Biology Chapter 12.2: The Structure of DNA

According to Chargaff's rule of base pairing, which pattern is true of DNA?

A=T, and C=G.

What does a nucleotide not contain?

An amino acid

What are the chemical components of DNA?

DNA is a nucleic acid made up of nucleotides joined into long strands or chains by covalent bonds.

Why did scientists have to use tools other than microscopes to solve the structure of DNA?

DNA is too small to be examined with a light microscope- the only kind of microscope available at the time.

What factors describe the structure of DNA?

Double helix, Nucleotide polymer, and sugar-phosphate backbone.

Describe the discoveries that led to the modeling of DNA.

Erwin Chargaff discovered that the % of adenine and thymine, or cytosine and guanine, bases are almost equal in any sample of DNA. (A)=(T) and (G)=(C) known as Chargaff's rule; Rosalind Franklin's X-ray diffraction photograph shows the pattern that indicated the structure of DNA is helical; James Watson and Francis Crick, thanks to Franklin's X-ray photograph, were able to build a model that explained the specific structure and properties of DNA (DNA's double helix and complementary base pairing).

List the chemical components of DNA.

Nucleotides, each with a deoxyribose molecule (5-carbon sugar molecule), a phosphate group, and a nitrogen-containing base. The four bases are adenine (A), thymine (T), guanine (G), and cytosine (C).

The two "backbones" of the DNA molecule consist of?

Phosphates and sugars

What is NOT true about the structure of DNA?

That it contains adenine-guanine pairs.

What clues helped scientists solve the structure of DNA?

The clues in Franklin's X-ray pattern enabled Watson and Crick to build a model that explained the specific structure and properties of DNA.

What does the double-helix model tell us about DNA?

The double-helix model explains Chargaff's rule of base pairing and how the two strands of DNA are held together.

Base Pairing

The two strands of DNA held together by hydrogen bonds between the nitrogenous bases adenine and thymine, and between guanine and cytosine.

What are hydrogen bonds so essential to the structure of DNA?

They are the force that hold the paired nitrogenous bases together. Because hydrogen bonds are weak bonds, the two strands of DNA are easily separated-a characteristic that is important to DNA's function.

Did Watson and Crick's model account for the equal amounts of thymine and adenine in DNA? Explain.

Watson and Crick's model depicted DNA as a double helix with adenine and thymine paired together. This pairing accounts for the equal amounts of thymine and adenine in DNA.

Describe Watson and Crick's model of the DNA molecule.

Watson and Crick's model is composed of two anti-parallel strands that are connected by hydrogen bonds between nitrogenous bases. Hydrogen bonds form between adenine and thymine and between cytosine and guanine.

The bonds that hold the two strands of DNA together come from where?

Weak hydrogen bonds between nitrogenous bases.