Goal #1:

DNA STRUCTURE

11/21/11

I. Genes Sections of DNA that hold instructions to make you!

1. Is made of…–Carbon–Oxygen–Nitrogen–Hydrogen–Phosphorus

II. DeoxyriboNucleic Acid

This is why we studied

chemistry!

2. Sugar-phosphate backbone• deoxyribose and phosphates from

the nucleotides connected together

3. Nucleotides• These repeating units made of

Sugar + Phosphate + Base are the basic structure of DNA

a. Sugar - Deoxyribose

1. A sugar that makes up DNA2. De-oxy-ribose (ribose sugar short 1

oxygen)

b. Phosphate Group

• One phosphorous atom surrounded by four Oxygen atoms.

c. Nitrogenous Base1. DNA is like a language

with four letters. Those four letters are short hand for the following molecules:

2. A – Adenine 3. T – Thymine4. C – Cytosine5. G - Guanine

6. Purines vs. Pyrimidines

a. Purines- nitrogenous bases with a double ring of carbon and nitrogen• Adenine and Guanine

b. Pyrimidines- nitrogenous bases with a single ring of carbon and nitrogen

• Thymine and Cytosine

What bases belong where the white circles are?

Sides of ladder are made of deoxyribose sugars & phosphates

Rungs (steps) of ladder are made of Nitrogenous Bases

DNA is often referred to as a ladder because of its ladder-like structure…Let’s use this analogy!

III. Double helix1. The two sides of the ladder are twisted to create the double helix structure

2. James Watson and Francis Crick developed the DNA model

3. they constructed it as a spiral staircase called a double helix

4. Rosalind Franklin and Maurice Wilkins took X-ray photographs of DNA crystals before Watson and Crick’s work – these photos were used by Watson & Crick.

4. Watson, Crick and Wilkins were awarded the Nobel Prize in 1962

5. Franklin died before 1962 and was not recognized for her contribution because she was already deceased (of cancer)…

6. DNA Twistsa. DNA is generally found as a right-handed twist, but researcher’s have now discovered that DNA sometimes has a left-handed twist.

1. B-DNA: right handed twist

2. Z-DNA: left handed twist

b. DNA is coiled into chromosomes during cell divisionc. DNA is found as stringy chromatin in the cell most of the time.