DNA: The Molecule of Heredity Ch. 12 Notes: Thursday - Tuesday Test (Ch. 12-13): Wednesday, 10/13/2010

DNA Introduction DNA is the genetic material of life DNA structure is a double helix Discovered by James Watson and Francis Crick

DNA Structure Made of repeated subunits/monomers Nucleotide – 3 part subunit of DNA molecule 3 subunits sugar (deoxyribose) phosphate group (phosphorous and 4 oxygens) nitrogen base adenine (A) thymine (T) guanine (G) cytosine (C)

DNA is a Long Polymer Chain of subunits shaped in a helix Looks like a twisted ladder The sides of the ladder are the sugar-phosphate bonded groups and the rungs are the nitrogen bases. See picture on board / draw in notes

Using the Code A nucleotide sequence provides information to assemble amino acids. In turn, amino acids assemble to make proteins. SO, GENES ARE DNA CODES FOR MAKING PROTEINS!!!

RNA RNA carries out the instructions of DNA in the cell. Differs from DNA in 3 ways: RNA is single stranded; not double like DNA RNA uses ribose sugar; not deoxyribose RNA has uracil (U) instead of thymine, still acts the same by binding to adenine.

Types of RNA mRNA – messenger RNA brings codes from nucleus to cytoplasm. rRNA – ribosomal RNA links onto mRNA to assemble amino acids. tRNA – transfer RNA transports amino acid to ribosome to assemble protein.

Transcription The process of making RNA from DNA. In the nucleus, sections of nucleotides from DNA replicate the gene – code sections of RNA to be sent out for protein production. Ex: DNA code TGATTC will make RNA code ACUAAG. Codon – a 3 nucleotide section that codes for amino acids.

Codons Every different amino acid – has its own signature codon. (Example, methionine is coded by the codon AUG.) Find the corresponding amino acid using the genetic code in your book. (p. 303) AAA GCC UUC Find all the possible codons for isoleucine

Translation The process of decoding mRNA codons into the amino acid sequence of proteins. Example: GGC links to tRNA carrying the sequence CCG to produce an amino acid. What tRNA would TTG link to? What amino acid would be coded for?

Mistakes in Transcription and Translation Point mutation – a single mistake in DNA transcription to RNA where one nitrogen base is replaced by another. Single change. Frameshift mutation - when one base gets inserted or deleted throwing off the entire sequence. Extensive change. (SEE EXAMPLES)

Chromosomal Mutations Mutagen – environmental condition that causes mutation. Radiation, heat, chemicals . . . Mutation - a change in the normal genetic code. Deletion - a part of a chromosome is removed. Insertion - extra material is added, leading to nonfunctional genes. Inversion - codes flip-flop - out of order. Translocation - part of a chromosome is cut out and bonds to a different chromosome.

Objectives: Friday, 11/4/05 Notes: after lecture, you should be able to describe the function of DNA polymerase, helicase, and RNA polymerase explain the central theme of molecular biology Lab: after lab activity, you should be able to understand base pairing rules analyze molecular basis of heredity / DNA

Central Dogma (Theme) of Molecular Biology DNA RNA Proteins

Replication Double helix must be unwound. This requires the helicase enzyme. The unwound strands separate and act as templates for the formation of 2 new strands. The addition of new nucleotides is determined by base-pairing rules. This addition (polymerization) requires the DNA polymerase enzyme.

RNA vs. DNA there are 3 major differences between the 2 forms of nucleic acids Composition of sugar backbone (reflects name) RNA - ribonucleic acid (ribose) DNA - deoxyribonucleic acid (deoxyribose) number of strands: RNA = 1 and DNA = 2 RNA does not have thymine as a nitrogen base, instead uracil (U) is substituted in its place

Transcription: mRNA Production Short segment of DNA (gene) is transcribed into mRNA for movement out of the nucleus to the ribosome DNA is used as a template to make a complementary piece of “messenger RNA”. This requires the aid of the RNA polymerase enzyme.

Translation: Protein Synthesis mRNA transcript arrives at the ribosome to act as the genetic code for protein assembly proteins are composed of a unique sequence of amino acids. mRNA carries the code for the order and type of amino acids to be included in the protein. The “genetic code” is the unique order of triplet codons located on the mRNA strand.

What does a “Gene” really do? It is simply a blueprint in the DNA that tells how to build a protein. “WHO” we are genetically is really just a collection of “WHAT” proteins are expressed in our phenotype.

Transcription / Translation Lab Obtain the following from Mr. Smith: 1 per student an mRNA transcript (little slip of paper) a genetic “dictionary” - Genetic Code Lab Worksheets - 3 pages Work on your own, but check your work with those around you. Remember, you each possess your own code, so you won’t get the same sequences as everyone else.