AS Biology Cambridge DNA and protein synthesis flashcards

All 23 cards

1. Card 1

   Define the term 'polynucleotide strand' in the context of DNA structure.

   A polynucleotide strand is a polymer made up of repeating monomer units called nucleotides. In DNA, two such strands run in opposite directions, forming a double helix.

2. Card 2

   Describe the components that make up a single nucleotide.

   Each nucleotide is composed of three main parts: a phosphate group, a deoxyribose sugar, and a nitrogenous base. These components are essential for forming the DNA structure.

3. Card 3

   Explain the concept of 'antiparallel' strands in a DNA molecule.

   Antiparallel refers to the orientation of the two polynucleotide strands in DNA. They run in opposite directions, meaning that the 5' end of one strand aligns with the 3' end of the other, and vice versa.

4. Card 4

   Describe how hydrogen bonds contribute to the stability of the DNA double helix.

   Hydrogen bonds form between complementary nitrogenous bases on opposite strands of the DNA molecule. These weak bonds collectively hold the two polynucleotide strands together, maintaining the double helix structure.

5. Card 5

   Explain the complementary base pairing rule in DNA.

   The complementary base pairing rule states that adenine (A) always pairs with thymine (T), and cytosine (C) always pairs with guanine (G). This specific pairing ensures the consistent width of the DNA double helix and is crucial for replication.

6. Card 6

   Distinguish between purine and pyrimidine bases, providing examples from DNA.

   Purine bases have a double-ring structure and include adenine and guanine. Pyrimidine bases have a single-ring structure and include thymine and cytosine. In DNA, a purine always pairs with a pyrimidine.

7. Card 7

   Describe the structure and function of the sugar-phosphate backbone in DNA.

   The sugar-phosphate backbone forms the structural framework of each DNA strand. It consists of alternating deoxyribose sugars and phosphate groups linked by phosphodiester bonds, providing stability and protecting the nitrogenous bases.

8. Card 8

   Define a phosphodiester bond and explain where it is found in a DNA strand.

   A phosphodiester bond is a covalent bond that links the phosphate group of one nucleotide (at its 5' end) to the carbon 3 of the deoxyribose sugar of an adjacent nucleotide (at its 3' end). These bonds form the sugar-phosphate backbone.

9. Card 9

   Explain the significance of a complete turn of the double helix occurring every 10 base pairs.

   The consistent helical structure of DNA, with a complete turn every 10 base pairs, is a fundamental characteristic. This regular coiling contributes to the molecule's stability and its ability to be efficiently packaged within the cell.

10. Card 10

    Outline the first step in the semi-conservative replication of DNA.

    The first step in semi-conservative replication is the unwinding of the DNA double helix. This process exposes the individual strands, making them accessible for replication.

11. Card 11

    Describe the role of the helicase enzyme in DNA replication.

    Helicase is an enzyme responsible for breaking the hydrogen bonds between the complementary nitrogenous bases of the two DNA strands. This action causes the double helix to separate, forming a replication fork.

12. Card 12

    Explain the process of activation of free nucleotides before they are incorporated into a new DNA strand.

    Free nucleotides are activated by the addition of two extra phosphate groups. This phosphorylation provides the necessary energy for the formation of phosphodiester bonds during DNA synthesis.

13. Card 13

    How do both original DNA strands act as template strands during replication?

    During replication, each of the separated original DNA strands serves as a template. Activated free nucleotides then pair up with their complementary bases on each template strand, guiding the synthesis of new strands.

14. Card 14

    Describe the function of DNA polymerase in the synthesis of a new DNA strand.

    DNA polymerase adds activated nucleotides one by one to the new growing DNA strand, following the complementary base pairing rule. It also forms phosphodiester bonds between adjacent nucleotides, creating the polynucleotide chain.

15. Card 15

    Explain the directionality of DNA synthesis by DNA polymerase.

    DNA polymerase can only add nucleotides in the 5' to 3' direction. This directional constraint has significant implications for how the leading and lagging strands are synthesized during replication.

16. Card 16

    Distinguish between the synthesis of the leading strand and the lagging strand during DNA replication.

    The leading strand is synthesized continuously in the 5' to 3' direction, moving towards the replication fork. In contrast, the lagging strand is synthesized discontinuously in the 5' to 3' direction, away from the replication fork, forming Okazaki fragments.

17. Card 17

    What are Okazaki fragments and on which strand are they formed?

    Okazaki fragments are short segments of newly synthesized DNA that are formed on the lagging strand during DNA replication. They are created because DNA polymerase can only synthesize DNA in the 5' to 3' direction.

18. Card 18

    Describe the role of the ligase enzyme in DNA replication.

    The ligase enzyme is responsible for joining the Okazaki fragments together on the lagging strand. It forms phosphodiester bonds between these fragments, creating a continuous new DNA strand.

19. Card 19

    Explain why the process of DNA replication is described as 'semi-conservative'.

    DNA replication is semi-conservative because each newly formed DNA molecule consists of one original (parental) strand and one newly synthesized strand. This mechanism conserves half of the original DNA molecule in each new copy.

20. Card 20

    Evaluate the importance of complementary base pairing for accurate DNA replication.

    Complementary base pairing is crucial for accurate DNA replication as it ensures that the correct nucleotides are incorporated into the new strands. This precision minimizes errors and ensures that the genetic information is faithfully passed on to daughter cells.

21. Card 21

    How does the antiparallel nature of DNA strands influence the replication process?

    The antiparallel nature means that while one template strand can be read continuously by DNA polymerase, the other must be read discontinuously. This leads to the formation of a leading strand and a lagging strand, each synthesized differently.

22. Card 22

    Explain the significance of the 5' and 3' ends of a nucleotide in forming phosphodiester bonds.

    The 5' end of a nucleotide contains the phosphate group, while the 3' end contains the hydroxyl group on the deoxyribose sugar. The phosphodiester bond forms specifically between the phosphate of one nucleotide at its 5' end and the 3' carbon of the sugar of another nucleotide.

23. Card 23

    Compare the structure of a purine base with that of a pyrimidine base.

    Purine bases (adenine and guanine) have a double-ring structure, consisting of a six-membered ring fused to a five-membered ring. Pyrimidine bases (cytosine and thymine) have a simpler single-ring structure, comprising only a six-membered ring.

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