Biology Test 5 PDF

Chapter 8. ​ Guiding Questions & Linking Questions Answered C2.1 How do cells distinguish between the many signals they receive? Cells distinguish signals based on specificity of receptor-ligand interactions: ​ Receptors on the cell membrane or within the cell are designed to bind only to...

Chapter 8. ​ Guiding Questions & Linking Questions Answered C2.1 How do cells distinguish between the many signals they receive? Cells distinguish signals based on specificity of receptor-ligand interactions: ​ Receptors on the cell membrane or within the cell are designed to bind only to particular signaling molecules (ligands). ​ Different receptor types (G-protein coupled receptors, tyrosine kinase receptors, ion channels, etc.) recognize distinct signals and initiate unique pathways. ​ Cell type-specific expression of receptors ensures that only the appropriate cells respond to a given signal. ​ Signal transduction pathways amplify and process signals differently, leading to varied cellular responses. C2.1 What interactions occur inside animal cells in response to signals? After a signal binds to a receptor, intracellular interactions include: 1.​ Activation of Second Messenger Systems ○​ Example: Epinephrine activates G-protein coupled receptors (GPCRs), leading to cAMP production and further intracellular responses. 2.​ Phosphorylation Cascades ○​ Example: Insulin binding activates tyrosine kinase receptors, triggering a cascade that regulates glucose uptake. 3.​ Gene Expression Changes ○​ Some signals lead to changes in transcription factors, altering gene expression (e.g., melatonin regulating circadian rhythms). 4.​ Vesicle Trafficking & Membrane Transport ○​ Insulin signaling promotes GLUT4 vesicle fusion to increase glucose uptake. 5.​ Cytoskeletal Reorganization ○​ Signals like cytokines can trigger actin remodeling, affecting cell shape and movement. C3.1 What are the roles of nerves and hormones in the integration of body systems? Both nerves and hormones coordinate body functions but differ in mechanisms: ​ Nervous System (Rapid, Electrical Signals) ○​ Uses neurons to transmit electrical impulses rapidly. ○​ Example: Neurotransmitters like acetylcholine or epinephrine transmit signals across synapses to control muscles and reflexes. ​ Endocrine System (Slower, Chemical Signals via Hormones) ○​ Uses hormones transported in the bloodstream for long-term regulation. ○​ Example: Insulin and glucagon regulate blood sugar, while melatonin controls circadian rhythms. ​ Integration of Both Systems ○​ The hypothalamus links the nervous and endocrine systems, releasing hormones that influence glands (e.g., the adrenal gland releases epinephrine under stress). Linking Questions What are the roles of cell membranes in the interaction of a cell with its environment? ​ Membranes contain receptors that detect external signals (hormones, neurotransmitters). ​ Regulate transport of substances through channels and transporters (e.g., insulin promotes glucose uptake). ​ Allow cell-to-cell communication via membrane-bound signaling molecules and gap junctions. ​ Protect the cell by controlling what enters and exits. What patterns exist in communication in biological systems? 1.​ Specificity of signaling – Each receptor only binds specific ligands. 2.​ Amplification of signals – Small signals trigger larger cascades (e.g., cAMP in GPCR pathways). 3.​ Integration of signals – Cells process multiple signals simultaneously to determine responses. 4.​ Feedback regulation – Negative and positive feedback loops maintain homeostasis (e.g., insulin/glucagon balance).  5.