DNA Replication (bio test 5)

Why semiconservative?

Each new DNA molecule has one original strand and one newly synthesized strand

How does DNA polymerase know which nucleotides to add to the new strand during replication?

It follows base-pairing rules based on the original DNA strand

Why is DNA replication important of cell division and overall health?

• Helps ensure that each new cell created during cell division gets a complete/correct set of genetic instructions

• Protects against harmful mutations

• The original strand is a reliable guide

Topoisomerase

• Helps relax the tightly coiled DNA ahead of the replication fork by preventing super coiling/re-coiling

• Relieves tension as the helix unwinds

Helicase

• Unzips the DNA by breaking hydrogen bonds between base pairs

• Creates 2 single strands with a replication fork

Primase

• Adds short RNA primers

  • These RNA primers act as a starting point for DNA polymerase

DNA polymerase

• Adds new DNA nucleotides to the growing strand

• Proofreads for errors

• Removes RNA primers

• Creates leading and lagging strands

Ligase

• Joins the gaps between Okazaki fragments to create a continuous strand

• Joins specifically at the sugar-phosphate backbone

Replication fork

the Y-shaped region where DNA is unwound and replication is actively taking place

Okazaki fragments

short pieces of DNA made on the lagging strand during replication

Single-stranded binding proteins (SSBs)

bind to the separated DNA strands to prevent them from rejoining during replication

Chargaff’s rule

• A = T

• C = G

• Amounts are equal

What type of bond joins complementary base pairs?

Hydrogen bond

If a DNA molecule contains 40% cytosine, what percent adenine would you expect it to contain?

10%

At what point does DNA replication occur?

during the synthesis phase (S phase)

What is the main risk of having a DNA polymerase that lacks proofreading?

could cause mutations in the genetic information/instructions that could lead to certain syndromes, cancer, and miscarriage if unborn

If a cell had mostly mutated polymerase, what problems might arise during cell division?

structure/function differences and problems with the cell

Order the steps of DNA replication

1. Occurs during S phase

2. Topoisomerase 

3. Helicase

4. SSBs

5. Primase

6. DNA polymerase

7. Ligase

8. 2 DNA strands are formed

Why is the lagging strand synthesized in short fragments rather than continuously like the leading strand?

Because DNA polymerase can only build from the 5’ to 3’ direction, and the lagging strand runs in the opposite direction

Explain how DNA polymerase contributes to both the speed and accuracy of DNA replication. Why is this dual role important for the cell?

• Speed: Quickly adds complementary nucleotides to build the new DNA strand

• Accuracy: Proofreads and corrects mistakes to prevent mutations

• Why it's important: Ensures DNA is copied quickly and correctly, allowing cells to divide while maintaining accurate genetic information