High School Biology : Understanding Replication Processes

Study concepts, example questions & explanations for High School Biology

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Example Questions

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Example Question #8 : Dna Replication

Which of the following RNA molecules is responsible for carrying the code that will be read at the ribosome in order to create a protein? 

Possible Answers:

snRNA

tRNA

rRNA

mRNA

Correct answer:

mRNA

Explanation:

Messenger RNA, or mRNA, is the RNA strand that is transcribed from the gene found on DNA. It is responsible for being read by a ribosome in order to create a protein.

Ribosomal RNA (rRNA) forms a structural component of the ribosomes. Transfer RNA (tRNA) carries amino acid residues and provides an anticodon to add the amino acids to the growing protein at the ribosome. Small nuclear RNA (snRNA) are found in the nucleus and help regulate transcription and maintain telomere length.

Example Question #1 : Understanding Replication Processes

DNA replication is semi-conservative. This means that __________.

Possible Answers:

both double strands have a newly created strand and an original template strand

both double strands have different percentages of nucleotides

parts from each original strand will be used as templates when creating the new double helix, resulting in a patchwork combination of both original and newly-synthesized nucleotides

an entirely new synthesized DNA molecule is created, while the original double helix stays together

Correct answer:

both double strands have a newly created strand and an original template strand

Explanation:

DNA replication involves the separation of the two original DNA strands. Both of these strands are then replicated using DNA polymerase. This results in two DNA double helices, each with a new strand and an original strand.

Consider this example, in which the parent strands are represented by "P" and the daughter strands are represented by "D."

Before replication there are two parent strands: PP

The parent strands are split: P   P

Daughter strands are made for each parent strand: PDDP

The fully-replicated double strands separate: PD   DP

Each final strand has one parent strand (old DNA) and one daughter strand (new DNA).

Example Question #5 : Dna

The process of DNA replication is considered semiconservative. DNA is created by using another DNA strand as a template, and building a new complementary strand onto the pre-existing strand. Each new DNA molecule contains one strand from the parent template, and one newly synthesized strand.

A single DNA molecule (one double-helix) undergoes three rounds of replication. After the final replication is complete, how many of the DNA molecules present do not contain any part of the original template?

Possible Answers:

Six

Two

Eight

Zero

Four

Correct answer:

Six

Explanation:

O=Original strand, N=New strand

Before any replications: OO

After one round of replication, both new double-helices contain one strand from the original double-helix and one newly synthesized strand.

1 replication: ON1, N1O

After the second replication, there are now four double-helix molecules. Two contain original strands in combination with new strands, and two contain only new strands.

2 replications: ON2, N2N1, N1N2, N2O

After the thrid replication event there will be eight total molecules. Of these, six will contain only new strands and two will contain a combination of original and new strands.

3 replications: ON3, N3N2, N2N3, N3N1, N1N3, N3N2, N2N3, N3O

There must always be two double-helices that contain original strands, as there are always only two original strands and they do not disappear.

Example Question #351 : High School Biology

DNA polymerase is the protein that adds new nucleotides to the elongating DNA strand during replication. In order for DNA polymerase to bind the template strand and add new nucleotides, a free 3' hydroxyl group must be exposed to accept the first nucleotide.

Which of the following is created to provide a free 3' hydroxyl group, enabling the initiation of DNA replication?

Possible Answers:

DNA polymerase II

Single-strand binding protein

DNA primer

RNA primer

Replication fork

Correct answer:

RNA primer

Explanation:

RNA primer is the correct answer. A protein called RNA primase reads the existing DNA strand and adds a short sequence of RNA nucleotides. DNA polymerase then builds onto the 3' end of the RNA primer. After replication, the RNA primer is removed and replaced with DNA nucleotides.

Example Question #352 : High School Biology

DNA polymerase only functions in the 3'-to-5' direction. This means that it adds nucleotides to a free 3' hydroxyl group. DNA is replicated on both strands simultaneously. Since DNA is anti-parallel (the strands run in opposite directions), one new strand is being created continuously, while the other is being created in fragments.

