DNA Biology

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Chargaff

DNA – The Watson and Crick model

1962 Nobel Prize“scientists were convinced that itcould not be the molecule of life”

The DoubleHelix

Rosalind FranklinX-ray crystallography

Why is DNA important?

DNA is the blueprint or recipe for how to make proteins.

Proteins are what cells are made of, their primary structure.

Proteins are what enzymes are made of, and enzymes control all the chemical reactions in living things. (metabolism)

Deoxyribonucleic acid

• Polymer composed of nucleotides.

• Nucleotides composed of:– Sugar (deoxyribose)– Phosphate– 1 of 4 different kinds of

nitrogenous bases– A T C G

What they discovered……

The Watson and Crick Model• They defined DNA

structure.– Sugar bonds to phosphate

groups alternately forming a “twisted ladder” shape.

– Ladder rungs = bases joined by hydrogen bonds

–A only bonds w/ T (in DNA) – A bonds w/ U (in RNA)– G bonds with C.

DNA and RNA Structure and Function

RNA DNA____________________Ribose Deoxyribose Nitrogenous bases – ACGU Nitrogenous bases – ACGTAlpha helix Double helixNucleus and ribosome Nucleus onlyTOOL of protein synthesis BLUEPRINT of protein synthesis

Nucleotide w/ cytosine

Transcription Translation

mRNA tRNA

Code break the Code

Triplet = codon triplet = anti-codon

Nucleus ribosome

Protein synthesis begins withDNA in the Nucleus.

Transcription (cont.)

RibosomesMade of rRNA

In the cytoplasm or on the rough ER

Site of Protein Synthesis

The Genetic Code: A triplet codeCodons: 20 amino acids, 64 possible codons

Translation: tRNA is an “Amino Acid Taxi service”

Single-stranded RNA

Anticodon complements

mRNA codon.

aa

Translation…

• The order of the tRNA molecules determines the order of the amino acids in the protein molecule.

• It’s the order and type of amino acids that give a protein it’s qualities… How? (Cow?

Ho? Howl?)

Note tR

NA leavin

g

Note bond forming…

Next tRNA arrives

anticodon

Peptide formation is primary structure of the protein!• Secondary

• Tertiary

• Quaternary• Remember?

Gene Mutation…

• changes the sequence of bases in the DNA

• are rare (one in 100 million cell divisions).

• caused by mutagens– Radiation (radioactivity, X-rays, UV light)– Chemicals (pesticides, cigarette chemicals)