Biology Study Guide: Key Concepts & Processes
Understanding Evolution by Natural Selection
Natural selection is a core mechanism of evolution, where organisms with traits that enhance survival and reproduction in their environment are more likely to pass on those advantageous genes to offspring.
Scientific Theory vs. Everyday Usage
In science, a theory is a well-substantiated explanation supported by extensive evidence, unlike its casual use in everyday language.
Characteristics of Living Things
Living organisms share key characteristics: respiration, movement, response to stimuli, reproduction, growth, and dependence on their environment.
Variables in Scientific Experiments
- Independent Variable: The factor manipulated or changed by the scientist.
- Dependent Variable: The factor being measured or observed.
- Control Variable: Factors kept constant to ensure a fair test.
Atoms, Elements, and Molecules
Subatomic Particles and Their Effects
- Changing the number of protons creates a different element.
- Changing the number of neutrons creates an isotope.
- Changing the number of electrons creates an ion (cation or anion).
Chemical Bonds and Polarity
- Non-polar bonds: Electronegativity difference between 0.0 and 0.4.
- Polar bonds: Electronegativity difference between 0.5 and 1.4.
- Ionic bonds: Electronegativity difference of 1.5 and above.
The Chemistry of Life
Properties of Water and Their Importance
Water’s unique properties, such as its thermal properties, ability to act as a universal solvent, and cohesion and adhesion, are crucial for supporting life processes and habitats.
Cohesion, Surface Tension, and Adhesion
- Cohesion: Water molecules sticking to each other due to weak bonds.
- Surface tension: The force acting on the surface of a liquid due to cohesion.
- Adhesion: Water molecules sticking to other substances.
Polarity of Water
Water is a polar molecule because of the polar covalent bonds between oxygen and hydrogen atoms.
Functional Groups in Organic Molecules
Important functional groups include hydroxyl, methyl, carbonyl, carboxyl, amino, phosphate, and sulfhydryl groups.
Macromolecules: Carbohydrates, Proteins, and Nucleic Acids
Carbohydrates
Carbohydrates are composed of monosaccharides linked together by glycosidic bonds to form polysaccharide chains.
Proteins
Changes in temperature, pH, or exposure to chemicals can alter the internal interactions and shape of proteins.
Nucleic Acids: DNA and RNA
- DNA: Double-stranded helix, repository of genetic information.
- RNA: Usually single-stranded, involved in protein synthesis and gene regulation.
Complementary and Antiparallel Nature of Nucleic Acid Strands
Nucleic acid strands are complementary and antiparallel due to specific base pairing (A-T, C-G).
Cell Structure and Function
Eukaryotic vs. Prokaryotic Cells
Both eukaryotic and prokaryotic cells have a plasma membrane, cytoplasm, and ribosomes. Eukaryotic cells are typically larger, have a true nucleus, and possess membrane-bound organelles for compartmentalization of functions.
The Endomembrane System
The endomembrane system, including the nuclear envelope, lysosomes, vesicles, ER, and Golgi apparatus, works together to modify, package, tag, and transport proteins and lipids.
Types of Endocytosis
- Phagocytosis (“cell eating”): Engulfing large particles.
- Pinocytosis (“cell drinking”): Taking in small amounts of fluid and solutes.
- Receptor-mediated endocytosis: Specific uptake of molecules via receptors.
The Fluid Mosaic Model of the Plasma Membrane
The fluid mosaic model describes the plasma membrane as a dynamic structure composed of phospholipids, cholesterol, proteins, and carbohydrates.
Cellular Transport
Passive Transport: Diffusion and Osmosis
- Diffusion: Movement of molecules from high to low concentration.
- Osmosis: Movement of water across a semipermeable membrane from low to high solute concentration.
- Facilitated diffusion: Movement of molecules with the help of transport proteins.
Active Transport
Active transport requires energy to move molecules against their concentration gradient.
Energy and Metabolism
ATP: The Energy Currency of Life
ATP stores and transfers energy from the breakdown of food molecules to cellular processes.
Redox Reactions
Redox reactions involve the transfer of electrons between substances, with one substance undergoing oxidation (losing electrons) and another undergoing reduction (gaining electrons).