​ Conserved mechanisms – Many signaling pathways (like GPCRs and tyrosine kinases) are evolutionarily conserved across species. How does the diversity of the proteins produced contribute to the function of the cell? ​ Receptor Diversity – Different receptors allow cells to respond to a variety of signals. ​ Enzymatic Pathways – Proteins in signaling cascades (kinases, second messengers) control cellular functions. ​ Structural Proteins – Actin and tubulin help with cell movement and shape changes in response to signals. ​ Transcription Factors – Signal-driven gene expression regulates adaptation and cellular responses. ​ Transport Proteins – Membrane proteins like GLUT4 control nutrient uptake in response to insulin. ​ ​ ​ ​ AHL C2.1.3 – Functional Categories of Signaling Chemicals in Animals ​ Signaling systems have evolved multiple times, leading to a wide range of signaling chemicals. ​ Hormones: Produced by endocrine glands, transported via the bloodstream, act on distant targets, and have long-lasting effects. (Examples: insulin, thyroxine, testosterone) ​ Neurotransmitters: Released at synapses, diffuse across a small gap to target neurons, act quickly, and have short-lived effects. (Examples: dopamine, acetylcholine) ​ Cytokines: Small proteins secreted by various cells, act on nearby or the same cell, regulate immune responses, and affect gene expression. (Examples: interleukin, interferon) ​ Calcium ions: Function in neurons and muscle cells, regulated by channels, and play a role in contraction and signaling. AHL C2.1.5 – Localized and Distant Effects of Signaling Molecules ​ Hormones act on distant targets by traveling through the bloodstream. ​ Neurotransmitters act locally, diffusing across a synaptic gap (20-40 nm) to specific postsynaptic neurons. ​ Contrast: Hormones affect multiple targets and have widespread, long-lasting effects; neurotransmitters have localized, short-term effects. AHL C2.1.4 – Chemical Diversity of Hormones and Neurotransmitters ​ Signaling chemicals vary in composition, function, and transport methods. ​ Hormones: ○​ Amines – Derived from amino acids, water-soluble, fast-acting (e.g., melatonin, thyroxine). ○​ Peptides – Chains of amino acids, water-soluble, fast-acting (e.g., insulin, glucagon). ○​ Steroids – Derived from cholesterol, lipid-soluble, bind intracellularly, slow-acting but long-lasting (e.g., testosterone, progesterone). ​ Neurotransmitters: Diverse structures, including amines (dopamine), esters (acetylcholine), amino acids (glutamate), and gases (nitric oxide). AHL C2.1.1 – Receptors as Proteins with Binding Sites for Specific Signaling Chemicals ​ Ligand: A molecule that binds to a receptor to initiate a response. ​ Receptors are proteins that specifically bind ligands and trigger cellular responses. ​ Types: ○​ Transmembrane receptors – Located on the plasma membrane; bind hydrophilic ligands. ○​ Intracellular receptors – Found in cytoplasm or nucleus; bind hydrophobic ligands like steroid hormones. AHL C2.1.6 – Differences Between Transmembrane and Intracellular Receptors ​ Transmembrane receptors: ○​ Have hydrophilic regions outside and inside the cell, with a hydrophobic middle in the membrane. ○​ Bind to hydrophilic ligands (e.g., peptide hormones). ​ Intracellular receptors: ○​ Fully hydrophilic, found in the cytoplasm or nucleus. ○​ Bind to lipid-soluble ligands (e.g., steroid hormones). ​ Ligand Entry: Hydrophobic ligands can pass through membranes, while hydrophilic ligands need receptors on the cell surface. AHL C2.1.7 – Initiation of Signal Transduction Pathways by Receptors ​ Signal transduction: The process of converting an external signal into a cellular response. ​ Steps: ○​ Ligand binds to the receptor. ○​ Receptor activates intracellular molecules. ○​ Signal cascade amplifies the response. ○​ Cellular response is triggered. ​ First messenger: The external ligand. ​ Second messenger: Internal molecules (e.g., cyclic AMP) that mediate responses. ​ Pathways: ○​ G protein-coupled receptors (GPCRs) – Activate G proteins, triggering intracellular signaling. ○​ Tyrosine kinase receptors – Activate phosphorylation cascades (e.g., insulin signaling). ○​ Intracellular receptor pathways – Ligand-receptor complex acts as a gene regulator. General Cell Responses to the Binding of a Signaling Molecule When a signaling molecule (ligand) binds to its receptor, the target cell can respond in several ways, including: 1.​ Gene Expression Changes – Activating or repressing specific genes to modify protein production. 2.​ Enzyme Activation/Inhibition – Modifying metabolic pathways to increase or decrease reactions. 3.​ Ion Channel Opening/Closing – Allowing ions like Ca²⁺ or Na⁺ to enter or leave the cell, affecting membrane potential. 4.​ Cytoskeletal Rearrangement – Changing cell shape, movement, or adhesion properties. 5.