Washu Biol 1020

This study guide covers fundamental concepts in introductory biology, focusing on the chemical basis of life, macromolecule structure and function, cell structure and function (prokaryotic vs. eukaryotic), cellular respiration, photosynthesis, cell communication, and cell division (mitosis and meiosis). It emphasizes key definitions, processes, and the importance of these concepts in living organisms.

Note 1: Introduction to Biological Chemistry: Water and its Properties

Water is the foundation of life as we know it, primarily due to its unique chemical properties. It's a polar molecule, meaning it has a slightly positive charge on the hydrogen atoms and a slightly negative charge on the oxygen atom. This polarity arises because oxygen is more electronegative than hydrogen, pulling electrons closer and creating a dipole moment. This polarity allows water molecules to form hydrogen bonds with each other and other polar molecules, giving rise to cohesion, adhesion, and high surface tension. Cohesion allows water molecules to stick together, crucial for water transport in plants. Adhesion allows water to stick to other surfaces, like the walls of plant xylem. Water also has a high specific heat capacity, meaning it takes a lot of energy to raise its temperature, helping to stabilize temperatures in organisms and aquatic environments. Its high heat of vaporization means it takes a lot of energy to change it from liquid to gas, allowing for evaporative cooling. Finally, ice is less dense than liquid water, which allows aquatic life to survive under frozen surfaces. A common misconception is that only hydrogen bonds define water's properties; Van der Waals forces also contribute.

Note 2: Biological Macromolecules: Carbohydrates

Carbohydrates are essential organic molecules serving as primary sources of energy and structural components in living organisms. They are composed of carbon, hydrogen, and oxygen, typically in a 1:2:1 ratio. Monosaccharides, such as glucose, fructose, and galactose, are the simplest carbohydrates and serve as the building blocks for more complex carbohydrates. Disaccharides consist of two monosaccharides joined by a glycosidic linkage, formed through dehydration reactions (e.g., sucrose is glucose + fructose). Polysaccharides are long chains of monosaccharides, such as starch (energy storage in plants), glycogen (energy storage in animals), and cellulose (structural component of plant cell walls). Starch exists in two forms: amylose (linear) and amylopectin (branched). The branching in amylopectin allows for faster glucose release. Cellulose's beta-glucose linkages make it indigestible for most animals, highlighting the importance of enzyme specificity. Common misconceptions include believing all carbohydrates are unhealthy; complex carbohydrates provide sustained energy and essential fiber.

Note 3: Biological Macromolecules: Lipids

Lipids are a diverse group of hydrophobic molecules, crucial for energy storage, insulation, and cell membrane structure. Key types include fats, phospholipids, and steroids. Fats (triglycerides) are composed of glycerol and three fatty acids, joined by ester linkages. Saturated fats have no double bonds in their fatty acid tails, making them solid at room temperature and often associated with heart disease. Unsaturated fats have one or more double bonds, creating kinks in the tails, making them liquid at room temperature. Phospholipids have a polar (hydrophilic) phosphate head and two nonpolar (hydrophobic) fatty acid tails, making them amphipathic and crucial for cell membrane formation. Steroids, like cholesterol, have a four-ring carbon skeleton and serve as precursors for hormones. Cholesterol is essential for cell membrane fluidity and hormone synthesis, though high levels can contribute to plaque formation. It's a common misconception to think all fats are bad. Essential fatty acids, like omega-3s, are vital for health and must be obtained from the diet.

Note 4: Biological Macromolecules: Proteins

Proteins are the workhorses of the cell, performing a vast array of functions including catalysis, transport, structural support, and signaling. They are composed of amino acids, each containing an amino group, a carboxyl group, a hydrogen atom, and a unique R-group bonded to a central carbon. Amino acids are linked together by peptide bonds, formed through dehydration reactions. Protein structure is organized into four levels: primary (amino acid sequence), secondary (alpha helices and beta sheets stabilized by hydrogen bonds), tertiary (3D folding due to interactions between R-groups), and quaternary (arrangement of multiple polypeptide chains). Protein folding is crucial for function, and misfolding can lead to diseases like Alzheimer's and Parkinson's. Enzymes are biological catalysts, proteins that speed up chemical reactions by lowering the activation energy. They are highly specific, with each enzyme catalyzing a particular reaction or set of reactions. A common misconception is that proteins are only for muscle building; they perform many essential functions throughout the body.

