Chapter 16

Question 1

What is the significance of Frederick Griffith’s experiment in 1928?

Answer 1

Griffith’s experiment demonstrated the phenomenon of transformation, where a substance from heat-killed pathogenic bacteria could transform non-pathogenic bacteria into a pathogenic form. This suggested that some “heritable substance” was responsible for this transformation.

Question 2

What did Oswald Avery, Maclyn McCarty, and Colin MacLeod discover?

Answer 2

They confirmed that the transforming substance identified by Griffith was DNA, establishing DNA as the molecule responsible for heredity.

Question 3

Describe the Hershey-Chase experiment and its significance.

Answer 3

The Hershey-Chase experiment used bacteriophages labeled with radioactive isotopes to show that DNA, not protein, is the genetic material. They found that only the DNA entered bacterial cells and directed the production of new phages.

Question 4

What are Chargaff’s rules?

Answer 4

Chargaff’s rules state that in any given species, the amount of adenine (A) equals thymine (T), and the amount of guanine (G) equals cytosine (C). This provided evidence for the base-pairing mechanism in DNA.

Question 5

What is the structure of DNA as discovered by Watson and Crick?

Answer 5

DNA is a double helix with two strands running in opposite directions (antiparallel). The strands are held together by hydrogen bonds between complementary base pairs (A with T and G with C).

Question 6

Explain the semiconservative model of DNA replication.

Answer 6

The semiconservative model of DNA replication states that each new DNA molecule consists of one old (parental) strand and one newly synthesized strand. This was confirmed by the Meselson-Stahl experiment.

Question 7

What is the role of helicase in DNA replication?

Answer 7

Helicase unwinds the DNA double helix at the replication fork, separating the two strands to allow replication to occur.

Question 8

What is the function of single-strand binding proteins?

Answer 8

Single-strand binding proteins stabilize the unwound DNA strands, preventing them from re-annealing or forming secondary structures.

Question 9

Describe the role of topoisomerase in DNA replication.

Answer 9

Topoisomerase relieves the strain caused by the unwinding of DNA by making temporary cuts in the DNA strands and then rejoining them.

Question 10

What is the function of primase in DNA replication?

Answer 10

Primase synthesizes a short RNA primer that provides a starting point for DNA polymerase to begin DNA synthesis.

Question 11

How does DNA polymerase III function in DNA replication?

Answer 11

DNA polymerase III adds nucleotides to the 3’ end of the RNA primer, synthesizing the new DNA strand in the 5’ to 3’ direction.

Question 12

What is the role of DNA polymerase I in DNA replication?

Answer 12

DNA polymerase I removes the RNA primers and replaces them with DNA nucleotides.

Question 13

Explain the function of DNA ligase in DNA replication.

Answer 13

DNA ligase joins the Okazaki fragments on the lagging strand by forming phosphodiester bonds between the sugar-phosphate backbones of the fragments

Question 14

What is the difference between the leading and lagging strands in DNA replication?

Answer 14

The leading strand is synthesized continuously in the direction of the replication fork, while the lagging strand is synthesized discontinuously in short fragments called Okazaki fragments, away from the replication fork.

Question 15

What is the trombone model of DNA replication?

Answer 15

The trombone model describes how the lagging strand loops out to allow DNA polymerase to synthesize Okazaki fragments in a coordinated manner with the leading strand synthesis.

Question 16

How does DNA proofreading and error correction work?

Answer 16

DNA polymerase has proofreading activity that detects and corrects mismatched nucleotides during DNA synthesis. If an incorrect nucleotide is added, the polymerase removes it and replaces it with the correct one.

Question 17

What is nucleotide excision repair?

Answer 17

Nucleotide excision repair is a DNA repair mechanism that removes damaged DNA segments and replaces them with the correct nucleotides using a DNA polymerase and DNA ligase.

Question 18

What are telomeres and their function?

Answer 18

Telomeres are repetitive DNA sequences at the ends of linear chromosomes that protect the chromosome from degradation and prevent the loss of important genetic information during replication.

Question 19

What is the role of telomerase in germ cells?

Answer 19

Telomerase extends the telomeres in germ cells, ensuring that the genetic material remains intact and is not lost during cell division.

Question 20

How do mutations affect protein synthesis?

Answer 20

Mutations can alter the nucleotide sequence of a gene, leading to changes in the amino acid sequence of the protein. This can result in nonfunctional proteins or proteins with altered functions, potentially causing genetic disorders.