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Biology 1201A Chapter Notes - Chapter 12: Dna Ligase, Dna Replication, Okazaki Fragments

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orchidshark702
18 Dec 2017
School
Western University
Department
Biology
Course
Biology 1201A
Professor
Jennifer Waugh

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Document Summary

An enzyme that catalyzes the unwinding of dna template strands. Stabilizes the single stranded dna and keeps the two strands from binding back together. An enzymes that relieves the over-twisting and strain on. Dna ahead of the replication fork by cutting dna into smaller pieces. A short rna nucleotide chain made of rna that is laid down as the first series of nucleotides in a new dna strand. Discontinuous replication: replication in which a dna strand is formed in short lengths that are synthesized in the opposite direction to dna unwinding. Relatively short fragments of dna synthesized on the lagging strand. A dna strand assembled in the direction of dna unwinding. The dna strand assembled discontinuously in the opposite direction of unwinding. An enzyme that assembles complementary nucleotide chains during dna replication. A specialized polymerase responsible for removing rna primers and replacing them with dna. Tethers dna polymerase 3 to the dna template making replication more efficient.

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Related Questions

Order the following steps of the DNA replication process fromfirst to last. (From 1 to 8)

DNA ligase joins Okazaki fragmments together

Elongation of leading strands occurs continuosly and elongationof lagging strands occurs via generation of Okazaki fragments. Bothare synthesized in 5' to 3' direction.

DNA polymerase I removes the RNA primers and replaces them withDNA nucleotides

DNA polymerase III starts adding DNA nucleotides to the 3' endof the existing RNA chain.

Helicase untwists the double helix at the replication fork

Single-stranded binding proteins bind the unpaired DNA strands,keeping them from re-pairing.

Topoisomerase helps releive the strain caused by DNA untwisting.It breaks, swivels and rejoins DNA strands.

Primase starts a complementary RNA chain using parental DNAstrand as a template

Double check to see if I got these right? 3 questions

Some Processes Involved in DNA Replication

1.The replication origin is identified.

2 DNA primase builds RNA primer.

3Okazaki fragments are spliced by DNA ligase.

4Helicases bind and uncoil the DNA double helix.

5 RNA primer is the starting point for DNA polymerase.

6 DNA replication ends at the telomere where DNA codes fortermination.

7 DNA polymerase adds complementary nucleotides in the 5' to 3'direction in short segments called Okazaki fragments.

The sequence in which the events numbered above occur during DNAreplication of the lagging strand: Number 1 - 7 in order.

I put: 1,4,2,5,7,3,6

__________________Question 2:

Some Functions of Enzymes

  1. Build DNA strands
  2. Build RNA primers
  3. Build mRNA strand
  4. Cleave DNA strands
  5. Splice Okazaki fragments

Enzyme:
Helicase :4
DNA ligase :5
RNA primase :1
RNA polymerase :3
DNA polymerase:2

Question 3:

like mRNA, tRNA has a ribose sugar, U instead of T, and issingle stranded. Unlike mRNA, which remains a long single strand ofnucleotides, tRNA folds so that some areas pair up.

The resulting structure has an anticodon on one end and a site foran amino acid to attach on the other end. There is basecomplementarity (A pairs with U and G pairs with C) between an mRNAcodon and tRNA anticodon.

If the amino acid tyrosine attaches to a tRNA, which of thefollowing anticodons could be at the opposite end of the tRNAmolecule?

Select one:

a. ATA and ATG

b. UAU and UAC

c. AUA and AUG

d. AGA and AGU

I picked B.

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.