Question

identify the structure

1. ____________ enzyme that untwist dna
2. ____________ fragments of copied dna created on the lagging strand
3. ____________ the strand that is copied in a continuous way
4. ____________ binds okazaki fragments
5. ____________ builds a new dna strand by adding complementary bases
6. ____________ stabilizes the dna molecule during replication
7. ____________ strand that is copied discontinuously
8. ____________ initiates the synthesis dna by creating a short rna segment
9. ____________ enzyme that break the hydrogen bonds between bases

Explanation:

To solve this, we recall the components and enzymes involved in DNA replication:

1. Enzyme that untwist DNA

Step1: Recall DNA replication enzymes. Helicase unwinds, but topoisomerase untwists (relieves supercoiling). Wait, correction: Topoisomerase (or sometimes called gyrase in prokaryotes) untwists DNA. But often, the enzyme that untwists (relieves torsion) is topoisomerase. However, if "untwist" refers to unwinding the double helix, Helicase does that. Wait, the question says "untwist" (supercoiling vs. unwinding). Let's check standard terms:

• Topoisomerase (or Gyrase) relieves supercoiling (untwists the overwound DNA ahead of replication fork).
• Helicase unwinds the double helix (breaks H-bonds between bases).

But the term "untwist" here might refer to relieving supercoiling. However, sometimes "untwist" is used for unwinding. Let's confirm:

2. Fragments of copied DNA on lagging strand

Step1: Lagging strand is synthesized in fragments called Okazaki fragments.

3. Strand copied continuously

Step1: The leading strand is synthesized continuously (5’→3’ direction, same as replication fork movement).

4. Binds Okazaki fragments

Step1: DNA Ligase joins (binds) Okazaki fragments with phosphodiester bonds.

5. Builds new DNA strand (adds complementary bases)

Step1: DNA Polymerase III (in prokaryotes) or DNA Polymerase δ/ε (in eukaryotes) adds complementary nucleotides to build the new strand.

6. Stabilizes DNA during replication

Step1: Single-Strand Binding Proteins (SSBPs) bind to single-stranded DNA to prevent reannealing and stabilize it.

7. Strand copied discontinuously

Step1: The lagging strand is synthesized discontinuously (as Okazaki fragments).

8. Initiates DNA synthesis (short RNA segment)

Step1: Primase is an RNA polymerase that synthesizes a short RNA primer to initiate DNA replication.

9. Enzyme that breaks H-bonds between bases

Step1: Helicase breaks the hydrogen bonds between complementary bases to unwind the DNA double helix.

Final Answers (filling the blanks):

1. Topoisomerase (or Gyrase) / Helicase (context-dependent; if "untwist" = relieve supercoiling: Topoisomerase; if "untwist" = unwind helix: Helicase)
2. Okazaki fragments
3. Leading strand
4. DNA Ligase
5. DNA Polymerase (III in prokaryotes, δ/ε in eukaryotes)
6. Single-Strand Binding Proteins (SSBPs)
7. Lagging strand
8. Primase
9. Helicase

(Note: For question 1, there’s some ambiguity, but “Topoisomerase” is more accurate for “untwisting” (relieving supercoiling), while “Helicase” unwinds the helix. Adjust based on textbook definitions.)

Answer:

To solve this, we recall the components and enzymes involved in DNA replication:

1. Enzyme that untwist DNA

Step1: Recall DNA replication enzymes. Helicase unwinds, but topoisomerase untwists (relieves supercoiling). Wait, correction: Topoisomerase (or sometimes called gyrase in prokaryotes) untwists DNA. But often, the enzyme that untwists (relieves torsion) is topoisomerase. However, if "untwist" refers to unwinding the double helix, Helicase does that. Wait, the question says "untwist" (supercoiling vs. unwinding). Let's check standard terms:

• Topoisomerase (or Gyrase) relieves supercoiling (untwists the overwound DNA ahead of replication fork).
• Helicase unwinds the double helix (breaks H-bonds between bases).

But the term "untwist" here might refer to relieving supercoiling. However, sometimes "untwist" is used for unwinding. Let's confirm:

2. Fragments of copied DNA on lagging strand

Step1: Lagging strand is synthesized in fragments called Okazaki fragments.

3. Strand copied continuously

Step1: The leading strand is synthesized continuously (5’→3’ direction, same as replication fork movement).

4. Binds Okazaki fragments

Step1: DNA Ligase joins (binds) Okazaki fragments with phosphodiester bonds.

5. Builds new DNA strand (adds complementary bases)

Step1: DNA Polymerase III (in prokaryotes) or DNA Polymerase δ/ε (in eukaryotes) adds complementary nucleotides to build the new strand.

6. Stabilizes DNA during replication

Step1: Single-Strand Binding Proteins (SSBPs) bind to single-stranded DNA to prevent reannealing and stabilize it.

7. Strand copied discontinuously

Step1: The lagging strand is synthesized discontinuously (as Okazaki fragments).

8. Initiates DNA synthesis (short RNA segment)

Step1: Primase is an RNA polymerase that synthesizes a short RNA primer to initiate DNA replication.

9. Enzyme that breaks H-bonds between bases

Step1: Helicase breaks the hydrogen bonds between complementary bases to unwind the DNA double helix.

Final Answers (filling the blanks):

1. Topoisomerase (or Gyrase) / Helicase (context-dependent; if "untwist" = relieve supercoiling: Topoisomerase; if "untwist" = unwind helix: Helicase)
2. Okazaki fragments
3. Leading strand
4. DNA Ligase
5. DNA Polymerase (III in prokaryotes, δ/ε in eukaryotes)
6. Single-Strand Binding Proteins (SSBPs)
7. Lagging strand
8. Primase
9. Helicase

(Note: For question 1, there’s some ambiguity, but “Topoisomerase” is more accurate for “untwisting” (relieving supercoiling), while “Helicase” unwinds the helix. Adjust based on textbook definitions.)