Question 1

A scientist isolates a DNA sample from a eukaryotic cell and finds that 30% of the bases are cytosine. According to Chargaff's rules, what percentage of the bases should be adenine?

Accepted Answer

$$20\%$$

Question 2

Which of the following best explains why Okazaki fragments are formed during DNA replication in eukaryotic cells?

Accepted Answer

DNA polymerase can only synthesize DNA in the $$5' \rightarrow 3'$$ direction, so the lagging strand is synthesized discontinuously.

Question 3

A mutation changes the DNA sequence $$5'-ATG\ GCT\ TTT\ TGA-3' to$$ $$5'-ATG\ GCT\ TAT\ TGA-3'. $$What type of mutation has occurred, and what is the likely effect on the protein?

Accepted Answer

Missense mutation; one amino acid is changed.

Question 4

Which experiment provided the strongest evidence that DNA, not protein, is the genetic material in viruses?

Accepted Answer

Hershey–Chase experiment using $$^{32}P$$ and $$^{35}S$$ labeling of bacteriophages.

Question 5

A DNA template strand has the sequence $$3'-TAC\ GGA\ CTT-5'. $$What is the corresponding mRNA sequence produced during transcription?

Accepted Answer

$$5'-AUG\ CCU\ GAA-3'$$

Question 6

Which of the following best describes the role of telomerase in eukaryotic cells?

Accepted Answer

It extends the ends of linear chromosomes using an RNA template.

Question 7

A patient’s cells are found to have a mutation that prevents the removal of introns from pre-mRNA. What is the most likely consequence?

Accepted Answer

The mature mRNA will contain noncoding sequences, potentially leading to abnormal proteins.

Question 8

In the lac operon, what is the expected outcome when lactose is present and glucose is absent?

Accepted Answer

High expression of the lac operon genes due to relief of repression and activation by CAP–cAMP.

Question 9

Which of the following statements about the genetic code is correct?

Accepted Answer

It is degenerate, meaning multiple codons can specify the same amino acid.

Question 10

A forensic scientist analyzes DNA from a crime scene using short tandem repeats (STRs). Why are STRs particularly useful for DNA profiling?

Accepted Answer

They are highly variable among individuals, allowing for discrimination between unrelated people.

Question 11

Which enzyme is responsible for synthesizing the RNA primer required for DNA polymerase to begin replication?

Accepted Answer

Primase

Question 12

A mutation results in the insertion of two nucleotides into a coding sequence. What is the most likely effect on the resulting protein?

Accepted Answer

A frameshift mutation, altering the reading frame and likely changing many downstream amino acids.

Question 13

Which of the following best describes the difference between prokaryotic and eukaryotic DNA replication?

Accepted Answer

Eukaryotic chromosomes have multiple origins of replication, while prokaryotic chromosomes usually have one.

Question 14

A researcher observes that after two generations in the Meselson–Stahl experiment, DNA samples show both intermediate and light densities. What does this observation support?

Accepted Answer

Semiconservative replication, where each new DNA molecule contains one parental and one new strand.

Question 15

Which of the following is a direct result of alternative splicing in eukaryotic cells?

Accepted Answer

A single gene can produce multiple protein isoforms.

Question 16

During translation, which ribosomal site holds the tRNA carrying the growing polypeptide chain?

Accepted Answer

P site

Question 17

Which of the following best explains why a one-nucleotide insertion can have a more severe effect on a protein than a single-nucleotide substitution?

Accepted Answer

It causes a frameshift, altering all downstream codons and possibly introducing a premature stop codon.

Question 18

Which of the following statements about the Human Genome Project is correct?

Accepted Answer

It revealed that most of the human genome does not encode proteins.

Question 19

Which of the following is NOT a function of DNA polymerase during replication?

Accepted Answer

Synthesizing DNA in the $$3' \rightarrow 5'$$ direction

Question 20

A bacterial cell is exposed to high levels of glucose and no lactose. What is the expected expression level of the lac operon?

Accepted Answer

Very low, because the repressor remains bound and CAP–cAMP activation is minimal.

Molecular Basis of Inheritance: DNA, Replication, Transcription, Translation, Mutations, and Gene Regulation

Guida di studio - Domande di pratica

Study guide - Flashcard