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Lecture 3

Lecture 3 - Molecular Basis of Life - September 25.docx

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University of Toronto St. George
Keriann Mc Googan

September 25, 2012. Lecture 3 – Molecular Basis of Life Not a Matter of Chance  Convergence: evolution of similar adaptations in unrelated groups of animals o Marsupial faunas in Australia and South America o Lens in aquatic organisms  Adaptations occurred 8 different times (in each animal or in 8 animals?) The Mechanism of Natural Selection?  Darwin had difficulty explaining source of variation  Blending inheritance  Fleeming Jenkin o Blending inheritance leads to little or no variation  Tall mom, short dad, blended together to create medium-sized offspring o Selection works to REMOVE variants  Finches with big beaks live, small beaks die, removal of small beaks o What about NEW types of variation?  New types of variants have to be acquired from outside initial range  E.g., elephants evolving from a shrew type creature requires some mechanism for such drastic change In The News…  “Junk DNA” has a purpose! (duh)  Majority of unknown DNA discovered to have the purpose of controlling what happens to our genes/what is done with them/where they go/their function  Still some “junk” DNA; the purpose of which remains unknown  I think they’re wrong…. Why is it important to understand the molecular basis of life?  Understand HOW genes work and how traits are transmitted from one generation to the next o Human evolution o Adaptation o Variation  Molecular genetics links biology to chemistry and physics o Scientific overlap helps provide a consistent framework of the biology behind how things like evolution and genetics work  Provides important data for reconstructing evolutionary history What is genetics?  Study of how genes work  Genes = units of heredity  Knowledge of mechanisms of heredity recent Cells  Fundamental units of life in living organisms  Prokaryotic cells o Found in single-celled organisms o Don’t have chromosomes or a nucleus  Eukaryotic cells o Multicellular organisms  Composed of carbohydrates, lipids, nucleic acids, proteins o Have a nucleus and chromosomes/DNA  Somatic Cells o Body cells (muscle, tissue, blood, organs, etc.)  Gametes o Sex cells (sperm cells and egg cells) o Combine to form early form of human: zygote DNA: What is it?  Deoxyribonucleic acid  Double-stranded molecule that contains genetic code  Majority of chromosomes  Directs all cellular functions  Chemical bases of DNA = recipe for making proteins  Proteins: responsible for chemical, structural, and regulatory processes in the body DNA: Structure  Discovered by Watson and Crick in 1953  Nucleotides  Double helix  Bases o Adenine, guanine, cytosine, thymine o A + T, G + C DNA and inheritance  Preserves a message o Repeating four base structure o Vast number of distinct forms  Replicable o Spread to offspring DNA: Replication  Catalysis  Enzymes: proteins that initiate and direct chemical reactions in the body o Enzymes break bonds o Exposed bases attract complementary nucleotides o Two parental nucleotide chains serve as models for replicate strands Protein Synthesis  Proteins: complex, three-dimensional structures/molecules that function through ability to bind to other molecules o Hemoglobin  Found in red blood cells, able to bind to oxygen and carry it throughout the body o Enzymes  Enhance chemical reactions/break DNA bonds to start transcript
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