1. Who was Friedrich Miescher and what was his significant contribution to the study of genetic material?

Friedrich Miescher was a German chemist who, in 1869, isolated a substance from cell nuclei. He termed this substance 'nuclein' due to its nuclear origin. His discovery marked the beginning of understanding the chemical composition of genetic material, distinguishing it from other cellular components.

2. What were the defining characteristics of 'nuclein' that led to its reclassification as nucleic acid?

'Nuclein' was characterized by its unique proportions of nitrogen and phosphorus, which were distinct from proteins. Additionally, its slightly acidic nature was a key property. These chemical features led to its later reclassification as nucleic acid, highlighting its unique biochemical identity.

3. According to P. A. Levene, what are the three basic components that make up nucleic acids?

P. A. Levene determined that nucleic acids are composed of three basic components: a phosphate group, a five-carbon sugar, and a nitrogen-containing base. These three units combine to form a nucleotide, which is the fundamental building block of both DNA and RNA.

4. Differentiate between purines and pyrimidines, and list the specific bases that fall into each category for DNA.

Purines are nitrogenous bases with a double-ring structure, while pyrimidines have a single-ring structure. In DNA, the purines are adenine (A) and guanine (G). The pyrimidines in DNA are thymine (T) and cytosine (C).

5. How does the nitrogenous base composition of RNA differ from that of DNA?

The nitrogenous base composition of RNA differs from DNA primarily in one base. While both DNA and RNA contain adenine, guanine, and cytosine, RNA contains uracil (U) instead of thymine (T). This substitution is a key distinguishing feature between the two nucleic acids.

6. Define a nucleotide and explain how different nucleotides are distinguished from one another.

A nucleotide is the basic repeating unit of nucleic acids, consisting of a five-carbon sugar, a phosphate group, and a nitrogen-containing base. Nucleotides are differentiated by the specific nitrogenous base they contain. For example, an adenine nucleotide contains adenine, while a guanine nucleotide contains guanine.

7. Explain the formation of long nucleotide chains, specifically mentioning the type of bond involved.

Long nucleotide chains are formed through phosphodiester bonds. These covalent bonds link the 5' phosphate group of one nucleotide to the 3' hydroxyl group of the adjacent nucleotide. This process occurs via a dehydration synthesis reaction, creating the sugar-phosphate backbone of DNA and RNA strands.

8. State Chargaff's rules and explain their significance for the structure of double-stranded DNA.

Chargaff's rules state that in double-stranded DNA, the amount of adenine (A) always equals the amount of thymine (T), and the amount of guanine (G) always equals the amount of cytosine (C). This implies an equal proportion of purines and pyrimidines. These rules were crucial for Watson and Crick in deducing the specific base pairing (A-T and G-C) in the double helix structure.

9. What critical information did Rosalind Franklin's X-ray diffraction analysis provide regarding DNA's structure?

Rosalind Franklin's X-ray diffraction analysis provided crucial evidence indicating DNA's helical structure. Her data showed a diameter of approximately 2 nanometers and a complete helical turn every 3.4 nanometers. This precise structural information was instrumental for Watson and Crick in developing their double helix model.

10. What was the key feature of the double helix model proposed by James Watson and Francis Crick in 1953?

The key feature of Watson and Crick's double helix model was that DNA consists of two strands oriented with their bases pointed inward. These bases form specific pairs: adenine with thymine, and guanine with cytosine. This specific base pairing and the helical arrangement explained how genetic information could be stored and replicated.

11. Which single-celled organism did Joachim Hammerling use in his experiments to study the role of the nucleus in heredity?

Joachim Hammerling used Acetabularia, a single-celled green algae, in his experiments. This organism was ideal because of its large size and distinct morphological regions (foot, stalk, and cap), allowing for grafting experiments to investigate the nucleus's influence on cellular development.

12. What did Joachim Hammerling's experiments with Acetabularia demonstrate about the nucleus?

Hammerling's experiments demonstrated that the nucleus, located in the 'foot' of the Acetabularia cell, dictates the morphology of the 'cap.' Grafting experiments showed that the cap's development consistently matched the species of the foot, proving that the nucleus directs cellular development and contains the genetic information.

13. What concept did Frederick Griffith introduce through his work with Streptococcus pneumoniae?

Frederick Griffith introduced the concept of a 'transforming principle' through his experiments with different strains of Streptococcus pneumoniae. He showed that hereditary information could be transferred from dead pathogenic bacteria to living non-pathogenic bacteria, causing the latter to become pathogenic.

