STRUCTURE OF DNA PART 2

7activestudio

4 Apr 201604:40

Summary

TLDRThe DNA double helix model, as proposed by Watson and Crick, is a molecular structure consisting of two anti-parallel chains held together by hydrogen bonds between complementary base pairs: adenine with thymine and cytosine with guanine. This arrangement forms a spiral ladder with a uniform distance maintained by the base pairs and a constant ratio of purines to pyrimidines across species. The sugar-phosphate backbone forms the sides of the ladder, while the base pairs create the rungs of the helix, which coils in a right-handed fashion with 10 base pairs per turn, each separated by 34 angstroms and 36 degrees.

Takeaways

🌟 The DNA structure is a double helix, a model proposed by Watson and Crick.
🔍 DNA consists of two long, parallel chains that run in opposite directions, known as anti-parallel arrangement.
🧬 Each DNA strand is composed of a sugar (deoxyribose), phosphate molecules, and nitrogenous bases.
🔒 The bases adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G) through hydrogen bonds.
🔬 The base pairing follows the principle of complementary base pairing, with A=T and G=C ratios being constant within a species.
🔄 Chargaff's rules state that the amount of adenine is always equal to thymine, and the amount of guanine equals cytosine.
🌀 The sugar-phosphate backbone forms the outside of the DNA structure, with the base pairs in the center.
🎢 The DNA molecule is twisted in a right-handed fashion, with a diameter of about 20 angstroms.
📏 Each turn of the DNA helix includes 10 base pairs or 20 nucleotides, with a uniform distance maintained by hydrogen bonds.
📐 The angle between successive nucleotide pairs is 36 degrees, and each turn of the helix is approximately 34 angstroms long.
🔍 The presence of hydrogen bonds was first observed by Linus Pauling in 1954, contributing to the stability of the DNA structure.

Q & A

What is the molecular model of DNA that is widely accepted?
-The widely accepted molecular model of DNA is a double helix structure proposed by Watson and Crick.
How are the two strands of DNA in a double helix arranged in relation to each other?
-The two strands of DNA in a double helix are arranged in an anti-parallel manner, with the 3' end of one strand opposite to the 5' end of the other strand.
What is the significance of the anti-parallel arrangement of DNA strands?
-The anti-parallel arrangement allows for the complementary base pairing, where adenine pairs with thymine and cytosine pairs with guanine.
What are the components of a nucleotide in a DNA chain?
-A nucleotide in a DNA chain consists of one pentose sugar (deoxyribose), two phosphate molecules, and three nitrogenous bases (adenine, guanine, cytosine, and thymine).
How do the bases in the two strands of DNA interact with each other?
-The bases in the two strands of DNA interact through weak hydrogen bonds, with adenine bonding to thymine by two hydrogen bonds and guanine to cytosine by three hydrogen bonds.
Who first observed the presence of hydrogen bonds in the DNA structure?
-Linus Pauling first observed the presence of hydrogen bonds in the DNA structure in 1954.
What is the base ratio in a DNA molecule, and how does it vary between species?
-The base ratio in a DNA molecule is such that the amount of adenine is always equal to thymine, and the amount of guanine is always equal to cytosine. This ratio may vary from species to species but remains constant for a given species.
Who discovered the base ratio rule in DNA, and what is it known as?
-Erwin Chargaff discovered the base ratio rule, which is known as Chargaff's rules.
What are the components of the side railing of the DNA ladder?
-The side railing of the DNA ladder is composed of sugar and phosphate molecules that alternate with each other and are held together by strong chemical bonds.
How is the DNA molecule coiled, and what is the diameter between the two strands?
-The DNA molecule is coiled in a right-handed fashion, and the diameter between the two strands of DNA is 20 angstroms.
What are the structural features of a DNA helix turn, and how many base pairs does it accommodate?
-Each turn of the DNA helix includes one major groove and one minor groove, accommodating 10 base pairs or 20 nucleotides.
What is the angle separating two successive nucleotide pairs in a DNA helix, and what is the length of each turn?
-The angle separating two successive nucleotide pairs in a DNA helix is 36 degrees, and the length of each turn is 34 angstroms.

Outlines

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🌀 DNA Double Helix Structure

The paragraph describes the double helix model of DNA, a structure proposed by Watson and Crick. It highlights that DNA consists of two anti-parallel chains that twist around each other, forming a spiral ladder. Each chain is made up of nucleotides containing a pentose sugar (deoxyribose), phosphate groups, and nitrogenous bases. The bases adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C), creating a complementary relationship between the two strands. The weak hydrogen bonds between these base pairs maintain the uniform distance between the strands. The paragraph also mentions the discovery of the base pairing ratio by Chargaff and the structural characteristics of the DNA molecule, including its right-handed coiling, diameter, and the number of base pairs per turn.

