Introduction to Biology

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

Key Biological Concepts

• Cell theory: The cell is the basic unit of life, all living organisms are composed of cells, and all cells arise from pre-existing cells.
• Genes: Units of heredity made of DNA that provide instructions for building proteins and other essential molecules.
• Evolution: The process by which populations of organisms change over time.
• Homeostasis: The ability of an organism to maintain a stable internal environment despite external changes.
• Energy: Life depends on the ability of organisms to obtain and utilize energy, often through photosynthesis or cellular respiration.

Hierarchical Organization of Life

• Biosphere: all the environments on Earth that support life.
• Ecosystems: consist of all living things in a particular area, along with nonliving components.
• Communities: the array of organisms inhabiting a particular ecosystem.
• Populations: consist of all individuals of a species within a specific area.
• Organisms: individual living things.
• Organs and Tissues: organs consist of multiple tissues, which are groups of similar cells performing specific functions.
• Cells: the basic unit of life.
• Organelles: functional components within cells.
• Molecules: chemical structures consisting of atoms.

Domains of Life

• Bacteria: One of the two prokaryotic domains.
• Archaea: The other prokaryotic domain; many live in extreme environments.
• Eukarya: Domain that includes all eukaryotic organisms (protists, fungi, plants, and animals).

Natural Selection

• Natural selection is a primary mechanism of evolution.
• Individuals with traits better suited to their environment tend to survive and reproduce at higher rates.
• Over time, this leads to the accumulation of advantageous traits in a population.

Scientific Method

• Observation: The process of gathering information about the natural world.
• Hypothesis: A tentative explanation or prediction based on observations.
• Experimentation: Controlled tests designed to support or refute a hypothesis.
• Data Analysis: Interpreting experimental results to draw conclusions.
• Conclusion: States whether the hypothesis was supported or refuted.

Cell Biology

• Cell biology is the study of cells, their structure, function, and behavior.
• It encompasses the physiological properties, metabolic processes, signaling pathways, life cycle, chemical composition, and interactions of cells with their environment.

Cell Structures

• Plasma Membrane: The outer boundary of the cell, composed of a phospholipid bilayer with embedded proteins.
• Regulates the movement of substances in and out of the cell.
• Nucleus: Contains the cell's genetic material (DNA) and controls cellular activities.
• Cytoplasm: The region between the plasma membrane and the nucleus, containing various organelles and the cytosol.
• Ribosomes: Responsible for protein synthesis.
• Endoplasmic Reticulum (ER): A network of membranes involved in protein and lipid synthesis.
• Rough ER: Contains ribosomes and is involved in protein synthesis and modification.
• Smooth ER: Involved in lipid synthesis, detoxification, and calcium storage.
• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for transport.
• Mitochondria: Responsible for cellular respiration and ATP production.
• Lysosomes: Contain enzymes for breaking down cellular waste and debris.

Cell Types

• Prokaryotic Cells: Simpler cells lacking a nucleus and other complex organelles.
• Bacteria and Archaea.
• Eukaryotic Cells: More complex cells with a nucleus and membrane-bound organelles.
• Found in protists, fungi, plants, and animals.

Cell Membrane

• The cell membrane is composed of a phospholipid bilayer with embedded proteins.
• Phospholipids have a hydrophilic (polar) head and hydrophobic (nonpolar) tails.
• Proteins in the membrane can act as channels, carriers, receptors, or enzymes.

Membrane Transport

• Passive Transport: Movement of substances across the membrane without energy input.
• Diffusion: Movement of molecules from an area of high concentration to an area of low concentration.
• Osmosis: Movement of water across a semipermeable membrane from an area of high water concentration to an area of low water concentration.
• Facilitated Diffusion: Movement of molecules across the membrane with the help of transport proteins.
• Active Transport: Movement of substances across the membrane with energy input (ATP).
• Moves substances against their concentration gradients.

Cellular Respiration

• Cellular respiration is the process by which cells convert glucose into ATP, the energy currency of the cell.
• Glycolysis: Glucose is broken down into pyruvate in the cytoplasm.
• Krebs Cycle (Citric Acid Cycle): Pyruvate is further broken down in the mitochondria, releasing carbon dioxide and generating high-energy electron carriers (NADH and FADH2).
• Electron Transport Chain: Electrons from NADH and FADH2 are passed along a series of protein complexes, driving the production of ATP.

Photosynthesis

• Photosynthesis: The process by which plants and other organisms convert light energy into chemical energy.
• Light-Dependent Reactions: Light energy is used to split water molecules, generating ATP and NADPH.
• Light-Independent Reactions (Calvin Cycle): ATP and NADPH are used to convert carbon dioxide into glucose.

Cell Communication

• Cells communicate through chemical signals.
• Reception: A signal molecule binds to a receptor protein on or in the target cell.
• Transduction: The signal is converted into a form that can bring about a cellular response.
• Response: The cell responds to the signal, often by activating or deactivating genes or enzymes.

Cell Cycle

• The cell cycle is the series of events that occur as a cell grows and divides.
• Interphase: The cell grows and replicates its DNA.
• G1 Phase: Cell grows and carries out normal functions.
• S Phase: DNA is replicated.
• G2 Phase: Cell prepares for division.
• Mitotic Phase (M Phase): The cell divides.
• Mitosis: The nucleus divides.
  • Prophase: Chromosomes condense and become visible.
  • Metaphase: Chromosomes line up along the metaphase plate.
  • Anaphase: Sister chromatids separate and move to opposite poles of the cell.
  • Telophase: Chromosomes decondense and nuclear envelopes reform.
• Cytokinesis: The cytoplasm divides, resulting in two daughter cells.

Meiosis

• Meiosis is a type of cell division that produces gametes (sperm and egg cells) with half the number of chromosomes as the parent cell.
• Meiosis I: Homologous chromosomes separate.
• Prophase I: Homologous chromosomes pair up and exchange genetic material through crossing over.
• Metaphase I: Homologous chromosome pairs line up along the metaphase plate.
• Anaphase I: Homologous chromosomes separate and move to opposite poles of the cell.
• Telophase I: Chromosomes arrive at the poles, and the cell divides.
• Meiosis II: Sister chromatids separate.
• Similar to mitosis, but with half the number of chromosomes.

Genetics

• Genes: Units of heredity made of DNA that provide instructions for building proteins and other essential molecules.
• Chromosomes: Structures within the nucleus that contain DNA.
• Genotype: The genetic makeup of an organism.
• Phenotype: The observable characteristics of an organism.
• Alleles: Different versions of a gene.

DNA Structure

• DNA is a double helix composed of nucleotides.
• Each nucleotide consists of a sugar (deoxyribose), a phosphate group, and a nitrogenous base (adenine, guanine, cytosine, or thymine).
• Adenine pairs with thymine (A-T), and guanine pairs with cytosine (G-C).

RNA Structure

• RNA is similar to DNA but is single-stranded and contains the sugar ribose instead of deoxyribose.
• RNA contains uracil (U) instead of thymine (T).

Protein Synthesis

• Transcription: DNA is transcribed into mRNA in the nucleus.
• Translation: mRNA is translated into protein on ribosomes in the cytoplasm.
• Codons: Three-nucleotide sequences on mRNA that specify particular amino acids.
• tRNA: Transfers amino acids to the ribosome.

Mutations

• Mutations are changes in the DNA sequence.
• Mutations can be spontaneous or caused by mutagens (e.g., radiation, chemicals).
• Mutations can be harmful, beneficial, or neutral.