Biology Chapter on Genetic Experiments

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What was the main objective of the Hershey-Chase experiment?

To study the life cycle of bacteriophages

To determine if RNA was the genetic material

To confirm the role of DNA in inheritance (correct)

To demonstrate the structure of proteins

The Hershey-Chase experiment concluded that protein was the genetic material in phages.

False

Which bacterial strain was used by Hershey and Chase in their experiments?

Escherichia coli

According to Chargaff's rules, Adenine (A) is always equal to _____ (T).

Thymine Signup and view all the answers

What radioactive isotope was used to label DNA in the Hershey-Chase experiment?

32P Signup and view all the answers

Match the following terms with their definitions:

Bacteriophage = A virus that infects bacteria. Chargaff's Rules = Adenine = Thymine, Guanine = Cytosine. Transforming Principle = The substance responsible for genetic transformation. Progeny Phages = Newly formed phages that can infect other cells. Signup and view all the answers

What did Fraenkel-Conrat and Singer discover about RNA?

RNA is the genetic material in TMV. Signup and view all the answers

What happens to the bacterial cell once the progeny phages are formed?

The bacterial cell lysis, releasing the newly formed phages. Signup and view all the answers

DNA is made up of ribonucleotides.

False Signup and view all the answers

What structural feature of DNA allows it to form a double helix?

The antiparallel arrangement of polynucleotide strands. Signup and view all the answers

The _____ forms the backbone of nucleic acids, consisting of alternating sugar and phosphate groups.

polynucleotide strand Signup and view all the answers

Match the following components with their roles in DNA structure:

Adenine = Purine nitrogenous base Thymine = Pyrimidine nitrogenous base Deoxyribose = Sugar in DNA nucleotides Antiparallel strands = Opposing directionality of DNA strands Signup and view all the answers

What phenomenon did Fred Griffith observe in 1928?

Transformation Signup and view all the answers

Avery's experiments confirmed that proteins were responsible for the transforming activity.

False Signup and view all the answers

What did the transforming substance resemble chemically according to Avery's research?

DNA Signup and view all the answers

In Griffith's experiments, the virulent form of Streptococcus pneumoniae was referred to as the ___ form.

smooth Signup and view all the answers

Match the following scientists with their contributions:

Fred Griffith = Discovery of transformation Oswald Avery = Identification of the transforming substance Colin MacLeod = Co-researcher with Avery Maclyn McCarty = Co-researcher with Avery Signup and view all the answers

Which of the following processes describes nonvirulent bacteria acquiring genetic virulence?

Transformation Signup and view all the answers

Griffith proposed that a 'transforming principle' existed within dead virulent bacteria.

True Signup and view all the answers

What role did DNA-degrading enzymes play in Avery's experiments?

They abolished the transforming activity. Signup and view all the answers

Griffith isolated two strains of S. pneumoniae known as the smooth (S) and ___ (R) forms.

rough Signup and view all the answers

Which of the following supports the conclusion that DNA is the genetic material?

Absorption of ultraviolet light Signup and view all the answers

Study Notes

Chapters 10-11 - DNA and Chromosome Structure

This course covers DNA and chromosome structure, specifically relating to genetics (BIOL2301).
The sessions were held on October 7th, 2024, instructed by Sara Good.

Agenda

1. Characteristics of genetic material
2. DNA and RNA structure

Characteristics of Genetic Material

All living organisms share a common genetic language: nucleic acids.
The acceptance of nucleic acids as genetic material came after 1950, as a lack of understanding of DNA structure hindered acceptance previously.
Four essential characteristics of genetic material:
- Complex information storage
- Faithful replication during cell division
- Encoding of phenotypes, expressed as traits
- Capacity to vary, reflecting genetic diversity among species and individuals.

DNA and RNA Structure

This section discusses the structure of DNA and RNA.

Early Studies of DNA by Chemists

1868: Johann Friedrich Miescher isolated nuclei from pus, discovering nuclein.
Late 1800s: Several researchers discovered the physical basis of heredity lies in the nucleus.
Late 1800s/Early 20th Century: Albrecht Kossel identified four nitrogenous bases in DNA. Phoebus Aaron Levene discovered DNA's structure as repeating nucleotides, proposing the tetranucleotide hypothesis.
1940s-1950s: Erwin Chargaff and colleagues disproved the tetranucleotide hypothesis, introducing Chargaff's rules.

Early Studies of DNA by Biologists

Biologists sought to identify genetic material also involving chemists unraveling DNA structure.
Gregor Mendel laid the groundwork for understanding heredity in 1866,
By the early 1900s, biologists inferred genes were located on chromosomes, which are composed of DNA and protein.
Crucial experiments on bacteria and viruses in the early 20th century provided evidence supporting DNA as the genetic material over protein.

Discovery of Transforming Principle

1928: Fred Griffith observed transformation in Streptococcus pneumoniae.
Definition of Transformation: Nonvirulent bacteria acquire genetic virulence from dead virulent bacteria, leading to permanent change.
Griffith isolated different strains of S. pneumoniae, including virulent (smooth, S) and nonvirulent (rough, R) forms.

Identification of Transforming Principle

Oswald Avery, initially skeptical of Griffith's findings, embarked on further research to identify the transforming substance.
Avery, MacLeod, and McCarty successfully repeated Griffith's experiments, isolating and partially purifying the transforming substance.
Their research revealed the transforming substance resembles DNA, not protein, refuting protein as the carrier of genetic information.
Enzymatic tests showed proteins are not responsible for the transforming activity, whereas DNA-degrading enzymes abolished it.
The transforming substance precipitated similarly to purified DNA and absorbed ultraviolet light like DNA, supporting its DNA nature.

