Question

what is a nucleotide?
a. a type of protein that carries oxygen.
b. a mutation that alters the genetic code
c. the basic structural unit of dna and rna
d. an enzyme that facilitates dna replication

which mutation occurs when one nucleotide is replaced by another in the dna sequence?
a. frameshift mutation
b. insertion mutation
c. substitution mutation
d. deletion mutation

what is the impact of a mutation on a gene?
a. it eliminates the gene from the dna
b. it has no effect on the organism
c. it always leads to a beneficial trait
d. it can change the gene’s function or expression

Explanation:

First Question: What is a nucleotide?

• Option a: The protein that carries oxygen is hemoglobin, not a nucleotide. Eliminate a.
• Option b: A mutation altering genetic code is not a nucleotide (nucleotides are structural units). Eliminate b.
• Option c: Nucleotides are the basic building blocks (structural units) of DNA and RNA. This matches the definition.
• Option d: Enzymes for DNA replication (like DNA polymerase) are not nucleotides. Eliminate d.

• Option a: Frameshift mutations are from insertions/deletions, not single - nucleotide replacements. Eliminate a.
• Option b: Insertion mutation is adding a nucleotide, not replacing. Eliminate b.
• Option c: Substitution mutation is precisely the replacement of one nucleotide with another. This fits.
• Option d: Deletion mutation is removing a nucleotide, not replacing. Eliminate d.

• Option a: Mutations don't typically eliminate a gene from DNA (they alter the gene's sequence). Eliminate a.
• Option b: Mutations can have effects (e.g., harmful, beneficial, or neutral), so "no effect" is not always true. Eliminate b.
• Option c: Mutations don't always lead to beneficial traits (can be harmful or neutral). Eliminate c.
• Option d: Mutations can change a gene's function (e.g., via amino - acid changes in proteins) or its expression (e.g., regulatory mutations). This is correct.

Answer:

c. The basic structural unit of DNA and RNA

Second Question: Which mutation occurs when one nucleotide is replaced by another in the DNA sequence?