6.1.1

The Search for the Genetic Material

●In the early 1900s, scientists struggled to identify
which molecule contains the genes that are
involved in inheritance.

●In the mid 1800s, Gregor Mendel, the father of
genetics, discovered that “heritable factors” were
passed down from parent to offspring.

●In 1910, Thomas Hunt Morgan proved that genes
are carried on chromosomes and are the
mechanical mechanism of inheritance.

●This narrowed down the identity of the genetic
material to the two types of molecules found in
chromosomes: proteins and DNA.

Drag and Drop

Gregor Mendel discovered ​

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, while Thomas Hunt Morgan ​ ​

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Heritable Factors

proved that genes are carried on chromosomes

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​ ​ ​

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Transformation is defined as a change in genotype and phenotype due to the assimilation of foreign DNA by a cell

In 1928, Frederick Griffith experimented with a bacterium that causes pneumonia in mammals. He used two strains of the bacteria, a pathogenic
(disease-causing) one, and a nonpathogenic (harmless) strain.

Griffith’s
Experiment

In 1944, three scientists (Avery, McCarty, and MacLeod) announced that the transforming “principle” from Griffith’s experiment was DNA.

Avery-McCarty-Macleod Experiment

Alfred Hershey and Martha Case in 1952, who performed experiments that showed DNA was the genetic material of a bacteriophage known as T2.

Hershey-Chase Experiment

• He found that when the pathogenic bacteria were killed with heat and then
  mixed with living nonpathogenic bacteria, the living cells became pathogenic.

• He called this phenomenon transformation, now defined as a change in genotype and phenotype due to the assimilation of foreign DNA by a cell.

• Griffith did not know what the transforming “principle” was. It could have been
  carbohydrates, proteins, or nucleic acids from the heat killed bacteria cells.

Griffith’s Experiment

Griffith’s
Experiment

●Bacteria of the “S”
(smooth) strain are
pathogenic because
they contain a sugar
capsule that protects
them from an
animal’s immune
system.

●The “R” (rough) strain
lack a capsule and
are nonpathogenic.

Multiple Choice

What was the primary objective of Griffith's experiment?

• To study the role of DNA in bacterial transformation

• To study the role of RNA in bacterial transformation

• To study the role of proteins in bacterial transformation

• To study the role of lipids in bacterial transformation

Multiple Choice

What organism did Griffith use in his experiment?

• E. coli

• S. pneumoniae

• S. aureus

• L. lactis

• In their experiment, they isolated different solutions containing the heat-killed S bacteria cells and examined in which solutions transformation still occurred
  with the R strain bacteria.

• Only the solutions with the S strain DNA still intact led to transformation of the R strain bacteria.

• The scientific community was very skeptical of these findings. Many scientists still supported the theory that proteins were the genetic material.

Avery-McCarty-Macleod Experiment

Avery-McCarty-
Macleod Experiment

Multiple Choice

What was the primary objective of the Avery-McCarty-Macleod experiment?

• To study the role of DNA in bacterial transformation

• To study the role of RNA in bacterial transformation

• To study the role of proteins in bacterial transformation

• To study the role of lipids in bacterial transformation

Multiple Choice

Which of the following statements accurately describes the conclusion drawn from the Avery-McCarty-Macleod experiment?

• DNA is not the genetic material responsible for bacterial transformation

• Proteins are the genetic material responsible for bacterial transformation

• RNA is the genetic material responsible for bacterial transformation

• DNA is the genetic material responsible for bacterial transformation

• A bacteriophage (or just “phage”) is a virus that infects bacteria.

• T2 viruses are composed of almost entirely DNA and protein. When they infect a bacteria cell (specifically E. Coli), T2 reprograms its host cell to produce viruses, until the cell finally ruptures.

• Their experiment involved radioactively labeling the proteins and DNA of T2 viruses and seeing which of the two were found in the bacteria cells that were infected by the virus.

• The results showed that the viruses transferred their DNA, not their proteins, into the bacteria cells.

Hershey-Chase Experiment

Hershey-Chase
Experiment

Multiple Choice

What organism did Hershey and Chase use in their experiment?

• Escherichia coli

• Streptococcus pneumoniae

• Bacillus subtilis

• T2 bacteriophage

Multiple Choice

How did Hershey and Chase label the DNA and proteins in the T2 bacteriophage?

• They labeled the DNA with radioactive sulfur and the proteins with radioactive phosphorus.

• They labeled the DNA with radioactive phosphorus and the proteins with radioactive sulfur

• They labeled both the DNA and the proteins with radioactive sulfur

• They labeled both the DNA and the proteins with radioactive phosphorus.

Multiple Choice

What was the conclusion of the Hershey-Chase experiment?

