AP Biology: Chemistry of Life

• AP Biology covers a wide range of biological topics, from the molecular level to ecosystems

Chemistry of Life

• Living organisms are composed of matter, which is made up of elements
• Key elements in living organisms include carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur (CHNOPS)
• Compounds are combinations of elements, and their properties differ from those of their constituent elements
• Water's properties, such as cohesion, adhesion, high specific heat, and evaporative cooling, are crucial for life
• pH is a measure of hydrogen ion concentration; living systems are sensitive to pH changes
• Carbon's ability to form diverse molecules is the basis of organic chemistry
• Macromolecules include carbohydrates, lipids, proteins, and nucleic acids
• Carbohydrates serve as energy sources and structural components
• Lipids include fats, oils, phospholipids, and steroids; they are important for energy storage, insulation, and cell membrane structure
• Proteins have diverse functions, including enzymes, structural components, and hormones
• Nucleic acids (DNA and RNA) store and transmit genetic information

Cell Structure and Function

• Cells are the basic unit of life
• Prokaryotic cells (bacteria and archaea) lack a nucleus and other membrane-bound organelles
• Eukaryotic cells (protists, fungi, plants, and animals) have a nucleus and membrane-bound organelles
• The plasma membrane controls the movement of substances in and out of the cell
• The nucleus contains the cell's DNA and controls cell activities
• Ribosomes synthesize proteins
• The endoplasmic reticulum (ER) is involved in protein synthesis (rough ER) and lipid synthesis (smooth ER)
• The Golgi apparatus modifies, sorts, and packages proteins
• Lysosomes contain enzymes for intracellular digestion
• Mitochondria are responsible for cellular respiration and ATP production
• Chloroplasts (in plant cells) are responsible for photosynthesis
• The cytoskeleton provides structural support and facilitates movement
• Cell junctions (e.g., tight junctions, gap junctions) allow for communication and interaction between cells

Cellular Energetics

• Metabolism encompasses all chemical reactions in an organism
• Enzymes are biological catalysts that speed up reactions by lowering activation energy
• Factors such as temperature, pH, and substrate concentration affect enzyme activity
• Cellular respiration is the process of converting glucose into ATP
• Glycolysis occurs in the cytoplasm and breaks down glucose into pyruvate
• The Krebs cycle (citric acid cycle) occurs in the mitochondria and generates ATP, NADH, and FADH2
• The electron transport chain (ETC) uses NADH and FADH2 to create a proton gradient, which drives ATP synthesis (oxidative phosphorylation)
• Fermentation is an anaerobic process that allows glycolysis to continue in the absence of oxygen
• Photosynthesis is the process of converting light energy into chemical energy (glucose)
• The light-dependent reactions occur in the thylakoid membranes and convert light energy into ATP and NADPH
• The Calvin cycle (light-independent reactions) occurs in the stroma and uses ATP and NADPH to fix carbon dioxide into glucose

Cell Communication and Cell Cycle

• Cells communicate through various signaling pathways
• Reception, transduction, and response are the three stages of cell signaling
• Types of signaling include direct contact, paracrine signaling, endocrine signaling, and synaptic signaling
• The cell cycle is a series of events that lead to cell growth and division
• Interphase (G1, S, and G2 phases) is the period of cell growth and DNA replication
• Mitosis is the process of nuclear division (prophase, metaphase, anaphase, telophase)
• Cytokinesis is the division of the cytoplasm
• Cell cycle checkpoints ensure proper DNA replication and chromosome segregation
• Cancer results from uncontrolled cell growth and division

Heredity

• Genes are units of heredity made of DNA
• Chromosomes are structures that carry genes
• Meiosis is a process that produces haploid gametes (sperm and egg cells)
• Fertilization restores the diploid number
• Mendelian genetics explains patterns of inheritance (law of segregation, law of independent assortment)
• Punnett squares are used to predict the genotypes and phenotypes of offspring
• Sex-linked traits are carried on sex chromosomes (e.g., X chromosome)
• Non-Mendelian inheritance patterns include incomplete dominance, codominance, multiple alleles, and polygenic inheritance
• Linked genes tend to be inherited together
• Genetic recombination (crossing over) increases genetic variation

Molecular Genetics

• DNA is the hereditary material
• DNA structure: double helix with nucleotides (sugar, phosphate, and nitrogenous base)
• DNA replication: DNA polymerase synthesizes new DNA strands using the existing strands as templates
• Transcription: RNA polymerase synthesizes RNA from a DNA template
• Translation: ribosomes synthesize proteins using mRNA as a template
• The genetic code is a set of rules that specifies how nucleotide sequences are translated into amino acid sequences
• Mutations are changes in DNA sequence; they can be spontaneous or induced
• Viruses are infectious particles that replicate within host cells
• Biotechnology uses biological systems to develop products and technologies
• Restriction enzymes cut DNA at specific sequences
• Gel electrophoresis separates DNA fragments by size
• PCR (polymerase chain reaction) amplifies DNA
• DNA sequencing determines the nucleotide sequence of DNA
• Genetic engineering involves manipulating genes to alter organisms' traits

Evolution

• Evolution is the change in the genetic makeup of a population over time
• Evidence for evolution includes fossils, comparative anatomy, embryology, and molecular biology
• Natural selection is the mechanism of evolution; individuals with advantageous traits are more likely to survive and reproduce
• Genetic variation is the raw material for evolution
• Sources of genetic variation include mutation, gene flow, and sexual reproduction
• Hardy-Weinberg equilibrium describes a non-evolving population
• Factors that can cause evolution include natural selection, genetic drift, gene flow, and mutation
• Speciation is the process by which new species arise
• Reproductive isolation is necessary for speciation to occur
• Macroevolution refers to broad patterns of evolutionary change above the species level

Ecology

• Ecology is the study of interactions between organisms and their environment
• Populations are groups of individuals of the same species living in the same area
• Communities are groups of populations of different species living in the same area
• Ecosystems include communities and their physical environment
• Biomes are large geographic areas characterized by specific climates and vegetation
• Population ecology focuses on factors that affect population size and density
• Community ecology focuses on interactions between species (competition, predation, symbiosis)
• Food chains and food webs illustrate the flow of energy and nutrients in ecosystems
• Energy flow is unidirectional; energy is lost as heat at each trophic level
• Nutrient cycles (e.g., carbon cycle, nitrogen cycle) involve the movement of nutrients through ecosystems
• Conservation biology aims to protect biodiversity
• Human activities (e.g., deforestation, pollution, climate change) threaten biodiversity