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BMCB 658 Lecture Notes - Lecture 26: Helicase, Primase, Single-Stranded Binding Protein

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School
UNH
Department
Biochemistry, Molecular & Cellular Biology
Course
BMCB 658
Professor
Carrie A.May

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Document Summary

Dna synthesis is initiated at specific sites called origins. Synthesis is always 5" 3" polymerases. Enzymes responsible for the template-dependent synthesis are called. Separation of two original stands and synthesis of two new daughter stands using the original strands as templates. Semi-conservative replication: each daughter strand contains one template strand and one newly synthesized strand. E. coli bacteria were grown for a prolonged time in a medium with 14nh4cl as the sole source of nitrogen; as a result, cells contained only 15n-dna. Cells were then grown in a medium containing only 14nh4cl. After one generation of growth in the 14nh4cl medium, cellular dna was. After two generations of growth in the 14nh4cl medium, one half of cellular. Dna was the 14n,15n-dna hybrid and one-half was 14n-dna. Heavy 15n dna forms band at bottom of tube. Light 14n dna forms band at top of tube. Dna with 50-50 mix of 15n and 14n forms band at halfway position in tube.

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Related Questions

DNA replication is Escherichia coli begins at a unique site called the:
origin of responsiveness.
origin of replication.
replication origination site.
oriDNA.
start site.

During the replication of prokaryotic DNA,
both strands are simultaneously synthesized in a continuous manner.
one strand is synthesized in a continuous manner and the other is synthesized by reverse transcription.
both stands are simultaneously synthesized in short pieces which are later joined by DNA ligase.
one strand is synthesized continuously and the other is synthesized in short segments.
both strands are synthesized continuously, but the lagging strand is synthesized only after the leading strand has been completely replicated.
The primase enzyme
synthesizes a short stretch of RNA complementary to a part of the template DNA strand.
synthesizes a short stretch of DNA that is complementary to a part of the template strand of DNA.
acts as the recognition site to which DNA polymerases bind to start the replication process.
replaces the RNA primers used to initiate DNA replication with DNA polymerase.
ligates the nicks formed by discontinuous replication along the lagging strand.

1. In addition to identifying the genetic material, the experiments of Avery, MacLeod, and McCarty with different strains of Streptococcus pneumoniae demonstrated that
DNA is a double helix.
DNA may be taken up by bacterial cells and be active.
DNA is present in bacteriophage T2.
eukaryotic cells may be genetically transformed.
DNA binds to the cell wall of the bacterium.
2. In order to show that DNA in cell extracts is responsible for genetic transformation in Streptococcus pneumoniae, important corroborating evidence should indicate that _______ also destroy transforming activity.
temperatures high enough to kill cells
enzymes that hydrolyze proteins
enzymes that hydrolyze DNA
enzymes that hydrolyze polysaccharides
enzymes that hydrolyze RNA
3. Based on what you have learned about the experiments conducted by Griffith and Avery and colleagues with bacteria, which of the following would result in transformation of living R cells?
Pure RNA from S cells
Cell-membrane extracts from S cells
A mixture of pure RNA and protein from S cells
Cell-free extracts from S cells
Pure protein from S cells
4. A-T base pairs in a DNA double helix
form three hydrogen bonds with each other.
are more heat-stable than G-C base pairs.
are of a substantially different length than G-C base pairs.
are not accessible to DNA binding proteins.
are chemically distinct from G-C base pairs.
5. If 23 percent of the bases in a sample of double-stranded DNA are adenine, what percentage of the bases are uracil?
27
50
0
73
23
6. The uniform diameter of the DNA structure provides evidence for
antiparallel DNA strands.
a right-handed helix.
a double-stranded helix.
3′ end phosphorylation.
purine–pyrimidine pairing.
7. If a sequence of one strand of DNA is 5′-TGACTATC-3′, what is the complementary strand?
5′-ACTGATAG-3′
3′-TGACTATC-5′
3′-ACTGATAG-5′
3′-ACTGATAG-3′
5′-TGACTATC-3′
8. What structural aspect of the DNA facilitates dissociation of the two DNA strands for replication?
3′ end phosphorylation
Purine–pyrimidine pairing
Antiparallel DNA strands
Covalent bonds between sugars and phosphate groups
Hydrogen bonding between paired bases
9. If the Meselson–Stahl density gradient experiment had resulted in two bands of DNA molecules after only one round of replication, one containing only 15N and the second only 14N, this result would have indicated that replication was
unidirectional.
dispersive.
conservative.
bidirectional.

