1. DNA Structure & Replication

2. DNA and its Structure
DNA stands for deoxyribonucleic acid and carries the genetic information in all types of living organisms
DNA consists of two strands of nucleotides wound together in a spiral called a double helix

3. DNA and its structure Each nucleotide is composed of:
A phosphate group
A sugar molecule
One of four different nitrogenous bases:
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
The phosphate and sugar parts of the nucleotides form the sides of the ladder in the DNA double helix

4. DNA and its structure
The nitrogenous bases of the nucleotides extend toward the center of the double helix, forming the rungs of the ladder
Each base is matched with a complementary base in the other strand
In accord with the base-pairing rules:
Adenine (A) pairs with Thymine (T)
Guanine (G) pairs with Cytosine (C)
The two strands are held together by hydrogen bonds formed between the paired bases

5. DNA and its structure

6. dna & Chromosomes
Chromosomes are thread-like structures located inside the nucleus of animal and plant cells
Each chromosome contains a DNA molecule, which contains multiple genes
Chromosomes are not always visible; They usually sit around uncoiled and as loose strands called chromatin
When it is time for the cell to divide, they condense and wrap up very tightly
The tightly-wound DNA is the chromosome

7. DNA & chromosomes
Chromosomes look like an “X” and they are usually found in pairs
Scientists count individual strands of chromosomes because not every organism has pairs
Humans have 46 chromosomes (or 23 pairs)
Peas only have 12 chromosomes, and dogs have 78
More chromosomes does NOT equal a more complex or intelligent creature

8. Dna & chromosomes

9. DNA Replication
Replication is the process where DNA makes a copy of itself
It produces two new DNA molecules that are identical to the original DNA molecule
Each of the new DNA molecules carry the same genetic information as the original DNA molecule

10. DNA Replication Why does DNA need to copy?
It’s simple: Cells divide for an organism to grow or reproduce, and every new cells needs a copy of the DNA or instructions to know how to be a cell
DNA replicates right before a cell divides

11. DNA Replication DNA replication is semi-conservative
That means that when it makes a copy, one half of the old strand is always kept in the new strand
This helps reduce the number of copy errors (a.k.a. mutations)

12. DNA Replication
During replication, enzymes called helicases separate DNA strands by moving along the strand and breaking the hydrogen bonds between base pairs
The Y-shaped region that results when the two strands separate is called a replication fork
Each old strand is used as a template to form a new DNA strand

13. DNA Replication
Next, enzymes called DNA polymerase add complementary nucleotides (free floating in the nucleus) to each of the original strands
The result is two separate and identical DNA molecules that are ready to move to new cells for in cell division
In each new DNA double helix, one strand is from the original molecule, and one strand is new (hence the name, ‘semi-conservative’)

14. DNA replication

15. DNA Replication

16. Brainpop video & quiz activity