Chapter 15: DNA and Gene Synthesis and Repair
replication fork/bubble
- A Y-shaped point that results when the two strands of a DNA double helix separate so that the DNA molecule can be replicated - Single fork in Prokaryotic cells - 100s of forks in Eukaryotic cells - Replication will proceed in both directions (form a bubble)
Put the following steps of DNA replication in chronological order.1. Single-stranded binding proteins attach to DNA strands.2. Hydrogen bonds between base pairs of antiparallel strands are broken.3. Primase binds to the site of origin.4. DNA polymerase binds to the template strand.5. An RNA primer is created. 1, 2, 3, 4, 5 3, 1, 2, 4, 5 2, 1, 3, 5, 4 3, 2, 1, 5, 4
2, 1, 3, 5, 4
If a sample of DNA is composed of 30 percent thymine, what percentage of guanine should be in the sample? 20 percent 30 percent 70 percent 0 percent
20 percent
In the Hershey-Chase experiment, the material that entered cells upon infection by T2 virus was labeled with which radioactive isotope? See Section 15.1 (Page) . 3H 35S 32P Both 32P and 35S
32P
At a specific area of a chromosome, the following sequence of nucleotides is present where the chain opens to form a replication fork:3' C C T A G G C T G C A A T C C 5'An RNA primer is formed starting at the underlined T (T) of the template. Which of the following represents the primer sequence? 5' A C G U U A G G 3' 5' G C C T A G G 3' 3' G C C T A G G 5' 5' G C C U A G G 3' 5' A C G T T A G G 3'
5' A C G U U A G G 3'
The end of a single strand of DNA with the phosphate group attached to the number 5 carbon of its terminal deoxyribonucleotide is the .
5' end
DNA primary structure
5' end has the phosphate group 3' end has the free OH sugar-phosphate backbone phosphodiester bond between 5' phosphate and 3' OH 1'-nitrogenous base 2' OH-ribose. H'-deoxyribose
Telomerase synthesizes DNA in the __________direction. 3' → 5' 5' → 3'
5' → 3'
Which complementary strand would be synthesized from the following portion of a DNA molecule? 3′ AACCGTAATTCG 5′ 5′ TTGGCATTAAGC 3′ 3′ AACCGTAATTCG 5′ 3′ TTGGCATTAAGC 5′ 3′ AACCGUAAUUCG 5′
5′ TTGGCATTAAGC 3′
The following DNA sequence occurs at the start of a DNA strand. Which of the sequences would be most likely to bind to this sequence to initiate DNA replication in a cell? 3′ AATTGCAGATTCA 5′ 5′ TTAACGTCTAA 3′ 3′ TTAACGTCTAA 5′ 3′ UUAACGUCUAA 5′ 5′ UUAACGUCUAA 3′
5′ UUAACGUCUAA 3′ (need primer which is RNA to start replication)
In an analysis of the nucleotide composition of DNA, which of the following will be found? G + C = T + A A + C = G + T A = C A = G and C = T
A + C = G + T
If DNA polymerase fails to correct an error, which of the following would occur? Cell death Telomere addition A mutation Centrifugation
A mutation
How do cells correct a damaged base in double-stranded DNA? Only the mismatched bases are removed and replaced. All of the DNA on the "mismatched" strand is removed and replaced. A section of the DNA containing the mismatched base is removed and replaced. Escherichia coli cannot repair damaged bases after DNA replication is completed.
A section of the DNA containing the mismatched base is removed and replaced.
Conservative DNA replication would result in which of the following? After one generation, both of the daughter DNA strands would pair in a double helix. No DNA replication would occur. After one generation, a mixture of parental DNA and daughter DNA would be presented in a double helix. After one generation, a daughter strand and a parental strand would pair in a double helix.
After one generation, both of the daughter DNA strands would pair in a double helix.
Which of the following best describes the composition of DNA monomers? All of the monomers contain ribose connected to one of four nitrogenous bases. All of the monomers contain a cytosine base connected to a deoxyribose. All of the monomers contain a phosphate group and a nitrogenous base connected to a deoxyribose. All of the monomers contain a phosphate group connected to a nitrogenous base.
All of the monomers contain a phosphate group and a nitrogenous base connected to a deoxyribose.
For a science fair project, two students decided to repeat the Hershey and Chase experiment, with modifications. They decided to label the nitrogen of the DNA, rather than the phosphate. They reasoned that each nucleotide has only one phosphate and two to five nitrogens. Thus, labeling the nitrogens would provide a stronger signal than labeling the phosphates. Why won't this experiment work? Amino acids (and thus proteins) also have nitrogen atoms; thus, the radioactivity would not distinguish between DNA and proteins. There is no radioactive isotope of nitrogen. Radioactive nitrogen has a half-life of 100,000 years, and the material would be too dangerous for too long. Although there are more nitrogens in a nucleotide, labeled phosphates actually have 16 extra neutrons; therefore, they are more radioactive.
