🧑🏽🔬history of science review
13.1 Discovery of DNA Structure and Function
Last Updated on August 1, 2024
The discovery of DNA's structure and function revolutionized our understanding of genetics. Scientists like Griffith, Avery, and Hershey-Chase proved DNA was the genetic material. Their work laid the foundation for Watson and Crick's groundbreaking double helix model.
The double helix structure explained how genetic information is stored, replicated, and passed on. This discovery sparked the DNA revolution, leading to advances in molecular biology and biotechnology that continue to shape our world today.
DNA as Genetic Material
Experiments Demonstrating DNA as Genetic Material
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Top images from around the web for Experiments Demonstrating DNA as Genetic Material
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- In the 1920s, Frederick Griffith's experiments with Streptococcus pneumoniae demonstrated the existence of a "transforming principle" that could convert harmless bacteria into virulent strains
- Suggested that genetic information could be transferred between organisms
- Avery, MacLeod, and McCarty's experiments in the 1940s identified DNA as the "transforming principle" responsible for the changes observed in Griffith's experiments
- Provided the first evidence that DNA carries genetic information
- Hershey and Chase's experiments in 1952 used radioactive labeling to show that DNA, not protein, enters bacterial cells during viral infection
- Confirmed that DNA is the genetic material
Chargaff's Rules and DNA Composition
- Chargaff's rules, developed in the late 1940s, stated that in DNA:
- The amount of adenine (A) always equals the amount of thymine (T)
- The amount of guanine (G) always equals the amount of cytosine (C)
- Provided key insights into the structure of DNA
- Suggested a complementary relationship between the nitrogenous bases
- Hinted at the potential for base pairing in the DNA structure
DNA's Double Helix Structure
Composition and Arrangement of DNA
- DNA is composed of two antiparallel polynucleotide strands that wind around each other to form a right-handed double helix
- The sugar-phosphate backbones of the two strands are on the outside of the helix, while the nitrogenous bases face the interior
- The nitrogenous bases form complementary base pairs through hydrogen bonds:
- Adenine (A) pairs with thymine (T)
- Guanine (G) pairs with cytosine (C)
Significance of the Double Helix Structure
- The double helix structure provides a mechanism for the precise replication of genetic information during cell division
- Each strand can serve as a template for the synthesis of a new complementary strand
- The complementary base pairing in the double helix allows for the faithful transmission of genetic information from one generation to the next
- Ensures that genetic information is accurately copied and passed on to daughter cells
- The structure also helps protect the genetic information from damage
- The interior location of the nitrogenous bases shields them from potential chemical or physical damage
DNA's Role in Genetics
DNA as a Blueprint for Life
- DNA serves as the blueprint for an organism's structure, function, and development
- Encodes the instructions for the synthesis of proteins, which carry out most cellular functions
- The genetic information in DNA is stored in the sequence of nucleotides along the polynucleotide strands
- Each set of three nucleotides (a codon) specifies a particular amino acid
Central Dogma of Molecular Biology
- During transcription, the genetic information in DNA is copied into a complementary RNA molecule called messenger RNA (mRNA)
- Allows the genetic information to be transported out of the nucleus
- The mRNA carries the genetic information from the nucleus to the ribosomes in the cytoplasm, where translation occurs
- The amino acids specified by the codons are assembled into proteins
- DNA replication ensures that each daughter cell receives an identical copy of the genetic information during cell division
- Allows for the faithful transmission of traits from parent to offspring (heredity)
Discoverers of DNA's Structure
Watson and Crick's Double Helix Model
- James Watson and Francis Crick proposed the double helix model of DNA structure in 1953
- Based on X-ray crystallography data and the known chemical properties of DNA
- Watson and Crick's model explained how DNA could replicate and how genetic information could be stored and transmitted
- Revolutionized the field of molecular biology
- Awarded the Nobel Prize in Physiology or Medicine in 1962 for their work on DNA structure
Contributions of Franklin and Wilkins
- Rosalind Franklin's X-ray diffraction images, particularly the famous "Photo 51," provided crucial evidence for the helical structure of DNA
- Also revealed the spacing between the nucleotide bases
- Maurice Wilkins, Franklin's colleague, shared her X-ray crystallography data with Watson and Crick
- Helped them refine their model of DNA structure
- Franklin's contributions were not fully recognized until after her death in 1958
- Her work was essential to the discovery of the double helix structure
Key Terms to Review (24)
Molecular biology revolution: The molecular biology revolution refers to the transformative period in the 20th century when significant advances in understanding the molecular mechanisms of biological processes were achieved, particularly regarding DNA structure and function. This revolution marked a shift from classical genetics to a focus on molecular interactions, leading to groundbreaking discoveries such as the structure of DNA and the processes of transcription and translation, which are fundamental to all life forms.
