Three rules of DNA Structure

From The School of Biomedical Sciences Wiki
(Difference between revisions)
Jump to: navigation, search
 
Line 1: Line 1:
The structure of [[DNA|DNA]] has been determined based upon three important rules. The first is known as '[[Chargaff's rules|Chargaff's rules]]'. [[Erwin Chargaff|Erwin Chargaff]] introduced a chemical technique which is used to measure the amount of [[Base pairs|base pairs]] present in a DNA [[Molecule|molecule]], prior to the work done by [[James watson|Watson]] and [[Francis Crick|Crick]] in 1953&nbsp;<ref>International Edition - Genetics, Analysis of Genes and Genomes, 7th Edition, Hartl and Jones, Chapter 2 - DNA Structure and Genetic Variation, Page 42</ref>. Chargaff's rules state that, for a particular species, the amount of [[Guanine|Guanine]] is equal to the amount of [[Cytosine|Cytosine]] (both base pairs, through triple [[Hydrogen bond|hydrogen bond]] formation). Therefore [G]=[C], and similarly, the amount of [[Adenine|Adenine]] is equal to the amount of [[Thymine|Thymine]] ([A]=[T]), through double hydrogen bond formation)&nbsp;<ref>International Edition - Genetics, Analysis of Genes and Genomes, 7th Edition, Hartl and Jones, Chapter 2 - DNA Structure and Genetic Variation, Page 43</ref>. It also states that the amount of [[Adenine|Adenine]] and [[Thymine|Thymine]] bases varies in accordance&nbsp;with the amount of [[Guanine|Guanine]] and [[Cytosine|Cytosine]] bases, however, the amount of [[Purine|purine]] bases ([A]+[G]) is always equal to the amount of [[Pyrimidine|pyrimidine]] bases ([T]+[C]).  
+
[[Image:Dna]]
 +
 
 +
The structure of [[DNA|DNA]] has been determined based upon three important rules. The first is known as '[[Chargaff's rules|Chargaff's rules]]'. [[Erwin Chargaff|Erwin Chargaff]] introduced a chemical technique which is used to measure the amount of [[Base pairs|base pairs]] present in a DNA [[Molecule|molecule]], prior to the work done by [[James watson|Watson]] and [[Francis Crick|Crick]] in 1953&nbsp;<ref>International Edition - Genetics, Analysis of Genes and Genomes, 7th Edition, Hartl and Jones, Chapter 2 - DNA Structure and Genetic Variation, Page 42</ref>. Chargaff's rules state that, for a particular species, the amount of [[Guanine|Guanine]] is equal to the amount of [[Cytosine|Cytosine]] (both base pairs, through triple [[Hydrogen bond|hydrogen bond]] formation). Therefore [G]=[C], and similarly, the amount of [[Adenine|Adenine]] is equal to the amount of [[Thymine|Thymine]] ([A]=[T]), through double hydrogen bond formation)&nbsp;<ref>International Edition - Genetics, Analysis of Genes and Genomes, 7th Edition, Hartl and Jones, Chapter 2 - DNA Structure and Genetic Variation, Page 43</ref>. The triple hydrogen bond between G=C has a stronger bond than A=T so it requires higher temperature to denature the bond. It also states that the amount of [[Adenine|Adenine]] and [[Thymine|Thymine]] bases varies in accordance&nbsp;with the amount of [[Guanine|Guanine]] and [[Cytosine|Cytosine]] bases, however, the amount of [[Purine|purine]] bases ([A]+[G]) is always equal to the amount of [[Pyrimidine|pyrimidine]] bases ([T]+[C]).  
  
 
The second rule was formed on the work&nbsp;carried out&nbsp;by [[Rosalind Franklin|Franklin]] and [[Maurice Wilkins|Wilkin]]. Due to their x-ray diffraction of [[DNA|DNA]] fibres, they were able to conclude that a [[DNA|DNA]] molecule has a double helix structure, formed&nbsp;by 2 strands of polymers twisted around&nbsp;each other&nbsp;<ref>Molecular Biology of the Cell, 5th Edition, Alberts, Johnson, Lewis, Raff, Roberts, Walter, Chapter 4: DNA, Chromosomes, and Genomes, page 197</ref>.  
 