​ Secretion of Substances – Inducing the release of hormones, neurotransmitters, or other molecules. 6.​ Cell Growth or Division – Triggering mitosis or apoptosis (programmed cell death) when necessary. AHL C2.1.9 – G-Protein Coupled Receptors (GPCRs) and Signal Transduction ​ Structure & Function of GPCRs:  ○​ Transmembrane receptors with seven α-helices spanning the membrane. ○​ Bind extracellular ligands and activate intracellular G proteins. ​ Activation of GPCRs: ○​ Ligand binds to the extracellular domain of the GPCR. ○​ GPCR undergoes a conformational change, activating an associated G-protein. ○​ The G-protein exchanges GDP for GTP and dissociates into active subunits. ○​ These subunits interact with intracellular enzymes or ion channels, triggering cellular responses. ​ Effects of GPCR Activation: ○​ Initiation of second messenger pathways (e.g., cAMP, IP₃, DAG). ○​ Regulation of cellular metabolism, neurotransmission, and hormone signaling. ​ Examples of Ligands Targeting GPCRs: ○​ Epinephrine (adrenaline) ○​ Dopamine ○​ Serotonin ○​ Histamine ○​ Glucagon C3.1.12 – Epinephrine Secretion and the "Fight or Flight" Response ​ Epinephrine is secreted by the adrenal glands in response to stress, preparing the body for intense activity. ​ Mechanism of Action: ○​ Epinephrine binds to adrenergic receptors (a type of GPCR). ○​ This activates a G-protein, which then stimulates adenylyl cyclase. ○​ Adenylyl cyclase converts ATP into cyclic AMP (cAMP), a second messenger. ○​ cAMP activates protein kinase A (PKA), leading to multiple cellular effects. ​ Effects of Epinephrine: ○​ Skeletal muscles – Increases glycogen breakdown, providing energy for contraction. ○​ Liver – Stimulates glycogenolysis (glycogen breakdown) and gluconeogenesis (glucose production). ○​ Bronchi and Bronchioles – Relaxation of smooth muscle, increasing airflow. ○​ Heart Rate & Cardiac Output – Increases to pump oxygenated blood efficiently. ○​ Blood Vessels – Vasodilation in muscles, vasoconstriction in non-essential organs. AHL C2.1.10 – Epinephrine Receptor and cAMP Second Messenger System ​ Epinephrine activates adrenergic receptors (GPCRs), leading to:  1.​ G-protein activation, which stimulates adenylyl cyclase. 2.​ cAMP production, which acts as a second messenger. 3.​ Activation of protein kinase A (PKA), which phosphorylates target proteins. 4.​ Cellular responses such as increased glucose availability, improved oxygen intake, and enhanced cardiac function. C3.1.11 – Melatonin and Circadian Rhythms ​ Circadian Rhythm: A 24-hour biological cycle regulating sleep-wake patterns. ​ Role of Suprachiasmatic Nucleus (SCN): ○​ Located in the hypothalamus, acts as the body’s internal clock. ○​ Detects light changes via signals from the retina. ○​ Regulates melatonin release based on light exposure. ​ Melatonin Secretion: ○​ Secreted by the pineal gland in response to darkness. ○​ Suppressed by light exposure (especially blue light). ○​ Helps induce sleep and regulate the circadian cycle. ​ Effects of Melatonin: ○​ Promotes sleepiness and relaxation. ○​ Lowers body temperature for sleep. ○​ Synchronizes biological rhythms with the environment. Mechanism of Action of Melatonin as a Signaling Molecule ​ Melatonin binds to G-protein coupled receptors (MT1 and MT2) in target cells, triggering intracellular signaling pathways. ​ These receptors are found in the brain (suprachiasmatic nucleus), retina, immune cells, and peripheral organs. ​ Melatonin influences: 1.​ Circadian Rhythm Regulation – Signals darkness, adjusting sleep-wake cycles. 2.​ Temperature Reduction – Prepares the body for sleep. 3.​ Antioxidant Effects – Protects cells from oxidative stress. 4.​ Immune Modulation – Enhances immune function. Effects of Melatonin on the Body ​ Sleep Regulation – Induces sleep and synchronizes the biological clock. ​ Body Temperature – Lowers core body temperature for sleep initiation. ​ Hormonal Regulation – Influences reproductive hormones and stress response. ​ Metabolism – Affects insulin sensitivity and energy regulation. ​ Immune Function – Enhances immune responses and reduces inflammation. AHL C2.1.11 – Tyrosine Kinase Receptors & Insulin Signaling Definition of Phosphorylation and Kinase ​ Phosphorylation: The addition of a phosphate group (PO₄³⁻) to a molecule, often a protein, altering its function. ​ Kinase: An enzyme that catalyzes phosphorylation, transferring phosphate groups from ATP to target proteins. Action of Receptors with Tyrosine Kinase Activity ​ Tyrosine kinase receptors (RTKs) are membrane receptors that mediate signaling by phosphorylating target proteins. ​ Example: Insulin Receptor (IR) 1.