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Lecture 2

Lecture 2 - The Biological Basis of Life – Part 1

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Esteban Parra

The Biological Basis of Life – Part 1 In Memoriam - Sir Francis Crick: 1916-2004 - He discovered the structure of DNA - Was very important in deciphering the genetic code* - DNA, to RNA to proteins Cells, the Basic Units of Life - Cells are the basic units of life. o Bacteria and more complex cells known as eukaryotes - Cells of bacteria and blue-green algae lack nuclear membrane. These unicellular organisms are known as prokaryotes. - Cells of other life forms, including multicellular plants and animals, have a nucleus in which the genetic material is organized on chromosomes. These organisms are composed of eukaryotic cells. - A representation of the typical prokaryote and eukaryote cells is shown in the next slide. Prokaryotic vs. Eukaryotic Cells - Eukaryotic have a nucleus  so the genetic information is found there o DNA is located in the nucleus of the cell o And in the cytoplasm, there are important organelles found, including the mitochondria o (mitochondria DNA is passed from the mother) DNA, the Molecule of Life - The instructions to carry out all the activities required by most living systems are stored in a molecule called DNA (deoxyribonucleic acid). Some life forms are based on a related molecule, RNA (ribonucleic acid). - The structure of DNA was deciphered more than 50 years ago (1953) by Francis Crick and James Watson. - Let’s review the structure of this important molecule, key for the transmission of the instructions of life from generation to generation. - It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material o They were able to explain how the genetic material was past from one generation to the next Other Researchers Involved in the Race to Find the Structure of the DNA - Rosalind Franklin o Chemists who specialized in x-ray picture of moleucules - Maurice Wilkins o DNA was the molecule that was responsible for genetic material (this was known but the structure was unknown) o It was known that the basis (components of DNA) has different proportions  A was similar to T while C was similar to G - Linus Pauling o Everyone thought he was going to be the one who would find the structure of DNA o In 1953, he proposed The Structure of DNA - Key elements of the DNA molecule are the nitrogenous bases, nitrogen containing ring compounds of two main classes, purines and pyrimidines o These rings contain nitrogen o There are two structures that are important for bones o Purine – adamines and guatamine (A and G)  Have two rings o Pyrimidines – C and T  Have one ring The Nucleotides - Nucleotides consist of a nitrogen-containing base, a five carbon sugar (deoxyribose, in the case of DNA, ribose in the case of RNA), and phosphate groups. - Nucleotides are the basic units of nucleic acids. - Free nucleotides have three phosphate groups deoxyadenosine triphosphate - When they are incorporated into DNA, they lose two of the three phosphates Deoxadenosine monophosphate Bonding - Nitrogenous bases can form hydrogen bonds with one another - Adenine forms two hydrogen bonds with thymine, - Guanine forms three hydrogen bonds with cytosine - This is how when DNA separates, you are able to figure out the pairing strand that will be newly synthesized DNA Structure - DNA is a polymer made of deoxynucleotides - Nucleotides are linked together via phosphodiester bonds -
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