A form and Z form of double stranded DNA differ in the handedness of their helices, nucleotide sequences, and configuration of base to sugar. Based on these properties, which one of the following statements defines a correct combination for A and Z forms of DNA?
Left handed double helix and syn-configuration for base to sugar arrangement in the A form DNA and right handed double helix and anti-configuration for the base to sugar arrangement for the Z form DNA.
DNA Double Helix Forms
Double-stranded DNA can exist in several different forms, with the most common being the B-form DNA found under physiological conditions. Other forms like A-DNA and Z-DNA also exist and have distinct structural properties, including the handedness of the helix and the configuration of the base relative to the sugar.
Properties of A and Z Forms Described in the Provided Option
According to the properties described in the provided correct option text, we can define the characteristics attributed to A-form DNA and Z-form DNA as follows:
- A-form DNA: This form is described as having a left-handed double helix. The configuration of the base relative to the sugar in the nucleotide is described as syn-configuration.
- Z-form DNA: This form is described as having a right-handed double helix. The configuration of the base relative to the sugar in the nucleotide is described as anti-configuration.
Let's summarize these properties as described:
| DNA Form | Handedness of Double Helix | Base to Sugar Configuration |
|---|---|---|
| A-form DNA | Left-handed | syn-configuration |
| Z-form DNA | Right-handed | anti-configuration |
Based on the properties listed in the provided options, the statement that describes A-form DNA as a left-handed double helix with syn-configuration for the base to sugar arrangement, and Z-form DNA as a right-handed double helix with anti-configuration for the base to sugar arrangement is the one matching the provided correct answer text.
Configuration of Base to Sugar
The configuration of the base relative to the sugar refers to the orientation around the glycosidic bond connecting the nitrogenous base to the deoxyribose sugar. The two primary configurations are:
- Anti-configuration: In this orientation, the base is positioned away from the sugar ring. This is the most common configuration found in B-DNA and is also present in A-DNA.
- Syn-configuration: In this orientation, the base is positioned over the sugar ring. This configuration is less common in standard DNA forms but is observed in Z-DNA, particularly for purines.
The provided correct answer text describes specific configurations for A-DNA (syn) and Z-DNA (anti), which should be considered according to the question's parameters.
Handedness of Double Helix
The handedness of a double helix refers to the direction in which the strands twist around the central axis:
- Right-handed helix: The strands twist clockwise as they move away from the viewer. B-DNA and A-DNA are right-handed helices.
- Left-handed helix: The strands twist counter-clockwise as they move away from the viewer. Z-DNA is a left-handed helix.
According to the provided correct answer text, A-form DNA is described as left-handed, and Z-form DNA is described as right-handed.
Reviewing the provided options against the description in the correct answer text, the statement that precisely matches these attributed properties for A and Z forms of DNA represents the correct combination based on the question's premise.
Important Questions from Conformation of Proteins and Nucleic acids
Which one of the following statements is true regarding amino acids?
The following statements are made
A. B form of DNA has ~10 base pairs/turn and A form of DNA has ~2.3Å helix rise per base pair
B. Both the A and B form of DNA have wider major groove and narrow minor groove
C. The crystalline nature of cellulose is brought about by α (1 → 4) linkage between the glucose subunits.
D. The double bonds in natural lipids are always cis, which provides fluidity to the plasma membrane.
Which of the following combinations represent the correct statements?
Analysis of a homotetrameric protein and a double stranded DNA (that had been incubated in standard buffer) on native gels revealed that they migrated true to their physical states (tetrameric nature of the protein and double stranded nature of the DNA). Following hypotheses were made for the effect of adding high salt to the incubation mix and subsequent analysis on native gels.
A. The protein would migrate as a homotetramer and DNA in double stranded form.
B. The protein would migrate as a monomer but DNA in double stranded form.
C. The protein would migrate as a homotetramer but the DNA in single stranded form.
D. The protein would migrate as a monomer and the DNA in single stranded form.
Which of the following combination of hypotheses is most likely?
Heating of some nucleic acids shows an increase in the absorbance at 260 nm (A260) typified by the plot shown above. The sharp transition midpoint is defined as melting temperature (Tm). Which one of the following nucleic acid samples is NOT expected to generate such a typical profile upon heating of its solution?
If the pyrollidine ring of proline is reduced to a linear form, the new amino acid will have
