Check/Test Your Knowledge Biology
replication - ANSWER: DNA synthesis begins at origins of _____________ and
proceeds in both directions.
replication fork - ANSWER: Synthesis at the _____________ ______ occurs in three
steps:
1. Helices *opens* the double helix, SSBPs *stabilize* the exposed single strands, and
topoisomerase *removes* twists downstream of the fork.
2. DNA polymerase *synthesizes the leading strand* after primase has *added* an RNA
primer.
3. The *lagging strand is synthesized* in Okazaki fragments that eventually are *joined*
together.
primase, ligase - ANSWER: In bacteria, the enzyme _____________, DNA polymerase
III, DNA polymerase I, and __________ work in sequence to synthesize *Okazaki*
fragments and link them into a *continuous strand*.
DNA polymerase adds nucleotides only to the free 3' -OH on a strand. Primase
synthesizes a short RNA sequence -- a primer -- that provides the free 3' end necessary
for DNA polymerase to start working. - ANSWER: Explain the function of primase
The need to begin DNA synthesis many times on the lagging strand requires many new
primers. Since bacterial DNA polymerase I is used to remove primers, it is required
predominantly on the primer-rich lagging strand. - ANSWER: Explain why DNA
polymerase I is used predominately on the lagging strand in bacteria.
somatic - ANSWER: Linear chromosomes *shorten* during standard DNA replication
because ____________ cells are unable to use the final RNA primer to replicate the
end of the lagging strand.
telomerase - ANSWER: Shortening is prevented in certain cells -- particularly those that
produce sperm and egg -- because _______________ adds short, repeated DNA
sequences to extend the template for the lagging strand. Standard enzymes of DNA
synthesis then use this template to complete the replication process.
Telomerase is needed only to replicate the ends of a linear DNA. Because bacterial
DNAs are circular, they lack ends and don't require telomerase. - ANSWER: Explain
why bacterial cells do not need telomerase.
Since telomerase works by extending one strand of DNA without any external template
and because DNA synthesis requires a template, telomerase must contain an internal
, template to allow it to extend a DNA chain. - ANSWER: Explain why telomerase has to
have a built-in template.
DNA synthesis - ANSWER: DNA polymerases occasionally add the wrong base during
_____ _____________.
proofreading - ANSWER: ___________________ by DNA polymerase and mismatch
repair of disincorporated bases sharply reduces the number of errors.
nucleotide excision repair - ANSWER: DNA is damaged frequently, and most of this
damage can be fixed by DNA repair systems such as ______________ __________
_________.
The mutation rate would rise because differences in base-pair stability and shape make
it possible for DNA polymerase to distinguish correct from incorrect base pairs during
DNA replication. - ANSWER: Explain how the mutation rate would be affected if all base
pairs had the same shape and degree of stability.
The enzymes that remove the dimer and surrounding DNA are specific to nucleotide
excision repair. DNA polymerase and DNA ligase work in both nucleotide excision
repair and normal DNA synthesis. - ANSWER: State which enzymes are specific for
nucleotide excision repair and which work in both normal DNA replication and in DNA
repair.
Labeling either DNA or proteins. - ANSWER: Researchers design experiments so that
only one thing is different between the treatments that are being compared. In the
Hershey-Chase experiment, what was this single difference?
The ability to synthesize DNA in the 3' --> 5' direction. Synthesis in the 3' --> 5' direction
would allow the DNA polymerase on what is normally the lagging strand to follow the
replication fork. - ANSWER: If you could engineer an activity into DNA polymerase to
allow both strands to follow the replication fork, what would this additional activity be?
Telomerase binds to the overhang at the end of a chromosome. Once bound, and using
its RNA template as a guide, it begins catalyzing the addition of deoxyribonucleotides to
the overhang in the 5' --> 3' direction, lengthening the overhang. This creates a single
strand of DNA that is then used as a template on which primase, DNA polymerase, and
ligase add deoxyribonucleotides to the lagging strand in the 5' -- 3' direction, restoring
the lagging strand to its original length. - ANSWER: How does telomerase prevent linear
chromosomes from shortening during replication?