Amino acids (and thus proteins) also have nitrogen atoms; thus, the radioactivity would not distinguish between DNA and proteins.
The Hershey-Chase experiment examined which of the following questions? Are genes made up of protein or of DNA? Is the replication of DNA semiconservative, conservative, or dispersive? What is the structure of DNA? Is there a connection between XP and DNA nucleotide excision repair?
Are genes made up of protein or of DNA?
What would be the consequence(s) for DNA synthesis if primase were defective? See Section 15.3 (Page) . View Available Hint(s) Both leading and lagging strand synthesis would be incomplete. Both leading and lagging strand synthesis would be unaffected. Lagging strand synthesis would be incomplete; leading strand synthesis would be unaffected. Leading strand synthesis would be incomplete; lagging strand synthesis would be unaffected.
Both leading and lagging strand synthesis would be incomplete.
RNA primers must be present on which strand during DNA synthesis? See Section 15.3 (Page) . Both leading and lagging strands Only the lagging strand Neither strand Only the leading strand
Both leading and lagging strands
DNA polymerase forms what kind of bond between a phosphate group and a hydroxyl group? Ionic Hydrogen Covalent Double
Covalent
In trying to determine whether DNA or protein is the genetic material, Hershey and Chase made use of which of the following facts? DNA contains nitrogen, whereas protein does not. DNA contains purines, whereas protein includes pyrimidines. RNA includes ribose, whereas DNA includes deoxyribose sugars. DNA contains sulfur, whereas protein does not. DNA contains phosphorus, whereas protein does not.
DNA contains phosphorus, whereas protein does not.
Suppose you are provided with an actively dividing culture of E. coli bacteria to which radioactive thymine has been added. What would happen if a cell replicates once in the presence of this radioactive base? One of the daughter cells, but not the other, would have radioactive DNA. Neither of the two daughter cells would be radioactive. DNA in both daughter cells would be radioactive. Radioactive thymine would pair with nonradioactive guanine. All four bases of the DNA would be radioactive.
DNA in both daughter cells would be radioactive.
Cancer can occur when DNA is damaged. Which of the following statements about the cause of damage to DNA molecules is true? DNA molecules can be damaged in the absence of environmental toxins or radiation. Only environmental toxins such as cigarette smoke, aflatoxins, and other toxins in food can damage the structure of DNA. Excision repair enzymes are able to prevent all mutations in DNA. Small quantities of ultraviolet radiation have no effect on DNA structure.
DNA molecules can be damaged in the absence of environmental toxins or radiation.
The Hershey-Chase experiment answered the question of whether protein or DNA was the genetic material by learning whether ______. enzymes that destroyed DNA or destroyed protein prevented transformation of bacteria DNA or protein migrated at the same or different rates when centrifuged DNA could be radioactively labeled using 32Pprotein could be radioactively labeled using 35S DNA or protein from a virus entered bacterial cells during infection
DNA or protein from a virus entered bacterial cells during infection
Which DNA polymerase removes RNA primer and replaces it with DNA? DNA polymerase I DNA polymerase II DNA polymerase III All three of these DNA polymerases
DNA polymerase I
Which of the following enzymes will remove an RNA primer? DNA polymerase I DNA ligase DNA helicase Primase
DNA polymerase I
What proteins, are critical in removing RNA primers during the synthesis of the lagging strand? DNA polymerase I and DNA ligase Helicase, single-stranded DNA-binding proteins, and topoisomerase DNA polymerase I, DNA ligase, and Okazaki fragments Primase, DNA polymerase III, and sliding clamps
DNA polymerase I and DNA ligase
During DNA replication, mismatched bases are inserted approximately once in every 100,000 bases. The exonuclease activity of which enzyme repairs these mismatches? DNA polymerase III DNA ligase DNA polymerase I RNA polymerase
DNA polymerase III
If an error is found during proofreading of newly synthesized DNA, which of the following will remove the incorrect base? DNA polymerase III Okazaki fragments DNA ligase A replisome
DNA polymerase III
Which of the following enzymes is correctly matched to its function? Helicase—stabilizes single-stranded DNA Topoisomerase—breaks hydrogen bonds between nucleotides DNA polymerase III—adds nucleotides to the lagging strand DNA polymerase I—forms covalent bonds between Okazaki fragments
DNA polymerase III—adds nucleotides to the lagging strand
Why is the new DNA strand complementary to the 3' to 5' strands assembled in short segments? only short DNA sequences can extend off the RNA primers DNA polymerase can assemble DNA only in the 5' to 3' direction the replication forks block the formation of longer strands it is more efficient than assembling complete new strands DNA polymerase can assemble DNA only in the 3' to 5' direction
DNA polymerase can assemble DNA only in the 5' to 3' direction
Okasaki fragments are the result of _________. DNA polymerase only working in the 3' to 5' direction faulty helicase activity DNA polymerase only working in the 5' to 3' direction DNA ligase
DNA polymerase only working in the 5' to 3' direction
Which of the following statements is true of DNA synthesis? DNA polymerases catalyze the random addition of monomers to the DNA polymer chain. DNA polymerase requires a single-stranded template plus a primer to synthesize DNA. DNA polymerases add nucleotides in the 3′ to 5′ direction to complete the complementary strand. DNA synthesis proceeds in one direction from a point of origin.
