Chapter 14: DNA: The Genetic Material

Franklin obtained information from X-ray crystallography on DNA, which suggested that it is a helix. This implies that the X-ray crystallography data revealed a spiral shape for the DNA molecule, similar to a twisted ladder. The term "helix" accurately describes this structure, as it represents a three-dimensional shape with a spiral arrangement. The other options, such as ribbon, hollow cylinder, pleated sheet, and icosahedron, do not accurately represent the observed structure of DNA.

The replication of DNA is semiconservative because each new DNA molecule formed contains one original strand and one newly synthesized strand. This means that during replication, the two strands of the DNA molecule separate and each serves as a template for the synthesis of a new complementary strand. As a result, the two new DNA molecules formed are identical to the original molecule and each consists of one original strand and one newly synthesized strand. This process ensures the accurate transmission of genetic information from one generation to the next.

Hershey-Chase concluded from their experiment with T2 bacteriophage that DNA is the genetic material. This conclusion was based on their use of radioactive labeling to track the movement of DNA and proteins within the bacteriophage. They found that only the labeled DNA was transferred into the host bacteria, while the labeled proteins remained outside. This indicated that DNA, not proteins, was responsible for carrying the genetic information. Therefore, they concluded that DNA is the genetic material.

Chargaff's rule states that in DNA, the amount of adenine (A) is always equal to the amount of thymine (T), and the amount of guanine (G) is always equal to the amount of cytosine (C). This rule was discovered by Erwin Chargaff and provided crucial information for understanding the structure of DNA. Hershey and Chase conducted the famous blender experiment that confirmed DNA as the genetic material, Franklin contributed to the discovery of DNA's double helix structure through X-ray crystallography, and Watson and Crick proposed the double helix model of DNA.

Protein is not a component of nucleic acids. Nucleic acids are made up of three main components: organic nitrogen bases, sugar, and phosphate. Proteins, on the other hand, are macromolecules made up of amino acids and are not directly involved in the structure or function of nucleic acids.

Chargaff's rules state that in DNA, the base adenine (A) always pairs with thymine (T), and the base guanine (G) always pairs with cytosine (C). This means that A and T are complementary bases, as are G and C. This pairing is essential for the stability and replication of DNA, as it allows for the formation of hydrogen bonds between the bases. Therefore, the correct answer is that A pairs with T and G pairs with C.

DNA pol III synthesizes the leading strand as a continuous strand, meaning it can synthesize the entire strand in one go. However, the lagging strand is synthesized in segments called Okazaki fragments. These fragments are short segments of DNA that are synthesized in the opposite direction of the replication fork. They are then later joined together by DNA ligase to form a continuous strand. Therefore, Okazaki fragments are the correct answer.

DNA consists of two antiparallel strands of nucleotide chains. The strands are held together by hydrogen bonds. These bonds form between the nitrogenous bases of the nucleotides. The hydrogen bonds are relatively weak, allowing the two strands to separate during processes like DNA replication and transcription. However, they are strong enough to maintain the overall structure of the DNA molecule. The complementary base pairing between adenine and thymine, and between guanine and cytosine, is facilitated by these hydrogen bonds.

Helicase is the correct answer because it is an enzyme that unwinds the double-stranded DNA helix during DNA replication. It does this by breaking the hydrogen bonds between the base pairs, allowing the two strands to separate and serve as templates for the synthesis of new DNA strands. DNA polymerase, DNA ligase, DNA endonuclease, and DNA exonuclease are all enzymes involved in DNA replication or repair, but they do not specifically unwind the DNA helix like helicase does.

During DNA replication, the original double strand of DNA is unwound and each strand serves as a template for the synthesis of a new complementary strand. The term "semiconservative" refers to the fact that each new DNA molecule formed consists of one original strand and one newly synthesized strand. This ensures that the genetic information is preserved and passed on accurately to the daughter cells. The other options, such as disruptive, conservative, dispersive, and stabilizing, do not accurately describe the process of DNA replication.

DNA helicase is responsible for unwinding the double helix of DNA. This enzyme uses energy from ATP hydrolysis to separate the two strands of DNA, breaking the hydrogen bonds between the base pairs. This unwinding is necessary for DNA replication, transcription, and repair processes, as it allows access to the genetic information encoded in the DNA molecule. DNA helicase plays a crucial role in ensuring accurate and efficient DNA replication by creating a replication fork and providing single-stranded templates for DNA polymerase to synthesize new DNA strands.

The correct answer is semiconservative method. In this method of DNA replication, each original strand acts as a template for the synthesis of a new complementary strand. As a result, each newly formed DNA molecule consists of one original strand and one newly synthesized strand. This process ensures the preservation of the original genetic information while allowing for the introduction of new genetic material. The term "semiconservative" refers to the fact that each newly formed DNA molecule is composed of one conserved (original) strand and one newly synthesized strand.

