HONR 1034 Chapter Notes - Chapter 11: Semiconservative Replication, Dna Replication, Ammonium Chloride

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DNA Replication and Recombination

I. DNA is reproduced by semiconservative replication

A. Watson-Crick: knew that if the double helix is separated each nucleotide would have an affinity

for its complementary nucleotide

1. Secondary structure of the DNA molecule → determines function

2. Double-helix → two strands antiparallel attached by nucleotides

a) Complementarity: if you know the sequence of one you know the sequence of

the other

b) Major grooves are where proteins interact in the DNA → essential to the

function because replication can’t happen without the help of proteins

c) Each strand serves as a template when separated

B. Semiconservative replication: when the strands are unwound and each serves as a template to

create a new strand that is complementary to the old strand

II. The Meselson-Stahl experiment

A. Did an experiment using e coli that replicates really fast → with each division of one cell you

get two more → exponential growth → about half an hour per division

B. Shows that semiconservative replication is how bacterial cells produce new DNA molecules

C. First step: Medium for growth contained heavy molecule of nitrogen (N15 - is heavy because it

contains one more neutron than normal nitrogen) label this test tube

D. N15 and N14 are distinguishable through technique of sedimentation equilibrium centrifugation

1. The molecule they’re testing is passing through the gradient of another heavy metal

2. Molecules of DNA reach equilibrium when their density equals the density of the

gradient medium (Had ammonium chloride and nitrogen) label this test tube

E. N15 is stable, radioisotopes aren’t → is more dense than normal N

1. Showed a single band

F. Second step: N15 labeled DNA is transferred to a medium with N14

1. After several generations, almost all the N containing E. coli had the heavier isotopeN15

cells transferred to a medium with only NH4Cl, so all new synthesis created E coli with

the lighter isotope of nitrogen

2. After two divisions showed one strand of N14 and one of N15

3. Third division showed one of each

G. Did the same process by extracting and passing the DNA through the gradient of heavy metals, but

when they equalize there is an intermediate band that is purple

H. After the second round/generation and process, there are two bands; the

intermediate band and a lighter band

I. If you continue, two appearance of two bands continues but the intensity of the two

bands is not the same and they correspond to the proportions of the

III. DNA replication

A. Replication starts at the origin of replication → specific sequence(s) within the genome that are

usually less stable (have more AT base pairings → AT has two bonds and GC has 3 so it’s a

little less stable)

B. Replication forks (what is created as the strands separate) form → as the process continues it’s

as if it’s moving along the structure

C. If the replication is bidirectional, two forks form migrating in opposite directions from origin

D. Replicon: the length of DNA being synthesized (from one initiation to the end)

IV. Replication in E coli

A. Double-stranded circular DNA with oriC and Ter (are one circular chromosome)

1. The entire chromosome constitutes one replicon

2. OriC: origin of replication → where proteins bind; only one in E coli

3. Ter: termination region

B. Because they’re circular, you have two forks that are moving until they reach the terminal region

and they merge and form two new molecules that separate

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Related Questions

1.When a protein binds to DNA at a site defined by a particular nucleotide sequence, with which parts of the DNA does the protein primarily interact?

A. the phosphate and deoxyribose groups in the DNA backbone

B. the phosphate and deoxyribose groups in the DNA backbone, and hydrophobic interactions with the nucleotide bases

C. nucleotide bases within the major grooves of the DNA

D. nucleotide bases within the major and minor grooves of the DNA

E. none of the above

2. Which of the following proteins binds to DNA with sequence specificity?

A. POI Ill holoenzyme

B. DnaA

C. DnaB

D. Dam methylase

E. Both B and D

3. Which of the following is NOT a functional parallel among all known cellular systems of DNA replication?

A. Replication is initiated at specific sites

B. Replication is continuous on the leading strand and discontinuous on the lagging strand

C. DNA replication is semiconservative

D. Replication forks move away from the origin in one direction

E. Nucleases, polymerases and ligases replace RNA primers with DNA and seal the remaining nick

4. A DNA polymerase cannot synthesize a DNA strand de novo (from the beginning) from a mixture of dNTPs. Which of the following explains the role of the primer in the reaction promoted by this enzyme?

