Introduction to Cell Biology

• Biology is the scientific study of life, examining the structure, function, growth, origin, evolution, and distribution of living organisms

Cell Biology

• The cell theory states that all living organisms are composed of one or more cells
• The cell is the basic unit of structure and organization in organisms
• Cells arise from pre-existing cells
• Cells are broadly classified into prokaryotic and eukaryotic cells
• Prokaryotic cells lack a nucleus and other membrane-bound organelles
• Bacteria and Archaea are prokaryotes
• Eukaryotic cells have a nucleus and other membrane-bound organelles, like mitochondria and endoplasmic reticulum
• Eukarya includes protists, fungi, plants, and animals
• Key cellular structures include the plasma membrane, cytoplasm, and genetic material (DNA)
• The plasma membrane is a selectively permeable barrier regulating substance passage into and out of the cell
• The cytoplasm is a gel-like substance within the cell containing organelles and cytosol
• DNA carries the cell's genetic information, organized into chromosomes in eukaryotes
• Organelles perform specific functions within the cell
• Mitochondria produce ATP through cellular respiration
• Ribosomes are responsible for protein synthesis
• Endoplasmic reticulum (ER) is involved in protein and lipid synthesis
• The Golgi apparatus modifies, sorts, and packages proteins
• Lysosomes contain enzymes for intracellular digestion
• The cytoskeleton provides structural support and facilitates cell movement
• Centrioles (in animal cells) are involved in cell division
• Cell division occurs through mitosis (for growth and repair) and meiosis (for sexual reproduction)
• Mitosis results in two identical daughter cells
• Meiosis results in four genetically different haploid cells

Genetics

• Genetics is the study of heredity and variation of inherited characteristics
• Gregor Mendel is considered the father of genetics; he discovered basic inheritance principles via pea plant experiments
• Genes are the units of heredity, composed of DNA sequences
• Alleles are different forms of a gene
• Genotype refers to an organism's genetic makeup
• Phenotype refers to the observable characteristics
• Homozygous individuals have two identical alleles for a gene
• Heterozygous individuals have two different alleles
• Dominant alleles mask the expression of recessive alleles in heterozygous individuals
• Mendel's law of segregation states that allele pairs separate during gamete formation
• Mendel's law of independent assortment states that genes for different traits are inherited independently
• Chromosomes consist of DNA and proteins; genes are located on chromosomes
• DNA is a double-stranded helix of nucleotides
• Nucleotides consist of a sugar, phosphate group, and nitrogenous base
• The nitrogenous bases in DNA are adenine (A), guanine (G), cytosine (C), and thymine (T)
• RNA is a single-stranded nucleic acid that plays a role in protein synthesis
• RNA contains uracil (U) instead of thymine (T)
• DNA replication is the process by which DNA is copied
• Transcription is the process by which RNA is synthesized from DNA
• Translation is the process by which proteins are synthesized from RNA
• The genetic code is the set of rules by which information encoded in genetic material (DNA or RNA) is translated into proteins
• Mutations are changes in the DNA sequence
• Mutations can be spontaneous or induced by mutagens
• Gene expression is the process by which the information encoded in a gene is used to synthesize a functional gene product (protein or RNA)
• Biotechnology involves the use of living organisms or biological systems to develop or make products
• Genetic engineering involves the manipulation of genes to alter the characteristics of an organism

Evolutionary Biology

• Evolution is the change in the heritable characteristics of biological populations over successive generations
• Charles Darwin proposed the theory of evolution by natural selection
• Natural selection is the process by which individuals with advantageous traits are more likely to survive and reproduce
• Adaptation is the process by which organisms become better suited to their environment
• Fitness refers to the ability of an organism to survive and reproduce
• Evidence for evolution comes from fossils, comparative anatomy, embryology, and molecular biology
• Homologous structures are structures in different species that have a common ancestry
• Analogous structures are structures in different species that have similar function but different ancestry
• Vestigial structures are structures in organisms that have lost their original function
• The fossil record provides evidence of the history of life on Earth
• Biogeography is the study of the distribution of species and ecosystems in geographic space and through geological time
• Microevolution refers to changes in allele frequencies within a population
• Macroevolution refers to the evolution of new species and higher taxonomic groups
• Mechanisms of microevolution include mutation, gene flow, genetic drift, and natural selection
• Gene flow is the transfer of genetic variation from one population to another
• Genetic drift is the change in allele frequencies due to chance events
• Speciation is the process by which new species arise
• Allopatric speciation occurs when populations are separated by a geographic barrier
• Sympatric speciation occurs when populations diverge without geographic isolation
• Phylogeny is the study of the evolutionary relationships among organisms
• Phylogenetic trees are diagrams that depict these relationships
• The biological species concept defines a species as a group of organisms that can interbreed and produce fertile offspring
• Mass extinctions are events in which a large percentage of species go extinct in a relatively short period of time

Ecology

• Ecology is the study of the interactions between organisms and their environment
• An ecosystem consists of all the living organisms (biotic factors) and non-living components (abiotic factors) in a particular area
• Abiotic factors include sunlight, temperature, water, nutrients, and soil
• Biotic factors include interactions among organisms, such as competition, predation, and symbiosis
• A population is a group of individuals of the same species living in the same area
• A community is a group of interacting populations of different species
• The biosphere is the global sum of all ecosystems; it is the zone of life on Earth
• Energy flow in ecosystems begins with primary producers (autotrophs) that convert sunlight into chemical energy through photosynthesis
• Consumers (heterotrophs) obtain energy by feeding on other organisms
• Food chains and food webs describe the flow of energy through ecosystems
• Trophic levels represent the different feeding levels in a food chain or food web
• Ecological pyramids illustrate the relative amounts of energy, biomass, or numbers of organisms at each trophic level
• Nutrient cycles describe the movement of essential elements through ecosystems
• Key nutrient cycles include the water cycle, carbon cycle, nitrogen cycle, and phosphorus cycle
• Competition occurs when organisms compete for the same resources
• Predation occurs when one organism (the predator) feeds on another organism (the prey)
• Symbiosis is a close and long-term interaction between two different species
• Mutualism is a symbiotic relationship in which both species benefit
• Commensalism is a symbiotic relationship in which one species benefits and the other is neither harmed nor helped
• Parasitism is a symbiotic relationship in which one species benefits and the other is harmed
• Population growth is influenced by birth rates, death rates, immigration, and emigration
• Carrying capacity is the maximum population size that an environment can support
• Community structure is influenced by factors such as species diversity, keystone species, and disturbance
• Ecological succession is the process of change in the species structure of an ecological community over time
• Conservation biology is the study of protecting and managing Earth's biodiversity
• Threats to biodiversity include habitat loss, invasive species, pollution, climate change, and overexploitation