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This quiz aims to provide a basic overview of DNA replication. Although I use the names of prokaryotic (bacterial) enzymes, the following principles of DNA replication are applicable to eukaryotes also (e.g. humans).

A multiple-choice quiz by doublemm. Estimated time: 5 mins.

Author
doublemm

Time
5 mins

Type
Multiple Choice

Quiz #
339,532

Updated
Jul 23 22

# Qns
10

Difficulty
Average

Avg Score
6 / 10

Plays
539

Awards
Top 35% Quiz

One at a Time - Single Page - Timed Game

Question 1 of 10

1. In order to expose DNA bases (which act as a template for DNA replication) the two strands of DNA are first separated by initiator proteins, and helicase continues to separate the strands along the length of the molecule. As separation occurs, single-stranded binding proteins attach. What is the purpose of these single-stranded proteins? Hint

They attract the replication machine

They prevent the strands from reannealing

They attract complimentary base pairs

They provide energy for helicase to work

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Question 2 of 10

2. Single-stranded sections of DNA allow DNA polymerase III to work. What name is given to the point at which the DNA strands diverge, where polymerase activity is found? Hint

The replication plate

The replication spoon

The replication fork

The replication knife

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Question 3 of 10

3. Separated DNA strands have their nucleotide bases exposed, able to hydrogen bond with free nucleotides found in the cell. T nucleotides form two hydrogen bonds with A nucleotides and C nucleotides form three hydrogen bonds with G nucleotides. What type of interaction is a hydrogen bond? Hint

Dipole-dipole attractions

Covalent bonds

Ionic bonds

Van der Waals forces

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Question 4 of 10

4. DNA polymerase III is responsible for joining together the free nucleotides which attach to a template strand of DNA. This enzyme is restricted in that it only works in one direction, a 5' to 3' (5 prime to 3 prime) direction. What do 5' and 3' refer to in this case? Hint

The charge of the ends of a DNA molecule

The position of the carbon atoms in the sugar ring of a DNA nucleotide

The size of the ends of the DNA molecule

The number of hydrogen bonds between bases

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Question 5 of 10

5. Several DNA monomers (known as nucleotides) are joined together by high energy phosphodiester bonds. The energy required for the formation of these bonds is provided by the degradation of a molecule made up of two inorganic phosphate groups. What is the name of this molecule? Hint

Pyrophosphate

Heliophosphate

Hydrophosphate

Nitrophosphate

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Question 6 of 10

6. Another limitation of DNA polymerase III is that it can only work if there is a pre-existing adjacent -OH group on which to add a new nucleotide (DNA monomer). These -OH groups are provided by primers. Which of the following best describes a primer? Hint

A protein

A looped strand of DNA

A short strand of RNA

An tRNA/mRNA hybrid

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Question 7 of 10

7. Since DNA polymerase III can only work in a 5' to 3' direction, only one strand of DNA can be synthesised continuously. This is called the leading strand. The second strand is synthesised discontinuously, forming several short stretches of DNA, known as Okazaki fragments. What name is given to this second strand? Hint

The following strand

The lagging strand

The incomplete strand

The subordinate strand

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Question 8 of 10

8. Primers, which aid the initiation of DNA replication, must be removed and replaced by DNA nucleotides so that the replication process can be completed. Another enzyme, DNA polymerase I, is responsible for removing primers and replacing them with DNA nucleotides. What name is given to the activity by which this enzyme removes primers? Hint

Exonuclease

Amylase

Depolymerase

Reverse transcriptase

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Question 9 of 10

9. The ability of DNA polymerase III to produce a perfectly complementary strand of DNA to the template strand is limited. Even this enzyme's proof-reading mechanisms are not 100% efficient. What all-important natural phenomenon does this lead to? Hint

Gamete formation

Mutation

Convergent evolution

Sterility

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Question 10 of 10

10. In the final stages of DNA replication, once primers have been excised and replaced with DNA nucleotides, there remains a gap (or nick) between the newly synthesised adjacent fragments. Which enzyme completes the DNA replication process by joining these nicks? Hint

Ligase

Hydrolase

Phosphatase

Carboxylase

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Quiz Answer Key and Fun Facts

Answer: They prevent the strands from reannealing

The point at which the DNA initially opens is known as the origin of replication. The initiator proteins exploit these A-T rich sections of DNA as they contain few hydrogen bonds and so require little energy to break.
Helicase moves along the DNA molecule separating the anti-parallel strands, using energy provided by ATP hydrolysis.

