Introduction to Biology & Cell Biology

• Biology is the scientific study of life, examining the structure, function, growth, origin, evolution, and distribution of living organisms.
• Biology recognizes the cell as the basic unit of life, genes as the basic unit of heredity, and evolution as the mechanism that drives the formation of new species.
• Living organisms are organized into a hierarchy, from molecules and cells to tissues, organs, organ systems, organisms, populations, communities, ecosystems, and the biosphere.
• Biology encompasses a broad range of fields, including biochemistry, microbiology, botany, zoology, and ecology.

Cell Biology

• Cell biology is the study of cells, their physiological properties, structure, organelles, interactions with their environment, life cycle, division, and death.
• The cell theory states that all living organisms are composed of one or more cells, the cell is the basic unit of life, and all cells arise from pre-existing cells.
• Cells are broadly classified as prokaryotic (lacking a nucleus and other membrane-bound organelles) or eukaryotic (possessing a nucleus and membrane-bound organelles).
• Key cellular structures include the plasma membrane, cytoplasm, nucleus, ribosomes, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and cytoskeleton.
• The plasma membrane is a selective barrier that regulates the passage of substances into and out of the cell, composed of a phospholipid bilayer with embedded proteins.
• The nucleus contains the cell's genetic material (DNA) and controls cellular activities through gene expression.
• Ribosomes are responsible for protein synthesis, translating mRNA into polypeptide chains.
• Mitochondria are the powerhouses of the cell, generating ATP through cellular respiration.
• The endoplasmic reticulum (ER) is involved in protein synthesis and folding (rough ER) and lipid synthesis (smooth ER).
• The Golgi apparatus processes and packages proteins into vesicles for transport to other cellular locations or secretion.
• Lysosomes contain enzymes that break down cellular waste and debris.
• The cytoskeleton provides structural support, facilitates cell movement, and plays a role in cell division, comprising microtubules, microfilaments, and intermediate filaments.
• Cell communication occurs through chemical signals, such as hormones and neurotransmitters, that bind to receptors on target cells.
• Cell division occurs through mitosis (for growth and repair) or meiosis (for sexual reproduction).
• Apoptosis is programmed cell death, a critical process for development and tissue homeostasis.

Genetics

• Genetics is the study of heredity and variation of inherited characteristics.
• Genes are the basic units of heredity, composed of DNA sequences that encode proteins or regulate gene expression.
• DNA (deoxyribonucleic acid) is the genetic material of most organisms, a double-stranded helix composed of nucleotides containing a sugar, phosphate group, and nitrogenous base (adenine, guanine, cytosine, or thymine).
• RNA (ribonucleic acid) is involved in gene expression, including mRNA (messenger RNA), tRNA (transfer RNA), and rRNA (ribosomal RNA).
• The genome is the complete set of genetic material in an organism.
• Chromosomes are structures containing DNA, organized into genes.
• Genes are passed from parents to offspring through sexual reproduction.
• Genotype refers to the genetic makeup of an organism, while phenotype refers to its observable characteristics.
• Alleles are different versions of a gene.
• Homozygous individuals have two identical alleles for a gene, while heterozygous individuals have two different alleles.
• Dominant alleles mask the expression of recessive alleles in heterozygous individuals.
• Mendelian genetics describes the basic principles of inheritance, including segregation (separation of alleles during gamete formation) and independent assortment (alleles of different genes assort independently).
• Mutations are changes in the DNA sequence that can lead to genetic variation.
• Genetic engineering involves manipulating genes to alter the characteristics of an organism.
• Population genetics studies the genetic variation within and among populations.

Evolutionary Biology

• Evolutionary biology is the study of the processes that have shaped the diversity of life on Earth.
• Evolution is the change in the heritable characteristics of biological populations over successive generations.
• Natural selection is the mechanism by which organisms with traits that are better suited to their environment are more likely to survive and reproduce, passing those traits to their offspring.
• Adaptation is the process by which organisms evolve traits that enhance their survival and reproduction in a particular environment.
• Genetic drift is the random change in allele frequencies within a population, particularly significant in small populations.
• Gene flow is the movement of genes between populations, which can introduce new genetic variation.
• Mutation introduces new genetic variation into a population.
• Speciation is the process by which new species arise, often through reproductive isolation.
• Reproductive isolation occurs when populations can no longer interbreed and produce fertile offspring.
• Allopatric speciation occurs when populations are geographically isolated, while sympatric speciation occurs within the same geographic area.
• Phylogeny is the evolutionary history and relationships of a group of organisms, often represented as a phylogenetic tree.
• Evidence for evolution includes fossil records, comparative anatomy, embryology, biogeography, and molecular biology.
• Macroevolution refers to large-scale evolutionary changes, such as the origin of new species and major groups of organisms.
• Microevolution refers to small-scale evolutionary changes within a population, such as changes in allele frequencies.
• The modern synthesis of evolutionary theory combines Darwin's theory of natural selection with Mendelian genetics.