UNIT 4

Question 1

In his work with pneumonia-causing bacteria and mice, Griffith worked with an S strain of the bacteria, which was lethal to the mice and an R strain, which was not lethal to the mice. Griffith found that:

Answer 1

genetic information from S cells was transferred to R cells, making them pathogenic

Question 2

Which of the following facts did Hershey and Chase make use of in trying to determine whether DNA or protein is the genetic material?

Answer 2

DNA contains phosphorus, whereas protein does not.

Question 3

Which of the following describes the molecule shown below?

Answer 3

A DNA nucleotide with a purine nitrogenous base

Question 4

Which of the following did Rosalind Franklinʹs x-ray diffraction image allow Watson and Crick to conclude about the structure of DNA?

Answer 4

The structure of DNA is helical.

Question 5

Which of the following best describes the differences between sanger sequencing and next-generation sequencing?

Answer 5

Sanger sequencing sequences specific pieces of DNA and next-gen sequences all the DNA in a sample

Question 6

How may hydrogen bonds would hold together the short piece of double-stranded DNA shown below?

5’ – AGCTA – 3’

3’ – TCGAT - 5’

Answer 6

12

Question 7

In DNA replication, the resulting daughter molecules contain one strand of the original parental DNA and one new strand. What is the explanation for this phenomenon?

Answer 7

DNA replication is semiconservative

Question 8

A culture of E. coli has been propagated for many generations in media containing inorganic precursors that
carry a heavy isotope of nitrogen (15N). The cells are then grown for two generations in media containing a
light isotope of nitrogen (14N). The DNA is then purified and subjected to equilibrium density gradient
centrifugation. Which of the following shows where the DNA will be found?

Answer 8

3

Question 9

Which of the following sequences would base pair with the DNA molecule shown below?

5’- ATCGCTACGTAGC - 3’

Answer 9

3’- TAGCGATGCATCG - 5’

Question 10

What is the function of the enzyme topoisomerase in DNA replication?

Answer 10

To relieve the strain in the DNA ahead of the replication fork caused by the untwisting of the double helix

Question 11

What is the role of DNA ligase during DNA replication?

Answer 11

It joins Okazaki fragments together by creating phosphodiester bonds.

Question 12

Which enzyme catalyzes the elongation of a new DNA strand?

Answer 12

DNA polymerase

Question 13

Two replication forks are moving toward each other. Which of the following diagrams accurately shows the locations
of continuous synthesis (long arrows) and discontinuous synthesis (short arrows)?

Answer 13

C

Question 14

What enzyme breaks the hydrogen bonds between the two strands of double stranded DNA, unzipping the helix?

Answer 14

helicase

Question 15

Cytosine makes up 42% of the nucleotides in a sample of double-stranded DNA from an organism. Approximately what percentage of the nucleotides in this sample will be thymine?

Answer 15

8%

Question 16

In the polymerization of DNA, a phosphodiester bond is formed between a phosphate group of the nucleotide being added and which of the following from the last nucleotide in the new DNA strand?

Answer 16

the 3’ OH

Question 17

Which of the following processes occurs during transcription?

Answer 17

RNA is synthesized

Question 18

The genetic code is redundant (degenerate). What is meant by this statement?

Answer 18

More than one codon can specify the addition of the same amino acid.

Question 19

Which of the following molecular structures contain codons?

Answer 19

mRNA

Question 20

Which of the following statements best describes the significance of the promoter?

Answer 20

It is the recognition site for the binding of RNA polymerase.

Question 21

Place the following in order of occurrence: (a) release of primary RNA transcript, (b) unwinding of the DNA, (c) RNA polymerase binds to promoter, (d) export of mRNA to the cytoplasm for translation, (e) Addition of 5’ cap and polyA tail, (f) elongation step of transcription.

Answer 21

c, b, f, a, e, d

Question 22

Which molecule listed is responsible for delivering amino acids to the ribosomes?

Answer 22

tRNA

Question 23

The tRNA shown below would be carrying which amino acid in the cell? The sequence of the anticodon is shown and there is a codon table on the first question of the exam (and on the projector at the front of class).

Answer 23

Asp

Question 24

Which of the following processes is the first event to take place in translation in eukaryotes?

Answer 24

The small subunit of the ribosome binds to the 5’ end of the mRNA.

Question 25

During translation elongation, in which site do new tRNAs enter?

Answer 25

A site

Question 26

What is the function of the release factor during translation in eukaryotes?

Answer 26

It binds to the stop codon in the A site in place of a tRNA.

Question 27

Which of the following statements correctly describes the effect a nonsense mutation would have on a gene?

Answer 27

It introduces a premature stop codon into the mRNA.

Question 28

For the DNA sequence below, the top strand is a template strand for transcription. What would the sequence of the mRNA be? 3’-AGGCTACATGCTAGCATGCATG -5’ 5’-TCCGATGTACGATCGTACGTAC -3’

Answer 28

5’-UCCGAUGUACGAUCGUACGUAC -3’

Question 29

What amino acid sequence will be generated, based on the following mRNA codon sequence? 5′-GACUACAUGUCUUCGUUAUCCUUG-3′

Answer 29

Met-Ser-Ser-Leu-Ser-Leu

Question 30

In an operon, a repressor protein binds to which DNA element?

Answer 30

the operator

Question 31

Which of the following conditions is most likely to cause the lactose operon to be transcribed?

Answer 31

The levels of activated CAP and lactose levels are both high within the cell.

Question 32

Under what conditions does the trp repressor block transcription of the trp operon?

Answer 32

When the repressor binds to co-repressor, tryptophan.

Question 33

Muscle cells differ from nerve cells mainly because they

Answer 33

express different genes

Question 34

Gel electrophoresis enables scientists to determine which of the following about a DNA fragment?

Answer 34

size

Question 35

In eukaryotic cells, translation initiation occurs in the

Answer 35

cytosol

Question 36

What are epigenetic modifications?

Answer 36

the addition of reversible changes to histones and DNA

Question 37

Which of there following is (are ) involved in post-transcriptional control?

Answer 37

all of these choices are correct

Question 38

Which of the following are true about epigenetic modifications?

Answer 38

all the answers are correct

Question 39

What is the best definition for an enhancer?

Answer 39

An enhancer is a regulatory DNA sequence.

Question 40

Which statement is false?

Answer 40

RNA splicing only occurs in prokaryotes