Module 4 DNA/RNA Structure

Which strain of S. pneumoniae was virulent?

S strain

What does Griffith's experiment illustrate?

Bacteria can take up genetic information from their environment

Which of the following illustrates the sequence of events leading to the confirmation of nucleic acids as the genetic material of the cell?

Miescher's discovery, Griffith experiments, Avery experiments, Hershey-Chase experiments

Avery's work retested Griffith's hypothesis using a test tube assay. What was the purpose of Avery's experiment?

To determine the macromolecule responsible for genetic information

Hershey and Chase utilized phages in their research, because phages _____.

contain only nucleic acids and proteins

After a viral infection, radioactive phosphorus was found in the bacterial cells. This result occurred because _____.

Only viral DNA was inserted into the host cell

What is the shape of DNA called?

double helix

In DNA, adenine pairs with…

thymine

Which of the following is not a component of a nucleotide?

glucose

In DNA, guanine pairs with…

cytosine

If one strand of DNA is CGGTAC, the complementary strand would be:

GCCATG

If one strand of DNA is AGCTGA, the complementary strand would be:

TCGACT

What is a nucleotide composed of?

• sugar

• sugar phosphate backbone

• nitrogenous base

The creation of a phosphodiester bond involves the removal of ____ from the nucleotides:

water

The bonds in the sugar-phosphate backbone are _________, and the bonds between the nitrogenous bases are ________.

strong; weak

The 3' end of a DNA strand has a phosphate at the end.

False

Why does a DNA strand only "grow" in the 5' to 3' direction?

because DNA polymerase can only add nucleotides to the 3' end of the molecule

The DNA template strand is 5' ATCGGTTAACTAAAG 3'. What is the new strand?

3' TAGCCAATTGATTTC 5'

If the parent DNA strand is 5' ATCGATACTAC 3', what will the daughter strand be?

3' TAGCTATGATG 5'

Hydrogen bonds hold base pairs together in DNA. Which enzyme severs these bonds during replication?

Helicase

A mutation has caused a change in the shape of the topoisomerase enzyme. This would most likely affect _____.

the tension in the DNA double helix

Incorrect base pairing does occur during the replication process. However, most of these errors are corrected. Which enzyme is most directly involved in fixing these errors?

DNA polymerase

Which of the following is not true regarding DNA and RNA?

Only DNA bases form hydrogen bonds.

Which of the following is true regarding uracil?

It forms 2 hydrogen bonds with adenine

DNA is more stable than RNA because _____.

it can form a double helix and contains the base thymine

How does RNA differ from DNA?

RNA has one chain of nucleotides, DNA has two.

Which base is found in RNA but not DNA?

Uracil

DNA _____; RNA _____.

is always a double helix; forms many shapes

What is the role of DNA?

Stores and transmits genetic information that provides instructions for building proteins and controlling cell activities.

Meaning of "DNA is evolution."

Evolution depends on heritable changes. Since DNA stores hereditary information, changes in DNA provide the variation needed for evolution.

DNA and evolution

DNA is the basis of evolution because mutations and genetic variation in DNA can be inherited and acted on by natural selection over time.

Definition: Genes

sequences of DNA that control how bodies are shaped and how organisms react to environmental factors.

What molecule builds genes?

Genes are made of DNA.

What is the purpose of genes?

Genes contain coded instructions for making proteins. These proteins help determine traits and control how cells function.

How many genes control one phenotype?

A single gene can control one phenotype

How do genes outlive individuals?

Genes are passed from parents to offspring through reproduction, allowing genetic information to continue across generations.

Why genes are important

Genes are important because they contain the instructions for protein production, inheritance, growth, repair, and cell regulation.

Definition: Genotype

The genetic makeup (genes) possessed by an organism

Definition: Phenotype

The physical and observable manifestations (characteristics) of a gene

Phenotypes can be controlled by _____.

multiple genes or a single gene.

Friedrich Miescher (1869)

Discovered nucleic acid in the nucleus of cells.

How did Griffith's Experiment demonstrate the process of bacterial transformation?

Griffith proved that a non-virulent strain of bacteria could become virulent upon exposure to dead individuals of a virulent strain.

What did Frederick Griffith study when trying to find a vaccine?

Streptococcus pneumoniae (bacteria)

What did Frederick Griffith discover?

Bacterial transformation by testing how different bacterial strains affected mice.

What is bacterial transformation?

The process in which bacteria take in external genetic material and are genetically changed by it.

Observable trait of S-Strain Bacteria-

Bacterial colonies have a smooth edge

Hypothesis for Griffith's Experiment

If DNA from dead virulent S-strain bacteria is transferred to living R-strain bacteria, the R-strain bacteria will become virulent.

Observable trait of R-Strain Bacteria-

Bacterial colonies have a rough edge

What was the result of injecting live R strain bacteria into mice?

The mice lived

What was the result of injecting live S strain bacteria into mice?

The mice died

What was the result of injecting live R-strain bacteria and heat-killed S-strain bacteria into mice?

The mice died

How would the Griffith experiment results have changed if bacterial transformation did not exist?

If bacterial transformation did not exist, the R-strain would not gain genetic material from the S-strain, so the mice would survive.

Definition: Virulent

Something extremely severe, harmful, or infectious.

Independent Variable in Griffith's Experiment

The type of bacteria injected into the mice.

Dependent Variable in Griffith's Experiment

The survival of the mice (alive or dead).

What did Griffith conclude from his experiment?

That a 'transforming factor' from the dead S-strain transformed harmless R-strain bacteria into virulent bacteria.

Why did the combination of living R-Strain and dead S-Strain kill mice?

DNA from the dead S-strain entered the living R-strain bacteria, transforming them into virulent bacteria capable of causing disease.

Why was Griffith's experiment important?

