1. Replication
1 DNA
2 DNA

2. WHAT is replication?
“The process where a DNA molecule is copied to make two identical DNA molecules.”
Replication makes a REPLICA, a copy, of the original DNA

4. WHY does replication occur?
When a cell divides into two new cells, it needs to send a copy of the DNA to both new cells
We must replicate the DNA so that the genetic code can be given to both “daughter cells”

5. WHEN does replication occur?
DNA is replicated just before the cell divides
The time before cell division is called “interphase” – this is when replication occurs
Replication occurs during the S (synthesis) stage of interphase

6. WHERE does replication occur?
In the nucleus
Remember that DNA makes up the chromosomes, and these are in the nucleus. So replication must happen in the nucleus!

7. WHO has replication? Every living thing!
Includes all animals, plants, fungi, protists, and bacteria!

8. HOW does replication occur?
There are four steps in the process of replication.
Use these quick steps to help you remember the details:
Unzip DNA
Base Pairing
Build Backbone
Semi-Conservative Replication
UBBS

9. “Zippers” = DNA
“Teeth” = Nitrogenous Bases (A, T, G, C)

10. Identical patterns of bases in the new DNA molecules!
Parent
Strand
LOOK!
Identical patterns of bases in the new DNA molecules!
Daughter
Strands

11. HOW does replication occur?
Step One:
Unzip DNA
The parent DNA molecule is unzipped by an enzyme called “helicase.”
The enzyme separates the base pairs by breaking the weak hydrogen bonds between them.

12. Hydrogen Bonds Hydrogen bonds are weak.
A-T
has 2
H Bonds
G-C
has 3
H Bonds
Hydrogen bonds are weak.
This makes them easy to break and easy to rebuild.

13. HOW does replication occur?
Step Two:
Base Pairing
Free nucleotides floating in the nucleus form Hydrogen bonds with their complementary pair.
Adenine bonds with Thymine, and Guanine bonds with Cytosine.
The enzyme called “DNA Polymerase” is needed to build the new strands.
This happens on both sides of the double helix, making two double helices with the same base pairs in the same order.
“AT – GC!!!”

14. HOW does replication occur?
Step Three:
Build Backbone
The H bonds hold the base pairs together in the middle, but the sides of the molecule also need to join together.
The backbones are made of deoxyribose sugar and phosphate.
The phosphate bonds to the sugar, finishing the new DNA molecule.
Sugar
Phosphate

15. HOW does replication occur?
Step Four:
Semi-Conservative Replication
The final product is two identical DNA molecules.
Both molecules are half old and half new – they both include one original parent strand, and one new daughter strand.
Since half of the old molecule is kept, it is “semi-conservative.”

17. What happens if there’s a mistake?
Mistakes in this process do occur occasionally – these are mutations!!
Most mutations are so minor that they have no impact on the organism, and the cell has ways of correcting many mistakes.
Sometimes mutations can be harmful or helpful to the organism – the organism might get new traits or lose old traits – and these new characteristics can lead to the evolution of the species!