DNA polymerase requires a single-stranded template plus a primer to synthesize DNA.
Why are the results of studies of DNA replication in Escherichia coli applicable to the same process in humans? Because E. coli lives in the human gastrointestinal tract, it must replicate its DNA the same way that humans do. The chromosome structure of this organism is identical to that of humans. Most other organisms that could be used to study DNA are pathogenic to humans and, thus, difficult to work with. E. coli is not pathogenic. E. coli is similar to humans because it replicates its entire genome before every cell division.
E. coli is similar to humans because it replicates its entire genome before every cell division.
Which of the following statements is true about DNA replication in bacteria and eukarya? Eukaryotes can have multiple points of origin for DNA synthesis on each individual chromosome. Eukaryotic organisms exhibit unidirectional DNA replication because they have linear chromosomes. DNA replication in bacteria proceeds in one direction. Bacteria have linear chromosomes that are replicated in a bidirectional manner.
Eukaryotes can have multiple points of origin for DNA synthesis on each individual chromosome.
During DNA synthesis, why do eukaryotes have multiple replication bubbles? dNTPs have so much potential energy that several replication bubbles can be formed both before and after the origin of replication. Eukaryotes use DNA polymerase to proofread, and this results in several replication bubbles. Eukaryotes have multiple origins of replication. Okazaki fragments used to extend the lagging strand produce several replication bubbles.
Eukaryotes have multiple origins of replication.
In the Meselson-Stahl experiment, cells were grown for one generation in a growth medium containing a relatively heavy nitrogen isotope and then transferred to a new medium containing a lighter nitrogen isotope. After one round of DNA replication, what was true of the DNA in the cells? Half of the DNA strands contained only the light nitrogen isotope. All DNA strands contained only the light nitrogen isotope. All DNA strands contained only the heavy nitrogen isotope. All DNA strands contained both heavy and light nitrogen isotopes.
Half of the DNA strands contained only the light nitrogen isotope.
In polymerase chain reaction (PCR), heat separates the double-stranded DNA. The high temperature is used in place of which of the following enzymes? DNA polymerase III RNA primase Helicase Telomerase
Helicase
Which of the following represents the correct order of events as they occur in the process of DNA replication? (Note: all steps may not be listed, but steps given must be in the correct order.) Helicase opens helix, DNA polymerase III elongates primer and synthesizes leading and lagging strands, DNA ligase links fragments of DNA Helicase opens helix, DNA polymerase III synthesizes RNA primer of leading strand, DNA polymerase I excises primer and fills gap Primase synthesizes primer, DNA polymerase I excises primer, DNA polymerase III elongates primer and synthesizes leading and lagging strands Primase synthesizes RNA primer, DNA polymerase III synthesizes lagging and leading strands, and helicase opens helix
Helicase opens helix, DNA polymerase III elongates primer and synthesizes leading and lagging strands, DNA ligase links fragments of DNA
Which of the following proteins are important in opening the DNA helix? Primase, DNA polymerase III, and sliding clamps Helicase, single-stand DNA-binding proteins, and topoisomerase Primase, DNA polymerase III, sliding clamps, DNA polymerase I, and DNA ligase Okazaki fragments
Helicase, single-stand DNA-binding proteins, and topoisomerase
Which of the following is the type of bond between the nitrogenous bases in a DNA molecule? Covalent bonds Hydrogen bonds Ionic bonds Phosphodiester bonds
Hydrogen bonds
Which of the following best describes proofreading? During proofreading, proteins remove a section of DNA that contains the mismatched bases. Proofreading targets DNA damaged by radiation. Okazaki fragments are key in the success of proof-reading. In proofreading, DNA polymerase corrects the mismatched bases.
