DNA Structure

Unit 2-1 NotesMr. Hefti – Pulaski Biology

What are these?

What is this?

How are they related? [similar in

shape]

How are they related?

What is this?

[both contain instructi ons]

What is this?

A. DNA = blueprint for life• All living things possess DNA• Located in the nucleus• Chemical instructions for structure

and function• Unique code tells cells what to do

B. DNA is a “double helix”• Think - twisted ladder• There’s a left and right side

chemically bonded together in the middle • Held together by hydrogen bonds

C. DNA made of repeating units called nucleotides

• Here are the 3 parts of a nucleotide:

(please draw in notes)

D. Phosphate• Made of H, O and P• Phosphate links nucleotides together

E. Deoxyribose sugar

• 5 carbon sugar (pentagon shaped)• Made of C, H and O• Deoxyribose links phosphate and nitrogenous

base

F. Nitrogenous base

• Made up of C, H, O and N• Form rungs of ladder• 4 types:– Adenine (A)– Thymine (T)– Guanine (G)– Cytosine (C)

G. Base-pairing rules

• A always pairs with T• C always pairs with G

H. In conclusion…

• The combination of As, Ts, Cs, and Gs is what makes each organism unique• Human DNA composed of 3 billion

repetitions of those same 4 letters