Molecular Genetics: Transformation & Experiments

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Questions and Answers

What term did Griffith use to describe the transfer of virulence from S strain to R strain cells?

Transformation (correct)

Genetic exchange

Replication

Mutation

What was the significant finding of Avery, MacLeod, and McCarty's experiment regarding the ability to transform R strain cells?

Only carbohydrates could facilitate transformation.

Proteins were responsible for transformation.

RNA played a significant role in the process.

DNA was the transforming material. (correct)

In the Hershey and Chase experiment, which radioactive label was used to track the DNA of bacteriophages?

Radioactive sulfur-35

Radioactive phosphorus-32 (correct)

Radioactive iodine-131

Radioactive carbon-14

What did the results of the Hershey and Chase experiment conclude about genetic material?

DNA serves as the genetic material. Signup and view all the answers

What method did Avery, MacLeod, and McCarty use to determine which material was responsible for transformation?

Using a variety of chemical treatments Signup and view all the answers

Why did Avery, MacLeod, and McCarty conclude DNA was the genetic material?

Removal of proteins did not affect transformation capacity. Signup and view all the answers

What type of viruses did Hershey and Chase study to determine the genetic material?

Bacteriophages Signup and view all the answers

Which component of the bacteriophage did Hershey and Chase find inside the bacteria?

Bacteriophage DNA Signup and view all the answers

What key insight did Watson and Crick have about the structure of DNA?

DNA has a double helix structure composed of two intertwined chains. Signup and view all the answers

Which of the following describes the directionality of a single strand of DNA?

5′ to 3′ direction Signup and view all the answers

What stabilizes the double helix structure of DNA?

Hydrogen bonds between base pairs Signup and view all the answers

What are the specific base pairs formed in DNA?

A-T and G-C Signup and view all the answers

What type of backbone is found in a single strand of DNA?

Phosphodiester backbone Signup and view all the answers

How do the two strands of a DNA molecule compare to each other?

They specify the other by base-pair complementarity. Signup and view all the answers

How many hydrogen bonds does adenine form with thymine?

Two hydrogen bonds Signup and view all the answers

Which of the following statements about the grooves in the double helix structure of DNA is true?

The double helix features both major and minor grooves. Signup and view all the answers

What describes the orientation of the sugar-phosphate backbone of DNA?

It has both 3′ OH and 5′ PO4 ends. Signup and view all the answers

Which model of DNA replication involves both parental strands remaining intact?

Conservative model Signup and view all the answers

What does the semiconservative model of DNA replication imply?

Daughter strands consist of one parental strand and one new strand. Signup and view all the answers

What implication arises from Watson and Crick's observation about base pairing?

It suggests a copying mechanism for genetic material. Signup and view all the answers

What is a critical reason for DNA repair mechanisms in cells?

To maintain the integrity of genetic information. Signup and view all the answers

Why is replication considered discontinuous on one strand?

DNA polymerase can only add nucleotides in the 5′ to 3′ direction. Signup and view all the answers

Which function do telomeres serve in eukaryotic cells?

They protect chromosome ends from degradation. Signup and view all the answers

What is a role of telomerase in cell division?

It maintains and extends telomere length. Signup and view all the answers

What was the purpose of growing bacterial cells in a heavy isotope of nitrogen, $^{15}N$?

To track the replication of DNA Signup and view all the answers

What conclusion was drawn about the dispersive model of DNA replication based on the results?

It was rejected after the second round of replication. Signup and view all the answers

After the first round of replication, how many bands were observed with the semiconservative model?

One Signup and view all the answers

Which model of DNA replication was ultimately rejected based on the Meselson-Stahl experiment?

Conservative model Signup and view all the answers

What does the semiconservative model suggest about the daughter DNA strands?

They consist of mixed parental and new DNA. Signup and view all the answers

What was one key observation made by Meselson and Stahl after the second round of replication?

Only one band was observed at lower density. Signup and view all the answers

What are the three components required for DNA replication?

Parental DNA, enzymes, and nucleotides Signup and view all the answers

What type of experiment was conducted by Meselson and Stahl?

Centrifugation-based density analysis Signup and view all the answers

What distinguishes eukaryotic DNA replication from prokaryotic replication?

Eukaryotic replication involves multiple origins of replication. Signup and view all the answers

What is the role of DNA polymerase epsilon (Pol ε) in eukaryotic DNA replication?

It synthesizes the leading strand. Signup and view all the answers

Why are telomeres important in linear chromosomes?

They protect chromosome ends from nucleases. Signup and view all the answers

Which statement about the eukaryotic replication fork is accurate?

A subset of helicases is activated during the S phase. Signup and view all the answers

How do replication origins in eukaryotes differ from those in prokaryotes?

