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Nucleic Acids

A-Level AQA Biology

This pack of flashcards covers the intricate details of DNA replication. It includes the roles of enzymes like DNA helicase, polymerase, and ligase, the concept of 3' and 5' ends of DNA strands, the significance of leading and lagging strands, the formation and joining of Okazaki fragments, and the principles of semi-conservative replication demonstrated by the Meselson-Stahl experiment.

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"Describe the process of DNA replication in a cell."	"DNA replication is the process by which a cell duplicates its DNA before it splits in half to create new cells. This process occurs in the S-phase of interphase in the cell cycle. It involves the unwinding of the DNA double helix, separation of the two strands, and the formation of new complementary strands."
"Define the 3’ (prime) end and the 5’ (prime) end in the context of a DNA strand."	"In a DNA strand, the 3’ (prime) end and the 5’ (prime) end refer to the top and bottom of each strand. The number refers to which carbon within the deoxyribose sugar of the nucleotide is closest to the top/bottom."
"How does the enzyme DNA helicase contribute to DNA replication?"	"DNA helicase is an enzyme that breaks the hydrogen bonds between the complementary bases of the two DNA polymers within the double helix. This causes the double helix to unwind, and the two strands to separate or unzip, which is a crucial step in DNA replication."
"Explain the role of free-floating DNA nucleotides in DNA replication."	"Free-floating DNA nucleotides within the nucleus play a crucial role in DNA replication. If a free-floating DNA nucleotide aligns next to a complementary base on either template strand of DNA, then hydrogen bonds will form between them, creating a new strand of DNA."
"What is the replication fork in the context of DNA replication?"	"The replication fork is the point at which the unzipping of the DNA strands stops during DNA replication. Not all the DNA is unzipped in one go, as this increases the chances of copying errors resulting in mutations."
"Describe the role of DNA polymerase in DNA replication."	"DNA polymerase is responsible for forming the phosphodiester bond between nucleotides to create a new polymer chain of DNA. It can only attach at the 3’ end and moves along the template strand in the 3’ to 5’ direction."
"Define the terms 'leading strand' and 'lagging strand' in the context of DNA replication."	"The 'leading strand' is the new strand of DNA that is created in one continuous go as the enzyme moves towards the replication fork. The 'lagging strand' is the antiparallel strand where the DNA polymerase has to reattach at the 3’ end every time the replication fork unwinds further, creating small fragments of DNA called Okazaki fragments."
"What are Okazaki fragments and how are they formed?"	"Okazaki fragments are small fragments of DNA formed on the 'lagging strand' during DNA replication. They are created when the DNA polymerase has to reattach at the 3’ end every time the replication fork unwinds further."
"How does DNA ligase contribute to DNA replication?"	"DNA ligase is the enzyme that joins the Okazaki fragments together during DNA replication."
"Explain the concept of semi-conservative replication."	"Semi-conservative replication is a process where in DNA replication, one strand is conserved, and one new strand is created."
"Describe the experiment performed by Meselson and Stahl."	"Meselson and Stahl grew bacteria in a solution containing the 15N isotope, a heavier form of nitrogen. During replication, all the new DNA molecules incorporated this isotope in the nitrogenous base, proving the concept of semi-conservative replication."
"Describe the process of DNA replication in terms of the conservation of old DNA and the synthesis of new DNA."	"In DNA replication, 50% of the old DNA is always conserved, and 50% of the DNA is new. This is demonstrated by the DNA band settling at a lower point in the test-tube after centrifugation."
"How does the weight of DNA change after replication in a solution containing only the 14N lighter isotope of nitrogen?"	"After replication in a solution containing only the 14N lighter isotope of nitrogen, all the newly synthesized DNA will be lighter. This is demonstrated by all the DNA settling in the middle of the test-tube after centrifugation."
"Define the role of Helicase in the process of DNA replication."	"Helicase is the enzyme that unwinds and unzips the double helix during DNA replication."
"Define the role of DNA Polymerase in the process of DNA replication."	"DNA Polymerase is the enzyme that polymerizes the new DNA strand during DNA replication."
"Define the role of DNA Ligase in the process of DNA replication."	"DNA Ligase is the enzyme that joins the Okazaki fragments together during DNA replication."
"On which strand of the DNA are the Okazaki fragments located during replication?"	"The Okazaki fragments are located on the lagging strand during DNA replication."
"Does DNA polymerase attach to the 3’ or the 5’ end on the template strand during DNA replication?"	"During DNA replication, DNA polymerase attaches to the 3’ end on the template strand."

