DNA Structure (“transforming principle”) Human Genetics Chp. 9

A is a long section of a DNA molecule whose sequence of building blocks specifies the sequence of amino acids in a particular protein. A gene is a long section of a DNA molecule whose sequence of building blocks specifies the sequence of amino acids in a particular protein. Genes combine to form amino acids as letters combine to form words. Amino acids make proteins DNA Structure

DNA shape is a double helix DNA shape is a double helix View from the side View from the side Partially unwound double helix so you can see components Partially unwound double helix so you can see components DNA Structure

Views from the top ModelX-Ray Photo-51

DNA composed of nucleotides 1.Sugar (deoxyribose) 2.Phosphate group 3.Nitrogenous bases 1.Purines 1.Guanine (G) 2.Adenine (A) 2.Pyrimidines 1.Cytosine (C) 2.Thymine (T) DNA Structure (Where are they?)

A 5 C sugar and a phosphate group form the backbone A 5 C sugar and a phosphate group form the backbone DNA is directional DNA is directional Antiparallelism Antiparallelism the head to tail arrangement of the 2 entwined chains of DNA double helix the head to tail arrangement of the 2 entwined chains of DNA double helix DNA Structure

Nitrogenous bases Nitrogenous bases A, T, C, & G A, T, C, & G make up the rungs on the ladder make up the rungs on the ladder

Complementary Base Pairing Bases held together with Hydrogen bonds Bases held together with Hydrogen bonds Guanine pairs with Cytosine Guanine pairs with Cytosine Triple bond Triple bond Adenine pairs with Thymine Adenine pairs with Thymine Double bond Double bond

Minor Groove Minor Groove Major Groove Major Groove binding proteins interact with DNA in the major groove b/c backbone isn’t in the way binding proteins interact with DNA in the major groove b/c backbone isn’t in the way DNA Structure

Chromosomes – not just DNA! Chromosomes – not just DNA! 1/3 DNA 1/3 DNA Histone proteins Histone proteins Other DNA binding proteins Other DNA binding proteins also a small amount of RNA also a small amount of RNA All together the chromosome material is called Chromatin All together the chromosome material is called Chromatin DNA Structure

A single molecule of DNA can be 1 in. long How does it fit into a space that is 1 millionth that size? Histones proteins that DNA coils around DNA Structure 3D Video Clip3D Video Clip (Click next 4 times)

Nucleosome- A unit of the chromatic structure DNA Structure GREAT DIAGRAM (FIG. 9.11) ON PG 179 Clicker ? ’s Histones 2.DNA 3.“linking” histone

DNA Replication- Preserves genetic information Preserves genetic information S phase of Interphase S phase of Interphase Gives each new cell a complete set of operating instructions Gives each new cell a complete set of operating instructions 5’ to 3’ direction only 5’ to 3’ direction only 3 Hypothesized mechanisms for DNA Replication 3 Hypothesized mechanisms for DNA Replication ?

DNA Replication (cont.) SemiconservativeConservativeDispersive Each new molecule conserves half of the original double helix One double helix specifies creation of a second double helix Double helix shatters into pieces that then synthesize new DNA

Proved by Meselson and Stahl Marked DNA with 14 N 2 nd generation DNA had ½ 14 N and ½ 15 N

Replication Technology PCR- Polymerase Chain Reaction PCR- Polymerase Chain Reaction Uses DNA Polymerase to rapidly produce millions of copies of a specific DNA sequence of interest. Uses DNA Polymerase to rapidly produce millions of copies of a specific DNA sequence of interest. Perhaps the most successful technology to ever emerge from LIFE SCIENCE!!! Perhaps the most successful technology to ever emerge from LIFE SCIENCE!!! Many Uses Many Uses Forensics- Forensics- blood, convict, exonerate false accusations blood, convict, exonerate false accusations Agriculture, Vet., Medicine, Env. Sci., Agriculture, Vet., Medicine, Env. Sci., Microorganisms, viruses, parasites… Microorganisms, viruses, parasites…