What is the correct name of the fragments of the lagging strand?

Possible Answers:

Miyazaki fragments

Danzo-Shimura fragments

Goldfeld fragments

Okazaki fragments

Epstein fragments

Correct answer:

Okazaki fragments

Explanation:

The correct name of the fragments is Okazaki fragments. The lagging strand aligns in the 5'-to-3' direction (away from the replication fork), but must be read in the 3'-to-5' direction (toward the replication fork) by DNA ploymerase. The result is non-continuous synthesis of the strand in small fragments, called Okazaki fragments. DNA ligase fuses these fragments together later in the replication process.

Example Question #2 : Understanding Replication Processes

Which enzyme of DNA replication unzips the DNA molecule?

Possible Answers:

Ligase

Gyrase

Primase

Helicase

Correct answer:

Helicase

Explanation:

The enzyme helicase divides the two strands of the double helix; henceforth, single stranded binding (SSB) proteins stabilize the newly single strands, and prevent reannealing. The enzyme DNA gyrase ensures the double stranded areas beyond the replication bubbles do not supercoil, relieving the newly-added tension. Primase is a type of RNA polymerase that adds an RNA primer to the DNA to begin replication. DNA Polymerase III cannot begin replication without this primer. Ligase joins ends of Okazaki fragments that were produced on the lagging strand.

Example Question #354 : High School Biology

During DNA replication, what purpose does the enzyme primase serve?

Possible Answers:

Add RNA primers to allow for replication

To join Okazaki fragments of the lagging strand

To join Okazaki fragments of the leading strand

Unzip DNA to prepare it for replication

Correct answer:

Add RNA primers to allow for replication

Explanation:

The enzyme primase adds sequences of RNA to the DNA strand to begin replication. Primase is a type of RNA polymerase, and thus, it does not need a free 3' hydroxyl group as a substrate. The nucleotides it lays down act as a substrate for DNA polymerase. Okazaki fragments from the lagging strand are joined by ligase, and helicase is responsible for unzipping the DNA to prepare for replication.

Example Question #355 : High School Biology

DNA replication is considered to be a __________ process.

Possible Answers:

conservative

continuous

semi-conservative

non-conservative

Correct answer:

semi-conservative

Explanation:

During DNA replication, the parent strand is used as a template that the new strand uses to add the correct nucleotides (via complementary base pairing). The entire parent strand (template) is conserved, while the daughter strand is completely synthetic, meaning the nucleotides came from free nucleoside triphosphates (ATP, TTP, GTP, and CTP). Thus, DNA replication is said to be semi-conservative. The Meselson-Stahl experiment illustrated this principle through the use of different isotopes of nitrogen.

Example Question #3 : Understanding Replication Processes

A limitation of DNA polymerase III is that it cannot add new nucleotides without the direct action/product of which enzyme?

Possible Answers:

Gyrase

Ligase

Helicase

Primase

Correct answer:

Primase

Explanation:

Primase, like all RNA polymerases, can lay down nucleotides with their only substrate being the template strand. Even though the nucleotides are RNA, not DNA, they still have the substrate that DNA polymerase needs in order to add nucleotides—a free 3' . Since the difference between deoxyribose and ribose occurs at the 2' position, DNA polymerase can use either RNA or DNA as a substrate. Helicase and gyrase help with formation and maintenance of the replication bubble, however they indirectly help DNA polymerase add new nucleotides.

Example Question #357 : High School Biology

__________ binds the Okazaki fragments to the nucleotides that replace the RNA primers in the lagging strand.

Possible Answers:

Primase

Gyrase

Helicase

DNA ligase

Correct answer:

DNA ligase

Explanation:

DNA ligase catalyzes the formation of bonds between the Okazaki fragments and the DNA that has replaced the RNA primers on the lagging strand.

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