unit 3.1: replication

Replication

Replication

DNA makes a copy of itself prior to cell division

Central Dogma

Mechanism by which the information is transferred to the cell

sister chromatids

• at anaphase stage and at the end of cytokinesis

• each would have the genetic material

nucleus

Site

Semi-conservative

• Parental DNA strands separate into two

• Each separated strand serves as template for the synthesis of a complementary strand

• each double stranded daughter DNA molecule, will have one template strand and a newly synthesized strand

Bidirectional

occurs in two opposite directions

Conservative

Old strands bind together and new strands bind together

Non-conservative

each strands consists of old and new DNA

Helicase

Replication Machinery:

• Unwinds the two DNA strands at the replication fork

• Allows strands of DNA to open up into a replication bubble

Replication fork

the junction at which it expands

Single-strand DNA binding proteins (SSB)

Replication Machinery:

• Stabilize ssDNA as it forms so it will not anneal to reform the double helix

• Keeps the two strands separated

nucleases

Replication Machinery: SSB

• Protects ssDNA from hydrolysis done by ___

erroneous

Replication Machinery: SSB

• DNA in nature is double stranded so when it sees a single stranded DNA, it is assumed to be ___

DNA Gyrase (Topoisomerase II)

Replication Machinery:

• Releases the tensions (positive supercoils) ahead of the replication fork caused by the unwinding of the DNA helix

• It cuts the sequence further down the DNA to relieve tension of the DNA

Replication Origins

• Indicates the initiation site for DNA replication

• Point where DNA would unwind

Replication Bubble

Small region where parental strands have already separated and the complementary strand begins to be synthesized

Replication Fork

• both ends of the replication bubble

• Moves in opposite directions

Unwinding of parental strands

Replication Process:

1. through helicase protein binding creating a replication for

   1. replication fork and replication bubble will start to form

Stabilizing the ssDNA

Replication Process:

2. through the single-strand DNA binding proteins (SSB) at the replication fork

   1. to avoid the reannealing of the double helix

Primase binding

Replication Process:

3. to synthesize short RNA primer

it provides the 3’-OH group, to which new nucleotides are added

Replication Process: Primase binding

Why is RNA primer needed?

Primase

Replication Process: Primase binding

RNA polymerase enzyme that is responsible for copying short stretch of DNA template to produce primers

Primers

Replication Process: Primase binding

short strands of RNA that provide 3’ OH group where new nucleotides will be added

DNA polymerase binding at the DNA template

Replication Process:

4. adds DNA nucleotide at the RNA primer

DNA Polymerase III

Replication Process: DNA polymerase binding

• primary DNA replicating enzyme responsible for synthesizing new DNA strand from the DNA template; only adds new nucleotides to the existing strand

• cannot initiate synthesis of new DNA strand on its own without primers

Adding of nucleotides

Replication Process:

5. by DNA polymerase in a 5’ to 3’ direction to both parental DNA template

Discontinuous synthesis

Replication Process:

6. The other strand produced short fragments (Okazaki fragments),

DNA ligase

Replication Process: Discontinuous synthesis

These Okazaki fragments that are formed in the lagging strand (3’-5’) are later sealed together by ___

150-200 base pairs

Replication Process: Discontinuous synthesis

Length of Okazaki fragments

Leading strand

Replication Process: Discontinuous synthesis

synthesized continuously towards the replication fork

Lagging strand

Replication Process: Discontinuous synthesis

synthesized discontinuously away from the replication fork forming Okazaki fragments

DNA polymerase proofreading

Replication Process:

7. ___ the newly synthesized DNA and replacing incorrect bases

Polymerization

Replication Process: DNA Polymerase Main activities

• used by the DNA polymerase to add nucleotides to the growing chain during DNA synthesis

  • 5’ to a 3’ direction

Exonuclease

Replication Process: DNA Polymerase Main activities

• remove the incorrect nucleotides and replace them with the correct ones

  • 3’ to 5’ direction

Annealing helicase

Replication Process:

8. rewinding the DNA double helix and ligase sealing the sugar phosphate