Maurice Wilkins: Maurice Wilkins was a British physicist and molecular biologist who played a crucial role in the discovery of the structure of DNA. His work with X-ray diffraction images of DNA helped to provide critical evidence for the double helix model proposed by Watson and Crick, establishing a foundation for modern genetics and molecular biology.
Photo 51: Photo 51 is an X-ray diffraction image of DNA taken by Rosalind Franklin in 1952, which provided critical evidence for the helical structure of DNA. This iconic image was crucial in revealing the dimensions and arrangement of the DNA molecule, ultimately leading to the understanding of how genetic information is stored and transmitted.
Human Genome Project: The Human Genome Project was a groundbreaking international scientific research initiative aimed at mapping and understanding all the genes of the human species. This monumental project not only sequenced the entire human genome but also provided insights into the structure and function of DNA, laying the foundation for advancements in genetics, medicine, and biotechnology.
Rosalind Franklin: Rosalind Franklin was a British chemist and X-ray crystallographer whose work was critical in the discovery of the DNA double helix structure. Her meticulous research, particularly her X-ray diffraction images of DNA, provided key insights into the molecular structure of DNA, influencing the scientific community's understanding of genetics and heredity.
Ribosomes: Ribosomes are cellular structures that function as the site of protein synthesis, where messenger RNA (mRNA) is translated into amino acids to form proteins. They can be found floating freely in the cytoplasm or attached to the endoplasmic reticulum, linking them to the central processes of gene expression and cellular function. Their role is essential in translating the genetic code stored in DNA into functional proteins, which are vital for various cellular processes.
X-ray diffraction: X-ray diffraction is a powerful technique used to study the structure of materials at the atomic or molecular level by directing X-rays onto a sample and analyzing the pattern of scattered X-rays. This method has been crucial in determining the arrangement of atoms in crystals, making it instrumental in understanding biological structures like DNA and advancing fields such as nanotechnology and materials science.
Dna replication: DNA replication is the biological process by which a cell makes an identical copy of its DNA, allowing genetic information to be passed on during cell division. This process is essential for growth, development, and repair in living organisms, as it ensures that each new cell receives the same genetic blueprint as the original. The understanding of DNA structure and its function highlights how replication occurs with remarkable accuracy, involving various enzymes and proteins that facilitate this intricate process.
Nitrogenous bases: Nitrogenous bases are the fundamental components of nucleotides, which are the building blocks of nucleic acids like DNA and RNA. These bases are critical for encoding genetic information, as they pair specifically to form the rungs of the DNA double helix. There are five primary nitrogenous bases that play significant roles in genetics: adenine, thymine, cytosine, guanine, and uracil (the latter being found in RNA).
Central dogma of molecular biology: The central dogma of molecular biology is a framework that describes the flow of genetic information within a biological system. It explains how DNA is transcribed into RNA, which is then translated into proteins, highlighting the sequential processes that govern gene expression and protein synthesis. This concept is fundamental to understanding how genetic information dictates cellular functions and characteristics.
Translation: Translation is the process by which the information encoded in messenger RNA (mRNA) is used to synthesize proteins. This crucial step occurs in the ribosome, where tRNA molecules bring amino acids that correspond to the codons on the mRNA strand, ultimately leading to the formation of polypeptide chains. Understanding translation connects key concepts of how genetic information is expressed and its importance in cellular functions.
Hershey and Chase: Hershey and Chase refer to the groundbreaking experiment conducted by Alfred Hershey and Martha Chase in 1952, which provided strong evidence that DNA is the genetic material of viruses. Their work, using the T2 bacteriophage, showed that when these viruses infect bacteria, it is their DNA that enters the bacterial cells and directs the production of new viruses, thereby solidifying the understanding of DNA's role in heredity and function.