• DNA is the genetic material responsible for inheritance and bacterial transformation.

• Proteins are the genetic material responsible for inheritance and bacterial transformation.

• RNA is the genetic material responsible for inheritance and bacterial transformation

• Lipids are the genetic material responsible for inheritance and bacterial transformation

Multiple Choice

What was the significance of the Avery-McCarty-Macleod experiment in the field of genetics?

• It demonstrated that DNA is the genetic material responsible for bacterial transformation

• It established the Central Dogma of molecular biology

• It provided evidence for the semi-conservative model of DNA replication

• It confirmed the existence of the genetic code

Multiple Choice

Which of the following statements accurately describes the result of Griffith's experiment?

• The virulent strain of S. pneumoniae transformed into the non-virulent strain when heat-killed

• The non-virulent strain of S. pneumoniae transformed into the virulent strain when heat-killed

• Both the virulent and non-virulent strains of S. pneumoniae transformed into a new strain when heat-killed

• The virulent strain of S. pneumoniae remained virulent even when heat-killed

3 different experiments that support DNA and transformation

Determining the structure of
DNA

By the 1950s, it was already known that DNA is a polymer of nucleotides, but the specific shape and 3-D structure of DNA was still unknown.

Nucleotide components:

-Nitrogenous base

-A five-carbon sugar

-A phosphate group

Nucleotides

Each nucleotide is composed of three parts:

1.A phosphate group

2.

A pentose (5-carbon) sugar

a.

Deoxyribose

i.The carbon atoms in the pentose sugar are
numbered 1’ (“1 prime”) to 5’

ii.The nitrogenous base is bound to the 1’
carbon and the phosphate group is bound to
the 5’ carbon.

3.

A nitrogen-containing (nitrogenous) base

(DNA)

(RNA)

This shows the sugar that is in RNA vs the sugar that is in
DNA. You can see that they have a similar compositions but
the 2nd Carbon is different

There are two families of nitrogenous bases

Pyrimidines are bases with one ring
●Cytosine (C)

●Thymine (T)

●Uracil (U)

Purines are bases with two rings
●Adenine (A)

●Guanine (G)

Polynucleotides

• Nucleotides are joined together by a
  series of dehydration reactions to form a
  strand (polymer) called a polynucleotide.

Covalent bonds are formed between the 3’ carbon (of the pentose sugar) of one nucleotide and the phosphate group of the next nucleotide.

• The link between the 3’ carbon of one
  nucleotide and the 5’ carbon of the next
  nucleotide is called a phosphodiester
  linkage (Shown in diagram B)

New

Covalent

Bond

Diagram A

Diagram B

Polynucleotides

●Polynucleotides have two ends:

○ 3’ (hydroxyl) end

■nucleotides are added to the 3’
end of the growing strand.

○ 5’ (phosphate) end.

Phosphodiester

linkage

New nucleotides

added to the 3’ end

Multiple Choice

Monomer (subunit) of nucleic acids made up of a 5-carbon sugar, a phosphate group, and nitrogenous base.

• Nucleus

• Carbohydrate

• Nucleotide

• Phosphate group

Multiple Choice

Group that covalently bonds to the deoxyribose sugar along the sides of DNA

• Phosphate group

• Nitrogenous Bases

• Hydrogen Group

• Ladder steppers

Multiple Choice

Double ring nitrogenous bases. (A and G)

• Pyrimidines

• Purines

• Purina

• Puppy chow

Multiple Choice

Single-ring nitrogenous bases (C and T)

• Pyrimidine

• Purine

• Puppy Chow

• Purina

Multiple Choice

What are the components of a nucleotide?

• nitrogen base, phosphate group, and 5-carbon sugar

• 5 carbon sugar, purine, and pyrimidine

• nitrogen base and a phosphate group

• DNA, phosphate group, monosaccharide

Multiple Choice

Process of forming bonds by removing water molecules

• Dehydration

• Hydrolysis

Multiple Choice

Dehydration with nucleotides form what?

• Carbohydrate

• Nucleic Acid

• Protein

• Triglyceride

Multiple Choice

Type of bond formed when polynucluotides are formed

• Ester Linkage

• Peptide Bond

• Phosphodiester linkage

Explanation Slide...

The bond found between amino acids in a protein is a called a peptide bond. This is a type of covalent bonds specific to proteins. This is also why we call a protein a “polypeptide” since it has multiple peptide bonds.

Explanation Slide...

During a dehydration reaction, the water is removed to bind together a monomer with a growing polymer. The nucleotide is the monomer of nucleic acids.

Explanation Slide...

During dehydration, water is released forming a bond between monomers to form the polymer.