DNA polymerase is the correct answer because it is the enzyme responsible for catalyzing the synthesis of new DNA molecules. DNA polymerase adds nucleotides to the growing DNA strand during DNA replication, creating a complementary strand based on the template strand. It plays a crucial role in DNA replication and repair processes, ensuring accurate duplication of the genetic material. DNA ligase, DNA gyrase, DNA helicase, and DNA endonuclease are all enzymes involved in DNA replication and repair, but they have different functions and are not directly responsible for the synthesis of new DNA molecules.

Avery and his coworkers demonstrated the "transforming principle" as DNA. This is because they conducted an experiment where they treated a heat-killed strain of bacteria with various enzymes to break down different biomolecules. They found that only when DNA-degrading enzymes were used, the transforming ability was lost, indicating that DNA is responsible for the transfer of genetic information. Therefore, the correct answer is DNA.

Watson and Crick proposed the double helix model, which is the structure of DNA. This model was based on their analysis of existing data and their own experimental findings. Their model revolutionized the understanding of DNA and its role in genetic inheritance. Griffith, Avery, Franklin, and Beadle and Tatum made important contributions to the field of genetics, but they did not propose the double helix model.

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The correct sequence for DNA replication in E. coli is initiation, elongation, termination. Initiation is the first step where the DNA strands separate and replication begins. Elongation follows, during which new DNA strands are synthesized by adding complementary nucleotides to the original strands. Finally, termination occurs when the replication process is completed and the newly synthesized DNA strands separate from the original strands.

The two strands in the DNA molecule are complementary to each other, meaning that the sequence of nitrogen bases on one strand determines the sequence on the other. This complementary base pairing is crucial for DNA replication and the transmission of genetic information. The bases adenine (A) always pairs with thymine (T), and guanine (G) always pairs with cytosine (C). This complementary nature ensures that when DNA is replicated, each new strand will have the same sequence as the original strand, allowing for accurate transmission of genetic information.

The given sequence of DNA is AATTGCCGT. To find its complement, we need to replace each nucleotide with its complementary base. A pairs with T, T pairs with A, G pairs with C, and C pairs with G. Therefore, the complement of AATTGCCGT is TTAACGGCA.

The correct answer is DNA was the repository for hereditary information. This is because Hershey and Chase confirmed Avery's results that proteins were not responsible for carrying genetic information, but rather it was DNA that served as the repository for hereditary information. This discovery was a significant breakthrough in understanding the molecular basis of genetics and laid the foundation for further research in the field.

Hershey and Chase conducted an experiment known as the Hershey-Chase experiment in 1952. They used radioactive isotopes to label DNA and protein separately in T2 bacteriophages. By infecting bacterial cells with these labeled phages, they were able to determine that only the DNA, and not the protein, was injected into the bacterial cells. This experiment provided strong evidence that DNA, not protein, is the genetic material that specifies the new generation of viruses.

Based on the information given, it is stated that 14% of the DNA nucleotides contain T. Since DNA is composed of four different bases (A, T, C, G), and T represents 14% of the nucleotides, it can be inferred that the remaining 86% of the nucleotides must be composed of the other three bases (A, C, G). Therefore, the expected amounts of the other bases would be 14% A, 36% C, and 36% G.

Griffith's unexpected finding suggests that something in the nonvirulent bacteria was changed or altered when mixed with the dead virulent bacteria. The term "transformed" best describes this change or alteration, as it implies a conversion or modification of the nonvirulent strain into a virulent one. The other options, such as "activated," "translated," "transcribed," and "expressed," do not accurately capture the concept of a fundamental change in the bacteria's characteristics. Therefore, "transformed" is the most appropriate explanation for the observed behavior.

Replication always proceeds by adding new bases to the 3' end. In DNA replication, the enzyme DNA polymerase adds nucleotides to the growing DNA strand in a 5' to 3' direction. This means that the new bases are always added to the 3' end of the growing strand. The 3' end of the DNA molecule has a free hydroxyl group (-OH) which allows for the attachment of the new nucleotide. Therefore, the replication process occurs in the 3' to 5' direction on the template strand, resulting in the synthesis of a new DNA strand in the 5' to 3' direction.

The complementary DNA strand will have the same sequence as the original DNA strand, but with the bases paired differently. In DNA, adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C). Therefore, the complementary sequence to 5' ATGGTCAGT 3' would be 3' TACCAGTCA 3'.

The lagging strand is replicated in short fragments called Okazaki fragments, which are later joined together. This process is discontinuous because the replication of the lagging strand occurs in a series of starts and stops, rather than being continuously synthesized like the leading strand.

The correct answer is Franklin. X-ray crystallography is a technique used to determine the structure of molecules by analyzing the diffraction patterns produced when X-rays pass through a crystal. In the case of DNA fibers, this technique revealed a pattern that indicated a helical structure. Rosalind Franklin was a scientist who made significant contributions to the understanding of DNA structure through her X-ray crystallography experiments. Her work provided key insights into the dimensions and helical nature of DNA, which ultimately contributed to the discovery of the double helix structure by Watson and Crick.

