1. Unit 6 – DNA Structure and Replication
Chapter 8, Sections 2 & 3
New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
SC: Science (2005), SC: Grades 9-12, HS: Biology Standards B-4.1; B-4.2 and B-4.3

2. New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
DNA Structure
New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
SC: Science (2005), SC: Grades 9-12, HS: Biology Standards B-4.1; B-4.2 and B-4.3

3. DNA: The Molecule of Heredity
Objective: You will be able to describe the molecule of DNA
New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
SC: Science (2005), SC: Grades 9-12, HS: Biology Standards B-4.1; B-4.2 and B-4.3

4. DNA: the “Base”ics DNA – Deoxyribonucleic Acid
Unit of heredity in all living things
Contains the information for making proteins
Only in NUCLEUS
Made up of nucleotides
New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
SC: Science (2005), SC: Grades 9-12, HS: Biology
Standards B-4.1; B-4.2 and B-4.3

5. New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
DNA: The “Base”ics
Nucleotide
Sugar (Deoxyribose)
Phosphate
Nitrogen Base
New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
SC: Science (2005), SC: Grades 9-12, HS: Biology Standards B-4.1; B-4.2 and B-4.3

6. DNA: The “Base”ics Four Nitrogen Bases (DNA) Adenine (A) Thymine (T)
Cytosine (C)
Guanine (G)
New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
SC: Science (2005), SC: Grades 9-12, HS: Biology
Standards B-4.1; B-4.2 and B-4.3

7. DNA: the “Base”ics Adenine & Guanine = Purines
Cytosine & Thymine = Pyrimidines
Hint to remember…Look at the “Y”s !!
New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
SC: Science (2005), SC: Grades 9-12, HS: Biology
Standards B-4.1; B-4.2 and B-4.3

8. DNA: the “Base”ics
Chains are formed by joining the sugar of one nucleotide to the phosphate of the next.
“Sugar – Phosphate Backbone”

9. DNA: the “Base”ics Nitrogen bases come off of the sugar (deoxyribose)
Hydrogen bonds hold the bases together to form a pair
A always pairs with T
C always pairs with G
Called complementary bases
Hydrogen Bonds
Hydrogen Bonds
New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
SC: Science (2005), SC: Grades 9-12, HS: Biology
Standards B-4.1; B-4.2 and B-4.3

11. DNA: the “Base”ics Chargaff – 1950
amount of A always EQUALS amount of T
amount of G always EQUALS amount of C
Determined that A bonds to T and C bonds to G in the structure of DNA
Called the Chargaff rules or the
base pairing rules
New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
SC: Science (2005), SC: Grades 9-12, HS: Biology
Standards B-4.1; B-4.2 and B-4.3

12. Learning Check What is the name for DNA?
What information does DNA hold?
What are the monomers for DNA?
What are the 3 parts of a nucleotide?
What are the 4 bases in DNA?
What are the base pairing rules?
What holds the bases together in a DNA molecule?
New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
SC: Science (2005), SC: Grades 9-12, HS: Biology
Standards B-4.1; B-4.2 and B-4.3

13. Learning Check What is the complimentary strand of DNA? 5’ –ATCGCG -3’
New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
SC: Science (2005), SC: Grades 9-12, HS: Biology
Standards B-4.1; B-4.2 and B-4.3

14. DNA: the “Base”ics
Wilkins & Franklin – 1953 used x-ray diffraction of DNA; found DNA helical
What type of helix was unclear…

15. DNA: the “Base”ics
Watson & Crick (1953)– determined 3D “Double Helix” structure of DNA (twisted ladder)

16. New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
SC: Science (2005), SC: Grades 9-12, HS: Biology
Standards B-4.1; B-4.2 and B-4.3

17. DNA and Nucleotide Sequences
All organisms have DNA
All DNA is made of the same bases(4 different nucleotides)
How are we different from dogs, cats, trees, etc?
Different organisms are composed of different proteins
New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
SC: Science (2005), SC: Grades 9-12, HS: Biology
Standards B-4.1; B-4.2 and B-4.3

