All High School Biology Resources
Example Questions
Example Question #18 :Dna
Which DNA polymerase is responsible for exchanging RNA primers for DNA nucleotides during discontinuous replication?
DNA polymerase III
DNA polymerase V
DNA polymerase I
DNA polymerase II
DNA polymerase I
DNA polymerase I is the only polymerase that has 5'3' exonuclease activity. This means that it can remove nucleotides in the 5'3' direction. It also has 3'5' exonuclease activity, as does DNA polymerase III; this is like a "backspace" for nucleotides that have just been added and need to be removed. DNA polymerase II's functions are largely unknown, DNA polymerase V plays a complex role in DNA repair, not replication.
Example Question #19 :Dna
The formation of Okazaki fragments in eukaryotic DNA__________.
is required in neither the leading or the lagging strands
is required in the leading strand only
is required in both the leading and the lagging strands
is required in the lagging strand only
is required in the lagging strand only
Replication of DNA is both continuous and discontinuous, each form of replication occurring simultaneously. Continuous DNA synthesis occurs in the 3’5’ direction on the parent strand. This is often referred to as the leading strand with new nucleotides being added to the 3’ end. Discontinuous DNA synthesis occurs in the 5’3对父链的方向。这个链often referred to as the lagging strand. It is completed in short sequences of nucleotides called Okazaki fragments. Replication on the lagging strand begins with the addition of an RNA primer by the enzyme primase. Primase adds the RNA primers ahead of the 5’ end of the lagging. This allows DNA polymerase III to add the Okazaki fragments to fill in the space between primers. This process repeats itself until the entire strand has been replicated. DNA polymerase I then comes to exchange the RNA primer with DNA nucleotides, then DNA ligase reinforces the bonding between the fragments and the DNA nucleotides that replaced the RNA primer. Note that in both leading and lagging strand synthesis, nucleotides are added to the 3' end of the growing chain, thus synthesis always occurs in the 5'3' direction of the growing strand.
Example Question #20 :Dna
The leading strand is replicated__________, and the lagging strand is replicated__________.
discontinuously . . . discontinuously
discontinuously . . . continuously
continuously . . . discontinuously
continuously . . . continuously
continuously . . . discontinuously
Replication of DNA is both continuous and discontinuous, each form of replication occurring simultaneously. Continuous DNA synthesis occurs from the 3’ end to the 5’ end of the parent strand. This is often referred to as the leading strand with new nucleotides being added to the 3’ end. Discontinuous DNA synthesis occurs from the 5’ end to the 3’ end of the parent strand. This strand is often referred to as the lagging strand. It is completed in short sequences of nucleotides called Okazaki fragments. Replication on the lagging strand begins with the addition of an RNA primer by the enzyme primase. Primase adds the RNA primers ahead of the 5’ end of the lagging. This allows DNA polymerase III to add the Okazaki fragments to fill in the space between primers. This process repeats itself until the entire strand has been replicated. DNA polymerase I then comes to exchange the RNA primer with DNA nucleotides, then DNA ligase reinforces the bonding between the fragments and the DNA nucleotides that replaced the RNA primer. Once both the leading and lagging stranded have completed replication, the result is two identical strands of the original DNA molecule.
Example Question #21 :Dna
The enzyme helicase is required to__________.
produce RNA primers on the lagging strand so that DNA Polymerase III may add new nucleotides
unzip the double helix structure of DNA to commence replication
prevent the strands beyond the replication fork from supercoiling
bind Okazaki fragments to one another
unzip the double helix structure of DNA to commence replication
解旋酶酶解压缩的两条线double helix. Once unzipped, single stranded binding (SSB) proteins stabilize the newly single strands. The enzyme DNA gyrase ensure the double stranded areas beyond the replication fork do not supercoil onto one another. After stabilization of the replication fork, an enzyme complex known as DNA polymerase III commences the addition of nucleotides to the new strand. Proteins such as the beta clamp and clamp loader assist in keeping DNA polymerase III in its place on the strand of DNA, The enzyme primase adds sequences of RNA primers to the DNA strand to begin replication. DNA Polymerase III cannot begin replication without this primer. DNA ligase reinforces the bonding between the Okazaki fragments and the DNA nucleotides that replace the RNA primer.
Example Question #22 :Dna
DNA synthesis always occurs in the__________direction, so one new strand is synthesized continuously towards the replication fork, producing the__________strand. The other strand, known as the__________strand, forms away from the replication fork in small fragments.
5' to 3' . . . leading . . . lagging
4' to 3' . . . leading . . . Okazaki fragments
3' to 5' . . . lagging . . . leading
3' to 5' . . . leading . . . lagging
5' to 3' . . . lagging . . . leading
5' to 3' . . . leading . . . lagging
DNA synthesis always occurs in the5' to 3'direction, so one new strand is synthesized continuously towards the replication fork, producing theleadingstrand. The other strand, known as thelaggingstrand, forms away from the replication fork in small fragments.
DNA replication occurs both continuously and discontinuously at the same time. Nucleotides can only be added to a new strand of DNA on the 3' end, so the process has to start with the 5' end. As DNA continues to be split apart, the leading strand (growing in the direction towards the replication fork) can continuously add new nucleotides. However, for the lagging strand, the 5' to 3' direction is away from the replication fork, so new nucleotides are added in small chunks called Okazaki fragments as the DNA strand continues to separate.
Example Question #23 :Dna
The enzyme helicase opens the double helix of DNA at points called__________.
DNA split holes
telomere tears
primer points
replication forks
Okazaki fragments
replication forks
The enzyme helicase opens the double helix of DNA at points calledreplication forks.
The unwinding of the double helix of DNA is caused by an enzyme called helicase, which breaks the hydrogen bonds holding the complementary base pairs together, creating two template strands of DNA ready to begin the next step of replication. The place where this enzyme 'unzips' the DNA is called the replication fork.
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