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DNA: Stucture and Replication Lesson

Biology
by

christina i

on 5 March 2013

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Transcript of DNA: Stucture and Replication Lesson

What does DNA look like? DNA is a double-stranded polymer made up of nucleotides.
The nucleotides are made up of nitrogenous bases, deoxyribose sugars, and phosphate groups.

The nitrogenous bases are located in the center of the DNA, and are arranged in pairs where purines bond to pyrimidines.
Guanine (purine) bonds to cytosine (pyrimidine), and adenine (purine) bonds to thymine (pyrimidine). This pairing is referred to as complementary base pairing. DNA strands are labeled at 5’ and 3’. The 5’ begins with a phosphate group whereas the 3’ end begins with a hydroxyl group.
DNA is 0.34nm in diameter and contains 10 bases in one turn. Each turn is 3.4nm long. Two strands of DNA are linked together by hydrogen bonds between the nitrogenous bases, running anti-parallel to each other (one running 5’ to 3’ direction, and the other 3’ to 5’).
Thymine and adenine are double bonded to each other, whilst cytosine and guanine are triple bonded.
The Bases are attached to the deoxyribose sugars by glycosyl bonds.
The sugar is held with phosphodiester bonds; joining the two strands together. Bonding in the DNA DNA Replication DNA: Structure and Replication By: Christina Istomina Step 1: DNA must first be unwound from its double helix structure, into the two separate strands. Because of its strong hydrogen bonds, this is done by the DNA helicase. The two DNA strands are then kept separated by single-stranded binding proteins (SSBs). These 2 strands now serve as a template for DNA replication. Step 2: DNA gyrase helps relieve any tension caused by the unwinding of the DNA strands. Step 3: As the two DNA strands unwind they create an area of both unwinded and twisted DNA strands, this is called a replication fork.
DNA will being to replicate towards the direction of the replication fork on one of the strands (leading strand). On the other strand, replication will proceed away from the fork (lagging strand).
Sometimes, more than one replication fork is present. When two replication forks are are in close proximity to each other they create a replication bubble. This happens in eukaryotes, where there are many origin sites which allows for a faster DNA replication. Step 4: RNA primase begins to place RNA primer to the DNA template. It will be later removed. Step 5: The DNA is synthesized from 5’ to 3’. After the primer is added, DNA polymerase III is able to add free deoxyribonucleoside triphosphates on to the 3’ end of the elongating strand.
The polymerase uses the energy gained from breaking the bond between the first and second phosphate, to start the condensation reaction which adds the nucleotide to the elongating strand. The extra phosphates are recycled by the cell to make more nucleoside triphosphates. Step 6: DNA runs anti-parallel meaning only one strand can be continuously built, this is called the leading strand. It uses the 3’ to 5’ template as its guide and is built moving towards the replication fork. The lagging strand is made discontinuously in smaller pieces in the opposite direction of the replication fork. Step 7: DNA polymerase III builds small fragments along the lagging strand, these fragments are called Okazaki fragments. Step 8: RNA primers from the leading strand and fragments from the lagging strand are removed by DNA polymerase I. It then replaces them with the correct deoxyribonucleotides. Step 9:DNA ligase joins the Okazaki fragments together on the lagging strand by creating a phosphodiester bond. Step 11: Finally, the DNA polyermase I & III will ‘proofread’ the newly created DNA strands. It checks for any incorrectly paired nucleotides and cuts them off of the strand and replaces them. Step 10: The two newly created strands then automatically twist into a helix. DNA Replication Overview DNA: Structure and Replication By: Christina Istomina What does DNA look like? DNA is made up of nitrogenous bases, sugars, and phosphates.
The nitrogenous bases are located in the center of the DNA, and are arranged in pairs where purines bond to pyrimidines.
Guanine (purine) bonds to cytosine (pyrimidine), and adenine (purine) bonds to thymine (pyrimidine). This pairing is referred to complementary base pairing. DNA strands are labeled at 5’ and 3’. The 5’ begins with a phosphate group whereas the 3’ end begins with a hydroxyl group. Two strands of DNA are linked together by hydrogen bonds between the nitrogenous bases running anti-parallel to each other (one running 5’ to 3’ direction, and the other 3’ to 5’).
The Bases are attached to the deoxyribose sugars by glycosyl bonds.