The statement that the newly synthesized DNA is packaged into one nucleus, and the old DNA is packaged into another nucleus is false. In DNA replication, the newly synthesized DNA strands remain in the same nucleus as the original DNA strands. The process of DNA replication occurs in the nucleus of a cell, where the two strands of the DNA molecule are separated, and each strand serves as a template for the synthesis of a new complementary strand. The synthesis on each strand occurs in the opposite direction, which is known as antiparallel replication.

Watson and Crick proposed the correct answer. They are known for discovering the structure of DNA, which they described as a double helix. They determined that DNA consists of two polynucleotide chains that run in opposite directions and are held together by hydrogen bonding between pairs of bases. Their groundbreaking work in 1953 provided a crucial understanding of the physical structure of DNA, leading to significant advancements in the field of genetics.

Hydrogen bonds are the correct answer because they are responsible for stabilizing the complementary nitrogen bases in a DNA double helix. These bonds occur between the nitrogen bases, specifically between adenine and thymine, and between guanine and cytosine. Hydrogen bonds are relatively weak compared to other types of chemical bonds, but they are crucial for maintaining the structure and stability of the DNA molecule.

Griffith's work with Streptococcus is well-known in the field of microbiology. He conducted an experiment in which he injected mice with different strains of Streptococcus bacteria. Through his experiments, he discovered the phenomenon of bacterial transformation, where genetic material can be transferred between bacteria. This groundbreaking discovery laid the foundation for understanding the role of DNA in heredity and paved the way for further research in genetics.

The correct answer is that a bacteriophage typically attaches to the bacterium and then injects its nucleic acid into it, and then the ghost virus stays outside. Bacteriophages are viruses that infect bacteria. They have a specific structure that allows them to attach to the surface of bacteria and inject their genetic material (nucleic acid) into the bacterial cell. Once inside the cell, the viral nucleic acid takes over the cellular machinery to produce more phage particles. The "ghost virus" refers to the empty viral protein shell that remains outside the bacterium after the nucleic acid has been injected.

DNA polymerase requires an RNA primer to initiate DNA replication. This is because DNA polymerase can only add nucleotides to an existing strand of DNA or RNA. Therefore, an RNA primer is needed to provide the initial nucleotides for DNA polymerase to extend and synthesize a new DNA strand. Once the RNA primer is in place, DNA polymerase can then replace it with DNA nucleotides and continue the replication process.

The reading of the bases along the length of a nucleic acid molecule for either transcription or translation is done from the 5' end. The 5' end of a nucleic acid molecule refers to the end that has a phosphate group attached to the 5th carbon of the sugar molecule. This end is where the synthesis of RNA or protein begins, and the sequence of bases is read in the 5' to 3' direction.

The sides of the DNA double helix are made up of alternating units of phosphate groups and sugars. The phosphate groups and sugars form a backbone that holds the rungs of the ladder together. This alternating pattern of phosphate groups and sugars creates a stable structure and allows for the attachment of the nitrogenous bases, purines and pyrimidines, which form the rungs of the DNA ladder.

The chemical bond connecting one nucleotide with the next one along the nucleic acid chain is called a phosphodiester bond. This bond is formed between the phosphate group of one nucleotide and the sugar molecule of the next nucleotide. It plays a crucial role in the stability and integrity of the nucleic acid chain, allowing for the formation of the DNA double helix and the RNA single strand. The other options (C = C bond, hydrogen bond, hydrophobic bond, peptide bond) are not involved in connecting nucleotides in a nucleic acid chain.

Griffith's experiments involved the transfer of genetic material from one cell to another, which is known as transformation. He used bacteria and mice to demonstrate this process. By injecting a mixture of non-pathogenic and heat-killed pathogenic bacteria into mice, he observed that the non-pathogenic bacteria became pathogenic, acquiring the ability to cause disease. This suggested that the genetic material from the heat-killed bacteria had been transferred to the non-pathogenic bacteria, transforming them into pathogenic ones. Therefore, the correct answer is "the ability to transfer genetic materials from one cell to another."

If the chemical binds to adenine, it would prevent adenine from pairing with thymine during DNA replication. Adenine normally pairs with thymine, so if adenine is bound, there would be no available thymine to pair with, causing the replication process to stop. Therefore, the logical prediction of the outcome would be that DNA replication would stop if the chemical is applied prior to S in the cell cycle.

In the Hershey-Chase experiment, DNA was labeled with radioactive phosphorus and protein was labeled with radioactive sulfur. The purpose of the experiment was to determine whether DNA or protein was the genetic material that is passed from viruses to bacteria during infection. The virus-infected bacteria were expected to show the presence of the radioactive material that corresponds to the genetic material being transferred. Since DNA was labeled with radioactive phosphorus, it is expected that the virus-infected bacteria would show radioactive phosphorus, not radioactive sulfur. Therefore, the statement "The virus-infected bacteria showed radioactive phosphorus" is false.

DNA primase is an enzyme responsible for initiating DNA replication. It synthesizes a short RNA primer that is complementary to the DNA template strand. This RNA primer provides the starting point for DNA polymerase to bind and begin synthesizing a new DNA strand. The RNA primer is later removed and replaced with DNA by other enzymes. Therefore, the correct answer is that DNA primase creates a short RNA primer complementary to the DNA template.