2. Single-stranded sections of DNA allow DNA polymerase III to work. What name is given to the point at which the DNA strands diverge, where polymerase activity is found?

Answer: The replication fork

Quite simply, this structure is named for its shape - the molecule "forks" into two separated strands, each capable of acting as a template for free nucleotides. The replication fork constantly moves due to the action of helicase.

Answer: Dipole-dipole attractions

A hydrogen bond is the attraction between a partially positive hydrogen atom of one molecule and the lone pair of an electronegative atom of another molecule. They are relatively strong intermolecular interactions.
A nucleotides always bond with T nucleotides and C nucleotides always bond with G nucleotides. The larger purines (A and G) always bond with the smaller pyrimidines (T and C), maintaining a constant distance between the two DNA strands.

Answer: The position of the carbon atoms in the sugar ring of a DNA nucleotide

Deoxyribonucleotides (the monomers which make up DNA) contain a 5-carbon sugar ring (deoxyribose), with carbon atoms labelled 1' (1 prime) to 5' (5 prime). Phosphodiester bonds (which join the deoxyribonucleotides) form between the phosphate group attached to the 5' carbon and the -OH group attached to the 3' carbon. Each end of a DNA strand will have a carbon (3' or 5') which is not involved in a phosphodiester linkage.

The end which features a 3' carbon which is not involved in a phosphodiester linkage is referred to as the 3' end, and the end with a 5' carbon which is not involved in a phosphodiester linkage is referred to as the 5' end. DNA polymerase III will only carry out its polymerase activity in the 5' to 3' direction.

Answer: Pyrophosphate

Pyrophosphate is derived from deoxyribonucleoside triphosphates, which lose two phosphates (pyrophosphate), leaving behind deoxyribonucleotides (the monomers which make up DNA).
Pyrophosphate releases large amounts of energy via the hydrolysis of their phosphoanhydride bond. This process is a catalysed by pyrophosphatase.

Answer: A short strand of RNA

Primers are synthesised by primase and are hydrogen-bonded to a short section of the template DNA strand. The free -OH group (found on the 3' carbon) provides a starting point for DNA polymerase III activity.
RNA differs from DNA in that it only forms single strands, it contains ribose (instead of deoxyribose) and it contains the nucleotide uracil (instead of thymine (T)).

Answer: The lagging strand

Because the DNA strands are anti-parallel, only one runs in a 5' to 3' direction relative to the movement of the replication fork.
The fragments formed by the discontinuous replication of the lagging strand are named for Reiji Okazaki, who discovered them during his research into DNA replication.

Answer: Exonuclease

Since the leading strand is synthesised continuously, only one primer is required to initiate its synthesis. However, since several strands (Okazaki fragments) are synthesised in the lagging strand, many primers are needed - one for each new strand.
DNA polymerase I has two major functions - a 5' to 3' exonuclease, which removes RNA nucleotides (the primer) and a 5' to 3' polymerase, which replaces the RNA nucleotides with DNA nucleotides.

Answer: Mutation

DNA polymerase III proof-reads a strand of DNA as it synthesises it. A mis-pairing can be detected and subsequently corrected, but the occurrence of base mis-pairings still occurs. By definition, this leads to a mutation - a change in genomic sequence.

Although an aggregation of mutations may lead to convergent evolution or sterility, these are not direct consequences of a base-mispairing.

Answer: Ligase

The reason that DNA polymerase I is unable to join these strands is that there is no pyrophosphate present to provide the energy required to drive the polymerase activity.
Ligase, however, is driven by ATP and so completes this rapid, yet complex process.
The newly synthesised strand of DNA coils with the template strand to form a double helix - a new molecule of DNA.

Source: Author doublemm

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