The sugar is held with phosphodiester bonds; joining the two strands together. Bonding in the DNA Replication Step 1: DNA must first be unwound from its double helix structure, into the two separate strands. Because of its strong hydrogen bonds, it is unwound via the DNA helicase. The two DNA strands are kept separated by single-stranded binding proteins (SSBs). Step 2: DNA gyrase helps relieve any tension caused by the unwinding of the DNA strands. Step 3: As the two DNA strands unwind they create an area of both unwinded and twisted DNA strands, this is called a replication fork. Step 4: RNA primase begins to place RNA primer to the DNA template. It will be later removed. Step 5: After the primer is added, DNA polymerase III is able to add free deoxyribonucleoside triphosphates on to the 3’ end of the elongating strand. The polymerase uses the energy gained from breaking the bond between the first and second phosphate, to start the condensation reaction which adds the nucleotide to the elongating strand. The extra phosphates are recycled by the cell to make more nucleoside triphosphates. Step 6: DNA runs anti-parallel meaning only one strand can be continuously built, this is called the leading strand. It uses the 3’ to 5’ template as its guide and is built moving towards the replication fork. The lagging strand is made discontinuously in smaller pieces in the opposite direction of the replication fork. Step 7: DNA polymerase III builds in small fragments along the lagging strand, these fragments are called Okazaki fragments. Step 8: RNA primers from the leading strand and fragments from the lagging strand are removed by DNA polymerase I. It then replaces them it the correct deoxyribonucleotides. Step 9:DNA ligase joins the Okazaki fragments together on the lagging strand by creating a phosphodiester bond. Step 11: Finally, the DNA polyermase I & III will ‘proofread’ the newly created DNA strands. It checks for any incorrectly paired nucleotides and cuts them off of the strand. Step 10: The two newly created strands then automatically twist into a helix. DNA Replication Overview What does DNA look like? DNA is made up of nitrogenous bases, sugars, and phosphates.
The nitrogenous bases are located in the center of the DNA, and are arranged in pairs where purines bond to pyrimidines.
Guanine (purine) bonds to cytosine (pyrimidine), and adenine (purine) bonds to thymine (pyrimidine). This pairing is referred to complementary base pairing. DNA strands are labeled at 5’ and 3’. The 5’ begins with a phosphate group whereas the 3’ end begins with a hydroxyl group. Two strands of DNA are linked together by hydrogen bonds between the nitrogenous bases running anti-parallel to each other (one running 5’ to 3’ direction, and the other 3’ to 5’).
The Bases are attached to the deoxyribose sugars by glycosyl bonds.
The sugar is held with phosphodiester bonds; joining the two strands together. Bonding in the DNA Replication Step 1: DNA must first be unwound from its double helix structure, into the two separate strands. Because of its strong hydrogen bonds, it is unwound via the DNA helicase. The two DNA strands are kept separated by single-stranded binding proteins (SSBs). Step 2: DNA gyrase helps relieve any tension caused by the unwinding of the DNA strands. Step 3: As the two DNA strands unwind they create an area of both unwinded and twisted DNA strands, this is called a replication fork. Step 4: RNA primase begins to place RNA primer to the DNA template. It will be later removed. Step 5: After the primer is added, DNA polymerase III is able to add free deoxyribonucleoside triphosphates on to the 3’ end of the elongating strand. The polymerase uses the energy gained from breaking the bond between the first and second phosphate, to start the condensation reaction which adds the nucleotide to the elongating strand. The extra phosphates are recycled by the cell to make more nucleoside triphosphates. Step 6: DNA runs anti-parallel meaning only one strand can be continuously built, this is called the leading strand. It uses the 3’ to 5’ template as its guide and is built moving towards the replication fork. The lagging strand is made discontinuously in smaller pieces in the opposite direction of the replication fork. Step 7: DNA polymerase III builds in small fragments along the lagging strand, these fragments are called Okazaki fragments. Step 8: RNA primers from the leading strand and fragments from the lagging strand are removed by DNA polymerase I. It then replaces them it the correct deoxyribonucleotides. Step 9:DNA ligase joins the Okazaki fragments together on the lagging strand by creating a phosphodiester bond. Step 11: Finally, the DNA polyermase I & III will ‘proofread’ the newly created DNA strands. It checks for any incorrectly paired nucleotides and cuts them off of the strand. Step 10: The two newly created strands then automatically twist into a helix. DNA Replication Overview Role of the DNA A diagram of a nucleotide. Includes a phosphate group, deoxyribose sugar, and a nitrogenous base. The phosphate groups are bonded to a pentose sugar, running along the outside of the DNA strand. The pentose sugars are bonded to the nitrogenous base DNA (deoxyribonucleic acid) holds all the genetic information of an organism. It does this by the creation of proteins. The proteins made by DNA is what carries our genetic information. DNA replicates 'semiconservatively'. This means that each DNA molecule created is made up of one parent strand (a strand from the original DNA molecule) and a new synthesized strand. Diagram of a replication bubble James Watson and Francis Crick, using Rosalind Franklin’s X-ray diffraction patterns, discovered the DNA structure.
Without her x-rays Watson and Crick would not have created the model that led to their Nobel Prize. Franklin’s x-ray demonstrated the DNA’s double helix structure, which was information unknown at the time. Who discovered the DNA structure?
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