semiconservative.
10. The nucleoside analogue acyclovir, which is used to treat herpes simplex virus (HSV) infections, lacks a 3′ hydroxyl group (–OH). Predict what will happen if the host cell DNA polymerase incorporates a molecule of acyclovir into an elongating strand of HSV DNA.
The replication complex will no longer bind to origins of replication.
The DNA polymerase will only incorporate acyclovir molecules.
Acyclovir will bind single-strand binding proteins.
DNA polymerase will not be able to link a successive nucleotide.
Acyclovir will block the activity of the DNA helicase.
11. Which of the following does not demonstrate the stability of the DNA double helix?
Single-strand binding proteins are required to keep the strands apart.
Paired bases form hydrogen bonds.
High temperatures are required to denature it.
DNA synthesis requires energy.
DNA helicases require ATP.
12. What effect would a primase inhibitor have on DNA replication?
DNA polymerase would not be able to add bases to the DNA.
Primase would be blocked from joining the DNA replication complex.
Primase would not be able to provide primers for DNA polymerases.
DNA polymerase would not be able to use DNA as a template.
There would be no effect on DNA replication.
13. To replicate their DNA in a timely manner, most eukaryotic chromosomes
normally have uncoiled DNA.
have multiple origins of replication.
contain linear molecules of single-stranded DNA.
have two replication forks that move in the same direction.
are composed entirely of DNA.
14. Which statement about DNA replication is false?
Okazaki fragments are synthesized as parts of the leading strand.
Error rates for DNA replication are reduced by proofreading of the DNA polymerase.
The sliding clamp increases the rate of DNA synthesis.
Replication forks represent areas of active DNA synthesis on the chromosomes.
Ligases and polymerases function in the vicinity of replication forks.
15. In many eukaryotes, there are repetitive sequences called telomeres at the ends of chromosomes. After successive rounds of DNA replication, the _______ strand becomes shorter. In some cells, an enzyme called _______ repairs the shortened strand.
leading; telomerase
lagging; telomerase
lagging; DNA polymerase I
leading; DNA polymerase I
leading; replicase
16. A researcher studies normal human fibroblast cells. They can be maintained in culture but die off after about 30 cell generations. Unexpectedly, a colony of cells continues to survive and divide past 30 generations. Which scenario is most likely true for these cells?
DNA polymerase is constantly active.
Primase is able to extend the telomeres.
The mismatch repair system is extra efficient.
The telomerase gene is being expressed.
The cells do not need the ends of their chromosomes.
17. If DNA polymerase III introduces an incorrect nucleotide, what is the first corrective action made by the DNA repair system?
The replication complex excises the incorrect nucleotide.
The excision repair proteins remove the incorrect nucleotide.
The mismatch repair system scans for base-pairing mismatches.
There is no correction, because nucleotide errors by DNA polymerases are not repaired.
DNA ligase connects the correct nucleotide.
18. Choose the correct order of the following four events in the excision repair of DNA:
(1) Base-paired DNA is made complementary to the template.
(2) Damaged bases are recognized.
(3) DNA ligase seals the new strand to existing DNA.
(4) Part of a single strand is excised.
1, 2, 3, 4
2, 1, 3, 4
3, 4, 2, 1
2, 4, 1, 3
4, 2, 3, 1
19. Six complete cycles of PCR should result in a _______-fold increase in the amount of DNA.
64
32
12
128
6
20. When double-stranded DNA is heated to temperatures above 90°C, it denatures. Denaturation is a process that
breaks covalent bonds.
hydrolyzes DNA.
separates double-stranded DNA into two single strands.
causes new hydrogen bonds to form.
irreversibly destroys the double helical structure.

Multiply questions here

Q2. What is the consequence of chromosome inversion on meiosis? (work on a zygote with one normal chromosome and one chromosome with an inversion)

Q3. Search the web or read the textbook. Find a disease that is caused by translocation. What kind of translocation causes the disease?

Q4. Briefly explain how down’s syndrome or other trisomy is generated (3 sentences should be enough for you to explain this clearly)

Q5. I mutated a culture of wild type E. coli cells and wanted to isolate mutants that are unable to synthesize uracil (a nitrogen base in RNA). How can I achieve my goal? (try to finish your answer in 2-3 sentences)

Q6. For the ura- mutant isolated in Q5, I want to convert it to URA+ by transformation. Please tell me how I can achive this transformation with 3 SIMPLE sentences

Q7. What is the difference and relationship between an Hfr cell and an F+ cell?

Q8. I want to set up a mating between an Hfr strain and an F- (ade- his- bio-) strain and detect bio+ recombinant. Please design the experiment for me. (What genotype for Hfr do you need to choose? How will you select your recombinant? etc).

Q9. I want to use phage T2 to transducer the wild type ADE2 gene from the wild type E. coli strain to an ade2- E. coli mutant. How can I do this experimentally? (please briefly describe the approach, not experimental details such as incubation for 10 min, etc).

Q10. We talked about recombination in both eukaryotes and prokaryotes. Are there any differences in these two recombination ? (what are they if there are?)

Q11. Whose (or what) experiment proves that DNA is the genetic material?

Q12. What knowledge did Watson and Crick use in constructing the DNA model?

Q13. How does the double helix model support the three major functions of genetic materials?

Q14. What is the major chemical force that holds DNA and histone together? Hydrogen bonds

Q15. If I label E. coli cells in an N15 medium overnight and chase cells in an N14 medium for 2 generations, what fraction of cells still carry the N15 label?

Q16. If a 1000 kilobase fragment of DNA has five evenly spaced replication origins and DNA polymerase moves at 1 kilobase per second, how many seconds will a cell take to produce two daughter molecules?

Q17. DNA polymerases catalyze the polymerization of nucleotides. Use the formula for enzyme catalyzed reaction (see the example) to describe DNA polymerases. Example: Enzyme Substrate A + substrate B -------------------ïƒ product c + product D Q8. During DNA replication, what is the direction of the growing strand?

Q18. For DNA synthesis in cells, why are there a leading strand and a lagging strand?

Q19. The following is the DNA sequence of a template strand. If the primase begins to synthesize primers from the middle ‘g’, what will the primer sequence be? (assuming the primer can be 8 nucleotides long) 5’ GACTCTAgGACTCCT 3’

Q20. Both DNA polymerase I and DNA polymerase III synthesize DNA during DNA replication. Please state the different roles they played during DNA replication.