Note 5: Biological Macromolecules: Nucleic Acids

Nucleic acids (DNA and RNA) are responsible for storing and transmitting genetic information. They are polymers of nucleotides, each consisting of a sugar (deoxyribose in DNA, ribose in RNA), a phosphate group, and a nitrogenous base. DNA contains adenine (A), guanine (G), cytosine (C), and thymine (T), while RNA contains A, G, C, and uracil (U). DNA is a double helix, with two strands held together by hydrogen bonds between complementary base pairs (A-T, G-C). RNA is typically single-stranded and plays various roles in gene expression, including mRNA (messenger RNA), tRNA (transfer RNA), and rRNA (ribosomal RNA). DNA replication is the process of copying DNA, ensuring genetic information is passed on accurately during cell division. Transcription is the process of synthesizing RNA from a DNA template. Translation is the process of synthesizing proteins from an RNA template. The central dogma of molecular biology describes the flow of genetic information: DNA -> RNA -> Protein. A frequent misconception is that DNA is the only genetic material; RNA also serves as genetic material in some viruses.

Note 6: Cell Structure and Function: Prokaryotic vs. Eukaryotic Cells

Cells are the basic unit of life, and they can be classified as either prokaryotic or eukaryotic. Prokaryotic cells (bacteria and archaea) are simpler, smaller, and lack a nucleus and other membrane-bound organelles. Their DNA is located in a nucleoid region. Eukaryotic cells (protists, fungi, plants, and animals) are more complex, larger, and have a nucleus and other membrane-bound organelles, such as mitochondria, endoplasmic reticulum, and Golgi apparatus. The nucleus houses the cell's DNA and controls gene expression. Mitochondria are responsible for cellular respiration, generating ATP. The endoplasmic reticulum (ER) is involved in protein synthesis and lipid metabolism. The Golgi apparatus processes and packages proteins. Plant cells also have chloroplasts, which are responsible for photosynthesis. Cell size is limited by surface area-to-volume ratio; as a cell increases in size, its surface area increases more slowly than its volume, limiting the rate of nutrient uptake and waste removal. A common misconception is that prokaryotes are less evolved than eukaryotes; they are simply adapted to different environments.

Note 7: Membrane Structure and Function

The plasma membrane is a selectively permeable barrier that surrounds all cells, controlling the movement of substances in and out. It is composed primarily of a phospholipid bilayer, with proteins embedded within. The fluid mosaic model describes the membrane as a fluid structure with a mosaic of various proteins drifting laterally within the lipid bilayer. Membrane proteins perform various functions, including transport, enzymatic activity, signal transduction, cell-cell recognition, and intercellular joining. Passive transport (diffusion, osmosis, facilitated diffusion) does not require energy and moves substances down their concentration gradient. Active transport requires energy (ATP) and moves substances against their concentration gradient. Osmosis is the movement of water across a selectively permeable membrane from an area of high water concentration to an area of low water concentration. Cells in hypertonic solutions lose water, while cells in hypotonic solutions gain water. Plant cells have cell walls that prevent them from bursting in hypotonic solutions. A common misconception is that the membrane is rigid; it's a dynamic, fluid structure.

Note 8: Cellular Respiration: Harvesting Chemical Energy

Cellular respiration is the process by which cells convert glucose into ATP, the main energy currency of the cell. It is a catabolic pathway that breaks down glucose in the presence of oxygen. The overall equation is: C6H12O6 + 6O2 -> 6CO2 + 6H2O + ATP. Cellular respiration consists of four main stages: glycolysis, pyruvate oxidation, the citric acid cycle (Krebs cycle), and oxidative phosphorylation (electron transport chain and chemiosmosis). Glycolysis occurs in the cytoplasm and breaks down glucose into two molecules of pyruvate, producing a small amount of ATP and NADH. Pyruvate oxidation converts pyruvate into acetyl CoA. The citric acid cycle occurs in the mitochondrial matrix and further oxidizes acetyl CoA, releasing CO2, ATP, NADH, and FADH2. Oxidative phosphorylation occurs in the inner mitochondrial membrane and uses the electron transport chain to create a proton gradient, which drives ATP synthesis by ATP synthase (chemiosmosis). The majority of ATP is produced during oxidative phosphorylation. Fermentation is an anaerobic process that regenerates NAD+ for glycolysis when oxygen is not available. A common misconception is that respiration only occurs in animals; plants also respire to generate energy.

