Supercoiling of DNA can occur (choose all that apply):
A. when double stranded DNA is overwound
B. when double stranded DNA is underwound
C. when double stranded DNA is heated above it's Tm
D. when DNA is treated with nucleases
and
Generally, cellular DNA is:
A. Slightly underwound
B. Slightly overwound
C. Chemically unstable in basic solutions
D.Single stranded
i don't think it is C...I am thinking A or D
To determine the correct answers, let's go through each statement one by one:
1. Supercoiling of DNA can occur when double-stranded DNA is overwound (A) and when it is underwound (B). Supercoiling refers to the coiling of DNA upon itself, resulting in additional twists or turns in the helix. Overwound DNA has more twists compared to the relaxed state, while underwound DNA has fewer twists.
2. Supercoiling of DNA does not occur when double-stranded DNA is heated above its melting temperature (Tm) (C). Heating DNA above its Tm separates the two strands, resulting in denaturation rather than supercoiling.
3. Supercoiling of DNA does not occur when DNA is treated with nucleases (D). Nucleases are enzymes that break down nucleic acids, including DNA. Treating DNA with nucleases would lead to DNA degradation, rather than inducing supercoiling.
Now, let's move on to the second question:
4. Generally, cellular DNA is slightly underwound (A). Underwinding of DNA is a natural state in cells, where there are fewer twists compared to the relaxed state. This slight underwinding helps facilitate DNA replication and transcription processes in cells.
5. Cellular DNA is not slightly overwound (B). While overwinding can occur under certain circumstances, it is not the typical state of cellular DNA.
6. Cellular DNA is not chemically unstable in basic solutions (C). DNA is stable under a wide range of pH levels, including basic conditions.
7. Cellular DNA is not single-stranded (D). DNA is typically double-stranded, consisting of two complementary strands held together by hydrogen bonds between their base pairs.
Based on these explanations, the correct answers are:
For the first question: A and B.
For the second question: A.