In proofreading, DNA polymerase corrects the mismatched bases.
Why are individuals who suffer from xeroderma pigmentosum (XP) incredibly sensitive to DNA damage from ultraviolet (UV) light? The skin of individuals of XP is incredibly fair. Individuals with XP have a mutation in DNA polymerase III. Individuals with XP lack one or more enzymes involved in excising damaged DNA bases from the chromosomes. Patients with XP have a mutation in DNA polymerase I.
Individuals with XP lack one or more enzymes involved in excising damaged DNA bases from the chromosomes.
What is the role of DNA ligase in the elongation of the lagging strand during DNA replication? It unwinds the parental double helix. It joins Okazaki fragments together. It catalyzes the lengthening of telomeres. It synthesizes RNA nucleotides to make a primer. It stabilizes the unwound parental DNA.
It joins Okazaki fragments together.
A researcher did an assay on a solution and found the following enzymes: primase, DNA polymerase III, and sliding clamps. What part of DNA replication is this solution of enzymes capable of doing? Opening the DNA helix Lagging strand synthesis Leading strand synthesis Telomere synthesis
Leading strand synthesis
DNA synthesis is best characterized by which of the following statements? It is initiated only once at the replication fork during the synthesis of both strands. New nucleotides are added in the 5′ to 3′ direction on both the lagging and leading strands. It is initiated by an RNA primer at the 5′ end of the existing strand. It is continuous in the 5′ to 3′ direction on the lagging strand and discontinuous on the leading strand.
New nucleotides are added in the 5′ to 3′ direction on both the lagging and leading strands.
Primase is an example of an RNA polymerase. How is primase different than DNA polymerase? Primase does not require helicase. Primase does not require a primer. Primase does not require a DNA template. Primase adds nucleotides to a growing DNA strand in the 3′ to 5′ direction.
Primase does not require a primer.
What is the role of primase in the replication of DNA? Primase synthesizes the RNA primer. Primase opens the double helix. Primase stabilizes single-stranded DNA. Primase relieves twisting forces.
Primase synthesizes the RNA primer.
What is a major difference between eukaryotic DNA replication and prokaryotic DNA replication? DNA replication in prokaryotic cells is conservative. DNA replication in eukaryotic cells is semiconservative. DNA polymerases of prokaryotes can add nucleotides to both 3' and 5' ends of DNA strands; those of eukaryotes function only in the 5' → 3' direction. Prokaryotic chromosomes have a single origin of replication, whereas eukaryotic chromosomes have multiple origins of replication. Prokaryotic replication does not require a primer.
Prokaryotic chromosomes have a single origin of replication, whereas eukaryotic chromosomes have multiple origins of replication.
Which of the following statements about proofreading is correct? Proofreading requires DNA ligase to correct mistakes made during replication. Proofreading fixes 100 percent of the mistakes made during replication. Proofreading requires 3′ to 5′ exonuclease activity. Proofreading occurs after DNA replication is completed.
Proofreading requires 3′ to 5′ exonuclease activity.
Telomerase binds to the overhang at the end of a chromosome. Once bound, and using its _____template as a guide, it begins catalyzing the ____ of deoxyribonucleotides to the overhang in the ____ direction, lengthening the overhang. This creates a single strand of DNA that is then used as a template on which primase, ___ polymerase, and ligase add deoxyribonucleotides to the lagging strand in the ____ direction, restoring the lagging
RNA addition 5'-3' DNA 5'-3'
The synthesis of a new strand begins with the synthesis of a(n) _____. RNA primer complementary to a preexisting DNA strand poly(A) tail single-strand binding protein Okazaki fragment short pieces of DNA
RNA primer complementary to a preexisting DNA strand
Which of the following prevents unwound DNA from zipping up into a double-stranded DNA molecule? Single-strand DNA-binding proteins DNA helicase The primer RNA polymerase
Single-strand DNA-binding proteins
Which of the following cell types is likely to demonstrate the lowest level of telomerase activity? Somatic cells Germ cells Cancer cells Somatic cells, germ cells, and cancer cells are likely to demonstrate identical levels of telomerase activity.
Somatic cells
DNA ligase functions in which of the following? Synthesis of the lagging strand in the 3′ to 5′ direction Elongation of the leading strand in the 5′ to 3′ direction Mismatch repair Nucleotide excision repair
Synthesis of the lagging strand in the 3′ to 5′ direction
A bacterium is infected with an experimentally constructed bacteriophage composed of the T2 phage protein coat and T4 phage DNA. The new phages produced would have _____. T4 protein and T4 DNA. T2 protein and T4 DNA. T4 protein and T2 DNA. T2 protein and T2 DNA.
