BIOL 330 Exam 1: Experiments

The first solid evidence associating a specific gene with a specific chromosome came in the early 1900s, with his early experiments providing convincing evidence that the chromosomes are the location of Mendel’s heritable factors, who founded this?

Thoman Hunt Morgan

What was Frederick Griffith’s transformation experiment (1927)?

A key experiment showing that genetic material can be transferred between bacteria; specifically, it demonstrated that non-virulent bacteria could become virulent when exposed to heat-killed virulent strains

In Griffith’s experiment, when the living IIIS (virulent) was injected into the mouse what happened? What happened when the living IIR (avirulent) was injected? What happened when the heat-killed IIIS was injected?

IIIS = mouse dies

IIR = mouse lives

Heat-killed IIIS = mouse lives

In Griffith’s experiment, he injected living IIR and heat-killed IIIS into a mouse, what happened? What did this find?

The mouse died, but tissue analyzed found that living IIIS was recovered

• Transformation occurred

What did Griffith’s experiment find?

Griffith's experiment found that genetic material can be transferred from heat-killed virulent bacteria to avirulent bacteria, transforming the latter into virulent forms

• other words, chemical component of cells could introduce a new, heritable trait to a cell

Who showed avirulent strains of Diplococcus pneumoniae could be transformed to virulent strain?

Frederick Griffith

What was Oswald Avery, Maclyn MacLeod, and Colin McCarty (1944) experiment?

Avery, MacLeod, and McCarty demonstrated that DNA is the transforming principle by purifying DNA from heat-killed IIIS bacteria and showing it could transform IIR bacteria into virulent IIIS

What is the difference between Griffith’s experiment (1927) vs Avery, MacLeod, and MCarty’s (1944)

Griffith’s experiment identified the transforming principle, while Avery, MacLeod, and McCarty confirmed that DNA is the specific substance responsible for transformation

How did Avery, MacLeod, and McCarty’s experiment go about?

They purified DNA from heat-killed IIIS bacteria, mixed it with IIR bacteria, and analyzed the transformation of IIR bacteria into virulent IIIS.

In Avery, MacLeod, and McCarty’s (1944) experiment, what happened when they used the degredation enzymes?

The degrading enzymes showed that only DNase eliminated the transforming activity, confirming that DNA was the genetic material responsible for transformation

What did Avery, MacLeod, and McCarty’s experiment demonstrate?

Demonstrated transforming principle was DNA, not protein

• the first direct experimental proof that DNA is biomolecule responsible for hereditary

What was Hershey and Chase (1952) experiment?

The Hershey and Chase experiment used radioactively labeled DNA and protein in bacteriophages to determine that DNA, not protein, is the genetic material that is passed into bacterial cells during infection.

Who determined what:

Transformation principle?

DNA is the transforming activity?

DNA is the genetic material, not protein?

Frederick Griffith came up with the transformation activity

Avery, MacLeod, and McCarty identified that DNA is the transforming principle

Hershey and Chase confirmed that DNA, not protein, is the genetic material

What did Hershey and Chase use in their experiments?

Used Escherichia coli and bacteriophage T2

Used radioisotopes 32P and 35S

What was the fundamental concepts of Hershey and Chase’ experiment?

• DNA but not protein carries the genetic information for a new generation of phage

• Label DNA P because it has phosphorus not sulfur in its structure

• Label protein S because it has sulfur not phosphorus

What are the steps that went down in Hershey and Chase’ experiment?

1. Infect E. coli with T2 phage labeled with either 32P or 35S.

2. Allow phages to inject their genetic material into the bacteria.

3. Agitate (shake) to separate phages from bacteria.

4. Analyze the bacterial cells to detect which label was present, confirming that DNA entered the cells.

What are the steps that went down in Frederick Griffith’s experiment?

1. Injected mice with types of Streptococcus pneumoniae (rough and smooth variants)

2. Observed that smooth strain caused pneumonia and death, while rough strain did not

3. Mixed heat-killed smooth strain with live rough strain

4. Noted that mice developed pneumonia, demonstrating transformation

What are the steps that went down in Avery, MacLeod, and McCarty’s experiment?

1. Treated heat-killed smooth strain of Streptococcus pneumoniae with enzymes to degrade proteins, RNA, or DNA.

2. Mixed treated smooth strains with live rough strains.

3. Only the samples where DNA was not degraded resulted in transformation, confirming DNA as the transforming principle.

What did Hershey and Chase demonstrate through their experiment?

They demonstrated that most of the 32P labeled DNA had been transferred into the bacterial cell following adsorption

• DNA alone contains all necessary information for production of mature viruses

Could Hershey and Chase have used a radioactive isotope of carbon instead of 32P? Why or why not?

No, because carbon is a component of both DNA and protein, making it unsuitable for distinguishing between genetic material and proteins

Who demonstrated that RNA serves as genetic material for certain viruses?

Tobacco Mosaic Virus (TMV) by Heinz Fraenkel-Conrat and Bea Singer.

What is the virus reconstitution experiment?

The virus reconstitution experiment involves combining purified viral RNA with a protein coat to demonstrate that RNA alone can instruct the synthesis of new virus particles, confirming RNA's role as genetic material.

Who used a technique called X-ray crystallography to study molecular structure?

Maurice Wilkins and Rosalind Franklin

What is the difference between Rosalin Franklin and Watson and Crick?

Franklin: provided the data (critical evidence)

Watson and Crick: proposed that there were two outer sugar-phosphate backbones, with the nitrogenous bases paired in the interior, creating the double helix structure of DNA

Franklin’s X-ray crystallographic images of DNA allowed Watson and Crick to deduce that DNA was?

Helical

The X-ray images also enabled Watson to deduce the ____ of the helix and the spacing of the ______

Width and nitrogenous bases

Watson and Crick’s semiconservative model of replication predicts that when a double helix replicates?

Each daughter molecule will have one old strand (parent molecule) and one newly made strand

Why did Max Delbruck not believe the semiconservative model possible?

Because they reasoned that a tightly bound double-stranded helix of DNA should not be able to separate into its two constituent strands

What was Meselson and Stahl (1958) experiment?

A \experiment that used isotopes of nitrogen to demonstrate the semiconservative mechanism of DNA replication, showing that each newly synthesized DNA molecule contains one old strand and one new strand.

How did Meselson and Stahl’s experiment go about? Each step?

First, bacteria were grown in a medium containing heavy nitrogen (N-15), allowing them to incorporate the heavy isotope into their DNA

Second, the bacteria were transferred to a medium with normal (light) nitrogen (N-14) and allowed to replicate

Third, after each generation, density gradient centrifugation was performed to separate the DNA based on density, revealing the presence of hybrid DNA containing one heavy and one light strand after one replication cycle, thus supporting the semiconservative model

After the first round of replication, Meselson and Stahl observed?

One intermediate-density band (hybrid DNA containing one 15-N strand and one 14-N strand)

Meselson and Stahl could be confident of what conclusions?

• DNA replication is NOT conservative or dispersive but semiconservative

• If it had been conservative: one heavy band + one light band

• If had been dispersive: only one intermediata3e band that gradually becomes lighter