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Describe the process of DNA replication in a cell.

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DNA replication is the process by which a cell duplicates its DNA before it splits in half to create new cells. This process occurs in the S-phase of interphase in the cell cycle. It involves the unwinding of the DNA double helix, separation of the two strands, and the formation of new complementary strands.

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This ensures that each new cell receives an identical copy of the genetic information.","deleted_at":null,"flashcard_deck_id":"4zJBS","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1274312,"front":"Define the 3’ (prime) end and the 5’ (prime) end in the context of a DNA strand.","back":"In a DNA strand, the 3’ (prime) end and the 5’ (prime) end refer to the top and bottom of each strand. The number refers to which carbon within the deoxyribose sugar of the nucleotide is closest to the top/bottom.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"The 3' (prime) end and the 5' (prime) end of a DNA strand are determined by the numbering of carbon atoms in the deoxyribose sugar of the nucleotides. The 3' end refers to the carbon atom that is closest to the top/bottom of the strand, while the 5' end refers to the carbon atom that is furthest from the top/bottom. This numbering system is important for understanding the directionality and orientation of DNA strands during processes such as replication and transcription.","deleted_at":null,"flashcard_deck_id":"4zJBS","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1274313,"front":"How does the enzyme DNA helicase contribute to DNA replication?","back":"DNA helicase is an enzyme that breaks the hydrogen bonds between the complementary bases of the two DNA polymers within the double helix. This causes the double helix to unwind, and the two strands to separate or unzip, which is a crucial step in DNA replication.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"DNA helicase plays a crucial role in DNA replication by unwinding the double helix structure of DNA. This unwinding allows the two strands to separate, providing access for other enzymes and proteins involved in the replication process. This separation is essential for the accurate and efficient copying of the genetic information during DNA replication.","deleted_at":null,"flashcard_deck_id":"4zJBS","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1274314,"front":"Explain the role of free-floating DNA nucleotides in DNA replication.","back":"Free-floating DNA nucleotides within the nucleus play a crucial role in DNA replication. If a free-floating DNA nucleotide aligns next to a complementary base on either template strand of DNA, then hydrogen bonds will form between them, creating a new strand of DNA.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"Free-floating DNA nucleotides are essential for DNA replication as they serve as building blocks for the synthesis of new DNA strands. When they align with complementary bases on the template DNA strands, they form hydrogen bonds, allowing for the creation of a new DNA strand. This process is fundamental for the accurate and faithful replication of genetic information.","deleted_at":null,"flashcard_deck_id":"4zJBS","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1274315,"front":"What is the replication fork in the context of DNA replication?","back":"The replication fork is the point at which the unzipping of the DNA strands stops during DNA replication. Not all the DNA is unzipped in one go, as this increases the chances of copying errors resulting in mutations.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"The replication fork is a crucial structure in DNA replication. It forms when the double-stranded DNA molecule unwinds and separates into two single strands. At the replication fork, the DNA helicase enzyme unwinds the DNA, allowing the replication machinery to access the template strands for copying. The replication fork is dynamic and moves along the DNA molecule as replication progresses. It is essential for accurate and efficient DNA replication, as it ensures that only a small portion of the DNA is exposed at a time, reducing the risk of errors and mutations.","deleted_at":null,"flashcard_deck_id":"4zJBS","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1274316,"front":"Describe the role of DNA polymerase in DNA replication.","back":"DNA polymerase is responsible for forming the phosphodiester bond between nucleotides to create a new polymer chain of DNA. It can only attach at the 3’ end and moves along the template strand in the 3’ to 5’ direction.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"DNA polymerase plays a crucial role in DNA replication by catalyzing the formation of phosphodiester bonds between nucleotides. It adds nucleotides to the growing DNA strand in a specific direction, from the 3' end to the 5' end. This enzyme is essential for the accurate and efficient replication of DNA during cell division.","deleted_at":null,"flashcard_deck_id":"4zJBS","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1274320,"front":"Define the terms 'leading strand' and 'lagging strand' in the context of DNA replication.","back":"The 'leading strand' is the new strand of DNA that is created in one continuous go as the enzyme moves towards the replication fork. The 'lagging strand' is the antiparallel strand where the DNA polymerase has to reattach at the 3’ end every time the replication fork unwinds further, creating small fragments of DNA called Okazaki fragments.