1. Agenda: 3/26 Warm-up: Bill Nye – Understanding DNA
Homework: pp. 19 – 23
Answer Questions on p. 23
Warm-up: Bill Nye – Understanding DNA
DNA: Structure and Function
Overview: Reading & notes
Components
Building a model
- Computer Model
- Paper model
Preparation for tomato extraction

2. Video: Understanding DNA

3. Class Notebook
Page #
3/26
DNA Structure & Function

4. DNA → RNA → Protein “Central Dogma”
DNA and Biotechnology
DNA → RNA → Protein
“Central Dogma”

5. DNA Structure and Function
Requires an understanding of:
Backbone structure and direction
Bases names, structure and pairing
Difference in bonds: covalent bonds and hydrogen bonds
Requires Memorization

6. The structure of the DNA provides the function.
How does the structure of DNA allow it to be the instructional book of life?

7. Video- describing DNA DNA – packed into chromosomes

8. Chemical structure of DNA
HHMI's BioInteractive - The Chemical Structure of DNA

9. DNA: structure determines function
Chemical Structure
Composition
Type of atoms
Names
Bonds
Covalent bonds
Hydrogen bonds
Backbone
Bases
Helix

10. DNA structure – major parts
S = sugars
(deoxyribose)
P = Phosphate group
Nitrogenous Bases:
A= adenine
C= cytosine
G= guanine
T = thymine

11. Chemical composition Types of atoms? Combined to make macromolecules
Extremely strong forces hold the atoms together
Covalent bonds
Why are covalent bonds important?

12. The carbons on the sugar are numbered
The carbons on the sugar are numbered. The linkage between the phosphate group and the deoxyribose sugar are covalent bonds.

13. How is it put together? 3’ end joins the 5’ end of another base
The carbons on the sugar are numbered.
These linkages are covalent bond between the phosphate and sugar groups in the backbone
Note how the molecules are represented. The pentagons show the shape of the sugar but do not label the carbons.

14. Directional
DNA strands in the double helix are oriented in opposite directions
5’ -3’ strand with 3’ – 5’ strand (based on carbon bonds)

15. Structure of C and T
Structure of A and G
Structure of A and G
Structure of A and G
Two Base Types: Compare and contrast the 2 groups What do they have in common? How are they different?

16. 2 types of bases Purines Pyrimidine
Adenine and guanine
Pyrimidine
Cytosine and thymine
In the DNA helix, certain bases are complementary.
What does this mean?
Which bases are complementary?
Why?
What would happen if they were randomly paired?

17. Hydrogen bonds: relatively weak forces that hold the bases together in the double helix.

18. Hydrogen bonds in the double helix
How are the hydrogen bonds different from the covalent bonds?
Why are 2 types of bonds important for the functioning of DNA?

19. Building a Model
Molecular machines copy DNA
Your body produces billions of new cells every day. Each time one of your cells divides, it must first copy the genetic information contained within its nucleus. Copying the genetic information in one cell using this activity would take more than 95 years*, yet molecular machines in your cells accomplish this feat in about 6 to 8 hours.
In order to speed up the copying process, DNA replication begins at multiple locations along each chromosome. The two DNA strands are pulled apart and copied in both directions at the rate of about 50 nucleotides per second.**

20. Complementary base pairing
These models are based on the molecular structure of real nucleotides. The grey and white circles on the models represent partial positive and negative charges that form hydrogen bonds between complementary bases. These bonds work kind of like tiny magnets to hold the two DNA strands together. Complementary base-pairing ensures that DNA strands are copied accurately, with just a few errors for each round of replication. Forces between neighboring nucleotides stack the bases on top of one another and twist the DNA strands into a double-helix.

21. Building a DNA Model Build a DNA Molecule

22. Watson: creating the model

23. Biotech Objectives for a DNA model:
Label the functional groups on the sugars and carbons to determine the 5’ and 3’
Know the components of the DNA “backbone” & where they bond
Determine the location and function of hydrogen bonds
Demonstrate that the molecular structure & shape of the complementary pairs is critical
Identify the purine and pyrimidine bases & sizes
Know the names of the bases (not just letters)

24. Your model will be similar to this.

25. DNA Model

26. Review
Problem 19: The DNA molecule is shaped like a twisted ladder. :: DNA Learning Center

27. Questions about the model
What base does adenine pair with?
What base does guanine pair with?
What is the smallest unit of DNA called?
What is the shape of the DNA model?

28. Suppose you know that the sequence of bases on one DNA strand is AGCTCAG. What is the sequence on the opposite strand?
Referring to the above question, suppose that the 5’-most base on the given strand is the first A from the left to the right. What would the 5’-most base on the opposite strand?
Assume that a 100 base pair DNA double helix segment contains 45 cytosines. How many adenines are there?