The second rule was formed on the work&nbsp;carried out&nbsp;by [[Rosalind Franklin|Franklin]] and [[Maurice Wilkins|Wilkin]]. Due to their x-ray diffraction of [[DNA|DNA]] fibres, they were able to conclude that a [[DNA|DNA]] molecule has a double helix structure, formed&nbsp;by 2 strands of polymers twisted around&nbsp;each other&nbsp;<ref>Molecular Biology of the Cell, 5th Edition, Alberts, Johnson, Lewis, Raff, Roberts, Walter, Chapter 4: DNA, Chromosomes, and Genomes, page 197</ref>.  
  
The third, and probably the most important and well known rule, was made based on the observations of Watson and Crick in 1953&nbsp;<ref>International Edition - Genetics, Analysis of Genes and Genomes, 7th Edition, Hartl and Jones, Chapter 1 -Genes, Genomes and Genetic Analysis, page 6</ref>. Like Franklin and Wilkin, [[James Watson|James Watson]] and [[Francis Crick|Francis Crick]] observed that [[DNA|DNA]] formed a helical structure by the twisting of the polynucleotide chains. They also found that the 2 strands were anti-parallel, therefore one strand runs from 3' to 5' and the other 5' to 3'&nbsp;<ref>International Edition - Genetics, Analysis of Genes and Genomes, 7th Edition, Hartl and Jones, Chapter 1 - Genes, Genomes and Genetic Analysis, page 8</ref>, with the sugar phosphates on the outside and the nucleotide bases stacked on the inside, creating a stabilising force&nbsp;<ref>Molecular Biology of the Cell, 5th Edition, Alberts, Johnson, Lewis, Raff, Roberts, Walter, Chapter 4: DNA, Chromosomes, and Genomes, page 197</ref>. 1 turn of the helix is 3.4nm, with 10 bases per turn, therefore the rise per base is 0.34nm&nbsp;<ref>International Edition - Genetics, Analysis of Genes and Genomes, 7th Edition, Hartl and Jones, Chapter 2 - DNA Structure and Genetic Variation, Page 43</ref>. The diameter of the helix is 2nm in width. Interestingly, Watson and Crick found that&nbsp;[[Adenine|Adenine ]]always pairs up with [[Thymine|Thymine]], and [[Cytosine|Cytosine]] always pairs up with [[Guanine|Guanine]], which proves Chargaff's rule that the proportion of [A] is the same as [T], and similarly the amount of [G] is the same as [C]. They found that bases from either strand pair up using [[Hydrogen bonds|hydrogen bonds]]&nbsp;<ref>International Edition - Genetics, Analysis of Genes and Genomes, 7th Edition, Hartl and Jones, Chapter 2 - DNA Structure and Genetic Variation, Page 43</ref>. From this point in time onwards, scientists have been able to develop our understanding of [[DNA|DNA]], in terms of [[Mutation|mutation]], [[DNA_replication|replication]] and how it controls hereditary traits. All these rules have been invaluable in our understanding of [[DNA|DNA]].<br>
+
The third, and probably the most important and well known rule, was made based on the observations of Watson and Crick in 1953&nbsp;<ref>International Edition - Genetics, Analysis of Genes and Genomes, 7th Edition, Hartl and Jones, Chapter 1 -Genes, Genomes and Genetic Analysis, page 6</ref>. Like Franklin and Wilkin, [[James Watson|James Watson]] and [[Francis Crick|Francis Crick]] observed that [[DNA|DNA]] formed a helical structure by the twisting of the polynucleotide chains. They also found that the 2 strands were anti-parallel, therefore one strand runs from 3' to 5' and the other 5' to 3'&nbsp;<ref>International Edition - Genetics, Analysis of Genes and Genomes, 7th Edition, Hartl and Jones, Chapter 1 - Genes, Genomes and Genetic Analysis, page 8</ref>, with the sugar phosphates on the outside and the nucleotide bases stacked on the inside, creating a stabilising force&nbsp;<ref>Molecular Biology of the Cell, 5th Edition, Alberts, Johnson, Lewis, Raff, Roberts, Walter, Chapter 4: DNA, Chromosomes, and Genomes, page 197</ref>. 1 turn of the helix is 3.4nm, with 10 bases per turn, therefore the rise per base is 0.34nm&nbsp;<ref>International Edition - Genetics, Analysis of Genes and Genomes, 7th Edition, Hartl and Jones, Chapter 2 - DNA Structure and Genetic Variation, Page 43</ref>. The diameter of the helix is 2nm in width. Interestingly, Watson and Crick found that&nbsp;[[Adenine|Adenine always]] pairs up with [[Thymine|Thymine]], and [[Cytosine|Cytosine]] always pairs up with [[Guanine|Guanine]], which proves Chargaff's rule that the proportion of [A] is the same as [T], and similarly the amount of [G] is the same as [C]. They found that bases from either strand pair up using [[Hydrogen bonds|hydrogen bonds]]&nbsp;<ref>International Edition - Genetics, Analysis of Genes and Genomes, 7th Edition, Hartl and Jones, Chapter 2 - DNA Structure and Genetic Variation, Page 43</ref>. From this point in time onwards, scientists have been able to develop our understanding of [[DNA|DNA]], in terms of [[Mutation|mutation]], [[DNA replication|replication]] and how it controls hereditary traits. All these rules have been invaluable in our understanding of [[DNA|DNA]].<br>  
  