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"The leading strand is synthesized continuously in the direction of the replication fork, while the lagging strand is synthesized discontinuously in the opposite direction. This is due to the antiparallel nature of DNA strands. The lagging strand is synthesized in short fragments called Okazaki fragments, which are later joined together by DNA ligase. This process ensures efficient and accurate replication of the entire DNA molecule.","deleted_at":null,"flashcard_deck_id":"4zJBS","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1274324,"front":"What are Okazaki fragments and how are they formed?","back":"Okazaki fragments are small fragments of DNA formed on the 'lagging strand' during DNA replication. They are created when the DNA polymerase has to reattach at the 3’ end every time the replication fork unwinds further.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"Okazaki fragments are short segments of DNA that are synthesized on the lagging strand during DNA replication. They are formed because DNA polymerase can only synthesize DNA in the 5' to 3' direction. As the replication fork unwinds, the lagging strand is synthesized in short, discontinuous fragments, with each fragment starting with an RNA primer. These fragments are then joined together by DNA ligase to form a continuous strand. This process allows for efficient and accurate replication of the entire DNA molecule.","deleted_at":null,"flashcard_deck_id":"4zJBS","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1274325,"front":"How does DNA ligase contribute to DNA replication?","back":"DNA ligase is the enzyme that joins the Okazaki fragments together during DNA replication.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"DNA ligase plays a crucial role in DNA replication by joining the Okazaki fragments, which are short segments of DNA that are synthesized on the lagging strand during replication. These fragments are synthesized in the opposite direction of the replication fork, resulting in multiple fragments that need to be connected. DNA ligase catalyzes the formation of phosphodiester bonds between the adjacent fragments, creating a continuous DNA strand. This ensures the completion of DNA replication and the accurate transmission of genetic information.","deleted_at":null,"flashcard_deck_id":"4zJBS","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1274327,"front":"Explain the concept of semi-conservative replication.","back":"Semi-conservative replication is a process where in DNA replication, one strand is conserved, and one new strand is created.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"Semi-conservative replication is a fundamental process in DNA replication. It ensures that each new DNA molecule formed contains one original (conserved) strand and one newly synthesized strand. This mechanism allows for the accurate transmission of genetic information from one generation to the next. By conserving one original strand, the newly synthesized DNA molecule serves as a template for the next round of replication, maintaining the integrity and fidelity of the genetic code. This process was first proposed by Watson and Crick in 1953 and has since been confirmed through experimental evidence.","deleted_at":null,"flashcard_deck_id":"4zJBS","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1274332,"front":"Describe the experiment performed by Meselson and Stahl.","back":"Meselson and Stahl grew bacteria in a solution containing the 15N isotope, a heavier form of nitrogen. During replication, all the new DNA molecules incorporated this isotope in the nitrogenous base, proving the concept of semi-conservative replication.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"Meselson and Stahl conducted an experiment to investigate DNA replication. They used bacteria grown in a medium containing a heavy isotope of nitrogen (15N). By observing the density of DNA molecules in subsequent generations, they were able to demonstrate that DNA replication follows a semi-conservative mechanism, where each new DNA molecule consists of one original strand and one newly synthesized strand. This experiment provided crucial evidence for the understanding of how genetic information is faithfully passed on during cell division.","deleted_at":null,"flashcard_deck_id":"4zJBS","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1274336,"front":"Describe the process of DNA replication in terms of the conservation of old DNA and the synthesis of new DNA.","back":"In DNA replication, 50% of the old DNA is always conserved, and 50% of the DNA is new. This is demonstrated by the DNA band settling at a lower point in the test-tube after centrifugation.