DNA Structure and Base Pairing

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the characteristic of the two strands in double-stranded DNA?

They are parallel

They are identical

They are perpendicular

They are antiparallel (correct)

What is the purpose of Chargaff's rules?

To describe the base pairing rules in DNA (correct)

To describe the replication of DNA

To describe the transcription of DNA to RNA

To describe the structure of RNA

What is the shape of the most common form of DNA in nature?

Circular

Left-handed double helix

Right-handed double helix (correct)

Linear

What is the function of daunorubicin and doxorubicin?

To inhibit topoisomerase II and prevent DNA replication Signup and view all the answers

What is the base pairing rule for G and C?

G always pairs with C Signup and view all the answers

What is the significance of Z-DNA?

It is a rare left-handed double-helical form of DNA Signup and view all the answers

What is the result of cisplatin binding to DNA?

It causes structural distortion and malfunction of DNA Signup and view all the answers

If a sample of DNA has 10% G, what is the percentage of T?

40% Signup and view all the answers

What is the function of topoisomerases in DNA molecules?

To change the amount of supercoiling in DNA Signup and view all the answers

What is the basic packaging unit of chromatin?

Nucleosome Signup and view all the answers

What is the main difference between euchromatin and heterochromatin?

Euchromatin is less condensed, while heterochromatin is more condensed Signup and view all the answers

What is the function of histone H1 in chromatin?

To associate with linker DNA between nucleosomes Signup and view all the answers

During which stage of the cell cycle are chromosomes visible?

Mitosis Signup and view all the answers

What is the structure formed by the aggregation of histone H2A, H2B, H3, and H4?

Histone octamer Signup and view all the answers

What is the region specialized for ribosome assembly in the nucleus?

Nucleolus Signup and view all the answers

What is the name of the enzyme that introduces negative supercoiling into DNA in Escherichia coli?

DNA gyrase Signup and view all the answers

What happens to the double-helical DNA when it is denatured?

It becomes a single-stranded DNA Signup and view all the answers

What is the purpose of denaturation and renaturation of DNA in techniques like Southern blot and PCR?

To allow hybridization of probe DNA with target DNA Signup and view all the answers

What is the term for the process of complementary DNA strands coming back together?

Annealing Signup and view all the answers

What is the result of under- or overwinding the double helix in closed circular DNA molecules?

Supercoiling Signup and view all the answers

Why is negatively supercoiled DNA required for most biologic reactions?

Because it is wound more loosely than Watson-Crick DNA Signup and view all the answers

What is the purpose of adding a well-characterized probe DNA to a mixture of target DNA molecules?

To allow hybridization of probe DNA with target DNA Signup and view all the answers

What is the result of heating DNA, which can be reversed by slowly cooling?

Denaturation Signup and view all the answers

What is the typical structure of mitochondrial DNA and the DNA of most prokaryotes?

Closed circular Signup and view all the answers

Study Notes

DNA Structure

Double-stranded DNA has two antiparallel strands that are complementary.
Base pairing rules: A always pairs with T (2 hydrogen bonds), and G always pairs with C (3 hydrogen bonds).
As a result, the amount of A equals the amount of T, and the amount of G equals the amount of C.
Total purines (A and G) equal total pyrimidines (T and C), known as Chargaff's rules.

DNA Conformation

Most DNA occurs as a right-handed double-helical molecule known as Watson-Crick DNA or B-DNA.
The hydrophilic sugar-phosphate backbone of each strand is on the outside of the double helix.
Hydrogen-bonded base pairs are stacked in the center of the molecule, with about 10 base pairs per complete turn of the helix.
A rare left-handed double-helical form of DNA, known as Z-DNA, occurs in G-C–rich sequences.

DNA Function and Interaction

Antitumor drugs like daunorubicin and doxorubicin intercalate between DNA bases, interfering with topoisomerase II and preventing proper DNA replication.
Other drugs, such as cisplatin, bind tightly to DNA, causing structural distortion and malfunction.

Topoisomerases and Supercoiling

Topoisomerases are enzymes that can change the amount of supercoiling in DNA molecules by making transient breaks in DNA strands.
For example, DNA gyrase (DNA topoisomerase II) can introduce negative supercoiling into DNA.

Nucleosomes and Chromatin

Nuclear DNA in eukaryotes is found in chromatin associated with histones and non-histone proteins.
The basic packaging unit of chromatin is the nucleosome, where DNA is wound around a histone octamer.
Histone H1 is associated with linker DNA between nucleosomes, helping to package them into a solenoid-like structure.
Further condensation occurs to form the chromosome.

Chromatin Structure

Euchromatin corresponds to loosely associated nucleosomes (10-nm fibers).
Heterochromatin is more highly condensed, producing interphase heterochromatin and chromatin characteristic of mitotic chromosomes.

Denaturation and Renaturation of DNA

Double-helical DNA can be denatured by conditions that disrupt hydrogen bonding and base stacking, resulting in the "melting" of the double helix.
Denatured single-stranded DNA can be renatured (annealed) if the denaturing condition is slowly removed.
Renaturation is an important step in probing a Southern blot and in performing the polymerase chain reaction.

Organization of DNA

Large DNA molecules must be packaged to fit inside the cell and still be functional.
Mitochondrial DNA and the DNA of most prokaryotes are closed circular structures that can exist as relaxed circles or as supercoiled structures.
Supercoiling results from strain on the molecule caused by under- or overwinding the double helix.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz covers the features of double-stranded DNA, including antiparallel strands, complementary base pairing, and the relationships between A, T, G, and C.