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Example Questions
Example Question #1 : Understand Steps Of Replication
Which of the following represents a step necessary to create the lagging strand, but not the leading strand, during DNA replication?
DNA polymerase synthesizes template DNA from the parent strand
Helicase unwinds the parent strand of DNA
DNA ligase joins Okazaki fragments together
DNA is synthesized in the 5’ to 3’ direction
DNA ligase joins Okazaki fragments together
Okazaki fragments are only produced, and subsequently joined together, in the lagging strand to allow for replication in the opposite direction as replication fork movement. The leading strand, however, allows for continual replication.
All other choices reflect aspects of DNA replication for both the leading and lagging strands.
Example Question #2 : Understand Steps Of Replication
Point mutations __________.
All of the answer choices are correct
include nonsense mutations, which change an amino acid to a stop codon, affecting the entire polypeptide structure
include silent mutations, which have no effect on the organism's phenotype
include missense mutations, which only affect the codon in which the mutation occurs
All of the answer choices are correct
Point mutations replace a single nucleotide for a different one. This can change a certain codon to code for a different amino acid (missense), the same amino acid (silent), or lead to a stop codon (nonsense). Nonsense mutations are the most severe type of point mutation, as they will cause early termination of the protein.
Example Question #3 : Understand Steps Of Replication
How many copies of DNA would you have after ten replication cycles if you start with four copies?
This is really just a math equation. We need to double the amount of DNA each time it goes through a replication cycle.
Begin: 4
Cycle 1: 8
Cycle 2: 16
Cycle 3: 32
Cycle 4: 64
Cycle 5: 128
Cycle 6: 256
Cycle 7: 512
Cycle 8: 1024
Cycle 9: 2048
Cycle 10: 4096
After ten cycles, we would have 4096 copies from our original 4.
A shortcut calculation would be .
This is why PCR amplification is so effective.
Example Question #4 : Understand Steps Of Replication
Select the complementary strand of DNA for the following DNA segment.
5'-ACTTGACT-3'
5'-TGAACTGA-3'
5'-TCAGTTCA-3'
5'-AGTCAAGT-3'
5'-AGUCAAGU-3'
5'-AGTCAAGT-3'
The complementary strand will be going in the opposite direction (3'-5'). As a result, you will need to flip the direction in order for it to be complementary to the original strand. When pairing bases, remember that guanine (G) and cytosine (C) are paired with one another, and adenine (A) and thymine (T) are paired.
5'-ACTTGACT-3' Switch the direction.
3'-TCAGTTCA-5' Find the complement pairs.
5'-AGTCAAGT-3'
Example Question #5 : Understand Steps Of Replication
What is the function of the single-strand binding protein during DNA replication?
Prevent the separated strands from reannealing
Ensure both strands are replicated at similar rates
Recruit DNA polymerase
Synthesizing RNA primers
Prevent the separated strands from reannealing
Single-strand binding protein (SSB) binds the newly separated DNA strands to ensure that it does not reanneal during replication. This keeps the strands separate so that replication can occur.
All of the other answers describe the functions of other proteins. Primase synthesizes the RNA primers, which helps to recruit DNA polymerase. The structural basis for the replication of the leading and lagging strands ensures that replication follows the same rate on both strands.
Example Question #6 : Understand Steps Of Replication
Which enzymes are necessary to produce recombinant DNA?
Restriction enzymes and topoisomerase
Restriction enzymes and ligase
DNA polymerase and topoisomerase
DNA polymerase and ligase
Restriction enzymes and DNA polymerase
Restriction enzymes and ligase
Recombinant DNA technology involves combining genes from two sources, such as different species, into a single molecule.
Applying restriction enzymes to DNA will cleave the DNA into fragments, which can be isolated for specific genes. Ligase can then be used to fuse the fragments together into a full recombinant gene.
Topoisomerase is responsible for relieving tension in the winding of the DNA helix. DNA polymerase synthesizes new DNA from individual nucleotides, but would not be useful in fusing two types of DNA together.
Example Question #7 : Understand Steps Of Replication
What is the function of a helicase enzyme during DNA replication?
Add primers to the lagging strand
Scan for mismatches
Unwind the double-stranded DNA
Fix breaks in the sugar-phosphate backbone
Unwind the double-stranded DNA
Helicases are enzymes that separate annealed strands of nucleic acids. This function provides the single-stranded template used in replication.
Primase is responsible for adding DNA primers, DNA polymerase I scans for mismatched nucleotides and mutations, and ligase repairs breaks in the DNA backbone.
Example Question #8 : Understand Steps Of Replication
What is the purpose of polymerase chain reaction (PCR)?
Amplify a template DNA
Amplify a template RNA
Increase the efficiency of translation
Isolate tagged proteins
Amplify a template DNA
Polymerase chain reaction, or PCR, is commonly used in laboratories to increase the amount of a small biological sample. Given a small sample of DNA, the process replicates the sample to make numerous identical copies. These copies can then be studied directly, used to make protein products, or incorporated into genetic modification.
Other laboratory techniques can be used to achieve the results given by the other answer options.
Example Question #9 : Understand Steps Of Replication
What is the purpose topoisomerase during DNA replication?
Bring new nucleotides to the replication fork
Hold the DNA polymerases in place during replication
Identify unwanted isomers of nucleotides
Cut the phosphate backbone ahead of the replication fork to prevent the DNA from getting overwound
Cut the phosphate backbone ahead of the replication fork to prevent the DNA from getting overwound
DNA topoisomerases are the cell's solution to the "winding" problem. The double helical nature of DNA results in tension during the replication process that would interfere with the process. DNA topoisomerases cut the phosphate backbone to relieve this tension, and allow DNA to replicate properly.
Example Question #10 : Understand Steps Of Replication
What would be a direct result of a mutated, nonfunctional gene for primase in a cell?
Inability to replicate DNA
Inability to denature double-stranded DNA
Inability to transcribe DNA
Inability to maintain genetic fidelity
Inability to replicate DNA
Primase is an enzyme that is essential for the process of DNA replication. It synthesizes RNA primers so that DNA polymerase may begin replicating DNA. Mutation to the gene that codes for primase would damage the protein. Without primase, a cell would not be able to go through the process of replication because DNA polymerase would not properly bind the DNA.
RNA polymerase is responsible for transcribing DNA and helicase is responsible for unwinding the DNA double stranded helix.
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