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"During DNA replication, the old DNA serves as a template for the synthesis of new DNA strands. The process begins with the separation of the DNA double helix into two strands. Each separated strand then serves as a template for the synthesis of a complementary strand. This results in the formation of two identical DNA molecules, each consisting of one old strand and one newly synthesized strand. The conservation of old DNA and the synthesis of new DNA can be observed through techniques such as centrifugation, where the DNA band settles at a lower point in the test-tube.","deleted_at":null,"flashcard_deck_id":"4zJBS","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1274343,"front":"How does the weight of DNA change after replication in a solution containing only the 14N lighter isotope of nitrogen?","back":"After replication in a solution containing only the 14N lighter isotope of nitrogen, all the newly synthesized DNA will be lighter. This is demonstrated by all the DNA settling in the middle of the test-tube after centrifugation.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"The newly synthesized DNA will be lighter after replication in a solution containing only the 14N lighter isotope of nitrogen. This is evident from the DNA settling in the middle of the test-tube after centrifugation, indicating a change in weight due to the incorporation of the lighter nitrogen isotope during replication.","deleted_at":null,"flashcard_deck_id":"4zJBS","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1274348,"front":"Define the role of Helicase in the process of DNA replication.","back":"Helicase is the enzyme that unwinds and unzips the double helix during DNA replication.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"Helicase plays a crucial role in DNA replication by breaking the hydrogen bonds between the base pairs, allowing the double helix to unwind and separate. This creates the replication fork, providing access for other enzymes and allowing the replication process to proceed.","deleted_at":null,"flashcard_deck_id":"4zJBS","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1274355,"front":"Define the role of DNA Polymerase in the process of DNA replication.","back":"DNA Polymerase is the enzyme that polymerizes the new DNA strand during DNA replication.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"DNA Polymerase plays a crucial role in DNA replication by catalyzing the addition of nucleotides to the growing DNA strand. It ensures accurate replication by proofreading and correcting errors. It also helps in unwinding the DNA double helix and synthesizing the complementary DNA strand. Without DNA Polymerase, DNA replication would not be possible.","deleted_at":null,"flashcard_deck_id":"4zJBS","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1274364,"front":"Define the role of DNA Ligase in the process of DNA replication.","back":"DNA Ligase is the enzyme that joins the Okazaki fragments together during DNA replication.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"DNA Ligase plays a crucial role in DNA replication by joining the Okazaki fragments. These fragments are short segments of DNA that are synthesized on the lagging strand during replication. DNA Ligase seals the gaps between these fragments by catalyzing the formation of phosphodiester bonds. This ensures that the newly synthesized DNA strands are continuous and complete. Without DNA Ligase, the Okazaki fragments would remain separate, leading to incomplete replication and genetic errors.","deleted_at":null,"flashcard_deck_id":"4zJBS","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1274373,"front":"On which strand of the DNA are the Okazaki fragments located during replication?","back":"The Okazaki fragments are located on the lagging strand during DNA replication.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"During DNA replication, the lagging strand is synthesized in short fragments called Okazaki fragments. This is because DNA replication occurs in a 5' to 3' direction, and the lagging strand is oriented in the opposite direction. As a result, the lagging strand is synthesized discontinuously in small fragments, while the leading strand is synthesized continuously. Okazaki fragments are later joined together by DNA ligase to form a complete strand.","deleted_at":null,"flashcard_deck_id":"4zJBS","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}},{"id":1274385,"front":"Does DNA polymerase attach to the 3’ or the 5’ end on the template strand during DNA replication?","back":"During DNA replication, DNA polymerase attaches to the 3’ end on the template strand.","front_language":"English","back_language":"English","front_image":"","back_image":"","order":0,"explanation":"DNA polymerase attaches to the 3' end on the template strand during DNA replication. This is because DNA replication occurs in the 5' to 3' direction, and DNA polymerase can only add nucleotides to the 3' end of the growing DNA strand. By attaching to the 3' end, DNA polymerase can synthesize the new DNA strand in the correct direction.","deleted_at":null,"flashcard_deck_id":"4zJBS","original_id":null,"examMode":{"text":"","correct":"","incorrect":"","info":""}}]

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