Molecular Genetics-1️⃣DNA Replication Steps

Question 1

STAGE 1: Semi Conservative Replication and Seperating the Strands

What is Semiconservative Replication

Definition

Answer 1

When each new DNA molecule is made of one parent strand and one newly synthesized strand.

*ie: Parent Strand=TGGCA—>New Strand=ACCGT

Question 2

STAGE 1: Semi Conservative Replication and Seperating the Strands

What is the Process of Stage 1: Seperating the DNA Strands

DNA Replication

Answer 2

1. DNA gets unwound at origin replication (starting point)
2. Helicase enzyme binds to origin, unwinding the DNA by breaking H Bonds.
3. The now seperated strands make a replication fork
4. SSB (single stranded binding protein) keeps the seperated strands from reforming (reannaling)
   5.Topoisomerase enzyme relieves tension from strands that want to twist upon itself by cutting the sugar phosphate backbone, making the strands untwists itselves and then reseal it.

ENZYMES: Helicose & Topoisomerase|Key terms: origin,replication fork,SSB

Question 3

STAGE 2: BUILDING COMPLEMENTARY STRANDS

What is the Process of Stage 2: Building Complementary Strands

DNA Replication

Answer 3

After the strands are seperated…

1. Primase enzyme is used to add temporary RNA primers to each parent strand so nucleotides can be attached to something.
2. Elongation Phase: **DNA Polymerase III **adds the free nucleotides in 5’ to 3’ direction to each strand
3. One strand it built as the leading strand, the other built as the lagging strand
4. Termination Phase:Ligase joins the Okazaki fragments through phosphodiester bonds to make 2 new double straded daughter strands.

ENZYMES: Primase, DNA Polymerase III & Ligase

Question 4

What is the Process of Stage 3: Correcting Errors

DNA Replication

Answer 4

Background Info: the A-T, C-G base pairs might mismatch, a nucleotide could skip, etc. so proofreading is done so these errors are not permanent.
1. Exonuclease (cut from outside) :The replicatiion process stalls so DNA Polymerase I or II can act as exonuclease, cutting out the incorrect base and replacing it with the the correct one.
2. Endonuclease (cuts from the inside): If the base pair mismatch changes the width, enzyme group acts as endonuclease (cuts from the inside)
*Remaining Errors are mutations.

Key Terms: Polymerase I & II, Exo+Endo nuclease, mutations,