They can be adjusted based on developmental needs. Signup and view all the answers

What unique characteristic do archaeal and eukaryotic replication proteins share?

They exhibit similarities in DNA polymerases. Signup and view all the answers

What is a key challenge presented by the replication of linear DNA?

The ends of linear DNA present replication problems. Signup and view all the answers

Which of the following best describes the nature of eukaryotic replication origins?

They can have multiple replicons for rapid cell division. Signup and view all the answers

Study Notes

Transformation

Griffith discovered that genetic material could be transferred from one bacteria to another.
He observed a transfer of virulence from dead S strain bacteria to living R strain of bacteria.
He called this transformation.
He did not know the mechanism.
Transformation involves the physical transfer of genetic material between cells.

Avery, MacLeod, & McCarty

Repeated Griffith’s experiment using purified cell extracts.
Used protein digesting enzymes and DNA digesting enzymes.
Removal of all protein from the transforming material did not destroy its ability to transform R strain cells
DNA-digesting enzymes destroyed all transforming ability.
DNA is the genetic material, at least in bacteria.

Hershey & Chase

Used bacteriophages to investigate genetic material.
Bacteriophages infect bacteria.
Composed of only DNA and protein.
Wanted to determine what molecule is injected into bacteria.
Radioactive phosphorus (32P) was used to label bacteriophage DNA.
Radioactive sulfur (35S) was used to label bacteriophage protein.
Only the bacteriophage DNA entered the bacteria – DNA is the genetic material.

James Watson and Francis Crick

Determined the structure of DNA using evidence from Chargoff, Franklin, and others.
Not themselves involved in any experimentation.
Each DNA molecule was made up of two intertwined chains of nucleotides - a double helix.

Structure of DNA

Each strand of DNA is made up of a phosphodiester backbone.
The backbone is a repeating sugar and phosphate units joined by phosphodiester bonds.
A single strand of DNA extends in a 5’ to 3’ direction.

Double Helix of DNA

Two strands of DNA are arranged as a double helix.
This forms two grooves: the larger major groove, and the smaller minor groove.
Strands are connected via hydrogen bonds between bases on opposite strands.
Specific base-pairing: A-T, and G-C.
The helix has a consistent diameter and is stable due to the additive property of thousands of low-energy hydrogen bonds.

Base pairing

Base pairing is complementary between A and T, and G and C.
A forms two hydrogen bonds with T.
G forms three hydrogen bonds with C.
Two strands of DNA are not identical, but are complementary.

Antiparallel configuration

Each phosphodiester strand has an inherent polarity.
One end terminates in 3′ OH.
One end terminates in 5′ PO4.
The two strands of a single DNA molecule have opposite polarity to one another.

DNA replication

Requires a parental DNA molecule to copy.
Requires enzymes to do the copying (replication).
Replication is the process by which a DNA molecule is copied.

Three possible DNA replication models

Conservative model: parental strands remain intact; new DNA copies consist of all new molecules.
Semiconservative model: daughter strands each consist of one parental strand and one new strand.
Dispersive model: new DNA is dispersed throughout each strand of both daughter molecules after replication.

Meselson and Stahl

Performed an experiment to determine the correct model of DNA replication.
Grew bacteria in a heavy isotope of nitrogen 15N so that the DNA was denser than normal DNA.
Switched to media containing lighter 14N.
Extracted DNA from bacteria at various time intervals and centrifuged to separate by weight.
Supported the semiconservative model of DNA replication.

Eukaryotic Replication

More complex than prokaryotic replication.
Larger amount of DNA in multiple chromosomes.
Linear structure (versus circular chromosomes).

Eukaryotic Replication uses multiple origins

Multiple replicons – multiple origins of replications for each chromosome.
Not sequence specific; can be adjusted for example early in development.

Eukaryotic Replication fork is more complex

Before S phase, helicases are loaded onto possible replication origins, but not activated.
During S phase, a subset of these are activated, and the rest of the replisome assembled.
Priming uses a complex of both DNA polymerase α and primase.
DNA polymerase epsilon (Pol ε) synthesizes leading strand.
DNA polymerase delta (Pol δ) synthesizes lagging strand.

Enzymes that are similar between eukaryotes and archaea, but different from those in prokaryotes:
- DNA polymerases
- Replicative helicases
- Primases

Linear chromosomes have specialized ends

Telomeres are specialized structures found on the ends of eukaryotic chromosomes.
Composed of specific repeat sequences.
Protect ends of chromosomes from nucleases.
Maintain the integrity of linear chromosomes.
Not made by the replication complex.

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Description

Explore the foundational experiments in molecular genetics that revealed how genetic material is transferred between bacteria. This quiz covers Griffith's transformation, Avery's identification of DNA as the genetic material, and the Hershey-Chase experiment involving bacteriophages. Test your understanding of these key concepts in genetics.