Note 9: Photosynthesis: Capturing Light Energy

Photosynthesis is the process by which plants and other autotrophs convert light energy into chemical energy in the form of glucose. It occurs in chloroplasts and involves two main stages: the light reactions and the Calvin cycle. The light reactions occur in the thylakoid membranes and convert light energy into chemical energy in the form of ATP and NADPH. Chlorophyll absorbs light energy, which excites electrons. These electrons are passed along an electron transport chain, generating ATP and NADPH. Water is split to replace the electrons, releasing oxygen as a byproduct. The Calvin cycle occurs in the stroma and uses the ATP and NADPH produced during the light reactions to fix carbon dioxide (CO2) into glucose. Carbon fixation involves the enzyme RuBisCO incorporating CO2 into an organic molecule. The Calvin cycle regenerates its starting molecule, RuBP. C4 and CAM plants have adaptations to minimize photorespiration in hot, dry environments. Photosynthesis is essential for life on Earth, providing the oxygen we breathe and the food we eat. A common misconception is that plants only perform photosynthesis; they also perform cellular respiration.

Note 10: Cell Communication

Cell communication is crucial for coordinating cellular activities and maintaining homeostasis. Cells communicate through various signaling pathways, involving a signaling molecule (ligand), a receptor protein, and a signal transduction pathway. There are three main types of cell signaling: direct contact (gap junctions, cell-cell recognition), local signaling (paracrine signaling, synaptic signaling), and long-distance signaling (endocrine signaling). In direct contact, cells communicate through physical contact. In local signaling, cells release signaling molecules that affect nearby cells. In long-distance signaling, cells release hormones that travel through the bloodstream to target cells throughout the body. Signal transduction pathways involve a series of molecular events that convert the initial signal into a cellular response. Common signal transduction pathways include phosphorylation cascades and second messengers (cAMP, calcium ions). Receptor proteins can be located on the cell surface (e.g., G protein-coupled receptors, receptor tyrosine kinases) or inside the cell (e.g., steroid hormone receptors). A common misconception is that only animal cells communicate; all cells, including plant and bacterial cells, communicate with each other.

Note 11: Cell Cycle and Cell Division: Mitosis

The cell cycle is an ordered sequence of events that culminates in cell division. It consists of two main phases: interphase and the mitotic (M) phase. Interphase is the period of cell growth and DNA replication, consisting of G1, S, and G2 phases. The M phase includes mitosis (nuclear division) and cytokinesis (cytoplasmic division). Mitosis is the process of dividing the nucleus into two identical nuclei, ensuring that each daughter cell receives a complete set of chromosomes. Mitosis consists of five main stages: prophase, prometaphase, metaphase, anaphase, and telophase. Prophase: chromosomes condense, and the mitotic spindle forms. Prometaphase: the nuclear envelope breaks down, and microtubules attach to the chromosomes at the kinetochores. Metaphase: chromosomes align at the metaphase plate. Anaphase: sister chromatids separate and move to opposite poles of the cell. Telophase: chromosomes decondense, and the nuclear envelope reforms. Cytokinesis is the division of the cytoplasm, resulting in two separate daughter cells. In animal cells, cytokinesis occurs through the formation of a cleavage furrow. In plant cells, cytokinesis occurs through the formation of a cell plate. A common misconception is that mitosis creates sex cells; mitosis creates identical somatic (body) cells.

Note 12: Cell Cycle and Cell Division: Meiosis

Meiosis is a type of cell division that produces gametes (sex cells) with half the number of chromosomes as the parent cell. It is essential for sexual reproduction, introducing genetic variation. Meiosis involves two rounds of cell division: meiosis I and meiosis II. Meiosis I separates homologous chromosomes, while meiosis II separates sister chromatids. Prophase I is a unique stage where homologous chromosomes pair up and undergo crossing over, exchanging genetic material. This creates recombinant chromosomes, increasing genetic diversity. Metaphase I: homologous chromosome pairs align at the metaphase plate. Anaphase I: homologous chromosomes separate, but sister chromatids remain attached. Telophase I: chromosomes arrive at opposite poles, and the cell divides. Meiosis II is similar to mitosis, separating sister chromatids. The end result of meiosis is four haploid gametes, each with a unique combination of genes. Genetic variation is introduced through crossing over, independent assortment of chromosomes, and random fertilization. Errors in meiosis can lead to aneuploidy, a condition where cells have an abnormal number of chromosomes. Down syndrome (trisomy 21) is an example of aneuploidy. A common misconception is that crossing over occurs in mitosis; it's unique to meiosis and a critical source of genetic diversity.

Browse public study notes