T4 protein and T4 DNA.
Which enzyme catalyzes the synthesis of DNA from its own RNA template? Primase Ligase Telomerase DNA polymerase
Telomerase
Telomere shortening puts a limit on the number of times a cell can divide. Research has shown that telomerase can extend the life span of cultured human cells. How might adding telomerase affect cellular aging? Telomerase will speed up the rate of cell proliferation. Telomerase would have no effect on cellular aging. Telomerase shortens telomeres, which delays cellular aging. Telomerase eliminates telomere shortening and retards aging.
Telomerase eliminates telomere shortening and retards aging.
When the chromosome of a eukaryote is examined, one will find that a unique DNA structure is present at the free end. What is this structure called? Origin of replication Replication fork Telomere Sliding clamp
Telomere
How does DNA polymerase add dNTP monomers to the growing chain? The 3′ carbon of the DNA chain forms a covalent linkage with the phosphate group on the 5′ end of the dNTP. The base component of the dNTP hydrogen binds to the next base in the opposite chain. The 5′ carbon of the dNTP binds to the 3′ carbon of the chain. The triphosphate group of the dNTP binds to the base of the DNA chain.
The 3′ carbon of the DNA chain forms a covalent linkage with the phosphate group on the 5′ end of the dNTP.
If a cell could not produce DNA ligase, which of the following would occur? RNA primers would not be synthesized. The gaps between two Okazaki fragments would not be closed. The hydrogen bonds between nucleotides of two DNA strands would not be broken. The DNA polymerase would not stay on the DNA strand.
The gaps between two Okazaki fragments would not be closed.
Which of the following is a true statement about the replication of the leading strand during DNA synthesis? The production of the leading strand requires DNA ligase. The leading strand is made in the 3′ to 5′ direction. The leading strand is produced in the same direction that the replication fork is traveling. The leading strand contains Okazaki fragments.
The leading strand is produced in the same direction that the replication fork is traveling.
What is the difference between the leading strand and the lagging strand in DNA replication? The leading strand requires an RNA primer, whereas the lagging strand does not. The leading strand is synthesized continuously in the 5→3 direction, while the lagging strand is synthesized discontinuously in the 53 direction. The leading strand is synthesized in the 3→5 direction in a discontinuous fashion, while the lagging strand is synthesized in the 53 direction in a continuous fashion. There are different DNA polymerases involved in elongation of the leading strand and the lagging strand.
The leading strand is synthesized continuously in the 5→3 direction, while the lagging strand is synthesized discontinuously in the 53 direction.
Which statement is correct concerning DNA synthesis catalyzed by DNA polymerases? See Section 15.3 (Page) . The new DNA strand is synthesized in the 3'—>5' direction; the template strand is read in the 5'—>3' direction. The new DNA strand is synthesized in the 3—>5' direction; the template strand is read in the 3'—>5' direction. The new DNA strand is synthesized in the 5'—>3' direction; the template strand is read in the 3'—>5' direction. The new DNA strand is synthesized in the 5'—>3' direction; the template strand is read in the 5'—>3' direction.
The new DNA strand is synthesized in the 5'—>3' direction; the template strand is read in the 3'—>5' direction.
Why is a primer required for DNA replication to occur? The primer provides a starting point for DNA polymerase. The primer holds the DNA polymerase in place. The primer catalyzes the separation of the double-helix structure of DNA. The primer serves to join Okasaki fragments.
The primer provides a starting point for DNA polymerase.
Researchers found E. coli that had mutation rates 100 times higher than normal. Which of the following is the most likely cause of these results? The single-stranded binding proteins were malfunctioning. The DNA polymerase was unable to add bases to the 3' end of the growing nucleic acid chain. There were one or more mismatches in the RNA primer. The proofreading mechanism of DNA polymerase was not working properly.
The proofreading mechanism of DNA polymerase was not working properly.
The two strands of DNA are antiparallel. What does this result in for the double-stranded DNA molecule? Hydrogen bonds hold the base pairs together. The strands run in opposite directions. Phosphodiester bonds link the deoxyribonucleotide monomers. Only four bases (adenine, thymine, guanine, and cytosine) are present in DNA molecules.
The strands run in opposite directions.
DNA mutations that alter the sequence can be corrected by excision repair. Which of the following statements is true of this system? The system detects mutations because they produce an irregularity in the DNA molecule. In eukaryotes, a nucleotide excision repair does not occur. The original nucleotides causing the mutation are directly altered and left in the DNA molecule. The system functions only during DNA replication.
The system detects mutations because they produce an irregularity in the DNA molecule.