​ Insulin binds to the extracellular domain of its receptor (RTK). 2.​ The receptor undergoes autophosphorylation at tyrosine residues inside the cell. 3.​ This activates intracellular signaling pathways, including PI3K-AKT pathway. 4.​ Leads to movement of vesicles containing GLUT4 (glucose transporters) to the plasma membrane. 5.​ GLUT4 transports glucose into cells, lowering blood sugar levels. Insulin Secretion & Regulation ​ Secreted by beta cells of the pancreas in response to high blood glucose levels. ​ Helps maintain homeostasis by promoting glucose uptake, glycogen synthesis, and lipid storage.​ ​ ​ ​ Chapter 9 :​ Summary of Chapter 9 (Membranes & Transport Mechanisms) 1. Surface Area-to-Volume Ratio & Cell Size (B2.3.6 & B2.3.7) ​ As a cell grows, its surface area-to-volume ratio (SA/V) decreases. ​ A high SA/V is essential for efficient exchange of materials. ​ Large cells struggle to intake nutrients and remove waste, limiting their size. ​ Adaptations to increase SA/V for better exchange include: ○​ Flattening (e.g., red blood cells, Type I pneumocytes). ○​ Microvilli (e.g., kidney tubule cells). ○​ Invagination (e.g., folds in kidney tubules for ion transport). 2. Lipid Bilayers as Barriers (B2.1.2) ​ The hydrophobic core of membranes prevents the passage of large and hydrophilic molecules. ​ Membranes maintain concentration gradients by controlling permeability. ​ Low permeability molecules: ○​ Large molecules (proteins, starch, cellulose). ○​ Polar molecules (glucose, amino acids). ○​ Ions (Na⁺, Cl⁻, K⁺, PO₄³⁻). 3. Simple Diffusion (B2.1.3) ​ Passive movement of molecules from high to low concentration. ​ Non-polar molecules (O₂, CO₂) pass freely through the phospholipid bilayer. ​ Rate of diffusion depends on the concentration gradient. 4. Sodium-Glucose Cotransporters & Indirect Active Transport (B2.1.16) ​ Na⁺ and glucose enter cells together using a cotransporter. ​ Na⁺ moves down its concentration gradient, releasing energy. ​ This energy actively transports glucose into the cell (e.g., in intestines and kidneys). 5. Osmosis & Aquaporins (B2.1.5) ​ Water moves from low solute concentration to high solute concentration across membranes. ​ Aquaporins are protein channels that increase water permeability. ​ Osmosis is passive and does not require energy. 6. Facilitated Diffusion (B2.1.6)  ​ Channel proteins allow specific ions/molecules to diffuse across membranes. ​ Channels open or close to regulate permeability. ​ Diffusion is still passive and moves down the concentration gradient. 7. Active Transport & Pump Proteins (B2.1.7) ​ Uses ATP to move molecules against their concentration gradient. ​ Pump proteins work in one direction due to changes in shape. 8. Selectivity in Membrane Permeability (B2.1.8) ​ Simple diffusion allows non-selective movement based on size and polarity. ​ Facilitated diffusion & active transport allow selective permeability by controlling which substances enter or exit. Key Takeaways ​ Cell size is limited by SA/V ratio due to the need for efficient material exchange. ​ Lipid bilayers act as selective barriers, restricting large and hydrophilic molecules. ​ Diffusion, osmosis, and active transport regulate molecular movement across membranes. ​ Proteins (e.g., channels, pumps, cotransporters) provide selective transport mechanisms. ​ ​ ​ Chapter 10 Here’s a more detailed summary that aligns with the test objectives and guiding questions: Water and Solvation (D2.3.1) ​ Solvation is the process where a solvent dissolves a solute. ​ Water is a highly effective solvent because: ○​ It can form hydrogen bonds with polar solutes.  ○​ The partial positive (δ⁺) and partial negative (δ⁻) charges of water molecules interact with both positively and negatively charged ions. ○​ This allows water to dissolve a wide variety of polar molecules (e.g., sugars) and ionic compounds (e.g., salts). Water Movement and Osmosis (D2.3.2 - D2.3.3) Definitions of Key Terms ​ Hypertonic solution → Higher solute concentration compared to another solution. ​ Hypotonic solution → Lower solute concentration compared to another solution. ​ Isotonic solution → Equal solute concentration between two solutions. ​ Osmosis → The movement of water molecules from a hypotonic solution (lower solute concentration) to a hypertonic solution (higher solute concentration) across a selectively permeable membrane. Principles of Water Movement ​ Water is attracted to solutes, so it moves up the solute concentration gradient from an area of lower solute concentration (hypotonic) to higher solute concentration (hypertonic). ​ In isotonic conditions, water molecules move equally in both directions, achieving dynamic equilibrium with no net water movement. Effects of Water Movement in Cells Effects on Plant Tissue (D2.3.4 & D2.3.6) Plant cells regulate water movement differently than animal cells because they have both a plasma membrane and a rigid cell wall.  Environment Water Effect on Plant Cells Movement Hypotonic Water Turgid cell – Water fills the vacuole, causing the Solution enters cytoplasm to push against the cell wall, creating turgor pressure. This provides structural support to the plant. Isotonic No net Flaccid cell – Water moves in and out at equal rates, Solution movement leading to reduced turgor pressure. The plant may wilt slightly. Hypertonic Water exits Plasmolysis – Water leaves the cytoplasm, reducing Solution pressure and causing the plasma membrane to pull away from the cell wall. This can lead to permanent damage if prolonged. Effects on Animal Cells & Unicellular Organisms (D2.3.5) Animal cells lack a cell wall, making them more vulnerable to osmotic imbalances. Environment Water Effect on Animal Cells Movement Hypotonic Water enters Lysis – The cell swells and may burst due to osmotic Solution pressure. Example: Red blood cells undergo hemolysis. Isotonic No net Stable – Cells maintain their normal shape and Solution movement function. Hypertonic Water exits Crenation – The cell shrinks and becomes distorted. Solution Example: Red blood cells become shriveled. Osmoregulation in Unicellular Organisms  ​ Freshwater unicellular organisms (e.g., Paramecium) live in a hypotonic environment where water constantly enters their cells. ​ To prevent bursting, they actively expel water using contractile vacuoles. Osmoregulation in Multicellular Animals ​ Tissue fluids (extracellular fluids) must be isotonic to prevent cell damage. ​ The kidneys regulate solute concentration in blood plasma, preventing swelling or shrinkage of cells. Medical Applications of Isotonic Solutions (D2.3.7) ​ Intravenous (IV) fluids must be isotonic to prevent red blood cells from swelling or shrinking. ​ Tissues and organs used in transplants are stored in isotonic solutions to prevent osmotic stress and cellular damage. Water Potential and Movement (D2.3.8 - D2.3.11, HL Topics) Understanding Water Potential (Ψ) ​ Water potential (Ψ) is the measure of potential energy per unit volume of water. ​ Measured in kilopascals (kPa) or megapascals (MPa). ​ Pure water at standard atmospheric pressure and 20°C has a water potential of 0 kPa. ​ Water moves from areas of higher water potential to areas of lower water potential. Components of Water Potential Water potential is determined by two factors: 1.​ Solute Potential (Ψs)  ○​ The more solutes dissolved, the lower (more negative) the solute potential. ○​ Bonding between solute molecules and water reduces water's potential energy. ○​ Pure water (no solutes) has a solute potential of 0. 2.​ Pressure Potential (Ψp) ○​ Increases or decreases water potential depending on the hydrostatic pressure. ○​ Plant cells typically have a positive pressure potential due to turgor pressure. ○​ Xylem vessels transport water under tension, leading to negative pressure potential. Equation for Water Potential: Ψ=Ψs+ΨpΨ = Ψs + ΨpΨ=Ψs+Ψp Water Potential in Plant Tissues Condition Water Expected Water Effect on Plant Tissue Potential (Ψ) Movement Plant Tissue in Ψ = 0 (pure Water enters the Cells become fully turgid due Pure Water water) cell to increased pressure potential. Plant Tissue in Ψ of tissue < Water moves Cells gain water, possibly Hypotonic Ψ of solution into the tissue reaching full turgidity. Solution Plant Tissue in Ψ of solution < Water moves out Cells lose water, becoming Hypertonic Ψ of tissue of the tissue flaccid. If severe, Solution plasmolysis occurs. Water Movement Between Adjacent Cells ​ Water moves from cells with higher water potential to cells with lower water potential until equilibrium is reached.  ​ Example: In phloem loading, sucrose is pumped into phloem cells, lowering their water potential, which draws in water from surrounding cells via osmosis. Key Implications for Biology Factors Influencing Water Movement 1.​ Solute concentration (osmotic potential) 2.​ Hydrostatic pressure (pressure potential) 3.​ Presence or absence of a cell wall 4.​ Regulatory mechanisms (e.g., kidneys, contractile vacuoles) Implications of Solubility Differences ​ Water-soluble molecules (e.g., glucose, salts) dissolve easily and move freely within cells and tissues. ​ Lipid-soluble molecules (e.g., steroids, nonpolar gases) do not dissolve in water and require carriers or diffusion through membranes. ​ The ability of water to dissolve solutes affects nutrient transport, waste removal, and biochemical reactions. Chapter 11 Summary of B1.1 – Biological Molecules B1.1.1 – Carbon’s Chemical Properties & Molecular Diversity Carbon atoms form up to four covalent bonds, enabling the creation of diverse organic compounds. These include single, double, and branched or unbranched chains, as well as single or multiple rings. This versatility allows carbon to bond with elements such as hydrogen, oxygen, nitrogen, and phosphorus, forming essential biomolecules. B1.1.2 – Macromolecule Formation by Condensation Reactions Living organisms synthesize macromolecules by linking monomers via condensation reactions, which release water molecules. Examples include: ​ Polysaccharides (e.g., starch, glycogen) from monosaccharides ​ Polypeptides (proteins) from amino acids ​ Nucleic acids (DNA, RNA) from nucleotides B1.1.3 – Hydrolysis Reactions & Digestion of Polymers Hydrolysis breaks down polymers into monomers using water molecules, splitting them into -H and -OH groups. This process is essential for digestion, converting: ​ Polysaccharides → Monosaccharides ​ Polypeptides → Amino acids ​ Triglycerides → Fatty acids + Glycerol B1.1.4 – Monosaccharide Structure & Function Monosaccharides (e.g., glucose) exist mainly in ring forms (pentoses and hexoses). Glucose, due to its solubility, functions as a primary transport sugar in blood plasma. It is also chemically stable and releases energy via oxidation during cellular respiration. B1.1.5 – Polysaccharides as Energy Storage Compounds ​ Plants store energy as starch, with amylose (unbranched) and amylopectin (branched) structures. ​ Animals and fungi store glycogen, a highly branched polysaccharide. ​ These molecules are compact, insoluble, and can be easily broken down into glucose for energy. B1.1.6 – Cellulose as a Structural Polysaccharide Cellulose consists of beta-glucose molecules linked by 1-4 glycosidic bonds in an alternating up-down orientation. This arrangement forms straight, hydrogen-bonded microfibrils, giving cellulose high tensile strength, making it ideal for plant cell walls. B1.1.7 – Glycoproteins & Cell-Cell Recognition Glycoproteins in plasma membranes have oligosaccharide chains that enable cell recognition and adhesion. An example is ABO blood group antigens in human red blood cells. B1.1.8 – Hydrophobic Nature of Lipids Lipids are non-polar molecules, insoluble in water but soluble in non-polar solvents. They include fats, oils, waxes, and steroids, playing key roles in energy storage, membrane structure, and signaling. B1.1.9 – Formation of Triglycerides & Phospholipids ​ Triglycerides: Formed via condensation between glycerol and three fatty acids. ​ Phospholipids: Contain two fatty acids and a phosphate group attached to glycerol, with hydrophilic heads and hydrophobic tails, essential for membrane formation. B1.1.10 – Saturated vs. Unsaturated Fatty Acids ​ Saturated fats (single C-C bonds) are solid at room temperature. ​ Unsaturated fats (one or more C=C bonds) are liquid due to kinks in their structure. ​ Omega-3 