DNA Structure & Replication (Chp 7)

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Questions and Answers

What is the term used to describe the pairing of adenine with thymine and guanine with cytosine in DNA?

Base stacking

Antiparallel alignment

Complementary base-pairing (correct)

Covalent bonding

Which feature of DNA is described as having different widths with distinct structural roles?

Axis of helical symmetry

Conserved diameter

Major and minor groove (correct)

Antiparallel strands

How does DNA replication ensure that each daughter cell has an identical copy of DNA?

By using identical parental strands to create new strands (correct)

By combining strands from different sources

By synthesizing new DNA strands without original templates

By modifying existing DNA sequences in daughter strands

Which enzyme is primarily responsible for adding nucleotides to a growing chain during DNA replication?

Polymerase Signup and view all the answers

What characteristic of DNA allows it to undergo mutation?

Mutability Signup and view all the answers

What structural characteristic defines the orientation of the two strands of DNA?

Strands run in opposite directions, or are antiparallel Signup and view all the answers

Which experiment identified DNA as the transformation factor?

Avery's experiment Signup and view all the answers

What was the primary focus of Griffith’s experiment?

To identify strains of Pneumococcus Signup and view all the answers

What method did Hershey and Chase use to differentiate between DNA and proteins?

Radioactive labeling Signup and view all the answers

What conclusion can be drawn if a phage containing both DNA and RNA were used in the Hershey and Chase experiment?

Either DNA or RNA could be considered the hereditary material Signup and view all the answers

What role does DnaA play in the replication initiation process?

It binds to consensus sequences and bends the DNA. Signup and view all the answers

What type of virus was used in the Hershey and Chase experiment?

Bacteriophage Signup and view all the answers

Which of the following is NOT an essential characteristic of hereditary material?

Can quickly mutate Signup and view all the answers

How does the replication of the lagging strand differ from that of the leading strand?

It requires an RNA primer for initiation. Signup and view all the answers

Which of the following statements accurately describes DNA polymerase?

It requires a pre-existing strand to add nucleotides. Signup and view all the answers

Avery's experiment destroyed which of the following components to determine its role in transformation?

RNA Signup and view all the answers

What is the primary function of primase during DNA replication?

To synthesize RNA primers needed for initiating synthesis. Signup and view all the answers

What is the consensus sequence used for in the replication initiation process?

To attract replication enzymes to the origins of replication. Signup and view all the answers

What is the result of DNA replication as observed in bacteria?

It produces two daughter strands, each containing one parental and one new strand. Signup and view all the answers

Which experimental technique was used to distinguish between heavy and light nitrogen in the Meselson-Stahl experiment?

Ultracentrifugation in a CsCl gradient. Signup and view all the answers

What characterizes the directionality of DNA replication in bacteria?

Replication is bidirectional from a single origin. Signup and view all the answers

How fast can E.coli DNA polymerase replicate DNA?

1000 nucleotides per second. Signup and view all the answers

What was the primary evidence supporting bidirectional replication of DNA?

Pulse-chase labeling experiments demonstrated simultaneous replication at both ends. Signup and view all the answers

How many origins of replication can be found in the human genome?

10,000 origins. Signup and view all the answers

What would be observed in the Meselson and Stahl experiment if DNA replication was conservative?

Two bands, one for parental and one for daughter DNA. Signup and view all the answers

What is a characteristic feature of DNA replication in eukaryotic organisms?

Thousands of origins of replication are present in the genome. Signup and view all the answers

What is the role of DNA polymerase I in replication?

It removes RNA primers and adds DNA nucleotides. Signup and view all the answers

What is the primary function of DNA ligase during DNA replication?

To seal the gaps between resulting DNA segments. Signup and view all the answers

How does the proofreading ability of DNA polymerases work?

It relies on the removal of incorrect nucleotides by removing several nucleotides. Signup and view all the answers

What is the function of telomerase in eukaryotic cells?

To extend the telomeres at the ends of chromosomes. Signup and view all the answers

Why do differentiated somatic cells have limited lifespans?

They have virtually no telomerase activity. Signup and view all the answers

What is a consequence of telomere shortening in cells?