In humans, XP is a disorder of the nucleotide excision repair mechanism. These individuals are unable to repair DNA damage caused by ultraviolet light. Which of the following are the most prominent types of DNA lesions in individuals suffering from XP? Methylation of purines Mismatch errors Telomere shortening Thymine dimers
Thymine dimers
Which of the following is not part of the replisome? Primase Sliding clamp Topoisomerase Single-stranded DNA binding proteins
Topoisomerase
Which of the following prevents the DNA double helix from supercoiling? Topoisomerase Helicase Primase Sliding clamp
Topoisomerase
What is the function of topoisomerase? Topoisomerase ensures that the double-stranded DNA ahead of the replication fork does not become too tightly twisted. Topoisomerase keeps the separated stands from returning to the double-helical structure. Topoisomerase catalyzes the polymerization of ribonucleotides into RNA. Topoisomerase catalyzes the formation of phosphodiester bonds.
Topoisomerase ensures that the double-stranded DNA ahead of the replication fork does not become too tightly twisted.
repair of damage caused by sunlight
UV sunlight causes damage causes formation of thymine dimer causes formation of covalent bonds between adjacent thymine bases (kink in the DNA) DNA polymerase III cannot read this (skips these regions) large regions of un-replicated DNA
Which of these steps happens first when telomerase prevents linear chromosomes from shortening during replication? Using its RNA template as a guide, it catalyzes the addition of deoxyribonucleotides to the overhang. Telomerase shifts down the newly synthesized DNA and catalyzes the addition of a copy of a short DNA sequence to the end of a single strand. The double-stranded addition counteracts the shortening of the lagging strand. The standard complement of DNA synthesizing enzymes uses a template to produce a complementary strand.
Using its RNA template as a guide, it catalyzes the addition of deoxyribonucleotides to the overhang.
Which of the following would you expect of a eukaryote lacking telomerase? a reduction in chromosome length in gametes high sensitivity to sunlight a high probability of somatic cells becoming cancerous an inability to repair thymine dimers an inability to produce Okazaki fragments
a reduction in chromosome length in gametes
DNA secondary structure
antiparallel (5'-3' and 3'-5') arrow is the 3' end with the free OH between the bases are hydrogen bonds A-T= 2 H-bonds C-G=3 H-bonds double helix=more stable
bacterial chromosomes have a single point of origin
bacteria chromosome is a circle one origin of replication (much less DNA) DNA replication occurs in both directions
DNA synthesis reaction
dNTP's have three phosphate groups repelling one another because they are all negative a lot of potential energy last two phosphate groups are cleaved off and the energy produced is used to add the NTPs to the 3' end (hydrolysis reaction?)
DNA polymerase moves along the lagging strand . discontinuously in the 3′ to 5′ direction continuously in the 5′ to 3′ direction in the opposite direction as the leading strand only in the presence of ligase
discontinuously in the 3′ to 5′ direction
After DNA replication is completed, _____. one DNA double helix consists of two old strands and one DNA double helix consists of two new strands each new DNA double helix consists of one old DNA strand and one new DNA strand each of the four DNA strands consists of some old strand parts and some new strand parts each new DNA double helix consists of two new strands there are four double helices
each new DNA double helix consists of one old DNA strand and one new DNA strand
telomere
end of the chromosome on the leading strand, DNA polymerase just falls off (keeps adding nucleotides until it falls off) on the lagging strand no DNA polymerase is able to add the complementary base pairs to the small un-replicated region near the replication fork why? newly made strand only has a free 5' end no polymerase can add to the 5' end only the 3' end no room for the primer to be extended to create an okazaki fragment if kept like this, that's not good because single stranded DNA is prone to degradation problem- if the cell keeps dividing it will loose genetic information
For the viral labeling experiment, which additional piece of evidence would prove that the viral capsids were shaken off the bacterial cells by the agitation step? examination of the solution by electron microscopy to show that no capsids are present examination of the pellet by electron microscopy to show that no capsids are present testing of the solution for 32P radioactivity to show that none is present examination of the pellet by electron microscopy to show that capsids are present
examination of the pellet by electron microscopy to show that no capsids are present
The first step in the replication of DNA is catalyzed by _____. DNA polymerase ligase helicase primase single-strand binding protein
helicase
steps of replication
helicase- unwinds the double stranded DNA single stranded binding proteins-bind to the single unwound strand to prevent them from coming back together topoisomerase-binds to the double stranded DNA ahead of the replication fork. relieves the twisting forces caused by DNA polymerase. breaks phosphodiester bonds and then reseals them. need to do this bc if the DNA breaks ahead of the replication fork, this could be disasterous. primase-lays down a 3 base RNA primer for DNA polymerase to extend (provides the free 3' OH end) DNA polymerase III- extends the 3' end of the primase. adds dNTps. DNA polymerase I-removes the primer and replaces it with DNA ligase- seals okazaki fragments together (okazaki fragments occurs in the lagging strand of DNA synthesis)
As DNA replication continues and the replication bubble expands, the parental double helix is unwound and separated into its two component strands. This unwinding and separating of the DNA requires three different types of proteins: helicase, topoisomerase, and single-strand binding proteins.