The Hershey-Chase Experiment

Alfred Hershey and Martha Chase conducted a study on the T2 bacteriophage to determine which molecule between protein or DNA is transmitted during phage reproduction.
T2 bacteriophage is composed of approximately 50% protein and 50% DNA; it infects E. coli bacteria by injecting its genetic material.
Their experiment demonstrated that DNA, not protein, is the genetic material of phages.

Meanwhile Edwin Chargaff's Observations

Chargaff's rules: Adenine (A) equals thymine (T), and guanine (G) equals cytosine (C).
He found consistent base ratios in different DNA sources.

Watson and Crick's Discovery of DNA's Three-Dimensional Structure

Early investigations by Miescher, Kossel, Levene, Chargaff, and others laid the groundwork for understanding DNA's chemical composition and the role of nucleotides.
In 1947, William Astbury started studying DNA's three-dimensional structure using X-ray diffraction.
Rosalind Franklin's X-ray diffraction images from King's College (London) provided crucial insights into DNA's structure.
James Watson and Francis Crick, using this information, constructed models and incorporated Franklin's high-quality X-ray images, which led to the discovery of DNA's double helix structure.
Adenine bonding with thymine and guanine with cytosine allowed them to develop a model consistent with Chargaff's findings about base ratios, thus revealing DNA's double helix, with nucleotides forming complementary base pairs.

RNA as Genetic Material

While most organisms use DNA for genetic information, some viruses, like the tobacco mosaic virus (TMV), utilize RNA.
Ribonucleic acid (RNA) is essential for various biological processes, including protein synthesis and genetic regulation.
Fraenkel-Conrat and Singer produced hybrid viruses using RNA and protein from different TMV strands.
The hybrid viral progeny's resemblance to the strain of the isolated RNA confirmed RNA's role as a genetic material carrier.
In the same year, Alfred Gierer and Gerhard Schramm further confirmed TMV's RNA as the genetic material, thus proving that isolated RNA can infect tobacco plants, thereby initiating TMV particle production.

Primary Structure of DNA - Nucleotides

Nucleotides are the building blocks of nucleic acids, composed of a sugar molecule, a phosphate group, and a nitrogenous base.
DNA's sugar is deoxyribose; RNA's sugar is ribose.
DNA contains the Nitrogenous bases: purines (adenine(A) and guanine(G)) and pyrimidines (cytosine(C) and thymine(T)). RNA contains uracil(U) in place of thymine.
The nitrogenous base bonds covalently to the 1' carbon of the sugar creating a nucleoside. The phosphate group connects to the 5' carbon of the sugar, forming a nucleotide.

Primary structure of DNA - Polynucleotide Strands

Polynucleotide strands are chains of nucleotides linked by phosphodiester bonds.
The backbone comprises alternating sugars and phosphate groups.
Bases project away from the axis.
Polynucleotide strands have directionality; the 5' end has a free phosphate group, and the 3' end has a free hydroxyl group.
RNA utilizes the same phosphodiester linkages as DNA.

Secondary Structure of DNA - The Double Helix

The twisted structure formed by two polynucleotide strands is called the double helix.
The sugar-phosphate linkages are on the outside, while the bases are stacked in the interior.
The two strands run in opposite directions (antiparallel).
Hydrogen bonds hold complementary base pairs together (A with T and G with C).
Base stacking interactions stabilize the molecule.

Different Secondary Structures

B-DNA is most stable under physiological conditions; it's a right-handed helix, exhibiting a slim and elongated structure with major and minor grooves which play a role in protein binding for genetic regulation.
A-DNA is shorter, wider, and right-handed than B-DNA; it is observed under conditions with less water.
Z-DNA is a left-handed helix, characterized by a zigzagging sugar-phosphate backbone; it may be involved in gene expression.

Special DNA Structures

Hairpin loops (simple secondary structure of DNA): These involve intra-strand complementarity forming a stem-loop structure.
H-DNA is the triple-stranded structures that form when one strand pairs with double-stranded DNA from another part of the molecule, and it frequently appears in long stretches of only purines or pyrimidines in mammalian genomes
Methylated DNA: Methyl groups are added to nucleotide bases; this modification is related to gene expression in eukaryotes and influences DNA's three-dimensional structure.

DNA Packing in Eukaryotic Cells

DNA in eukaryotic cells is heavily packed.
Chromatin structure involves the nucleosome—the fundamental repeating unit of chromatin.
Nucleosomes consist of DNA wrapped around histone proteins.
Higher levels of chromatin packaging involve interactions among nucleosomes, and progressive coiling into 30nm fibers, 300nm loops, and 250nm wide fibers, etc.
Chromosomal puffs are regions of relaxed chromatin where active transcription happens.

DNase I Sensitivity

DNase I sensitivity to DNA correlates with the transcription of globin genes in chick embryos, suggesting chromatin structure changes during transcription.

Variation in DNA Methylation

Variation in DNA methylation at the agouti locus produces different coat colors in mice.

DNA at the Ends of Eukaryotic Chromosomes

Telomeric sequences are present at the ends of eukaryotic chromosomes. They consist of repetitive DNA sequences, which prevent the loss of critical genetic material during replication, and protect the chromosomes from fusion.

Mitochondrial Genome

Mitochondrial genomes are small, vary greatly in size, and encode specific products.
Humans have a circular mtDNA of 16,569 bases, encoding two rRNAs, 22 tRNAs, and 13 proteins.
Yeast mtDNA is larger than human mtDNA, encoding 2 rRNAs, 25 tRNAs, and 16 polypeptides.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz covers key concepts from genetic experiments, including the Hershey-Chase experiment and various discoveries regarding DNA and RNA. It addresses questions about protein as genetic material, Chargaff's rules, and the structural features of DNA. Test your understanding of these fundamental biological principles.