Chapter 7: DNA Structure and Replication Quiz

DNA Structure and Function

• Adenine (A) pairs with Thymine (T) via two hydrogen bonds, a weak chemical bond
• Guanine (G) pairs with Cytosine (C) via three hydrogen bonds
• '5'-3'' direction in DNA refers to the orientation of the sugar-phosphate backbone, with 5' end having a free phosphate group, and 3' end having a free hydroxyl group
• James Watson and Francis Crick proposed the double helix structure of DNA
• Rosalind Franklin's contribution to DNA was using X-ray diffraction to capture images that provided crucial insights into its structure
• Chargaff's rules of base composition revealed that the amount of A always equals the amount of T and the amount of G always equals the amount of C, leading to the complementary pairing of bases in DNA
• Avery, MacLeod, and McCarty Experiment demonstrated that DNA is the transforming principle, meaning DNA carries genetic information and can be passed down to succeeding generations
• Hershey-Chase Experiment confirmed DNA as the genetic material by showing that DNA, not protein, is transferred from bacteriophages to bacteria, resulting in phage progeny

DNA Base Pairing

• Base pairing in DNA refers to the specific bonding between complementary bases (A with T, and G with C).
• Antiparallel arrangement in DNA means the two strands run in opposite directions with 5' end of one strand aligning with the 3' end of the other strand
• Hydrogen bonds are the primary force responsible for base pairing in DNA
• DNA strands are antiparallel and run in opposite directions.

DNA structure and properties

• DNA has a double helix structure with two antiparallel strands, complementary base pairing, and a sugar-phosphate backbone holding them together
• Griffith's Transformation Experiment was significant because it demonstrated the existence of a 'transforming principle': a substance capable of changing the characteristics of bacteria
• '5'-3'' direction in DNA strands is essential as it dictates the direction of DNA replication and transcription
• DNA strands are antiparallel: they run in opposite directions (5'-3' and 3'-5')
• Chargaff's rules of base composition played a crucial role in determining the complementary base pairing in the DNA structure, providing a foundation for understanding its structure and replication

Key experiments and discoveries

• Hershey-Chase experiment proved that DNA, not protein, is the genetic material, by labeling phage DNA with phosphorus and phage protein with sulfur
• Avery, MacLeod, and McCarty Experiment identified DNA as the substance that carries genetic information and acts as the transforming principle
• Rosalind Franklin produced X-ray diffraction images of DNA, revealing its double helix structure
• Frederick Griffith's transformation experiment with Streptococcus pneumoniae demonstrated that genetic information can be transferred from one bacterium to another.
• Hershey and Chase's experiment using radioactive isotopes demonstrated that DNA is responsible for transmitting genetic information from one generation to the next.

DNA Composition

• Nucleotides are the building blocks of DNA and are comprised of:
• A sugar molecule (deoxyribose)
• A phosphate group
• A nitrogenous base (adenine, guanine, cytosine, or thymine)
• Phosphodiester bonds link nucleotides in DNA during synthesis
• Erwin Chargaff's rules of base composition established that 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), which plays a crucial role in DNA replication and transcription.

Genetic Material

• DNA serves as the genetic material due to its ability to:
• Replicate, allowing for the transmission of genetic information
• Store information in its base sequence
• Express information to produce proteins and other molecules
• Allow variation by mutation, driving evolution
• Genetic material must be able to replicate, store information, express information, and allow variation by mutation.

Historical Context and Significance

• Walter Sutton and Theodor Boveri observed parallels between chromosome partitioning into gametes and inheritance of genes, providing evidence that chromosomes carry genetic material
• DNA became a candidate for the hereditary material in 1923 due to its stable and chemically complex structure
• Proteins and RNA were also considered as candidates for the hereditary material due to their diverse functions and ability to carry genetic information, but RNA was not considered as stable as DNA.
• Rediscovery of Mendel's hereditary principles in 1900 revitalized research into understanding the mechanism of inheritance
• Rosalind Franklin's key finding from X-ray diffraction analysis was the DNA structure's double helix configuration, demonstrating its shape and arrangement
• According to the Watson and Crick model, the two DNA strands in a double helix are antiparallel and complementary, meaning that they run in opposite directions and their bases pair according to specific rules (A with T and G with C)
• '5'-3'' direction in DNA strands is important for defining the direction of replication and transcription, essential processes within the cell
• Chargaff's rules indicate that the proportion of adenine (A) always equals the proportion of thymine (T) and the proportion of guanine (G) always equals the proportion of cytosine (C) in a given sample of DNA
• Base pairing in DNA involves hydrogen bonds formed between specific pairs of nitrogenous bases - adenine (A) with thymine (T), and guanine (G) with cytosine (C)
• Hershey-Chase Experiment significantly confirmed DNA as the genetic material by demonstrating that DNA, not protein, is transferred from bacteriophages to bacteria
• Antiparallel arrangement in DNA structure is vital for maintaining the double helix structure and allowing for proper base pairing
• Chargaff's rules, which demonstrated the equal proportions of adenine and thymine and guanine and cytosine in DNA, were crucial for understanding complementary base pairing in DNA and its double helix structure
• Hydrogen bonds are the primary force responsible for base pairing in DNA due to their weak and specific interactions
• The '5'-3'' direction of DNA strands influences the direction of replication and transcription, crucial processes for maintaining genetic information
• Griffith's transformation experiments with Streptococcus pneumoniae, Avery, MacLeod, and McCarty Experiment, and Hershey-Chase Experiment contributed significantly to the discovery of the DNA double helix structure
• Hershey-Chase Experiment provided definitive evidence that DNA is the genetic material, confirming findings from Avery, MacLeod, and McCarty Experiment
• Avery, MacLeod, and McCarty Experiment demonstrated that DNA is the transforming principle responsible for carrying genetic information, laying the groundwork for understanding DNA as the core molecule of life.