DNA Structure Chapter 8

http://youtu.be/zwibgNGe4aY Be ready to write down 3 things you remember from the video!

DNA Stands for… DNA: Deoxyribonucleic acid Very large biomolecule made up of nucleotides Called the “blueprints of life” because it contains genetic information for the construction of proteins.

Floats freely in the cytoplasm of prokaryotes Protected in the nucleus of eukaryotes

Nucleotide: DNA subunit (monomer) made up of 3 parts Deoxyribose sugar Phosphate group Nitrogenous base

DNA Structure Made of 2 nucleotide chains that wrap around each other to form a double helix (looks like a spiral staircase) The sides: Alternating Sugar, phosphate, sugar, phosphate The middle: Nitrogen bases paired together.

Scientists Involved in Discovery of DNA James Watson & Francis Crick developed double helix model of DNA other scientists working on finding the structure: Rosalind Franklin Maurice Wilkins Linus Pauling Franklin Wilkins Pauling Watson & Crick’s model was inspired by 3 recent discoveries: Chargaff’s rules Pauling’s alpha helical structure of a protein X-ray crystallography data from Franklin & Wilkins

1953 article in “Nature” Watson and Crick Watson Crick

Nitrogenous Bases There are 2 groups of nitrogenous bases: purines and pyrimidines Purines: Made up of two rings of carbon and nitrogen Adenine (A), Guanine (G)

Pyrimidines: Bases that have one ring of carbon and nitrogen Thymine (T), Cytosine (C)

Identifying the structure… Purine + purine: too wide Pyrimidine + pyrimidine: too narrow Purine + pyrimidine: width consistent with X-ray data

pair with Pyrimidine (C, T) Conclusion: Purine (A, G) pair with Pyrimidine (C, T) Adenine (A) Thymine (T) Guanine (G) Cytosine (C)

Chargaff’s Base Pairing Rules DNA composition: “Chargaff’s rules” varies from species to species all 4 bases not in equal quantity bases present in characteristic ratio humans: A = 30.9% T = 29.4% G = 19.9% C = 19.8% 1947 That’s interesting! What do you notice?

A pairs with T “Always Together” G pairs with C “Get Closer” Chargaff’s Base Pairing Rules: A pairs with T “Always Together” G pairs with C “Get Closer”

Summary Summarize what we just talked about by: Come up with 3 alternate titles for our notes OR Drawing a picture to remember base pairing OR Writing about how DNA structure is like a staircase