unit 3.1: 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