The regularity of DNA's structure allows irregularities such as damaged bases to stand
out and be recognized by DNA repair proteins. - ANSWER: What aspect of DNA
structure makes it possible for the proteins of nucleotide excision repair to recognize
many different types of DNA damage?
replication - ANSWER: DNA synthesis begins at origins of _____________ and
proceeds in both directions.
replication fork - ANSWER: Synthesis at the _____________ ______ occurs in three
steps:
1. Helices *opens* the double helix, SSBPs *stabilize* the exposed single strands, and
topoisomerase *removes* twists downstream of the fork.
2. DNA polymerase *synthesizes the leading strand* after primase has *added* an RNA
primer.
3. The *lagging strand is synthesized* in Okazaki fragments that eventually are *joined*
together.
primase, ligase - ANSWER: In bacteria, the enzyme _____________, DNA polymerase
III, DNA polymerase I, and __________ work in sequence to synthesize *Okazaki*
fragments and link them into a *continuous strand*.
DNA polymerase adds nucleotides only to the free 3' -OH on a strand. Primase
synthesizes a short RNA sequence -- a primer -- that provides the free 3' end necessary
for DNA polymerase to start working. - ANSWER: Explain the function of primase
The need to begin DNA synthesis many times on the lagging strand requires many new
primers. Since bacterial DNA polymerase I is used to remove primers, it is required
predominantly on the primer-rich lagging strand. - ANSWER: Explain why DNA
polymerase I is used predominately on the lagging strand in bacteria.
somatic - ANSWER: Linear chromosomes *shorten* during standard DNA replication
because ____________ cells are unable to use the final RNA primer to replicate the
end of the lagging strand.
telomerase - ANSWER: Shortening is prevented in certain cells -- particularly those that
produce sperm and egg -- because _______________ adds short, repeated DNA
sequences to extend the template for the lagging strand. Standard enzymes of DNA
synthesis then use this template to complete the replication process.
Telomerase is needed only to replicate the ends of a linear DNA. Because bacterial
DNAs are circular, they lack ends and don't require telomerase. - ANSWER: Explain
why bacterial cells do not need telomerase.
Since telomerase works by extending one strand of DNA without any external template
and because DNA synthesis requires a template, telomerase must contain an internal
, template to allow it to extend a DNA chain. - ANSWER: Explain why telomerase has to
have a built-in template.
DNA synthesis - ANSWER: DNA polymerases occasionally add the wrong base during
_____ _____________.
proofreading - ANSWER: ___________________ by DNA polymerase and mismatch
repair of disincorporated bases sharply reduces the number of errors.
nucleotide excision repair - ANSWER: DNA is damaged frequently, and most of this
damage can be fixed by DNA repair systems such as ______________ __________
_________.
The mutation rate would rise because differences in base-pair stability and shape make
it possible for DNA polymerase to distinguish correct from incorrect base pairs during
DNA replication. - ANSWER: Explain how the mutation rate would be affected if all base
pairs had the same shape and degree of stability.
The enzymes that remove the dimer and surrounding DNA are specific to nucleotide
excision repair. DNA polymerase and DNA ligase work in both nucleotide excision
repair and normal DNA synthesis. - ANSWER: State which enzymes are specific for
nucleotide excision repair and which work in both normal DNA replication and in DNA
repair.
Labeling either DNA or proteins. - ANSWER: Researchers design experiments so that
only one thing is different between the treatments that are being compared. In the
Hershey-Chase experiment, what was this single difference?
The ability to synthesize DNA in the 3' --> 5' direction. Synthesis in the 3' --> 5' direction
would allow the DNA polymerase on what is normally the lagging strand to follow the
replication fork. - ANSWER: If you could engineer an activity into DNA polymerase to
allow both strands to follow the replication fork, what would this additional activity be?
Telomerase binds to the overhang at the end of a chromosome. Once bound, and using
its RNA template as a guide, it begins catalyzing the addition of deoxyribonucleotides to
the overhang in the 5' --> 3' direction, lengthening the overhang. This creates a single
strand of DNA that is then used as a template on which primase, DNA polymerase, and
ligase add deoxyribonucleotides to the lagging strand in the 5' -- 3' direction, restoring
the lagging strand to its original length. - ANSWER: How does telomerase prevent linear
chromosomes from shortening during replication?
The regularity of DNA's structure allows irregularities such as damaged bases to stand
out and be recognized by DNA repair proteins. - ANSWER: What aspect of DNA
structure makes it possible for the proteins of nucleotide excision repair to recognize
many different types of DNA damage?
