Cell Biology Study Materials — Transport, Enzymes, Metabolism, Tissues & Inquiry Flashcards

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Cell membrane

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The cell membrane (plasma membrane) is the outer boundary of a cell that separates the intracellular from the extracellular environment. It controls the movement of substances into and out of the cell, allows cell communication, and gives the cell its shape and structure.

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Fluid mosaic

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The fluid mosaic model describes the membrane as a flexible layer made of various molecules (lipids, proteins, cholesterol) that can move laterally, forming a mosaic. This structure allows dynamic movement of materials and membrane components.

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Phospholipids

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Phospholipids are lipids with a phosphate group that form a bilayer making up the main structure of the cell membrane. Their hydrophilic heads face the aqueous exterior and interior, while hydrophobic tails face inward, creating selective permeability.

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Selective permeability

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Selective permeability means the membrane allows only certain substances to pass while excluding others, based on size, charge, and solubility. This property enables cells to maintain homeostasis by regulating internal composition.

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Channel protein

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A channel protein is a large membrane protein that forms a pore allowing specific molecules (often ions or water-soluble compounds) to pass through the membrane without using ATP. Channels facilitate passive transport down a concentration gradient.

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Carrier protein

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Carrier proteins bind and transport specific large or polar molecules across the membrane and can use ATP to move substances against their concentration gradient. They are essential for active transport of ions and molecules like sodium and potassium.

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Diffusion

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Diffusion is the passive spreading of particles from regions of higher concentration to regions of lower concentration until evenly distributed. In cells it moves molecules like oxygen and carbon dioxide across membranes or through channel proteins.

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Osmosis

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Osmosis is the diffusion of water molecules through a selectively permeable membrane from an area of high water concentration to an area of low water concentration. It specifically involves water movement and affects cell volume and pressure.

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Active transport

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Active transport uses ATP to move substances across the membrane and can move molecules against their concentration gradient. Examples include pump-mediated transport of sodium and potassium using carrier proteins and vesicular processes like endocytosis and exocytosis.

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Endocytosis

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Endocytosis is a vesicular process where the cell membrane engulfs large particles or fluids from the extracellular environment to form internal vesicles. Specific forms include phagocytosis (cell eating) and pinocytosis (cell drinking).

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Surface area

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Surface area to volume ratio (SA:V) compares how much membrane area a cell has relative to its volume and influences transport efficiency. Cells with a large SA:V exchange materials more quickly; SA:V is calculated as SA/V.

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Solubility

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Solubility refers to whether a substance dissolves in lipids or water and affects membrane crossing; lipid-soluble molecules pass through the phospholipid bilayer more easily. Water-soluble substances typically require channel or carrier proteins and take longer to transport.

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Metabolism

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Metabolism is the sum of all chemical processes in the body that convert food into energy and building materials for life. It includes both catabolic reactions that release energy and anabolic reactions that use energy to build complex molecules.

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Catabolism

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Catabolism consists of destructive metabolic reactions that break complex molecules into simpler ones and release energy. Cellular respiration is a catabolic pathway that breaks down glucose to produce ATP.

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Anabolism

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Anabolism builds complex molecules from simpler ones and requires an input of energy. Examples include protein synthesis where amino acids are assembled into proteins for growth and repair.

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Cellular respiration

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Cellular respiration catabolises glucose to release energy as ATP and occurs aerobically in mitochondria (glycolysis, Krebs cycle, electron transport) or anaerobically in the cytoplasm (glycolysis and fermentation). Aerobic equation: $$C_6H_{12}O_6 + 6O_2 \to 6H_2O + 6CO_2 + 36-38\,ATP$$; anaerobic (lactic acid) yields up to 2 ATP.

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Glycolysis

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Glycolysis breaks one glucose into two pyruvate molecules and yields two ATP, occurring in the cytoplasm and not requiring oxygen. It is the first step of both aerobic and anaerobic respiration.

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Krebs cycle

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The Krebs cycle (citric acid cycle) further breaks down pyruvate-derived acetyl groups to $CO_2$, $H_2O$, and high-energy electron carriers like NADH, yielding 2 ATP per glucose. It takes place in the mitochondrial matrix and requires oxygen indirectly as part of aerobic respiration.

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ATP-ADP cycle

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The ATP-ADP cycle stores and releases cellular energy: energy from catabolism converts ADP + phosphate into energy-rich $ATP$, and when a phosphate is removed $ATP$ becomes $ADP$ releasing energy for work. This cycle powers processes like active transport, muscle contraction, and synthesis.

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Enzyme

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An enzyme is a protein catalyst that speeds up specific chemical reactions without being consumed in the process. Enzymes lower the activation energy required for reactions and are specific to substrates and working conditions like pH and temperature.

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Activation energy

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Activation energy is the energy required to initiate a chemical reaction. Enzymes function by lowering this energy barrier, allowing reactions to proceed faster under biological conditions.

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Lock and key

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The lock and key model describes enzyme specificity where the enzyme's active site fits a specific substrate like a key in a lock to form an enzyme-substrate complex. The enzyme then facilitates bond weakening and conversion to products and is released unchanged.

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Cofactors

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Cofactors are inorganic ions or molecules (e.g., Mn, Fe, Zn) required by some enzymes for activity, while coenzymes are organic molecules often derived from vitamins. These non-protein components assist in catalysis and substrate binding.

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Tissues

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Tissues are groups of similar cells working together to perform a specific function and form organs and systems. The main tissue categories are epithelial, connective, muscular, and nervous tissue.

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Nervous tissue

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Nervous tissue is composed of neurons (nerve cells) that transmit electrical impulses to control muscles, organs, and glands. It coordinates body functions and integrates information from internal and external environments.

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Hypothesis

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A hypothesis is a falsifiable, testable explanation formed from an observation that predicts a relationship between variables. Good hypotheses are specific, based on observable phenomena, and can be evaluated by experiments.

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Variables

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Variables in an experiment include the independent variable (manipulated), dependent variable (measured), and control variables (kept constant) to ensure validity. Clear identification and control of variables allow fair tests and reproducible results.