15- hereditary

What observation about DNA amount in somatic cells versus gametes supported DNA as genetic material

Somatic cells have twice the amount of DNA compared to gametes, consistent with Mendelian inheritance

Who discovered the transforming principle in bacteria

Frederick Griffith

What is transformation in bacteria

The process where one bacterial strain acquires heritable traits from another strain

Who identified DNA as the transforming agent

Oswald Avery

What did the Hershey-Chase experiment prove

DNA, not protein, is the genetic material that enters bacterial cells

What radioactive isotopes were used in the Hershey-Chase experiment

32P for DNA and 35S for protein

Why was phosphorus used to label DNA in Hershey-Chase experiment

DNA contains phosphorus but proteins do not

Why was sulfur used to label proteins in Hershey-Chase experiment

Proteins contain sulfur but DNA does not

What happened to the radioactive phosphorus in the Hershey-Chase experiment

It entered the bacterial cells, showing DNA is genetic material

What technique did Rosalind Franklin use to study DNA

X-ray crystallography

What did Chargaff’s rule state

The amount of adenine equals thymine and guanine equals cytosine

What model did Watson and Crick propose

The double helix structure of DNA

What are the main structural features of DNA

Double-stranded helix, uniform diameter, right-handed twist, antiparallel strands

What is the orientation of DNA strands

Antiparallel, one runs 5' to 3' and the other 3' to 5'

Where are the sugar-phosphate backbones and nitrogenous bases located in DNA

Backbone is outside and bases are inside

What type of bond links nucleotides in DNA

Phosphodiester bond

Which carbons are linked by phosphodiester bonds

The 3' carbon of one sugar to the 5' carbon of the next

What are the four main functions of genetic material

Storage of information, mutation capability, replication, and expression

Who demonstrated DNA replication in a test tube

Arthur Kornberg

What are the four DNA precursors used in replication

dATP, dCTP, dGTP, and dTTP

What are the three models of DNA replication

Semiconservative, conservative, and dispersive

Which model of DNA replication is correct

Semiconservative replication

Who confirmed the semiconservative model

Meselson and Stahl

What was used in Meselson and Stahl experiment

Heavy nitrogen (15N) labeling

What are the two main steps of DNA replication

Strand separation and addition of complementary nucleotides

In which direction are nucleotides added during DNA replication

5' to 3' direction

To which end are nucleotides added in a growing DNA strand

The 3' end

Where does the energy for nucleotide addition come from

Breaking the bonds between the three phosphate groups of dNTPs

What is the role of helicase

Unwinds the DNA double helix using ATP

What prevents unwound DNA strands from rejoining

Single-strand binding proteins

What is the function of primase

Synthesizes short RNA primers

What is a primer

A short RNA strand that provides a starting point for DNA synthesis

What is the primosome

A protein complex that includes primase and forms RNA primers

Which enzyme adds nucleotides during replication

DNA polymerase III

Why can DNA polymerase not start synthesis on its own

It requires a pre-existing strand or primer

What is the function of DNA polymerase I

Replaces RNA primers with DNA

What is the function of DNA ligase

Joins DNA fragments by forming phosphodiester bonds

What is the role of topoisomerase

Relieves tension and separates interlocked DNA molecules

What is a replication fork

The Y-shaped region where DNA is actively being replicated

What is the leading strand

The strand synthesized continuously toward the replication fork

What is the lagging strand

The strand synthesized discontinuously away from the replication fork

What are Okazaki fragments

Short DNA fragments formed on the lagging strand

Why are Okazaki fragments formed

Because DNA synthesis can only occur in the 5' to 3' direction

How are Okazaki fragments joined

By DNA ligase after primer replacement

How does replication differ in prokaryotes and eukaryotes

Prokaryotes have a single origin while eukaryotes have multiple origins

What happens at the ends of linear chromosomes during replication

DNA cannot be fully replicated, causing shortening

What are telomeres

Repetitive DNA sequences at chromosome ends

Why do telomeres shorten

Because no primer can bind at the very end of linear DNA

What is telomerase

An enzyme that adds telomeric sequences to chromosome ends

In which cells is telomerase active

Germ cells, stem cells, and most cancer cells

What is proofreading in DNA replication

DNA polymerase correcting incorrect nucleotides during synthesis

What is the error rate after proofreading

About 1 in a billion nucleotides

What is mismatch repair

A system that fixes incorrect base pairing after replication

How does mismatch repair distinguish strands

The template strand is methylated while the new strand is not

What is excision repair

Removal and replacement of damaged DNA segments

What can cause DNA damage requiring excision repair

Chemicals, radiation, and spontaneous reactions

What is PCR

A technique used to amplify DNA sequences

What are the three steps of PCR

Denaturation, annealing, and extension

What is required for PCR

DNA template, primers, DNA polymerase, and dNTPs

What happens during PCR denaturation

DNA strands are separated by heat

What happens during PCR annealing

Primers bind to complementary sequences

What happens during PCR extension

DNA polymerase synthesizes new DNA strands

Why does PCR result in exponential amplification

Each cycle doubles the number of DNA molecules

What are ddNTPs

Modified nucleotides lacking a 3' hydroxyl group

Why do ddNTPs stop DNA synthesis

They prevent addition of further nucleotides

What is the principle of Sanger sequencing

Chain termination using fluorescently labeled ddNTPs

How are DNA fragments separated in sequencing

By electrophoresis based on size

How is the DNA sequence determined in Sanger sequencing

By analyzing the order of fluorescently labeled terminated fragments