 
==== References  ====
 
==== References  ====
  
 
<references />
 
<references />

Latest revision as of 07:44, 5 December 2016

File:Dna

The structure of DNA has been determined based upon three important rules. The first is known as 'Chargaff's rules'. Erwin Chargaff introduced a chemical technique which is used to measure the amount of base pairs present in a DNA molecule, prior to the work done by Watson and Crick in 1953 [1]. Chargaff's rules state that, for a particular species, the amount of Guanine is equal to the amount of Cytosine (both base pairs, through triple hydrogen bond formation). Therefore [G]=[C], and similarly, the amount of Adenine is equal to the amount of Thymine ([A]=[T]), through double hydrogen bond formation) [2]. The triple hydrogen bond between G=C has a stronger bond than A=T so it requires higher temperature to denature the bond. It also states that the amount of Adenine and Thymine bases varies in accordance with the amount of Guanine and Cytosine bases, however, the amount of purine bases ([A]+[G]) is always equal to the amount of pyrimidine bases ([T]+[C]).

The second rule was formed on the work carried out by Franklin and Wilkin. Due to their x-ray diffraction of DNA fibres, they were able to conclude that a DNA molecule has a double helix structure, formed by 2 strands of polymers twisted around each other [3].

The third, and probably the most important and well known rule, was made based on the observations of Watson and Crick in 1953 [4]. Like Franklin and Wilkin, James Watson and Francis Crick observed that DNA formed a helical structure by the twisting of the polynucleotide chains. They also found that the 2 strands were anti-parallel, therefore one strand runs from 3' to 5' and the other 5' to 3' [5], with the sugar phosphates on the outside and the nucleotide bases stacked on the inside, creating a stabilising force [6]. 1 turn of the helix is 3.4nm, with 10 bases per turn, therefore the rise per base is 0.34nm [7]. The diameter of the helix is 2nm in width. Interestingly, Watson and Crick found that Adenine always pairs up with Thymine, and Cytosine always pairs up with Guanine, which proves Chargaff's rule that the proportion of [A] is the same as [T], and similarly the amount of [G] is the same as [C]. They found that bases from either strand pair up using hydrogen bonds [8]. From this point in time onwards, scientists have been able to develop our understanding of DNA, in terms of mutation, replication and how it controls hereditary traits. All these rules have been invaluable in our understanding of DNA.

References

  1. International Edition - Genetics, Analysis of Genes and Genomes, 7th Edition, Hartl and Jones, Chapter 2 - DNA Structure and Genetic Variation, Page 42
  2. International Edition - Genetics, Analysis of Genes and Genomes, 7th Edition, Hartl and Jones, Chapter 2 - DNA Structure and Genetic Variation, Page 43
  3. Molecular Biology of the Cell, 5th Edition, Alberts, Johnson, Lewis, Raff, Roberts, Walter, Chapter 4: DNA, Chromosomes, and Genomes, page 197
  4. International Edition - Genetics, Analysis of Genes and Genomes, 7th Edition, Hartl and Jones, Chapter 1 -Genes, Genomes and Genetic Analysis, page 6
  5. International Edition - Genetics, Analysis of Genes and Genomes, 7th Edition, Hartl and Jones, Chapter 1 - Genes, Genomes and Genetic Analysis, page 8
  6. Molecular Biology of the Cell, 5th Edition, Alberts, Johnson, Lewis, Raff, Roberts, Walter, Chapter 4: DNA, Chromosomes, and Genomes, page 197
  7. International Edition - Genetics, Analysis of Genes and Genomes, 7th Edition, Hartl and Jones, Chapter 2 - DNA Structure and Genetic Variation, Page 43
  8. International Edition - Genetics, Analysis of Genes and Genomes, 7th Edition, Hartl and Jones, Chapter 2 - DNA Structure and Genetic Variation, Page 43
Personal tools
Namespaces
Variants
Actions
Navigation
Toolbox