Chapter 3 The Biological Basis of Life

Introduction Genetics is the study of how one trait transfers from one generation to the next Involves process of evolution

THe Cell Basic unit of life for all organisms Prokaryotic Cells –Blue-green algae –3.7 bya Eukaryotic Cells –1.2 bya –Membrane bound nucleus and distinct organelles Two Cell types –Somatic –Gamates

DNA Structure Discovered in 1953 Composed of two complementary chains of nucleotides A single nucleotide contains –Deoxyribose sugar –Phosphate group –And one of four nitrogenous bases Adenine Guanine Thymine Cytosine

Structure Continued Double helix forms because adenine bonds to thymine or guanine bonds to cytosine Complementar y base bonding is key to replicating DNA

DNA Replication Key to growth and healing of all organisms It occurs before cell divides

Protein –3D molecules –Bind to other molecules –Hemoglobin – carries oxygen –Some are structural –Some are functional –Composed of amino acids, 8 must be obtained through diet

Protein synthesis Transcription Translation

Genes Sequence of DNA responsible for synthesis of protein or part of a protein Change in the DNA sequence is a mutation Gene action is very complex since not all segments of DNA are expressed during protein synthesis –Exons –Introns Regulatory Genes –Can switch DNA segments on or off

Cell Division -Mitosis and Meiosis Chromosone pairs –Humans = 23 –Chimpanzies and Apes = 24 –Autosomes –Female mammals – XX –Male mammals – XY Mitosis occurs in somatic cells Meiosis occurs in gamates

Mitosis

Meiosis More involved in evolution – sex cells Influences genetic variation Problems –Nondisjunction –Down SYndrome

New Frontiers DNA disc revolutionized biology and genetic research PCR technique was developed in 1986 and is used to analyze nucleotide sequences in very small segments of DNA Recombinant DNA Genetic Manipulation –Controversial –Stem cell research –Cloning Human Genome Project Debate topic: Stem cell research?