DNA Structure

A review

DNA Structure DNA (deoxyribonucleic acid) is a polymer

of nucleotides What are the 3 parts of a nucleotide?

a nitrogen basea pentose sugara phosphate group

DNA Structure Copy Figure 1 in your notes (on page 210)

DNA Structure What are the four bases?

AdenineThymineGuanineCytosine

Complete the chart and align the bases that pair up

Purines Pyrimidines

This type of pairing is called complementary base pairing

Why do the bases pair this way? Franklin and Wilkins studies show that DNA has

a constant diameter of 2nm If two purines bonded together, DNA would be

wider at some points (the same goes for two pyrimidines bonded)

What holds purines & pyrimidines together? These can only form in the A-T and G-C

arrangement This is the glue that holds the molecule together

and any other pairing would result in instability

G-C pair results in 3 Hydrogen

Bonds

A-T pair results in 2 Hydrogen

Bonds

Which pair is stronger (harder to pull apart)?

DNA Structure

What do purines have in common?six-membered ring joined to a five-membered

ring

What do pyrimidines have in common?single six-membered ring

Create an equation for the amount of A vs. T and G vs. C. Then, create a formula that shows the amounts of purines versus pyrimidines.

If a sample of DNA has 40% G, how much A, C, and T must there be?

Draw Figure 3 in your notes. Label the carbons 1’ to 5’.

DNA consists of two antiparallel strands, curled around in a double helix (like a spiral).

Antiparallel?Huh?• If one strand is going in a 3’ to 5’ direction, the other is oriented in a 5’ to 3’ direction

• i.e.

• How do you know which one is the 5’ end? 3’ end?

Activity Find a partner As a class, form two lines so that each partner

faces each other Now turn so that ne line looks toward the right

side of the room The other line look toward the left side of the

room Put your left hand on the shoulder of the person

standing in front of you Hold your right hand with your original partner

Activity Questions What does your torso represent? What does your left elbow represent? What does your left arm represent? What does your right hand represent? What type of interaction holds the two lines together? Have one partner choose a base Decide what base the other partner must be and

determine how many bonds form between you (3 or 2 fingers)

Where are the 5’ and 3’ ends of each strand? What would happen if two purines were together? What arrangement of bases would be easiest to

separate? Why would this be helpful?

Properties of DNA

3.4 nm

Properties of DNA The diameter of DNA is 2.0 nm Right handed helix (turns clockwise) There is one complete turn for every 10

nucleotides in 3.4 nm (billionth of a m)How many nm does each nucleotide take up?

Bases are stacked on top of each other Sugar-phosphate backbone + hydrogen

bonds between complementary bases make the double helix very stable

Sequence of Bases hold Genetic Information If you know the sequence of one strand, you can

determine the sequence of the second strand One strand can be used as a template to build a

new strand 5’ – ACGCGTTATCGA – 3’

What’s the sequence of the other? Direction?

What would be free at the 5’ end? 3’ end?

Do a little research…! What is the role of the Canadian Food Inspection Agency

with respect to biotechnology? What role does the Canadian Environmental Protection Act

play in regulating biotechnology? Why was bovine growth hormone approved for use in dairy

cattle in the United States but not in Canada? Why does Mexico have laws to limit the cultivation of

genetically modified corn? What countries have banned human cloning? What is

Canada’s position on this issue?