DNA Biology Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chargaff

DNA – The Watson and Crick model 1962 Nobel Prize “scientists were convinced that it could not be the molecule of life” The Double Helix Rosalind Franklin X-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 – ACGUNitrogenous bases – ACGT Alpha helixDouble helix Nucleus and ribosomeNucleus only TOOL of protein synthesisBLUEPRINT of protein synthesis Nucleotide w/ cytosine

TranscriptionTranslation mRNAtRNA Codebreak the Code Triplet = codontriplet = anti-codon Nucleusribosome Protein synthesis begins with DNA in the Nucleus.

Transcription (cont.)

Ribosomes Made of rRNA In the cytoplasm or on the rough ER Site of Protein Synthesis

The Genetic Code: A triplet code Codons: 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 tRNA leaving 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)