BIO-1801 Lecture Notes - Lecture 15: Semiconservative Replication, Helicase, Nucleic Acid Double Helix

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14 May 2018

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DNA and the Gene: Synthesis and Repair

Chapter Fifteen

I. Primary Structure of DNA

A. Each strand of DNA has

➢ Sugar/ phosphate backbone of deoxyribonucleotides (phosphodiester bonded)

➢ Exposed series of nitrogen-containing bases

B. DNA has directionality

➢ 3’ ed has a eposed hdrol group

➢ 5’ ed has a eposed phosphate group

➢ New ases added ol to 3’

II. Secondary Structure of DNA

A. Two DNA strands hydrogen bonded to form a double helix (hydrogen bond to

complimentary base first then for phosphodiester)

B. Antiparallel

C. The secondary structure is stabilized by complementary base pairing

➢ Adenine(A) and thymine (T)

➢ Guanine (G) with cytosine (C)

D. Parental strands serve as template for replication producing daughter strands.

III. DNA Synthesis: Three Early hypotheses

1. Semiconservative replication: (experiments of Meselson and Stahl)

➢ Parent strands separate and each is copied

➢ New double helix is half parent half daughter

2. Conservative replication: Stay together

3. Dispersive replication: Dispersed Fragments

IV. A Model for DNA synthesis

A. DNA Polymerases: enzymes that catalyze DNA Synthesis

➢ Ca add ew uleotides ol to the 3’ ed of a growig DNA hai.

➢ Daughter produed 5’ 3’

➢ Paret read 3’ 5’

➢ DNA polymerization requires E

➢ The monomers are nucleotides with three triphosphates (dNTPs)

• Removal of 2x phosphates provides E to form phosphodiester bonds

V. Where Does Replication Start?

A. Double helix separates at a specific sequence called the origin of replication

B. Forms replication bubble with two replication forks

➢ Bacteria form one replication bubble

➢ Eukaryotic form many on each chromosome

C. Replication bubbles grow in both directions (bidirectional replication)

VI. How is the helix opened and stabilized?

A. DNA helicase breaks hydrogen bonds between the two DNA strands to separate them.

B. Single-strand DNA-binding proteins (SSBPs) attach to the separated strands to prevent

them from closing.

C. Topoisomerase relieve tension from unwinding the DNA helix.

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Document Summary

Primary structure of dna: each strand of dna has. Sugar/ phosphate backbone of deoxyribonucleotides (phosphodiester bonded) Exposed series of nitrogen-containing bases: dna has directionality. 3" e(cid:374)d has a(cid:374) e(cid:454)posed h(cid:455)dro(cid:454)(cid:455)l group. 5" e(cid:374)d has a(cid:374) e(cid:454)posed phosphate group. Secondary structure of dna: two dna strands hydrogen bonded to form a double helix (hydrogen bond to complimentary base first then for phosphodiester, antiparallel, the secondary structure is stabilized by complementary base pairing. Guanine (g) with cytosine (c: parental strands serve as template for replication producing daughter strands. Dna synthesis: three early hypotheses: semiconservative replication: (experiments of meselson and stahl) Parent strands separate and each is copied. New double helix is half parent half daughter: conservative replication: stay together, dispersive replication: dispersed fragments. A model for dna synthesis: dna polymerases: enzymes that catalyze dna synthesis. Ca(cid:374) add (cid:374)ew (cid:374)u(cid:272)leotides o(cid:374)l(cid:455) to the 3" e(cid:374)d of a growi(cid:374)g dna (cid:272)hai(cid:374).

Related Questions

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.

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

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

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.

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

The uniform diameter of the DNA structure provides evidence for

	antiparallel DNA strands.
	a right-handed helix.
	a double-stranded helix.
	3â² end phosphorylation.
	purineâpyrimidine pairing.

If a sequence of one strand of DNA is 5â²-TGACTATC-3â², what is the complementary strand?

	5â²-ACTGATAG-3â²
	3â²-TGACTATC-5â²
	3â²-ACTGATAG-5â²
	3â²-ACTGATAG-3â²
	5â²-TGACTATC-3â²

What structural aspect of the DNA facilitates dissociation of the two DNA strands for replication?

