DNA Structure

DNA Structure Big Idea of Biology: Structure is related to Function. DNA Function: Instructions for making proteins—tens of thousands of proteins A way to pass the instructions to offspring How does its structure make this happen?

DNA is made of nucleotide building blocks Each nucleotide consists of: Phosphate group – PO3- Pentose sugar – 5 carbon Nitrogenous base – contains nitrogen

Nucleotides Phosphate Nitrogenous Base Pentose Sugar

4 Types of Nucleotides A Adenine T Thymine C Cytosine G Guanine

How are these nucleotides connected? Scientists played around with potential structures, like playing with Legos, to figure it out

Important Discovery! What does this indicate? Species are different in the pattern of bases The amount of A matches the amount of T and the amount of C matches the amount of G

Nitrogen bases have to pair a certain way! Each base will only bond with one other specific base. Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Form a base pair. Form a base pair.

But how could the nucleotides fit together? Double helix: Two connected strands with sugar-phosphate background on outside and base pairs connected on the inside Another important discovery!

Double helix

Why do bases pair like this? To fit: A 2-ring base has to pair with a 1-ring base To allow hydrogen bonding: A and T: 2 bonds C and G: 3 bonds

DNA Structure Because of this complementary base pairing, the order of the bases in one strand determines the order of the bases in the other strand.

A C T G G A T C

Build your own DNA molecule Twizzlers = Sugar-Phosphate backbone Marshmallows = Nitrogen bases Green = Guanine Orange = Cytosine Pink = Adenine Yellow = Thymine Toothpicks to hold it together Space your DNA so it has 8 base pairs: when your molecule is finished, twist it to see what it looks like as a double helix