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