DNA History, Structure, and Replication

DNA Today

PART I The History of DNA

Chargaff’s Rule Adenine must pair with Thymine Guanine must pair with Cytosine Bases form weak hydrogen bonds T A G C

DNA Structure Rosalind Franklin took an x-ray diffraction photograph of DNA. This photograph was later used to determine DNA’s double helix structure

DNA Structure In the 1950’s, Watson & Crick built the first model of DNA using Franklin’s x-rays

Rosalind Franklin and Watson & Crick

The History of DNA One of the most recent major advances in DNA history was the Human Genome Project in 2000!!

Components and Structure of DNA PART II Components and Structure of DNA

DNA Deoxyribonucleic Acid Two strands coiled = double helix

DNA Deoxyribonucleic Acid Sides = pentose sugar Deoxyribose bonded to phosphate

DNA Deoxyribonucleic Acid Rungs (center) = nitrogen bases bonded together by: weak hydrogen bonds

DNA: Deoxyribonucleic acid Made up of subunits called nucleotides Nucleotide made of: 1. Phosphate group 2. 5-carbon sugar 3. Nitrogenous base

DNA Nucleotide O O=P-O N CH2 O C1 C4 C3 C2 Phosphate Group 5 Nitrogenous base (A, G, C, orT) CH2 O C1 C4 C3 C2 5 Sugar (deoxyribose)

DNA P O 1 2 3 4 5 P O 1 2 3 4 5 G C T A

History Review

PART III DNA Replication

Replication Facts DNA has to be copied before a cell divides DNA is copied during the S or synthesis phase of interphase New cells will need identical DNA strands

Synthesis Phase (S phase) S phase during interphase of the cell cycle Mitosis -prophase -metaphase -anaphase -telophase G1 G2 S phase interphase DNA replication takes place in the S phase.

DNA Replication Begins at Origins of Replication New strands grow at the forks Replication Fork Parental DNA Molecule 3’ 5’

Question: DNA 5’-CGTATG-3’ What would be the complementary DNA strand for the following DNA sequence? DNA 5’-CGTATG-3’

Answer: DNA 5’-GCGTATG-3’ DNA 3’-CGCATAC-5’

DNA Damage & Repair Chemicals & ultraviolet radiation damage the DNA in our body cells Cells must continuously repair DAMAGED DNA

Chromatin, Chromosomes, and Genes Structure Chromatin: DNA and protein tightly packed together Histones: proteins that DNA wraps around HISTONES DNA

Chromatin, Chromosomes, and Gene Structure Chromosomes: Chromatin packs tightly together to form the chromosomes that you see in mitosis during the cell cycle. Genes: Specific pieces of DNA that code for specific traits.

Wrap Up In the end of DNA replication, each OLD strand of DNA has been COPIED to produce two NEW strands.