DNA STRUCTURE

• C. Nucleus

• DNA is found in the "Nucleus of eukaryotic cells." Eukaryotes have a membrane-bound nucleus that houses their genetic material, separating it from the rest of the cell's machinery.

In eukaryotic organisms, where is the primary location of DNA?
A. Cytoplasm
B. Ribosomes
C. Nucleus
D. Cell membran

• B. Cytoplasm

• Prokaryotes (like bacteria) lack a membrane-bound nucleus or nuclear membrane. So, their DNA exists freely in the cytoplasm, specifically in a region called the nucleoid.

where is DNA located in prokaryotic cells?
A. Nucleolus
B. Cytoplasm
C. Mitochondria
D. Golgi apparatus

• C. Contains genetic code

• DNA carries genetic information serves as the blueprint for all biological instructions required for an organism to develop, survive, and reproduce.

What is the primary function of DNA ?
A. Energy production
B. Protein synthesis
C. Contains genetic code
D. Transport of oxygen

• C. Deoxyribose (Sugar ribose backbone)

• DNA contains Deoxyribose (lacking an oxygen atom), whereas RNA contains Ribose

Which sugar forms the backbone of a DNA molecule?
A. Glucose
B. Ribose
C. Deoxyribose (Sugar ribose backbone)
D. Sucrose

What chemical component forms the alternating structural backbone of a DNA strand?

​A) Nitrogenous bases and amino acids

​B) Sugar (deoxyribose) and phosphate groups

​C) Ribose sugar and peptide bonds

​D) Purines exclusively linked by hydrogen bonds

✅(️​B)

structural integrity of the DNA strand relies on a sugar-phosphate backbone, where deoxyribose sugars are connected via phosphodiester bonds. This hydrophilic backbone protects the internal hydrophobic nitrogenous bases.

Which specific type of chemical bond links the successive nucleotides along the DNA backbone?

​A) Peptide bond

​B) Glycosidic bond

​C) Phosphodiester bond

​D) Disulfide bond

✅ ️(C)

Phosphodiester bonds link the 3' carbon of one sugar molecule to the 5' carbon of another via a phosphate group. Deficiencies or breaks in these bonds (single- or double-strand breaks) trigger DNA damage response pathways (e.g., ATM/ATR kinases) crucial in radiation oncology.

What forces stabilize the interaction between complementary nitrogenous bases on opposite strands of the DNA double helix?

​A) Covalent peptide linkages

​B) Hydrogen bonds

​C) Ester linkages

​D) Ionic salt bridges

✅️ 𝗕

Complementary base pairs (Adenine-Thymine with 2 hydrogen bonds, Cytosine-Guanine with 3 hydrogen bonds) are held together by hydrogen bonds. This allows the helix to "unzip" easily during DNA replication and transcription without breaking covalent backbone bonds.