helicase-binds at the replication fork. breaks the H bonds between the double strands topoisomerase-binds ahead of the replication fork. breaks covalent bonds in the DNA backbone ssbp-bind after replication fork. prevent H bonds from forming
lagging vs leading strand synthesis
leading strand-goes into the replication fork lagging-goes away from the replication fork leading strand-continuous lagging strand-discontinuous both synthesized 5' to 3' though by the end, both have a continuous strand
As the two parental (template) DNA strands separate at a replication fork, each of the strands is separately copied by a DNA polymerase III (orange), producing two new daughter strands (light blue), each complementary to its respective parental strand. Because the two parental strands are antiparallel, the two new strands (the leading and lagging strands) cannot be synthesized in the same way.
leading strand-only one primer needed. daughter DNA strand elongated into the replication fork. made continuously lagging strand-made in segments. multiple primers needed. daughter DNA strand elongated away from replication fork both-synthesized 5' to 3'
Short segments of newly synthesized DNA are joined into a continuous strand by _____. ligase DNA polymerase helicase primase single-strand binding protein
ligase
The lagging strand is . synthesized continuously synthesized by DNA polymerase III only made up of only DNA during replication made up of short DNA/RNA fragments during replication
made up of short DNA/RNA fragments during replication
DNA repair of mistakes caused during replication
mismatched pairs. DNA polymerase III can repair mismatches. can tell difference between template DNA and new DNA and can look for mismatches DNA polymerase III makes mistakes but repair narrows it down to about one error in about one billion nucleotides DNA polymerase can repair using exonuclease activity (does this as it goes along, can only remove the very last nucleotide so it has to catch it right away)
limitations to DNA polymerase
needs a template for replication needs an existing strand to extend can only extend the 3' end (NEEDS A FREE OH, NO OH NO EXTENSION)
telomerase, aging and cancer
normal aging cells have shortened chromosomes and limited cell division potential babies have longer chromosomes than older people cancerous cells that divide longer than they should have inappropriately active telomerase
1. ______are the short sections of DNA that are synthesized on the lagging strand of the replicating DNA. 2. During DNA replication, an open section of DNA, in which a DNA polymerase can replicate DNA, is called a _______ . 3. The enzyme that can replicate DNA is called_______ . 4. The new DNA strand that grows continuously in the 5' to 3' direction is called the ______ . 5. After replication is complete, the new DNAs, called _____, are identical to each other.
okazaki fragments replication fork DNA polymerase III leading strand daughter DNA
Shorter telomeres are associated with ___________. younger ages in humans higher t elomerase activity older ages in humans higher topoisomerase activity
older ages in humans
DNA replication is highly accurate. It results in about one mistake per billion nucleotides. For the human genome, how often would errors occur? on average, once or twice in the lifetime of an individual on average, six times each time the entire genome of a cell is replicated on average, once in a lifetime in 10 percent of the population on average, once every six cell divisions
on average, six times each time the entire genome of a cell is replicated
DNA replication is semiconservative and bi-directional
one old strand and one new strand occurs in both directions from the origin of replication
Due to the antiparallel nature of the DNA double helix, _________. View Available Hint(s) one strand is replicated and not the other one strand at a replication fork is synthesized in the direction of the fork, while the other is synthesized in the opposite direction away from the fork one strand at a replication fork is synthesized in the 5' to 3' direction of the fork, while the other is synthesized in the 3' to 5' direction both leading and lagging strands are synthesized in the direction of the replication fork
one strand at a replication fork is synthesized in the direction of the fork, while the other is synthesized in the opposite direction away from the fork
Semiconservative replication involves a template. What is the template? an RNA molecule single-stranded binding proteins one strand of the DNA molecule DNA polymerase contains the template needed.
one strand of the DNA molecule
are all cells replicating their DNA at once?
only in cells that are going to divide happens during S phase of interphase
telomerase
prevents the shortening of telomeres. reverse transcriptase in which an RNA template is used to create a DNA complementary strand binds to the 3' end of the ORIGINAL template strand it has its own RNA template binds to the 3' end and overhangs a little bit adds nucleotides that do not code for anything (tandem repeats) gets to a point where it is long enough that lagging strand synthesis will ensue ONLY ACTIVE IN CELLS THAT WILL PRODUCE GAMETES
The enzyme that synthesizes RNA primers for use in DNA replication is _______________. View Available Hint(s) primase ligase replicase DNA polymerase topoisomerase
primase
why did they think genetic material was protein and not DNA?
