Chapter 13

Until the 1940s, scientists thought __________ were the source of heritable information.

Proteins

What does DNA stand for?

Deoxyribonucleic acid

What are the two chemical components of chromosomes?

Proteins and DNA

Why did researchers originally think that proteins were genetic material?

The functions of proteins actually help in synthesizing genetic information, but scientists confused this with the proteins being the hereditary information themselves

What is the difference between the virulent and nonvirulent strains of Streptococcus Pneumonia studied by Frederick Griffith?

Virulent strains caused the disease, while nonvirulent strains did not

What was the purpose of Griffith's studies?

To create a vaccine for pneumonia

How did Griffith determine that hereditary information could be transmitted between two organisms in an unusual manner?

He injected four mice with different strains of the pneumonia; a virulent strain (S-strain), a nonvirulent strain (R-strain), a heat-killed virulent strain, and a heat-killed virulent strain mixed with a nonvirulent strain

Define transformation.

A change in the genotype and phenotype due to the assimilation of external DNA by a cell

What did Oswald Avery determine to be the transforming factor?

DNA

What was Avery's experimental approach?

He continued Griffith's work, and removed enzymes/isolated proteins to prove that DNA carried genetic information

What are the four main components of a bacteriophage?

Head, tail sheath, tail fiber, DNA

How does a bacteriophage destroy a bacterial cell?

1. Attaches to the bacterial cell with its tail

2. Injects its genetic material into the bacterial cell

3. The genes tell the bacterial cell to reproduce viral offspring like the bacteriophage

How did Hershey and Chase "label" viral DNA and viral protein so that they could be distinguished?

They used radioactive phosphorus (in nucleotides) and radioactive sulfur (in amino acids) so they could trace the movement of the viral DNA/proteins

What conclusion did Hershey and Chase come to based on their observations?

That DNA is the hereditary material, not proteins

What are the four nitrogenous bases that make up DNA?

Adenine, thymine, cytosine, guanine

What are Chargaff's rules state?

That adenine bonds with thymine and cytosine bonds with guanine

How did Chargaff compose his rules?

Through careful experimentation

What are the three components of a nucleotide?

Sugar, phosphate group, nitrogenous base

Who are the two men who built the first molecular model of DNA and shared the 1962 Nobel Prize for the discovery of its structure?

Watson and Crick

What was the role of Rosalind Franklin in the discovery of the double helix?

She used x-ray crystallography (x-ray diffraction images) and her photo 51 revealed the double helix shape

What is the difference between purines and pyrimidines?

Purines have a double ring of carbon and hydrogen, while pyrimidines only have one

What two nitrogenous bases are purines?

Adenine and thymine

What two nitrogenous bases are pyrimidines?

Cytosine and guanine

How did Watson and Crick's model explain the basis for Chargaff's rules?

They demonstrated that because of the structures of purines and pyrimidines, purines must bond with purines, and pyrimidines with pyrimidines, which supported adenine bonding with thymine and cytosine bonding with guanine

What nitrogenous base replaces thymine in RNA?

Uracil

Is adenine found in DNA, RNA, or both?

Both

Is thymine found in DNA, RNA, or both?

DNA

Is cytosine found in DNA, RNA, or both?

Both

Is guanine found in DNA, RNA, or both?

Both

Is uracil found in DNA, RNA, or both?

RNA

What is the 5' end of the nucleotide?

The 5-carbon sugar

What is the 3' end of the nucleotide?

The third carbon in the phosphate group

What is meant by the two strands of DNA being antiparallel?

The sugar on one strand is across from the phosphate on the other strand, and vice versa

What does the semiconservative model of replication state?

Two strands of DNA separate and each new strand is made up of one parent strand and one new strand

Who performed the experiments that confirmed the correct mechanism of DNA replication?

Meselson and Stahl

How did Meselson and Stahl create "heavy" DNA for their experiments?

They used radioactive nitrogen

Who performed the experiments that confirmed the correct mechanism of DNA replication?

Meselson and Stahl

How did Meselson and Stahl create "heavy" DNA for their experiments?

They used radioactive nitrogen

What did Meselson and Stahl prove through their experimentation?

That the semiconservative model is the correct mechanism of DNA replication

What are origins of replication?

Sites with short stretches of DNA that have a certain sequence of nucleotides where DNA replication begins

What is the difference between leading and lagging strands of DNA?

Leading strands are continuously built from the 5' end to the 3' end, while lagging strands are built in the opposite direction in fragments

What is the direction of synthesis of the new strand?

5' to 3'

What are Okazaki fragments?

Segments of the lagging strand that are 100-200 nucleotides long

What does helicase do?

Untwists and separates strands

What do single-strand binding proteins do?

Hold DNA strands apart

What does primase do?

Synthesizes RNA primer

What does DNA polymerase III do?

Adds DNA nucleotides to new strands

What does topoisomerase do?

Relieves the strain caused by unwinding

What does DNA ligase do?

Joins DNA fragments together

What does DNA polymerase I do?

Removes RNA primer and replaces it with DNA

List the steps that occur in the synthesis of a new strand of DNA.

1. Helicase unwinds DNA

2. Single-strand binding proteins stabilize the unwound DNA

3. Primase lays down the RNA primer

4. The leading strand is built by DNA polymerase III from the 5' end to the 3' end

5. The lagging strand is built by DNA polymerase III from the 3' end to the 5' end in fragments

6. Ligase links the new DNA fragments together

7. DNA polymerase I removes RNA primer