were constructed was still unclear. In one model, semiconservative replicati...