protein is more versatile. DNA is simple (only four base pairs) now they know that genetic information is contained in DNA not in proteins bc the DNA is what wound up inside the E. coli not the protein
exon repair
replaces thymine dimers with proper sequence (nucleotide excision repair) enzyme recognize damaged strand enzyme the cut out the damaged bases as well as some surrounding bases since DNA is complementary, DNA polymerase III can read the template and fill in the missing section ligase repairs the phosphodiester bonds, sealing repaired DNA failure to repair damaged DNA has consequences Xeroderma pigmentosum (lack excision repair and can have cancer)
The action of helicase creates _____. DNA fragments and replication forks primers and replication bubblesDNA fragments and replication bubbles replication forks and replication bubbles primers and DNA fragments
replication forks and replication bubbles
eukaryotic chromosomes have many points of origin
replication proceeds in both directions linear DNA
DNA replication (2 characteristics)
semi conservative (one original and one new) bi directional (proceeds in both directions)
In the Hershey-Chase experiment, bacterial cultures infected with a virus were agitated in a kitchen blender to . force the bacterial cells into a pellet ensure that the viral proteins were labeled with 35S ensure that the viral DNA was labeled with 32P after infection of the bacteria separate viral protein coats from the bacterial cells in the culture
separate viral protein coats from the bacterial cells in the culture
The primers used for DNA synthesis are _____. short DNA sequences short amino acid sequences (peptides) short RNA sequences proteins that bind to single-stranded DNA
short RNA sequences
Which of the following help(s) to hold the DNA strands apart while they are being replicated? DNA polymerase primase nuclease single-strand DNA binding proteins ligase
single-strand DNA binding proteins
The structure of a double-stranded DNA helix molecule can best be described as a . sugar-phosphate backbone with the complementary base pairs adenine-guanine and thymine-cytosine joined by hydrogen bonding sugar-phosphate backbone with adenine, thymine, guanine, or cytosine bases projecting toward the outside of the backbone sugar-phosphate backbone that is made up of adenine, thymine, guanine, or cytosine bases hydrogen-bonded to each other through phosphodiester bonds sugar-phosphate backbone with the bases of the complementary base pairs adenine-thymine and guanine-cytosine projecting toward the inside of the backbone
sugar-phosphate backbone with the bases of the complementary base pairs adenine-thymine and guanine-cytosine projecting toward the inside of the backbone
An old DNA strand is used as a _____ for the assembly of a new DNA strand. complement source of nucleotides template model primer
template
In the polymerization of DNA, a phosphodiester bond is formed between a phosphate group of the nucleotide being added and _____ of the last nucleotide in the polymer. a nitrogen from the nitrogen-containing base the 5' phosphate C6 the 3' OH
the 3' OH
The phosphate group is bonded to carbon of the deoxyribose sugar. the 3′ either the 5′ or the 3′ the 5′ the 5′ when the nitrogenous base is a purine and the 3′ when the nitrogenous base is a pyrimidine
the 5′
The leading and the lagging strands differ in that _____. the leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction the leading strand is synthesized at twice the rate of the lagging strand the leading strand is synthesized by adding nucleotides to the 3' end of the growing strand, and the lagging strand is synthesized by adding nucleotides to the 5' end the lagging strand is synthesized continuously, whereas the leading strand is synthesized in short fragments that are ultimately stitched together
the leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction the leading strand is synthesized at twice the rate of the lagging strand
purpose of DNA replication?
to double genetic information in preparation for cell division
genes are made up of DNA- viral labeling experiment
viral DNA is radioactive (phosphorus is radioactive-protein doesn't have phosphorus) viral protein is radioactive (sulfur is radioactive-DNA doesn't have sulfur) inject the E. coli with the virus with the radioactive DNA inject the E. coli with the virus with the radioactive protein agitate the cultures (so detach the viral capsids from the E. coli) centrifuge them DNA radioactive material winds up in the pellet (bottom) protein radioactive material winds up in solution DNA radioactive material wind up in the cell, while the protein radioactive material does not E coli with the radioactively labeled DNA become radioactive E coli with the radioactively labeled protein does not become radioactive at the time of this experiment, known that chromosomes contain genetic information but did not know whether it was DNA or protein
Viruses vs Bacteria
viruses-debetable life form. mode of replication-uses host to inject bacteria into cells bacteria-life form. mode of replication-binary division