It showed that hereditary information could be transferred between cells and helped lead to the discovery that DNA is genetic material.

Who is Erwin Schrödinger?

A Nobel Prize-winning physicist for his work on Quantum Mechanics

What was Schrödinger's proposal on "aperiodic crystal"?

That it contained genetic information due to the arrangement of its covalent bonds.

Definition: Aperiodic Crystal

A molecule that does not repeat its structure, allowing it to contain large amounts of information.

Who was influenced by the aperiodic crystal idea?

James Watson and Francis Crick

DNA as an Information Code

DNA can store an infinite amount of information through varying sequences of four nucleic acids.

What did most scientists believe the chemical that transformed bacteria was?

a protein

Which scientists demonstrated that DNA is the transforming principle by testing which molecules from heat-killed S bacteria could still transform R bacteria.

Avery, MacLeod, and McCarty

How did Avery and his colleagues prove protein was not the transforming factor?

By destroying proteins in S-strain extracts and finding that transformation still occurred.

How did Avery and his colleagues prove DNA was the transforming factor?

Using DNA depolymerases to destroy DNA prevented transformation, and the mice lived. This showed that DNA, not protein, caused transformation.

How did Avery rule out protein as the transforming factor?

He added an enzyme that destroys proteins to the heat-killed S-strain bacteria and mixed it with the live R-strain bacteria. The R-strain bacteria still transformed into S-strain bacteria, so protein was not the transforming factor.

What contribution did Erwin Chargaff make to the modern understanding of DNA structure?

He discovered base-pair rules, that DNA contains equal amounts of adenine and thymine, and equal amounts of guanine and cytosine.

What was the significance of Chargaff's work?

Chargaff's findings helped Watson and Crick determine that DNA bases pair specifically, which supported the double-helix model.

What is a test tube ASSAY?

A laboratory test done outside a living organism to observe a biological reaction under controlled conditions.

How do test tube assays work?

A test tube assay allows scientists to compare different treatments of substances under controlled conditions to observe specific reactions.

What were the benefits of Avery's use of an ASSAY over Griffith's experiment?

Avery's assay was more precise, easier to control, faster to repeat, and better at identifying which molecule caused transformation, rather than relying on whole mice.

Can you predict cytosine from thymine alone?

No. You can predict adenine from thymine because A pairs with T, but cytosine can only be predicted if the total base composition is known.

How does X-ray diffraction work?

X-ray diffraction works by shooting subatomic particles into a substance. The molecules diffract at specific angles and strike photo paper, producing a diffraction pattern.

What was the role of X-ray Diffraction in determining the structure of DNA?

It was determined that DNA has a double-helical structure by interpreting the pattern.

What was the significance of X-ray diffraction being used in the search for the structure of DNA?

X-ray diffraction allowed scientists to see DNA's dimensions and double-helix structure, helping them build an accurate model of DNA.

The role of Rosalind Franklin's data was_____.

Franklin's X-ray diffraction images, especially Photo 51, gave key evidence that DNA was a double helix. This allowed Watson and Crick to begin building models of the structure.

Describe the relationship between the polysaccharide found in the capsule and the virulence of the pneumococci.

Encapsulated pneumococci were more virulent because the polysaccharide capsule protected them from the host's immune system.

Definition: Bacteriophage

a virus that infects bacteria and uses the bacterial cell to make more viruses.

What is the structure of a bacteriophage?

It has a protein coat surrounding its genetic material (DNA) and attaches to bacteria to inject it.

Why did Hershey and Chase use bacteriophages in their experiment?

Bacteriophages contain only DNA and protein, making them useful for determining which molecule entered the bacteria and carried genetic information.

What radioactive element did Hershey and Chase use to label DNA in their experiment?

Radioactive phosphorus

What radioactive element did Hershey and Chase use to label protein in their experiment?

Radioactive sulfur

What was the purpose of the Hershey-Chase Experiment?

To see which entered bacteria: DNA or protein.

What were the results of the Hershey-Chase experiment?

Radioactive DNA entered the bacteria, while most of the radioactive protein remained outside, indicating that DNA is the genetic material.

How did Hershey-Chase prove DNA was genetic material?

Only radioactive phosphorus (DNA) entered the bacteria, while radioactive sulfur (protein) did not, proving DNA carries genetic information.

Human DNA is made up of approximately 30% thymine. What percentage of human DNA is made up of guanine?

Approximately 20%

What characteristics were known about DNA prior to Watson and Crick building their DNA model?

DNA was known to self-replicate, contain genetic information, consist of nucleotides with sugar, phosphate, and nitrogen bases, follow Chargaff's rules, and have a helical shape from X-ray data.

3 parts of a nucleotide

A nucleotide is made of a phosphate group, a 5-carbon sugar, and a nitrogenous base.

Nucleotides in DNA

Each nucleotide contains deoxyribose sugar, a phosphate group, and a nitrogenous base

Major chemical features of DNA

consists of two antiparallel strands twisted into a double helix with a sugar-phosphate backbone and four nitrogenous bases: adenine, thymine, guanine, and cytosine.

DNA double helix

a twisted ladder shape, made of two antiparallel strands held together by hydrogen bonds between bases.

What forms the backbone of DNA?

Alternating deoxyribose sugars and phosphate groups

What type of bonds link the sugars and phosphate groups in the DNA backbone?

Covalent bonds

Base Pairing in DNA

Adenine pairs with thymine using 2 hydrogen bonds, while guanine pairs with cytosine using 3 hydrogen bonds.

Purines

Nitrogenous bases with two rings.

Pyrimidines

Nitrogenous bases with one ring.

Which nitrogenous bases are purines?

Adenine and Guanine

Which nitrogenous bases are pyrimidines?

Cytosine and Thymine