genetics lecture 2: genetic code and replication

Which molecule was identified as the genetic material in the Avery-MacLeod-McCarty experiment?
A. RNA
B. Protein
C. DNA
D. Lipids

DNA

What was the key conclusion from Griffith’s experiment?
A. Proteins carry hereditary information
B. Heat-killed R strain is virulent
C. A substance from dead S cells transforms R cells
D. RNA transforms bacteria

A substance from dead S cells transforms R cells

What did the Hershey-Chase experiment confirm?
A. Proteins are the genetic material
B. DNA is only structural
C. DNA, not protein, enters bacterial cells
D. RNA is inherited by progeny phages

DNA, not protein, enters bacterial cells

Which radioactive isotope labeled DNA in the Hershey-Chase experiment?
A. Carbon-14
B. Sulfur-35
C. Phosphorus-32
D. Oxygen-18

Phosphorus-32

Which structure did Watson and Crick discover?
A. Triplex DNA
B. Antiparallel RNA
C. DNA double helix
D. Circular chromosome

DNA double helix

Which of the following is a pyrimidine?
A. Adenine
B. Guanine
C. Thymine
D. Histidine

Thymine

Which replication model was supported by Meselson and Stahl?
A. Dispersive
B. Conservative
C. Semiconservative
D. Nonlinear

Semiconservative

What happens to DNA density after two generations in 14N medium (Meselson-Stahl)?
A. One light and one intermediate band
B. Only heavy DNA
C. All light DNA
D. Two heavy bands

One light and one intermediate band

What type of replication occurs at the replication fork?
A. Circular
B. Linear and unidirectional
C. Bidirectional
D. Dispersive

Bidirectional

What is the function of primase?
A. Breaks hydrogen bonds
B. Adds dNTPs
C. Synthesizes RNA primers
D. Seals gaps

Synthesizes RNA primers

What direction does DNA polymerase III synthesize DNA?
A. 3′ to 5′
B. 5′ to 3′
C. Both directions
D. It depends on the strand

5′ to 3′

Which strand is synthesized discontinuously?
A. Template strand
B. Lagging strand
C. Leading strand
D. Sense strand

Lagging strand

What are Okazaki fragments?
A. RNA primers
B. Protein fragments
C. DNA pieces on the lagging strand
D. Damaged DNA segments

DNA pieces on the lagging strand

What removes RNA primers during replication?
A. DNA ligase
B. DNA polymerase I
C. Primase
D. Helicase

DNA polymerase I

Which DNA form has a left-handed helix?
A. A-form
B. B-form
C. Z-form
D. R-form

Z-form

The Avery-MacLeod-McCarty experiment used __________ to destroy DNA.

DNAase

Hershey and Chase used __________-labeled protein and __________-labeled DNA.

sulfur (35S), phosphorus (32P)

The DNA shape most commonly found in cells is the __________ form.

B

In double-stranded DNA, the number of purines equals the number of __________.

pyrimidines

The experimental technique used by Meselson and Stahl was __________ centrifugation.

density gradient

T/F: DNA was proven to be the genetic material through Griffith’s experiment.

false (Griffith’s experiment showed transformation, but Avery et al. proved it was DNA.)

Meselson and Stahl used radioactive sulfur to track DNA.

false (They used heavy nitrogen (15N).)

DNA polymerase requires an existing 3′ OH group to add nucleotides.

true

What key discovery was made in Griffith’s experiment?
A. DNA has a double helix structure
B. RNA is the hereditary material
C. A "transforming principle" can transfer traits between bacteria
D. DNA replicates semiconservatively

A "transforming principle" can transfer traits between bacteria

In the Avery-MacLeod-McCarty experiment, what treatment prevented transformation of R cells?
A. RNase
B. DNase
C. Proteinase
D. Heat treatment

DNase

What was the purpose of the blender in the Hershey-Chase experiment?
A. To lyse the bacterial cells
B. To destroy radioactive labels
C. To separate viral ghosts from infected bacteria
D. To measure DNA content

To separate viral ghosts from infected bacteria

Which isotope was used to label DNA in the Hershey-Chase experiment?
A. Carbon-14
B. Sulfur-35
C. Phosphorus-32
D. Nitrogen-15

Phosphorus-32

What conclusion did Meselson and Stahl draw after two rounds of DNA replication in 14N?
A. DNA replication is conservative
B. DNA replication is dispersive
C. DNA replication is semiconservative
D. DNA is made of RNA templates

DNA replication is semiconservative

Why was nitrogen-15 (15N) used in the Meselson-Stahl experiment?
A. To label protein
B. To track DNA density changes
C. To initiate replication
D. To denature DNA

To track DNA density changes

Which experiment provided the first evidence that DNA can transfer genetic traits?
A. Hershey-Chase
B. Meselson-Stahl
C. Avery-MacLeod-McCarty
D. Griffith’s experiment

Griffith’s experiment

What type of molecules were tested by Avery and colleagues to determine the “transforming principle”?
A. Sugars, RNA, DNA
B. Proteins, RNA, DNA
C. Lipids, proteins, carbohydrates
D. RNA, DNA, lipids

Proteins, RNA, DNA

In the semiconservative model of DNA replication, each new DNA molecule consists of:
A. Two newly synthesized strands
B. Two original strands
C. One original and one new strand
D. Alternating old and new segments

One original and one new strand

Which model suggests that both original DNA strands remain together after replication?
A. Semiconservative
B. Conservative
C. Dispersive
D. Replicative

Conservative

Which model proposes that each strand of both daughter DNA molecules contains a mix of old and new DNA?
A. Semiconservative
B. Conservative
C. Dispersive
D. Fragmented

Dispersive

Which result best supports semiconservative replication in the Meselson-Stahl experiment after one generation in 14N?
A. One heavy band
B. One light band
C. One intermediate band
D. Two distinct bands

One intermediate band

After two rounds of replication in the Meselson-Stahl experiment, which pattern ruled out the dispersive model?
A. All light DNA
B. One light and one intermediate band
C. One heavy band
D. Two intermediate bands only

One light and one intermediate band

After the second round of DNA replication in 14N, what did Meselson and Stahl observe?
A. One heavy and one light band
B. One intermediate band only
C. One light band and one intermediate band
D. Two light bands

One light band and one intermediate band

Which replication model is best supported by the appearance of both light and intermediate DNA after two rounds?
A. Dispersive
B. Conservative
C. Semiconservative
D. Random

Semiconservative

In the second generation of replication, how many DNA molecules are fully light (14N/14N)?
A. 0%
B. 25%
C. 50%
D. 100%

50%

Which outcome would be expected if DNA replicated conservatively after two rounds in 14N?
A. Two light bands
B. One intermediate and one light band
C. One heavy and one light band
D. Only light DNA

One heavy and one light band

Which enzyme synthesizes short RNA primers during DNA replication?
A. DNA polymerase I
B. Ligase
C. Primase
D. Gyrase

Gyrase