and Omega-6 fatty acids are polyunsaturated and important for health. B1.1.11 – Triglycerides in Energy Storage & Thermal Insulation Triglycerides store twice as much energy per gram as carbohydrates. Adipose tissue provides long-term energy reserves and serves as an insulator, reducing heat loss in warm-blooded animals. B1.1.12 – Phospholipid Bilayers in Membranes Phospholipids are amphipathic—hydrophilic heads face water, and hydrophobic tails face inward. This arrangement forms stable bilayers, the fundamental structure of cell membranes. B1.1.13 – Steroids & Membrane Permeability Steroids (e.g., oestradiol and testosterone) are non-polar and can diffuse through phospholipid bilayers, functioning as hormones in cell signaling.​ ​ Chapter 12 Summary of Carbohydrates and Lipids: Form and Function B1.1.1 - Carbon’s Unique Bonding Properties Carbon atoms form up to four covalent bonds, allowing for the creation of a vast range of organic molecules. These include single and double bonds, chains, branches, and rings. This diversity makes carbon the foundation of life. B1.1.2 - Macromolecule Formation (Condensation Reactions) Monomers (e.g., monosaccharides, amino acids, nucleotides) are linked by condensation reactions to form polymers like polysaccharides, polypeptides, and nucleic acids. Water is released during bond formation. B1.1.3 - Polymer Digestion (Hydrolysis Reactions) Hydrolysis is the reverse of condensation, breaking down polymers into monomers using water. Examples include digestion of starch into glucose, proteins into amino acids, and lipids into glycerol and fatty acids. B1.1.4 - Monosaccharides: Structure and Function Pentoses (C₅H₁₀O₅) and hexoses (C₆H₁₂O₆) exist in ring forms. Glucose, a highly soluble and transportable monosaccharide, serves as an efficient energy source due to its chemical stability and oxidative energy yield. B1.1.5 - Polysaccharides for Energy Storage Starch (plants) and glycogen (animals) are compact due to coiling and branching, making them ideal energy stores. They are relatively insoluble, preventing excessive osmosis, and glucose monomers can be added or removed efficiently. B1.1.6 - Structure and Function of Cellulose Cellulose consists of β-glucose monomers in alternating orientations, forming straight chains. These chains group into microfibrils, reinforced by hydrogen bonds, providing tensile strength for plant cell walls. B1.1.7 - Glycoproteins in Cell Recognition Glycoproteins, with attached oligosaccharides, enable cell-cell recognition and binding. The ABO blood group system is based on glycoproteins in red blood cells. B1.1.8 - Hydrophobic Nature of Lipids Lipids are insoluble in water due to a lack of charged groups, but they dissolve in non-polar solvents. They include fats, oils, waxes, and steroids. B1.1.9 - Formation of Triglycerides and Phospholipids Triglycerides are formed when glycerol bonds with three fatty acids via condensation reactions. Phospholipids consist of two fatty acids, glycerol, and a phosphate group, creating amphipathic molecules. B1.1.10 - Saturated vs. Unsaturated Fatty Acids Saturated fatty acids have no double bonds, making them solid at room temperature. Unsaturated fatty acids (monounsaturated or polyunsaturated) have double bonds, causing kinks in their structure and lowering melting points. B1.1.11 - Triglycerides for Energy Storage and Insulation Triglycerides are excellent long-term energy stores, providing twice the energy per gram as carbohydrates. Stored in adipose tissue, they also function as thermal insulators in warm-blooded animals. B1.1.12 - Phospholipid Bilayers in Membranes Phospholipids are amphipathic, with hydrophilic heads and hydrophobic tails. In water, they self-assemble into bilayers, forming the foundation of cell membranes. B1.1.13 - Steroids and Membrane Permeability Steroids, such as testosterone and oestradiol, have hydrophobic four-ring structures, allowing them to pass through phospholipid bilayers and regulate biological processes. Comparison of Carbohydrates and Lipids as Energy Storage Compounds  ​ Carbohydrates: Rapid energy release, short-term storage, soluble for easy transport. ​ Lipids: Higher energy yield, long-term storage, insoluble, and useful for insulation. ​ ​