BIO SCI 98 Chapter Notes - Chapter 4: Semiconservative Replication, Isotopes Of Nitrogen, Dna Polymerase

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blushmammoth506

19 Jun 2018

School

UC-Irvine

Department

Biological Sciences

Course

BIO SCI 98

Professor

RAZORENOVA/INLAY/MORRISETTE

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Page 363-376, 403

DNA replication- the duplication of the cellular genome

-Starts at specific locations on chromosome with DNA polymerase

-Bidirectional

-Each complementary strand is used as template strand to synthesize daughter strand

DNA Replication is Semiconservative

-Double helix is unwound and each parental strand is used as a template to make new

daughter strand → two daughter complexes, following A=T and C≡G rules ⇒

semiconservative replication

-Each daughter complex conserves one parental strand of DNA

-Conservative replication: two parental strands stay together as template

-Dispersive replication: DNA is synthesized randomly

-Meselson and Stahl experiment

-Grew E. coli in 15N = heavy

-Moved to 14N medium

-Parental strands: both strands are heavy, DNA synthesis incorporates light

nucleotides

-After one replication cycle, DNA was mixed density = either semiconservative or

dispersive

-After two replication cycles, DNA had one mixed and one light band = semiconservative

-Half should be 15N-14N mixed DNA and half should be 14N-14N

Replication is Initiated at Origins and Proceeds

Bidirectionally

- Density gradient experiments could not distinguish if replication occurred at one site or

multiple sites

-Plasmid was observed under microscope

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-Replicating DNA contained loops/bubbles

-DNA is not completely unwound → the strands only separate when replicated

-Point where DNA synthesis starts = origin of replication (ORI)

-Point where parental duplex separates and daughter duplexes forms = replication

fork

-Eukaryotic cells have multiple ORI bc they are longer and more complex

-Bidirectionally replicates → moving replication forks on either side

-Radioactive density heaviest at forks moving in opposite directions = replication

forks travel bidirectionally

-Plasmids replicate in single direction at their ends

-Phages replicate multiple times with a single replication fork

Replication is Semidiscontinuous

-DNA polymerases: enzymes that synthesize DNA

-Extend DNA only in 5'-3' direction → both daughter strands cannot be replicated

in same direction that replication fork moves

-Cannot initiate DNA chains = initiated by RNA primers, synthesized by primase

-Okazaki: one strand is synthesized in same direction as replication fork, the other strand

is synthesized in opposite direction

-DNA strands are antiparallel, but both strands are still synthesized 5'-3'

-Only one daughter strand is synthesized continuously, the other strand is made as

series of discontinuous fragments = semidiscontinuous

-Continuous strand = leading strand, discontinuous strand = lagging strand

-Short fragments produced on one strand = Okazaki fragments

-Each Okazaki fragment primed at 5' end by RNA, which is removed by nuclease to join

to another Okazaki fragment by ligase

DNA Polymerases Elongate DNA 5' → 3'

-All DNA polymerases require template strand

-DNA polymerases require primer strand complementary to template strand that contains

3' OH group to add nucleotide on

-DNA polymerases can only add to existing DNA → cannot synthesize with only

template

-Nucleotides are added on to 3' end of primer called primer terminus

-Double stranded DNA formed by primer and template called primed template

-Different dNTPs can bind to same active site on DNA pol I

-Only correct geometry of A=T or C≡G fits into active site

-3' OH group activated to attack alpha-phosphorus of incoming dNTP

-(dNMP)

+ dNTP → (dNMP)n+1

+ PP

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Document Summary

Dna replication- the duplication of the cellular genome. Starts at specific locations on chromosome with dna polymerase. Each complementary strand is used as template strand to synthesize daughter strand. Double helix is unwound and each parental strand is used as a template to make new daughter strand two daughter complexes, following a=t and c g rules semiconservative replication. Each daughter complex conserves one parental strand of dna. Conservative replication: two parental strands stay together as template. Grew e. coli in 15n = heavy. Parental strands: both strands are heavy, dna synthesis incorporates light nucleotides. After one replication cycle, dna was mixed density = either semiconservative or dispersive. After two replication cycles, dna had one mixed and one light band = semiconservative. Half should be 15n-14n mixed dna and half should be 14n-14n. Density gradient experiments could not distinguish if replication occurred at one site or multiple sites. Dna is not completely unwound the strands only separate when replicated.

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.

BIO SCI 98 Chapter Notes - Chapter 4: Semiconservative Replication, Isotopes Of Nitrogen, Dna Polymerase

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