Enzymes and Their Regulation
Enzymes are biological catalysts that speed up chemical reactions. Factors like pH and temperature can affect enzyme activity. Inhibitors can bind to enzymes and reduce their activity.
Cellular Respiration and Photosynthesis
Overview of Cellular Respiration
Cellular respiration converts oxygen and glucose into water, carbon dioxide, and ATP. It involves glycolysis, pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation.
Glycolysis
Glycolysis occurs in the cytoplasm and breaks down glucose into pyruvate, generating 2 ATP.
Pyruvate Oxidation
Pyruvate oxidation occurs in the mitochondria and converts pyruvate into acetyl CoA, releasing carbon dioxide.
Citric Acid Cycle (Krebs Cycle)
The citric acid cycle occurs in the mitochondria and generates ATP, NADH, and FADH2.
Oxidative Phosphorylation
Oxidative phosphorylation uses the electron transport chain and ATP synthase to generate ATP.
Fermentation
Fermentation is an anaerobic process that recycles NAD+ and produces a small amount of ATP. Examples include lactic acid fermentation and alcoholic fermentation.
Overview of Photosynthesis
Photosynthesis converts carbon dioxide and water into oxygen and glucose using light energy.
ATP Production in Chloroplasts
In chloroplasts, ATP is produced through chemiosmosis, where H+ ions are pumped into the thylakoid space and flow back through ATP synthase, generating ATP.
Calvin Cycle (Light-Independent Reactions)
The Calvin cycle uses ATP and NADPH from the light-dependent reactions to fix carbon dioxide into glucose.
Autotrophs vs. Heterotrophs
Autotrophs, like plants, produce their own organic compounds from carbon dioxide. Heterotrophs, like animals, consume organic molecules from other organisms.
DNA Replication and Repair
Enzymes Involved in DNA Replication
Key enzymes in DNA replication include DNA polymerases, helicase, ligase, primase, sliding clamp, topoisomerase, and single-strand binding proteins.
Leading and Lagging Strands
DNA replication is semi-conservative, with a leading strand synthesized continuously and a lagging strand synthesized in fragments.
DNA Repair Mechanisms
DNA repair mechanisms include proofreading, mismatch repair, and DNA damage repair pathways.
Cell Cycle and Cell Division
Phases of the Cell Cycle
The cell cycle consists of interphase (G1, S, G2 phases) and mitosis (or meiosis). Checkpoints ensure proper progression through the cycle.
Mitosis vs. Meiosis
- Mitosis: Produces two identical daughter cells.
- Meiosis: Produces four genetically diverse sex cells (gametes).
Stages of Meiosis
Meiosis I involves separation of homologous chromosomes, while meiosis II involves separation of sister chromatids.
Nondisjunction
Nondisjunction is the failure of chromosomes to separate properly during meiosis, which can lead to chromosomal abnormalities.
Genetics and Inheritance
Genotype vs. Phenotype
- Genotype: The genetic makeup of an organism.
- Phenotype: The observable traits of an organism.
Mendelian Genetics
Mendelian genetics describes the inheritance of traits based on dominant and recessive alleles.
Gene Expression and Regulation
Central Dogma of Molecular Biology
The central dogma states that genetic information flows from DNA to RNA to protein (or RNA directly to protein).
Mutations
Mutations are changes in the DNA sequence. They can be beneficial, neutral, or harmful.
Types of Mutations
- Nonsense mutations: Create a premature stop codon.
- Missense mutations: Change an amino acid.
- Silent mutations: Do not change the amino acid sequence.
- Frameshift mutations: Shift the reading frame of the genetic code.
RNA Processing and Protein Synthesis
RNA Processing in Eukaryotes
RNA processing includes adding a 5′ cap, a poly-A tail, and removing introns (splicing).
Ribosomes and tRNA
- Ribosomes: Composed of RNA and proteins, responsible for protein synthesis.
- tRNA: Carries amino acids to the ribosome during translation.
Stages of Translation
Translation involves initiation, elongation, and termination, resulting in the synthesis of a polypeptide chain based on the mRNA sequence.