Question

what forms the backbone of the dna strand?
a. nitrogenous bases
b. sugar - phosphate backbone
c. covalent bonds between nitrogenous bases
d. hydrogen bonds

which technology is used for amplifying specific dna sequences?
a. polymerase chain reaction (pcr)
b. gel electrophoresis
c. dna sequencing
d. crispr - cas9

which of the following statements about the double helix structure of dna is true?
a. it resembles a twisted ladder
b. it consists of three strands
c. it is a flat structure
d. it is made entirely of proteins

Explanation:

First Question: What forms the backbone of the DNA strand?

• Option a: Nitrogenous bases are the rungs of the DNA ladder, not the backbone.
• Option b: The sugar - phosphate backbone (deoxyribose sugar and phosphate groups) forms the outer structure (backbone) of the DNA strand.
• Option c: Nitrogenous bases are connected by hydrogen bonds (not covalent bonds between them to form the backbone), and covalent bonds between nitrogenous bases are not part of the backbone.
• Option d: Hydrogen bonds are between the nitrogenous bases of the two DNA strands, holding them together, not forming the backbone.

• Option a: Polymerase Chain Reaction (PCR) is a technique that repeatedly replicates a specific DNA segment, thus amplifying it.
• Option b: Gel electrophoresis is used to separate DNA fragments based on size, not for amplification.
• Option c: DNA sequencing is used to determine the order of nucleotides in a DNA molecule, not for amplification.
• Option d: CRISPR - Cas9 is a gene - editing tool, not for amplifying DNA sequences.

• Option a: The DNA double helix has two strands (like the sides of a ladder) with nitrogenous bases as rungs, and it is twisted, so it resembles a twisted ladder.
• Option b: DNA double helix has two strands, not three.
• Option c: The DNA double helix is a three - dimensional, twisted structure, not a flat structure.
• Option d: DNA is made of nucleotides (sugar, phosphate, nitrogenous base), not entirely of proteins.

Answer:

b. Sugar - phosphate backbone

Second Question: Which technology is used for amplifying specific DNA sequences?