A. The primer is an initiation protein with attached nucleotides that binds to the template and to which new nucleotides are added to the 3 ' end.

B. The primer is an initiation protein with attached nucleotides that binds to the template and to which new nucleotides are added to the 5' end.

C. The primer is a preexisting strand of RNA or DNA to which new nucleotides are added to the 3' end.

D. The primer is a preexisting strand of RNA or DNA to which new nucleotides are added to the 5' end.

E. The primer is a preexisting strand of DNA synthesized by DNA pol I, prior to replicative DNA synthesis by DNA pol Ill.

5. Universal features of DNA polymerases include:

A. 5'-3' exonuclease function.

B. Formation of an 'closed' conformation of the polymerase when the template-nucleotide base pair is correct.

C. Use of a single magnesium ion to orient reacting molecules and assist in dissipation of the negative charge that develops during nucleotidyl transfer.

D. Alignment of conserved residues in the active site for attack of the DNA primer by the 3 'OH on the incoming nucleotide.

E. Continuous unbinding and rebinding of the polymerase to the DNA template as each nucleotide is added.

byzantiumscorpion425

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.

What step in DNA replication precedes the pairing of complementary bases?

	A.	polymerization of DNA.
	B.	formation of the histone core.
	C.	mitotic division.
	D.	separation of the two strands.
	E.	joining of the two strands.

In eukaryotes, transcription occurs in the

	A.	ribosome.
	B.	mitochondria.
	C.	cell membrane.
	D.	cytoplasm.
	E.	nucleus.

Normal human body cells contain how many chromosomes?

	A.	46
	B.	22
	C.	23
	D.	44
	E.	42

Hershey and Chase performed an experiment in which they used radioactive isotopes to phosphorus and sulfur to label different components of bacterial viruses. Their results clearly showed that

	A.	the viruses did not contain protein.
	B.	genetic material normally contains radioactive isotopes.
	C.	the viruses did not contain DNA.
	D.	protein was entering into the infected bacteria.
	E.	DNA was entering into the infected bacteria.

A package of histones with DNA wrapped around them forms spherical structures called

	A.	nucleosomes.
	B.	lysosomes.
	C.	ribosomes.
	D.	nucleoli.
	E.	chromatin.

DNA replication

	A.	does not require proteins.
	B.	is constantly happening in a cell.
	C.	occurs in G1 of interphase.
	D.	takes place in the nucleus of the cell.
	E.	occurs in the cytoplasm of the cell.

The two subunits of the ribosome join during

	A.	promotion of transcription.
	B.	initiation of translation.
	C.	termination of transcription.
	D.	termination of translation.
	E.	elongation.

DNA replication of a single DNA molecule is referred to as semiconservative because

	A.	each of the two DNA molecules will consist of one parental strand and one newly synthesized strand.
	B.	all the DNA strands in the two DNA molecules will have both parental and newly synthesized DNA.
	C.	it results in two nonidentical DNA molecules.
	D.	of the two DNA molecules, one is made up totally of parental DNA, while the other is entirely newly synthesized DNA.
	E.	one DNA strand is replicated continuously, while the other must be replicated discontinuously.

The bases are bonded to what part of the backbone of the DNA molecule?

	A.	the 4â carbon atom of the sugar molecule.
	B.	the 3â carbon atom of the sugar molecule.
	C.	the 5â carbon atom of the sugar molecule.
	D.	the 1â carbon atom of the sugar molecule.
	E.	the 2â carbon atom of the sugar molecule.

HONR 1034 Chapter Notes - Chapter 11: Semiconservative Replication, Dna Replication, Ammonium Chloride

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