What is the primary model of DNA proposed by Watson and Crick in 1953?

The Watson-Crick model of DNA, which describes a right-handed double-stranded helix.

Which base pairs are bonded by 3 hydrogen bonds?

Guanine (G) and Cytosine (C).

True or False: A-DNA is more common in physiological conditions than B-DNA.

False. B-DNA is the most common physiological form found in high humidity and low salt concentration.

Fill in the blank: The rule stating that the number of purines equals the number of pyrimidines in DNA is known as ______.

Chargaff's Rule.

What type of DNA structure is formed when a third strand attaches to the major groove of B-DNA?

Triple-stranded DNA.

Riddle: I can be relaxed or twisted, but most often I'm the compact form of a double helix. What am I?

Supercoiled DNA.

Which type of topoisomerase does not require ATP to function?

Topoisomerase Type I.

What is the melting temperature (Tm) in DNA?

The specific temperature at which half of the DNA strands are denatured.

True or False: The primary structure of DNA is altered during denaturation.

False. The primary structure remains intact; only secondary and tertiary structures are altered.

The distance spanned by one turn of the B-DNA double helix is approximately ______.

3.4 nm (34 Å).

Which form of DNA is typically found under conditions of high salt concentration and low hydration?

A-DNA.

How many base pairs are present in one turn of B-DNA?

10 base pairs.

Fill in the blank: The structure formed by the wrapping of DNA around histone proteins is known as ______.

Nucleosome.

What is the function of topoisomerases in DNA?

To relieve torsional stress and manage the twists and turns in the DNA molecule.

Riddle: I’m a protein that helps DNA pack tightly, am I a histone or a lipid?

Histone.

Which enzyme introduces negative supercoils into DNA?

E. coli DNA Gyrase.

True or False: Hyperchromicity during DNA denaturation indicates a decrease in UV absorbance.

False. Hyperchromicity indicates an increase in UV absorbance as bases become exposed.

Fill in the blank: The structural feature that describes DNA strands running in opposite directions is known as ______.

Antiparallel strands.

What type of chromatin is loosely packed and actively involved in transcription?

Euchromatin.

How many types of histones are there and what are they?

There are five types: H2A, H2B, H3, H4 (core histones), and H1 (linker histone).

Which type of supercoil occurs when DNA is twisted in the same direction as the double helix?

Positive supercoils.

Fill in the blank: The process where DNA is replicated into more DNA is called ______.

DNA replication.

What is the diameter of the DNA double helix?

Approximately 2 nm (20 Å).

True or False: Four-stranded DNA structures are commonly found in DNA with low guanine content.

False. Four-stranded DNA structures are found in DNA with high guanine content.

What is the significance of the major and minor grooves in DNA?

They are important for DNA–protein interactions, which regulate gene expression.

Riddle: I am a structure that condenses at times but can decondense to allow transcription. What am I?

Facultative heterochromatin.

What type of DNA can be separated using gel electrophoresis?

Both single-stranded and double-stranded DNA.

Fill in the blank: Telomeres are repetitive sequences rich in ______ at the ends of eukaryotic chromosomes.

Guanine.

What effect does increasing salt concentration have on the melting temperature (Tm) of DNA?

It increases Tm by raising the stabilization of the DNA strands.

Which enzyme is crucial for DNA repair and replication processes?

Topoisomerase.