1. WARM UP
Which scientists performed experiments with viruses?
What type of viruses did these scientists use?
Name the scientist that experimented with two different strains of bacteria and mice?
What final conclusion did the scientists come to after their experiments.

2. KEY CONCEPT DNA structure is the same in all organisms.

3. DNA & RNA Nucleic Acids Ex. DNA and RNA Slide 2.35
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

4. DNA Location and Function
Location - in nucleus
Function - blueprint for life = determine genes (heredity), make proteins, cell division
Slide 3.37
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

5. DNA basic structure Discovered structure of DNA = double helix
Slide 2.35
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

6. DNA is composed of building blocks called nucleotides.
DNA is made up of two long chains of nucleotides.
Each nucleotide has three parts.
a phosphate group
a deoxyribose sugar
a nitrogen-containing base (A,T,C,G)
phosphate group
deoxyribose (sugar)
nitrogen-containing
base

7. The nitrogen containing bases are the only difference in the four nucleotides.

8. Watson and Crick determined the three-dimensional structure of DNA by building models.
They realized that DNA is a double helix that is made up of a sugar-phosphate backbone on the outside with bases on the inside.

9. Watson and Crick’s discovery built on the work of Rosalind Franklin and Erwin Chargaff.
Franklin’s x-ray images suggested that DNA was a double helix of even width.
Chargaff’s rules stated that A=T and C=G.
Discovered even nucleotide ratios
Adenine – Thymine
Cytosine – Guanine

10. Nucleotides always pair in the same way (Complementary Base Pairing)
The base-pairing rules show how nucleotides always pair up in DNA.
A pairs with T
C pairs with G
Because a pyrimidine (single ring) pairs with a purine (double ring), the helix has a uniform width. C G T A

11. The backbone is connected by covalent bonds.
The bases are connected by hydrogen bonds.
hydrogen bond
covalent bond

12. DNA Replication
Why do cells need to make a copy of their DNA?
The process of copying the DNA molecule
Occurs in the nucleus during interphase (S phase)
Is a “semi-conservative” process
DNA is used as a “Template” to make new DNA
Results in 2 strands of DNA that are half old and half new (2 semi conservative DNA molecules)

13. DNA Replication: semi conservative
DNA helicase uncoils and unzips DNA
New (daughter) nucleotides line up next to both old (parent) chains of the DNA
Figure 3.13
Slide 3.32

14. DNA Replication
DNA polymerase binds the new nucleotides together and “proofreads” the new strands for errors.
Results in 2 semi-conservative strands of DNA
Figure 3.13
Slide 3.32

15. DNA Replication
Final Result – 2 Semi-Conservative Strands of DNA

16. DNA triplets
Slide 3.37

17. DNA: the Genetic Code is carried in Triplets
Genetic code= order of nitrogenous bases in triplets of DNA
1 DNA triplet codes for 1 amino acid in a protein
Gene: is a DNA segment that carries the information for building proteins (or polypeptide chain)
Process Discussed further in Protein synthesis
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