chapter 15

Question 1

What two components make up chromosomes?

Answer 1

DNA and proteins.

Question 2

What experiment showed that DNA is the genetic material?

Answer 2

hersey chase experiment

Question 3

Why did scientists initially think genes were made of protein?

Answer 3

Proteins are more complex and variable compared to DNA, which has only four nucleotides.

Question 4

What did the Hershey-Chase experiment demonstrate?

Answer 4

It proved that DNA, not protein, is the hereditary material.

Question 5

What are the three models of DNA replication?

Answer 5

Semiconservative replication,Conservative replication,Dispersive replication

Question 6

three models of DNA replication

Semiconservative replication:

Answer 6

Each new molecule has one old strand and one new strand.

Question 7

Conservative replication

Answer 7

The original molecule remains intact, and a completely new molecule is formed.

Question 8

Dispersive replication

Answer 8

DNA is fragmented and recombined, mixing old and new DNA in each strand.

Question 9

What experiment confirmed the semiconservative replication model?

Answer 9

The Meselson-Stahl experiment using heavy and light nitrogen isotopes.

Question 10

In what direction does DNA synthesis occur?

Answer 10

DNA synthesis proceeds in the 5’ to 3’ direction.

Question 11

What enzyme catalyzes DNA synthesis?

Answer 11

DNA polymerase.

Question 12

What is a primer, and how is it synthesized?

Answer 12

A primer is a short RNA strand that provides a starting point for DNA polymerase. It is synthesized by the enzyme primase.

Question 13

What is the leading strand, and how is it synthesized?

Answer 13

The leading strand is synthesized continuously toward the replication fork.

Question 14

What is the lagging strand, and how is it synthesized?

Answer 14

The lagging strand is synthesized discontinuously in short fragments called Okazaki fragments, moving away from the replication fork.

Question 15

How are Okazaki fragments joined?

Answer 15

DNA ligase forms phosphodiester bonds (covalent) to link fragments into a continuous strand.

Question 16

What is the end-replication problem?

Answer 16

The lagging strand cannot complete synthesis at the very end of a chromosome, leaving a single-stranded overhang that shortens with each replication cycle.

Question 17

What enzyme prevents chromosome shortening?

Answer 17

Telomerase extends the telomeres, the repetitive sequences at chromosome ends.

Question 18

Why do telomeres shorten in somatic cells?

Answer 18

Somatic cells lack active telomerase, leading to progressive shortening with age.

Question 19

How accurate is DNA replication?

Answer 19

DNA replication has an error rate of one mistake per billion nucleotides.

Question 20

What is proofreading in DNA replication?

Answer 20

DNA polymerase detects and removes mismatched bases during synthesis.

Question 21

What is mismatch repair?

Answer 21

It is a system that corrects mismatched bases left after DNA replication.

Question 22

How does UV light damage DNA?

Answer 22

UV light induces thymine dimers, which create kinks in the DNA strand and block replication.

Question 23

What is nucleotide excision repair?

Answer 23

A repair system that removes damaged DNA, fills the gap with new DNA, and seals it with DNA ligase.

e.g., UV-induced thymine dimers) by removing the damaged strand and replacing it using the intact strand as a template.

Question 24

What is xeroderma pigmentosum (XP)?

Answer 24

A genetic disorder caused by defects in nucleotide excision repair, leading to UV sensitivity and increased cancer risk.

Question 25

What is the role of topoisomerase in DNA replication?

Answer 25

It relieves tension caused by unwinding the DNA helix.

Question 26

What is the replisome?

Answer 26

A dynamic molecular machine that coordinates the enzymes and proteins involved in DNA synthesis.

Question 27

What makes DNA polymerization energetically favorable?

Answer 27

The high potential energy of dNTPs (deoxyribonucleoside triphosphates) drives the reaction.

Question 28

What did the Hersey and chase experiment study

Answer 28

t2 virus infects and replicates becterium in ECOLI

Question 29

when does the T2 infection of Ecoli begin

Answer 29

when the virus injects into cell, genes direct production of new virus particles

Question 30

# hersey chase experiment what is left behind on viruses exterior protien coat

Answer 30

capsid is left behind on outside of cell

Question 31

where did hersey and chase grow their virus in the presence of what?

Answer 31

two radiotic isotopes of 32^Phosphate and 35^sulfar

Question 32

# hersey and chase experiment where was phosphate isotope incorporated into

Answer 32

The DNA

Question 33

Where was S incorporated into

Answer 33

protiens

Question 34

# hersey and chase what were used to infect ecoli cells

Answer 34

labeled viruses

Question 35

What do t2 viruses contain and don't contain

Answer 35

t2 protiens contain sulfur but not phosphorous

Question 36

what does DNA contain

Answer 36

phosphorous but not sufur

Question 37

what did hersey and chase find inside cell

Answer 37

radioactive dna | Proved that genes were composed of DNA

Question 38

What is DNA's structure?

Answer 38

1. DNA is a double helix with antiparallel strands. 2. It has a sugar-phosphate backbone and complementary base pairs (A-T and G-C).

Question 39

Which hypothesis for DNA replication was correct?

Answer 39

The semiconservative model was proven correct by the Meselson-Stahl experiment.

Question 40

What is the role of DNA polymerase?

Answer 40

DNA polymerase synthesizes new DNA by adding nucleotides to the 3' end of a growing strand.

Question 41

What is the difference between the leading and lagging strands during replication?

Answer 41

Leading strand: Synthesized continuously toward the replication fork. Lagging strand: Synthesized in short fragments (Okazaki fragments) away from the fork.

Question 42

What is the role of telomerase?

Answer 42

Telomerase extends the ends of linear chromosomes (telomeres) to prevent shortening during replication.

Question 43

What happens if DNA is not repaired?

Answer 43

Mutations accumulate, increasing the risk of diseases like cancer.

Question 44

Why is DNA considered a polymer?

Answer 44

DNA is a polymer because its nucleotides are linked by phosphodiester bonds between the sugar of one nucleotide and the phosphate group of another.

Question 45

What was the key technique used in the Meselson-Stahl experiment?

Answer 45

Density gradient centrifugation was used to separate DNA based on its density after replication in heavy (15N) and light (14N) nitrogen media.

Question 46

What is the function of DNA helicase?

Answer 46

DNA helicase unwinds the DNA double helix by breaking hydrogen bonds between the strands.

Question 47

What is the role of single-strand DNA-binding proteins (SSBPs)?

Answer 47

SSBPs bind to separated DNA strands to prevent them from reannealing.

Question 48

How does topoisomerase alleviate tension during replication?

Answer 48

Topoisomerase cuts and rejoins the DNA to relieve supercoiling caused by unwinding.

Question 49

What repetitive sequences are found in telomeres?

Answer 49

Telomeres consist of short, repeated sequences of bases (e.g., TTAGGG in humans).

Question 50

What are the two key types of errors during DNA synthesis?

Answer 50

Mismatched bases DNA damage

Question 51

Mismatched bases

Answer 51

Incorrect base pairing.

Question 52

DNA damage

Answer 52

From external factors like UV light or chemicals.

Question 53

What happens if the DNA repair systems fail?

Answer 53

Accumulated mutations can lead to diseases like cancer, where cells grow uncontrollably.

Question 54

What stabilizes the DNA double helix?

Answer 54

Hydrogen bonding between complementary bases (A-T and G-C). Base stacking interactions within the helix.

Question 55

Why is DNA synthesis considered bidirectional in eukaryotic cells?

Answer 55

Replication begins at multiple origins of replication, forming replication bubbles that grow in both directions.