	3â² end phosphorylation
	Purineâpyrimidine pairing
	Antiparallel DNA strands
	Covalent bonds between sugars and phosphate groups
	Hydrogen bonding between paired bases

If the MeselsonâStahl 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 3â² hydroxyl group (âOH). 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 90Â°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.

Match each term with its definition. Each term or definition is used only once

- A. B. C. D. E. F. G. H. I. J. K. L. M. N. O. P. Q. R. S. T.	right-spiraling common DNA form
- A. B. C. D. E. F. G. H. I. J. K. L. M. N. O. P. Q. R. S. T.	referencing the opposite orientation of hydrogen-bonded DNA strands
- A. B. C. D. E. F. G. H. I. J. K. L. M. N. O. P. Q. R. S. T.	viral particle whose natural host is a prokaryote
- A. B. C. D. E. F. G. H. I. J. K. L. M. N. O. P. Q. R. S. T.	universal holding that the number of purines always equals the number of pyrimidines
- A. B. C. D. E. F. G. H. I. J. K. L. M. N. O. P. Q. R. S. T.	nucleic acid base sequences able to form a double-stranded structure by virtue of matching base pairs
- A. B. C. D. E. F. G. H. I. J. K. L. M. N. O. P. Q. R. S. T.	5ââ 3â or 3ââ 5â
- A. B. C. D. E. F. G. H. I. J. K. L. M. N. O. P. Q. R. S. T.	nuclease able to cleave phosphodiester linkages in the DNA backbone
- A. B. C. D. E. F. G. H. I. J. K. L. M. N. O. P. Q. R. S. T.	the structure formed by two DNA strands twisted around a common axis in a spiral
- A. B. C. D. E. F. G. H. I. J. K. L. M. N. O. P. Q. R. S. T.	bacterial cycle of phage- infected cells resulting in cell destruction and viral release
- A. B. C. D. E. F. G. H. I. J. K. L. M. N. O. P. Q. R. S. T.	main access site for proteins that recognize specific DNA sequences
- A. B. C. D. E. F. G. H. I. J. K. L. M. N. O. P. Q. R. S. T.	a cytosine modification favoring Z DNA formation
- A. B. C. D. E. F. G. H. I. J. K. L. M. N. O. P. Q. R. S. T.	nucleic acid monomer consisting of a sugar, a phosphate group, and a nitrogenous base
- A. B. C. D. E. F. G. H. I. J. K. L. M. N. O. P. Q. R. S. T.	connects two nucleic acid sugar molecules via an ester bond
- A. B. C. D. E. F. G. H. I. J. K. L. M. N. O. P. Q. R. S. T.	hydrolyzes peptide bonds linking amino acids
- A. B. C. D. E. F. G. H. I. J. K. L. M. N. O. P. Q. R. S. T.	U or C in RNA
- A. B. C. D. E. F. G. H. I. J. K. L. M. N. O. P. Q. R. S. T.	a pentose sugar
- A. B. C. D. E. F. G. H. I. J. K. L. M. N. O. P. Q. R. S. T.	an enzyme that breaks down RNA
- A. B. C. D. E. F. G. H. I. J. K. L. M. N. O. P. Q. R. S. T.	either of the two nucleotide chains of a double helix
- A. B. C. D. E. F. G. H. I. J. K. L. M. N. O. P. Q. R. S. T.	a pyrimidine able to hydrogen bond with adenine
- A. B. C. D. E. F. G. H. I. J. K. L. M. N. O. P. Q. R. S. T.	a DNA configuration favored by high ionic strength and GC repeats

A.	protease
B.	lysis
C.	double helix
D.	bacteriophage
E.	complementary
F.	Chargaffâs rule
G.	B DNA
H.	major groove
I.	nucelotide
J.	antiparallel
K.	RNAse
L.	directionality
M.	phosphodiester linkage
N.	ribose
O.	Z DNA
P.	pyrimidine
Q.	methylation
R.	DNAse
S.	uracil
T.	strand

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BIO-1801 Lecture Notes - Lecture 15: Semiconservative Replication, Helicase, Nucleic Acid Double Helix

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