STRUCTURE OF DNA PART 2

Summary

The 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.