18. DNA and Nucleotide Sequences
The different ways the nucleotides (A,T,G,C) are arranged create different proteins
The order of nucleotides (ATCG) in each gene has the info to make a string of amino acids which make a specific protein
Just think…. Ant vs. Tan (same letters but very different things)
The sequence of nucleotides carries different genetic information
A-T-T-G-A-C vs. T-C-C-G-A-A
The closer related organisms are the more similar their DNA sequences
New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
SC: Science (2005), SC: Grades 9-12, HS: Biology
Standards B-4.1; B-4.2 and B-4.3

19. DNA sequence
Nucleotide sequence of chimp is similar to gorilla, but very different from a rose.
We can use nucleotide sequence to determine evolutionary relationships among organisms.
Can use nucleotide sequence to determine if 2 people are related or identify criminals.
New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
SC: Science (2005), SC: Grades 9-12, HS: Biology
Standards B-4.1; B-4.2 and B-4.3

20. Learning Check What is the structure of DNA? How is DNA organized?
Why are we different from other organisms and other people?
New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
SC: Science (2005), SC: Grades 9-12, HS: Biology
Standards B-4.1; B-4.2 and B-4.3

21. Closing
On the back of the sheet I just handed you, write the complementary strand of DNA for the following DNA sequence:
5’- TCGAAATCTACCGGTA- 3’
State Standard 4.1, 4.2, and 4.3

22. Replication New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
SC: Science (2005), SC: Grades 9-12, HS: Biology
Standards B-4.1; B-4.2 and B-4.3

23. Replication Objective: You will be able to
explain replication and create a
new strand of DNA through
replication.
New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
SC: Science (2005), SC: Grades 9-12, HS: Biology
Standards B-4.1; B-4.2 and B-4.3

24. DNA Replication DNA Replication – process of copying DNA
Occurs every time a cell reproduces in mitosis or meiosis
Occurs in the S phase of interphase in the cell cycle
Replication assures that every cell has a complete set of identical genetic info
Semi-conservative process - produces 2 copies that each contain one of the original strands and one entirely new strand
New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
SC: Science (2005), SC: Grades 9-12, HS: Biology
Standards B-4.1; B-4.2 and B-4.3

25. State Standard 4.1, 4.2, and 4.3

26. DNA is used as a “template” New strand is called a compliment
New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
SC: Science (2005), SC: Grades 9-12, HS: Biology
Standards B-4.1; B-4.2 and B-4.3

27. Steps of replication
Enzyme helicase breaks the weak hydrogen bonds at origins of replication between nitrogen base pairs and “unzips” the DNA strand
Happens at more than one origin of replication on DNA
Free nitrogen bases in nucleus join with the open DNA strand with the help of DNA polymerase
DNA polymerase – enzyme that bonds the nitrogen bases together
Two new strands of DNA are made
New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
SC: Science (2005), SC: Grades 9-12, HS: Biology
Standards B-4.1; B-4.2 and B-4.3

29. DNA Replication Replication is very fast Replication is very accurate
In humans, about 50 nucleotides every second at each replication origin
Replication is very accurate
Only about 1 error in 1 billion nucleotides
It has a built in “proofreading” function
DNA polymerase can detect errors and replace incorrect nucleotides
New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
SC: Science (2005), SC: Grades 9-12, HS: Biology
Standards B-4.1; B-4.2 and B-4.3

30. Learning Check What is DNA replication?
When does DNA replication happen?
Why does DNA replication happen?
What “unzips” the DNA molecule in replication?
What molecule helps bond the new nucleotides to the DNA template?
New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
SC: Science (2005), SC: Grades 9-12, HS: Biology
Standards B-4.1; B-4.2 and B-4.3

31. Learning Check
Make two daughter strands of DNA from the parent DNA below. Label template and daughter strands. Circle the TWO daughter DNA molecules.
A-T
T-A
C-G
G-C
New State Standards: H.B.2A.1 ; H.B.4A.1 ; H.B.4A.2
SC: Science (2005), SC: Grades 9-12, HS: Biology
Standards B-4.1; B-4.2 and B-4.3