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

• Complementary base bonding is key to replicating DNA

DNA Replication

• Key to growth and healing of all organisms

• It occurs before cell divides

Protein

• 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?