How DNA copies itself
Grade 9 Science Worksheet - Building Confidence
Circle the best answer.
Ari watches DNA polymerase build a new strand on an unzipped ladder. Which letters belong in the two blanks, left to right?
- T, then G
- A, then G
- U, then C
- T, then C
Bo sees DNA polymerase pause after building CATG. Which nucleotide does it add next?
- A, which pairs with the old C
- C, which copies the old C
- T, which pairs with the old C
- G, which pairs with the old C
Unzipped ladder (model, not to scale). Letters line up pair by pair from the left. Esme fills in the first and last letters of a new strand. Which letters belong in the two blanks, left to right?
- G, then A
- G, then T
- C, then A
- A, then T
Read this first
Enzyme job card (textbook facts)
enzyme job at the fork helicase opens the helix at the fork DNA polymerase adds matching nucleotides to the new strand ligase seals gaps in the new strand Kira reads the card. What does DNA polymerase do at the fork?
- It adds matching nucleotides to the 3′ end of the new strand
- It opens the helix by breaking the hydrogen bonds
- It copies the old letters onto the new strand
- It builds without mistakes, so nothing checks the new strand
Proofreading card (textbook facts)
step what the polymerase does adds a base pairs a new nucleotide with the old strand reads the base checks that the new base paired correctly fixes a wrong base releases the wrong nucleotide and adds the correct one Luz reads the proofreading card. DNA polymerase finds a wrong base in the new strand. What does it do?
- It leaves the wrong base, because copying makes no mistakes
- It releases the wrong nucleotide and adds the correct one
- It changes the old strand to match the wrong base
- It stops, and the cell starts over with new strands
Three ways to copy a double helix (model data)
model what each new double helix holds W short old and new pieces mixed along both strands X one helix holds both old strands and the other holds both new strands Y each helix holds one old strand and one new strand Milo compares three models of copying DNA. Which model is semiconservative replication, and why?
- Model Y, because each copy is made of two new strands
- Model W, because old and new pieces are mixed
- Model X, because the old strands stay together
- Model Y, because each copy keeps one old strand
Strand count after one round (model data)
molecule old strands new strands both copies together 2 2 copy 1 ? ? Pia reads the strand count after one round of copying. What fills the two ? cells for copy 1?
- 1 old strand and 1 new strand
- 2 old strands and 2 new strands
- 2 old strands and 0 new strands
- 0 old strands and 2 new strands
Ren watches the new strand ATG grow. Which end does DNA polymerase add the next nucleotide to?
- The 3′ end of the new strand, on the right
- The 5′ end of the old strand, on the right
- The 5′ end of the new strand, on the left
- The 3′ end of the old strand, on the left
Use this
Unzipped ladder (model, not to scale). Old strand, 3′ to 5′: GCTAAC. New strand: CGATTG. The ends of the new strand are not labeled. Letters line up pair by pair from the left.
Tala sees the old strand written 3′ to 5′, left to right. How is the new strand written, left to right?
- 5′ to 3′, because the two strands run in opposite directions
- 3′ to 5′, because the polymerase adds to the 5′ end
- 3′ to 5′, because a copy keeps the direction of its old strand
- Either way, because the ends do not change the pairing
Zee sees the new strand 5′ ATG 3′ on the old strand 3′ TACGG 5′. The polymerase adds one nucleotide. What does the new strand read now?
- 5′ ATGG 3′
- 5′ ATGC 3′
- 5′ CATG 3′
- 5′ ATGU 3′