Mindmap

Keywords

💡Double Helix

The term 'double helix' refers to the structure of DNA as proposed by Watson and Crick. It is a model where two strands of nucleotides are wound around each other in a spiral, resembling a twisted ladder. This structure is crucial to understanding how DNA is organized and how it functions biologically. In the script, it is mentioned that the DNA consists of two long and parallel chains that form a double helix, highlighting its fundamental role in the molecular biology of genetics.

💡Nucleotide

A nucleotide is the basic unit of DNA, composed of a sugar (deoxyribose), a phosphate molecule, and a nitrogenous base. The script explains that each chain of the DNA double helix is made up of nucleotides, which are essential for encoding genetic information. The sequence of these nucleotides determines the genetic code, making nucleotides a key component in the structure and function of DNA.

💡Anti-parallel Arrangement

The 'anti-parallel arrangement' describes the orientation of the two strands in the DNA double helix. The script mentions that one strand runs in the 5' to 3' direction, while the other runs in the 3' to 5' direction, which means they are oriented in opposite directions. This arrangement is critical for how DNA is replicated and read by cellular machinery.

💡Complementary Base Pairing

Complementary base pairing is a fundamental aspect of DNA structure where adenine (A) pairs with thymine (T) and cytosine (C) pairs with guanine (G). The script explains that this pairing is crucial for the stability of the DNA molecule and for the accurate replication of genetic information. The complementary nature of the base pairs ensures that the sequence of one strand can be used to determine the sequence of the other.

💡Hydrogen Bonds

Hydrogen bonds are the weak chemical bonds that hold the base pairs together in the DNA double helix. The script notes that these bonds are between one purine (adenine or guanine) and one pyrimidine (thymine or cytosine) on the opposite strand. The presence of hydrogen bonds was first observed by Linus Pauling in 1954, and they are essential for maintaining the structure of DNA.

💡Purines and Pyrimidines

Purines (adenine and guanine) and pyrimidines (thymine and cytosine) are the two types of nitrogenous bases found in DNA. The script explains that purines pair with pyrimidines through hydrogen bonds, which is a key feature of the DNA double helix. The ratio of purines to pyrimidines is always equal, as discovered by Erwin Chargaff, which is a fundamental principle in DNA chemistry.

💡Sugar-Phosphate Backbone

The 'sugar-phosphate backbone' is the structural framework of the DNA molecule, composed of alternating sugar and phosphate molecules. The script describes how this backbone forms the sides of the DNA ladder, with the nitrogenous bases in the center. This backbone is crucial for the stability and integrity of the DNA molecule.

💡Major and Minor Grooves

The 'major groove' and 'minor groove' are terms used to describe the grooves on the surface of the DNA double helix. The script mentions that each turn of the helix includes one major groove and one minor groove. These grooves are important for the interaction of DNA with proteins and other molecules, playing a role in processes such as transcription and replication.

💡Nitrogenous Bases

Nitrogenous bases are the components of nucleotides that determine the genetic code. The script identifies four types of nitrogenous bases in DNA: adenine, guanine, cytosine, and thymine. These bases are crucial for the structure and function of DNA, as they form the base pairs that make up the rungs of the DNA ladder.

💡Chromatography

While not explicitly mentioned in the script, chromatography is a technique often used in DNA analysis to separate and identify the components of DNA, such as the different nucleotides. It is relevant to the discussion of DNA structure and analysis, and understanding the separation of DNA components is key to studying its properties and functions.

💡DNA Replication

DNA replication is the process by which DNA is copied, and it is central to the function of DNA in cells. Although not directly mentioned in the script, the structure of the DNA double helix, with its complementary base pairing, facilitates the accurate replication of genetic information. Understanding the double helix structure is essential for grasping how DNA replication occurs.

Highlights

The widely accepted molecular model of DNA is a double helix structure.

Watson and Crick proposed the DNA double helix model.

DNA consists of two long, parallel chains of nucleotides.

The two strands of DNA are anti-parallel to each other.

The 3' end of one strand is opposite to the 5' end of the other.

The base pairing follows the rule of adenine with thymine and cytosine with guanine.

The sequence of bases in one strand is dependent on the other, creating complementary strands.

Hydrogen bonds link the base molecules of the two chains.

The presence of hydrogen bonds was first observed by Linus Pauling in 1954.

Adenine is always equal in amount to thymine, and guanine to cytosine.

The base ratio varies from species to species but remains constant within a given species.

Erwin Chargaff discovered the one-to-one ratio of purines to pyrimidines in DNA.

The sugar-phosphate backbone forms the sides of the DNA ladder.

The base pairs are in the center of the DNA molecule, forming the rungs of the twisted ladder.

The two chains of DNA coil in a right-handed fashion.

The diameter between the two strands of DNA is 20 angstroms.

Each turn of the helix includes one major groove and one minor groove.

Each turn of the helix accommodates 10 base pairs or 20 nucleotides.

The angle separating two successive nucleotide pairs is 36 degrees.

The length of each turn of the helix is 34 angstroms.