Progressively shorter life spans for cells. Signup and view all the answers

What happens to the 3'-OH end of a DNA strand during proofreading?

It moves into the enzyme's exonuclease site. Signup and view all the answers

What condition is associated with dyskeratosis congenita?

Defective gene responsible for normal telomerase function. Signup and view all the answers

Study Notes

DNA as the Hereditary Molecule of Life

Essential characteristics of hereditary material: Found in the nucleus, stable, sufficiently complex, accurately replicates itself, and mutable.
Foundational experiments:
- Griffith's experiment discovered the 'transformation factor' in Pneumococcus.
- Avery's experiment identified DNA specifically as the 'transformation factor'.
- Hershey and Chase confirmed DNA is the hereditary material using bacteriophage T2.

Griffith’s Experiment

Identified two strains of Pneumococcus: S strain (virulent) and R strain (non-virulent).
Each strain exhibited four antigenic types (I, II, III, IV).
Suggested the existence of a 'transformation factor'.

Avery’s Experiment

Used the same S and R strains as Griffith.
Systematically destroyed lipids, proteins, RNA, or DNA to determine what was needed for transformation.

Hershey and Chase Experiment

Utilized bacteriophage proteins labeled with radioactive sulfur (35S) and DNA labeled with phosphorus (32P).
Traced radioactive labels during infection to confirm that DNA, not protein, is the genetic material.

The DNA Double Helix

Structure consists of two complementary, antiparallel strands.
A pairs with T, and G pairs with C; this base pairing ensures genetic fidelity.
Characterized by an axis of helical symmetry, a conserved diameter, and major and minor grooves.

DNA Replication Process

Semiconservative and bidirectional replication: each parental strand serves as a template for a new strand.
In bacterial DNA replication, it proceeds bidirectionally from a single origin of replication.

Meselson-Stahl Experiment

Used cesium chloride gradient ultracentrifugation to distinguish DNA with heavy nitrogen (15N) from light nitrogen (14N).
Provided evidence supporting the semiconservative mechanism of DNA replication.

Replication Origins and Directionality

E. coli replication initiates at specific consensus sequences (oriC) and progresses bidirectionally.
Eukaryotic genomes possess thousands of origins, with the human genome containing approximately 10,000 origins.

Mechanism of DNA Replication in Bacteria

Initiation: DnaA binds to oriC, bends DNA, and breaks hydrogen bonds.
Unwinding: Helicase (DnaB) unwinds DNA strands while DnaC transports DnaB.
Nucleotide Addition: DNA polymerase requires an existing 3’ OH to add nucleotides. RNA primers synthesized by primase initiate replication.

Leading and Lagging Strand Synthesis

Leading strand synthesized continuously in the same direction as the replication fork.
Lagging strand synthesized discontinuously using Okazaki fragments in the opposite direction.

RNA Primer Removal and Fragment Ligation

DNA polymerase I removes RNA primers and fills in gaps with DNA.
DNA ligase seals the nicks between DNA segments.

Topoisomerase Function

Prevents supercoiling by catalyzing controlled cleavage and rejoining of DNA strands.

Proofreading and Error Correction

DNA replication errors occur once per billion nucleotides due to proofreading by DNA polymerase with 3’-to-5’ exonuclease activity.
Mismatched base pairs are corrected by removing incorrect nucleotides.

Telomeres and Aging

Telomeres are repetitive DNA sequences at the ends of linear chromosomes that cannot be fully replicated.
Telomerase, a protein-RNA complex, synthesizes telomeres, active primarily in germ-line and some stem cells.
Differentiated somatic cells lack telomerase activity leading to limited lifespan and the Hayflick limit (50-70 divisions).

Applications: Telomeres, Aging, and Cancer

Dyskeratosis congenita is a condition linked to defective telomerase function.
Abnormal reactivation of telomerase is associated with cancer proliferation.

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Description

This quiz covers DNA as the hereditary molecule of life, focusing on its essential characteristics and foundational experiments. Review key concepts such as the stability, complexity, and replication of DNA. Test your understanding of Chapter 7 and its implications in genetics.