14. Who were the scientists that characterized Griffith's 'transforming principle' as DNA?

Oswald Avery, Colin MacLeod, and Maclyn McCarty were the scientists who, in 1944, characterized Griffith's 'transforming principle' as DNA. Their meticulous experiments provided strong evidence that DNA, not protein or RNA, was the molecule responsible for genetic transformation.

15. What was the crucial experimental evidence that led Avery and colleagues to conclude DNA was the transforming principle?

The crucial evidence was that DNA-digesting enzymes, specifically DNase, destroyed all transforming activity. This indicated that the transforming material's properties closely resembled DNA, and its activity was unaffected by enzymes that digest lipids, proteins, or RNA, thus pinpointing DNA as the hereditary material.

16. What did the Hershey and Chase experiment definitively demonstrate regarding genetic material?

The Hershey and Chase experiment in 1952 definitively demonstrated that DNA, not protein, is the genetic material of bacteriophages. By labeling DNA with phosphorus-32 and protein with sulfur-35, they showed that only the DNA entered the bacterial cells to direct viral replication.

17. Provide one piece of circumstantial evidence that supported DNA's role as the genetic material before definitive experiments.

One piece of circumstantial evidence was that DNA is found where genetic functions occur, such as predominantly in the nucleus of eukaryotic cells, and also within mitochondria and chloroplasts. In contrast, proteins are abundant throughout the entire cell, making DNA's localized presence more indicative of its genetic role.

18. Describe the key characteristics of mitochondrial DNA (mtDNA) in most eukaryotes.

In most eukaryotes, mitochondrial DNA (mtDNA) is a circular duplex molecule. It replicates semi-conservatively and is typically free of associated proteins. Its size can vary significantly across different organisms, and its replication process relies on enzymes that are encoded by nuclear DNA.

19. What are the main features of chloroplast DNA (cpDNA) and how does it compare to mtDNA?

Chloroplast DNA (cpDNA) is considerably larger than mtDNA and contains a complete genetic system, including a protein-synthesizing apparatus. Similar to mtDNA, cpDNA is circular, double-stranded, and replicates semi-conservatively. It shares structural resemblances with prokaryotic DNA, supporting the Endosymbiont theory.

20. What is the Endosymbiont theory, and how do organellar DNA characteristics support it?

The Endosymbiont theory posits that mitochondria and chloroplasts originated from free-living prokaryotic organisms that were engulfed by ancestral eukaryotic cells. The similarities between organellar DNA (circular, double-stranded, semi-conservative replication, lack of associated proteins) and bacterial DNA provide strong evidence for this prokaryotic origin.

21. Which virus was used in early experiments to demonstrate that RNA could serve as genetic material?

The Tobacco Mosaic Virus (TMV) was used in early experiments in 1956 to demonstrate that RNA could serve as genetic material. Purified TMV RNA was shown to be capable of inducing characteristic lesions on tobacco leaves, proving its infectious and genetic nature.

22. What did the experiments by Fraenkel-Conrat and Singer involving reconstituted hybrid viruses further solidify?

The experiments by Fraenkel-Conrat and Singer, involving reconstituted hybrid viruses, further solidified the conclusion that RNA can be the genetic material. By combining RNA from one TMV strain with protein from another, they showed that the progeny virus always matched the RNA donor, confirming RNA's genetic role.

23. Describe the basic structure of a viral genome and its reliance on host cells.

A viral genome, whether DNA or RNA, is an infectious particle encased within a protein capsid. Viruses are obligate intracellular parasites, meaning they rely entirely on host cells for replication, transcription, and translation. They exhibit a limited host range, infecting only specific cell types or organisms.

24. What is the primary difference in the sugar component between DNA and RNA?

The primary difference in the sugar component is that DNA contains deoxyribose, while RNA contains ribose. Deoxyribose lacks an oxygen atom at the 2' carbon position, whereas ribose has a hydroxyl group at that position. This structural difference contributes to DNA's greater stability.

25. Besides the sugar, what is another key structural distinction between DNA and RNA molecules?

Another key structural distinction is in their nitrogenous bases. While both DNA and RNA contain adenine, guanine, and cytosine, DNA contains thymine, whereas RNA contains uracil. Uracil replaces thymine in RNA, pairing with adenine during transcription and in RNA structures.