Biology Chapter 12.2: Structure of DNA Flashcards

Questions and Answers

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.

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.

What is base pairing?

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

What does a nucleotide not contain?

An amino acid Signup and view all the answers

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

A=T, and C=G. Signup and view all the answers

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

Weak hydrogen bonds between nitrogenous bases. Signup and view all the answers

What is NOT true about the structure of DNA?

That it contains adenine-guanine pairs. Signup and view all the answers

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

Phosphates and sugars. Signup and view all the answers

List the chemical components of DNA.

Nucleotides, each with a deoxyribose molecule, a phosphate group, and a nitrogen-containing base: adenine (A), thymine (T), guanine (G), and cytosine (C). Signup and view all the answers

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

They are the force that hold the paired nitrogenous bases together. Signup and view all the answers

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; Rosalind Franklin's X-ray diffraction showed the helical pattern; Watson and Crick built a model based on this information. Signup and view all the answers

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. Signup and view all the answers

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

Watson and Crick's model is composed of two anti-parallel strands connected by hydrogen bonds between nitrogenous bases. Signup and view all the answers

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

Yes, Watson and Crick's model depicted DNA as a double helix with adenine and thymine paired together. Signup and view all the answers

What factors describe the structure of DNA?

Double helix, nucleotide polymer, and sugar-phosphate backbone. Signup and view all the answers

Study Notes

Chemical Components of DNA

DNA is a nucleic acid composed of nucleotides linked by covalent bonds.
Each nucleotide consists of a deoxyribose sugar, a phosphate group, and one of four nitrogenous bases: adenine (A), thymine (T), guanine (G), and cytosine (C).

Clues to DNA Structure

Rosalind Franklin's X-ray diffraction pattern provided critical insights, showing that DNA has a helical structure.
Erwin Chargaff observed that the proportions of adenine and thymine are equal, as are those of guanine and cytosine, leading to Chargaff's rule.

Double Helix Model

Watson and Crick developed the double-helix model, illustrating how the two DNA strands are anti-parallel and held together by base pairing.
The model supports Chargaff's rule, where A pairs with T and C pairs with G.

Base Pairing

Base pairs form through weak hydrogen bonds between nitrogenous bases: A with T, and C with G.
This specific pairing is crucial for the stability of the DNA structure.

Backbone Structure

The backbone of DNA consists of alternating phosphate and deoxyribose sugar units.

Importance of Hydrogen Bonds

Hydrogen bonds, while weak, are essential for holding the strands together, allowing DNA to separate easily during replication and transcription.

Misconceptions about DNA

Adenine does not pair with guanine; such pairs are not found in the DNA structure.

Additional Findings

The two strands of DNA run in opposite directions, a feature vital for their complementary nature and function in genetic processes.
The structure of DNA supports its roles in storage, transmission, and replication of genetic information.

Tools for Analysis

Early scientists could not use light microscopes because DNA is too small; they relied on X-ray diffraction and chemical analysis instead.

Summary of Discoveries

Chargaff's observations, Franklin's photographic evidence, and Watson and Crick's model culminated in a comprehensive understanding of DNA structure and function.

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Description

Test your knowledge of the structure of DNA with these flashcards from Biology Chapter 12.2. Each card explores key concepts such as the chemical components of DNA and the historical clues that led to its discovery. Ideal for biology students looking to reinforce their understanding of nucleic acids.