Messenger RNA: Messenger RNA (mRNA) is a single-stranded RNA molecule that carries genetic information from DNA to the ribosome, where proteins are synthesized. This process is essential because mRNA acts as a template for assembling amino acids in the correct order to form proteins, which are crucial for cellular functions and structures.
Antiparallel strands: Antiparallel strands refer to the orientation of the two complementary strands of DNA, where one strand runs in the 5' to 3' direction and the other runs in the 3' to 5' direction. This unique arrangement is crucial for the formation of the double helix structure and ensures proper base pairing between the nucleotides. The antiparallel configuration also plays a significant role in DNA replication and transcription processes.
Transcription: Transcription is the biological process in which the information encoded in a specific segment of DNA is copied into messenger RNA (mRNA). This process is essential for gene expression, as it allows the genetic code to be converted into a format that can be read and utilized by the cellular machinery to produce proteins. Transcription connects the structure of DNA with its functional role in the cell, highlighting how genetic information is expressed and regulated.
Base pairing: Base pairing refers to the specific hydrogen bonding between nucleobases in the DNA and RNA molecules, where adenine pairs with thymine (or uracil in RNA), and guanine pairs with cytosine. This complementary pairing is fundamental for the structure of DNA, allowing the double helix formation and accurate replication during cell division.
Sugar-phosphate backbone: The sugar-phosphate backbone is a fundamental structural component of nucleic acids, consisting of alternating sugar and phosphate groups that form the outer framework of DNA and RNA molecules. This backbone provides stability and support to the nucleic acid structure while enabling the attachment of nitrogenous bases, which carry genetic information. The integrity of the sugar-phosphate backbone is crucial for the overall function of DNA, especially during processes like replication and transcription.
Watson and Crick Model: The Watson and Crick Model is the double helix structure of DNA proposed by James Watson and Francis Crick in 1953, which explains how genetic information is stored and transmitted. This model is significant because it provides insight into the molecular basis of heredity, demonstrating how the arrangement of nucleotide bases allows for the replication and expression of genetic information.
Griffith's Experiments: Griffith's experiments, conducted in 1928 by Frederick Griffith, were pivotal in demonstrating that genetic material could be transferred between bacterial cells. This groundbreaking research involved the transformation of non-virulent strains of Streptococcus pneumoniae into virulent ones through exposure to heat-killed virulent bacteria. Griffith's work laid the foundation for understanding DNA as the carrier of genetic information, setting the stage for future discoveries related to DNA structure and function.
Chargaff's Rules: Chargaff's Rules refer to the observation made by biochemist Erwin Chargaff that in DNA, the amount of adenine (A) is equal to the amount of thymine (T), and the amount of guanine (G) is equal to the amount of cytosine (C). This crucial finding laid the groundwork for understanding the base pairing mechanism in DNA and was fundamental in the discovery of the double helix structure of DNA.
Avery, MacLeod, and McCarty: Avery, MacLeod, and McCarty were scientists who conducted groundbreaking experiments in 1944 that established DNA as the substance responsible for heredity. Their work showed that when they extracted DNA from a virulent strain of bacteria and introduced it to a non-virulent strain, the latter transformed into a virulent form. This pivotal experiment connected DNA to genetic inheritance, paving the way for future molecular biology studies.
Double helix: The double helix is the structure of DNA, consisting of two long strands that twist around each other, resembling a spiral staircase. This shape is crucial because it allows for the storage and replication of genetic information, with the sequence of nucleotide bases on each strand pairing specifically to encode the instructions for building proteins and maintaining life.
James Watson: James Watson is a molecular biologist and geneticist best known for co-discovering the structure of DNA in 1953 alongside Francis Crick. His work laid the foundation for modern genetics, influencing our understanding of heredity, molecular evolution, and the mechanisms of biological processes.
Francis Crick: Francis Crick was a British molecular biologist, biophysicist, and neuroscientist best known for co-discovering the structure of DNA along with James Watson in 1953. His work laid the groundwork for understanding genetic information and how it is passed on through generations, connecting him to the concepts of molecular evidence for evolution and the central dogma of molecular biology.