1. Chromosomes & DNA Replication

2. DNA & Chromosomes Prokaryotes Eukaryotes circular chromosomes
DNA is found in cytoplasm
Eukaryotes
Located in nucleus
1000x more DNA than prokaryotes
Number of chromosomes varies (human has 46, fruit flies has 8)

3. DNA Length Very long DNA in one human cell is one meter long
Ex: Imagine stuffing 300m of rope into your back pack

4. Chromosome Structure
Contain DNA & protein (histones) packed together called chromatin
Not visible until cell division

5. Chromosome Structure

6. DNA Replication Before a cell divides it copies its DNA (replication)
Each new cell now has a complete set of DNA
The DNA molecule separates into two strands
Two new strands follow the rules of base pairing (C with G, A with T)
EX: a sequence of base pairs with TACGTT would have a complimentary strand of ATGCAA

7. DNA Replication

8. Cell Reproduction Facts
Adults produce about 2 trillion cells a day
Replacement cells are exact copies of the old cells
Some cells, like hair & nails, are replaced constantly
Other cells, like brain & nerve cells are rarely replaced
Replicating DNA provides both daughter cells with a complete set of DNA.

9. Cells divide because
Large cells an inefficient. (diffusion of wastes/nutrients take too long)
Growth & Development
Replace old cells
Replace damaged cells