Biology Overview

Overview

This lecture covers the origin of life on Earth, basic biochemistry of living things, cell structure, genetics, mechanisms of inheritance, evolution by natural selection, comparison of bacteria and viruses, organ systems, and the basics of neural signaling.

Origin of Life and Early Earth

• Earth formed 4.5 billion years ago as a hot, rocky planet with water arriving via space rocks.
• Early Earth's cooling led to flooding and the creation of hydrothermal vents, where life likely began.

Biochemistry of Life

• Biology is the study of life, fundamentally based on chemistry.
• Carbohydrates provide quick energy; lipids store long-term energy and make cell membranes; proteins form tissues; nucleic acids make DNA.
• Enzymes are protein catalysts that speed up specific chemical reactions in living organisms.

Characteristics and Classification of Life

• Living things metabolize, grow, reproduce, respond to stimuli, and are made of cells.
• Two cell types: Eukaryotes (complex, membrane-bound organelles, DNA in nucleus) and Prokaryotes (simpler, no nucleus, DNA floats freely).
• Classification uses taxonomic ranks; each species has a unique genus and species name.

Homeostasis and Cell Membranes

• Homeostasis is the maintenance of stable internal conditions (like temperature, pH).
• The cell membrane is a semipermeable phospholipid bilayer controlling substance movement in/out.
• Diffusion is passive movement from high to low concentration; active transport uses ATP to move particles against the gradient.

ATP, Cellular Respiration, and Photosynthesis

• ATP (adenosine triphosphate) stores and supplies cellular energy.
• Cellular respiration in mitochondria converts glucose and oxygen into ATP, water, and CO₂.
• Heterotrophs get glucose from food; autotrophs (plants) make glucose via photosynthesis in chloroplasts.

DNA, Genes, and Protein Synthesis

• DNA is made of two strands of nucleotides (A, T, C, G) forming genes that code for proteins.
• Transcription copies a gene to mRNA; translation uses ribosomes and tRNA to assemble amino acids into proteins.

Genetics and Inheritance

• Humans have 20,000 protein-coding genes on 23 chromosome pairs; alleles are gene variants.
• Traits can be dominant or recessive; inheritance follows Mendelian patterns, but exceptions include incomplete dominance and codominance.
• Sex chromosomes (XX in females, XY in males) carry X-linked genes, affecting inheritance like color blindness.

Cell Division and Mutations

• Mitosis makes identical diploid cells for growth/repair; meiosis makes haploid gametes for reproduction.
• DNA is packaged as chromosomes, which can mutate by base changes or larger chromosomal changes (e.g., Down syndrome from trisomy 21).

Evolution and Natural Selection

• Mutations can be harmful, neutral, or beneficial; beneficial mutations aid survival and are passed on (natural selection).
• Evolution results from selection of the fittest organisms in an environment.

Bacteria, Viruses, and Organ Systems

• Bacteria are living prokaryotes treatable with antibiotics; viruses are non-living, only reproduce inside hosts, and not treatable by antibiotics.
• Humans have beneficial bacteria (symbiosis) for digestion.
• Complex organ systems (nervous, digestive, etc.) allow survival and function.

Nervous System and Neural Signaling

• The nervous system uses neurons to conduct electrical impulses (action potentials) via axons.
• Action potentials occur when the membrane potential reaches threshold; myelin sheaths speed up signal transmission.
• Neurons communicate via neurotransmitters across synapses.

Key Terms & Definitions

• Enzyme — Protein catalyst that speeds up specific chemical reactions.
• Homeostasis — Maintenance of stable internal conditions.
• Diffusion — Passive movement of particles from high to low concentration.
• ATP — Molecule that stores and transfers energy in cells.
• Gene — Segment of DNA coding for a trait/protein.
• Allele — Variant of a gene.
• Mitosis — Cell division producing identical cells.
• Meiosis — Cell division producing gametes with half the chromosomes.
• Mutation — Change in DNA sequence.
• Natural Selection — Process favoring survival/reproduction of better-adapted organisms.
• Neuron — Nerve cell transmitting electrical signals.
• Neurotransmitter — Chemical messenger between neurons.

Action Items / Next Steps

• Review the structure and functions of cell organelles.
• Practice using genetic charts (Punnett squares) for inheritance patterns.
• Study diagrams of the nervous system and major organ systems.