Chapter 12 Section 12-1 Pages 287-294 DNA Chapter 12 Section 12-1 Pages 287-294

What do the following have in common? Mitochondria Humans Frogs

They all contain DNA!

DNA Fun Facts!!! Did You Know?: Each one of your cells contains about 2-3 meters (8-10 feet) of DNA! If you unraveled the DNA from all of your cells, it would stretch to the moon over 300,000 times!

What Does DNA Do? DNA contains the genetic information for our cells. Our DNA tells our cells what proteins to make. The proteins determine how the cell functions. So DNA ultimately controls all cellular functions.

Deoxyribonucleic Acid The monomers of DNA are nucleotides. Each nucleotide has three parts: 1. Phosphate 2. Sugar (Deoxyribose) Phosphate 3. Nitrogen Base Sugar Nitrogen Base The nucleotides are put together during DEHYDRATION SYNTHESIS reactions.

Nitrogen Bases There are two different types of bases: Purines (2 rings) – Adenine and Guanine Pyrimidines (1 ring) – Thymine and Cytosine

Double Helix DNA looks like a twisted ladder. It is composed of two strands of nucleotides bonded together. The sides of the ladder are made of alternating sugars and phosphates. The “rungs” of the ladder are made of nitrogen bases.

The Double Helix

How do we know about DNA’s shape? The double helix is the model proposed by scientists James Watson and Francis Crick in 1953. They received a Nobel Prize in 1962 for their discovery Watson and Crick’s model was supported by evidence from other scientists like Rosalind Franklin and Maurice Wilkins who studied X-ray photographs of DNA.

Bonding Patterns The sugar-phosphate backbone is held together with strong covalent bonds. The nitrogen bases are held together by weak hydrogen bonds. The nitrogen bases bond in specific ways according to the Complementary Base Pairing Rule. A & T will only bond together. They form 2 H bonds. C & G will only bond together. They form 3 H bonds. The sequence of bases on one strand, will complement the sequence of bases on the other.

So… IF we have a strand of DNA with the following code: A T G G A A T C G A T THEN, the sequence of the complementary strand will be… T A C C T T A G C T A