Q: Which of the following best describes the central dogma of molecular biology?

$$\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}$$

Question 1

Which of the following best explains why many scientists initially believed proteins, rather than DNA, were the genetic material?

Accepted Answer

Proteins have a greater variety of 3D structures and functions than DNA.

Question 2

In Frederick Griffith’s 1928 experiment with *Streptococcus pneumoniae*, which result demonstrated the phenomenon of transformation?

Accepted Answer

Mice injected with a mixture of heat-killed S strain and live R strain died, and live S strain bacteria were recovered.

Question 3

Avery, MacLeod, and McCarty’s 1944 experiment built on Griffith’s work. What was their key finding?

Accepted Answer

DNA, not protein or RNA, is the transforming principle responsible for heredity.

Question 4

In the Hershey-Chase experiment, how did the researchers distinguish between DNA and protein to determine which was the genetic material?

Accepted Answer

They labeled DNA with $$^{32}\mathrm{P}$$ and protein with $$^{35}\mathrm{S}$$, then tracked which label entered bacterial cells.

Question 5

Which of the following correctly describes Chargaff’s rules?

Accepted Answer

The amount of adenine equals thymine, and the amount of guanine equals cytosine in DNA: $$[A] = [T]$$ and $$[G] = [C].$$

Question 6

Which model of DNA replication was supported by the Meselson-Stahl experiment, and what was the key evidence?

Accepted Answer

Semiconservative; after one round of replication in $$^{14}\mathrm{N}$$, DNA had intermediate density between $$^{15}\mathrm{N}$$ and $$^{14}\mathrm{N}.$$

Question 7

During DNA replication, which enzyme is responsible for joining Okazaki fragments on the lagging strand?

Accepted Answer

DNA ligase

Question 8

Which of the following statements about eukaryotic DNA replication is correct?

Accepted Answer

Eukaryotic chromosomes have multiple origins of replication and linear chromosomes with telomeres.

Question 9

Which of the following best describes the central dogma of molecular biology?

Accepted Answer

$$	ext{DNA} ightarrow 	ext{RNA} ightarrow 	ext{Protein}$$

Question 10

Which of the following is an exception to the central dogma?

Accepted Answer

Reverse transcription in retroviruses, where RNA is used to synthesize DNA.

Question 11

Which feature of the genetic code allows for silent mutations, where a change in the DNA sequence does not alter the amino acid sequence?

Accepted Answer

The code is degenerate; multiple codons can specify the same amino acid.

Question 12

Which of the following posttranscriptional modifications occurs in eukaryotic pre-mRNA but not in prokaryotic mRNA?

Accepted Answer

Addition of a 5' cap and a 3' poly-A tail

Question 13

A mutation in the anticodon loop of a tRNA molecule would most likely affect which process?

Accepted Answer

The ability of the tRNA to recognize and bind the correct mRNA codon during translation.

Question 14

Which of the following best describes the function of the lac operon repressor in *E. coli*?

Accepted Answer

It binds to the operator and blocks transcription when lactose is absent.

Question 15

How does the presence of glucose affect the lac operon in *E. coli*?

Accepted Answer

Glucose inhibits cAMP production, reducing CAP binding and decreasing lac operon transcription.

Question 16

Which of the following is a mechanism of epigenetic regulation of gene expression in eukaryotes?

Accepted Answer

DNA methylation, which can silence gene expression without changing the DNA sequence.

Question 17

Which of the following best describes the function of restriction endonucleases in recombinant DNA technology?

Accepted Answer

They cut DNA at specific sequences, allowing scientists to insert or remove genes.

Question 18

During gel electrophoresis, how are DNA fragments separated?

Accepted Answer

By size, with smaller fragments migrating faster through the gel matrix toward the positive electrode.

Question 19

Which enzyme is essential for the polymerase chain reaction (PCR), and why is it used?

Accepted Answer

Taq polymerase, because it is heat-stable and can withstand the high temperatures used to denature DNA.

Question 20

Which of the following is a real-world application of DNA fingerprinting, and what is the role of STRs in this process?

Accepted Answer

Forensic identification; STRs (short tandem repeats) are highly variable regions used to distinguish individuals.

General Biology Study Guide: DNA, Gene Expression, and Biotechnology

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