Untitled Flashcard Set

Fluid mosaic model describes cell membrane as a 2-dimensional liquid, like a mosaic, where various proteins, cholesterol, and glycolipids are embedded in or attached to a fluid phospholipid bilayer plasma membrane A selectively-permeable phospholipid bilayer forming the boundary of the cells selective permeability property of membrane that controls what enters and exits cell (important for homeostasis, cell communication, structural support, cell recognition, adhesion, separating interior of cell from outside) Why is the membrane "fluid"? membrane flexible; phospholipids and some proteins can move sideways within the membrane, lets cell change shape or allow materials to pass What makes the membrane a "mosaic"? Many proteins (integral + peripheral) embedded throughout. function and types of membrane proteins determine most of the membrane functions; they isially are anchored and move slowly types: transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, atttchment to cytoskeletoin and ECM) transport membrane protein channels or pumps that move molecules across the membrane; some use ATP (active transport) enzymatic activity membrane protein A protein built into the membrane may be an enzyme, carry out sequential steps of metaboilic pathways signal transduction membrane protein protein receptor binds to signal molecule (ex: hormone); changes shape and relays message into cell cell-cell recognition membrane protein glycoproteins that act as identification tags; important in immune system and embryo development intercellular joining membrane protein membrane proteins of adjacent cells may hook together in various kinds of junctions, such as gap junctions or tight junctions attatchment to cytoskeleton and ECM membrane protein helps cell maintain shape, stabilizes protein position, integrins attach to ECM to pass signals inward what molecules can penetrate semipermeable membrane easily non-polar molecules (O2, CO2), small uncharged polar molecules (water), hydrophobic molecules (lipids), small uncharged molecules (glycerol) what molecules struggle to penetrate semipermeable membrane ions, polar molecules, charged or larger molecules ex: glucode, sodium, potassium, chloride passive transport the movement of substances across a cell membrane without the use of energy by the cell - diffusion, osmosis-hypertonic, hypotonic, isotonic, facilitated transport diffusion Movement of molecules from an area of higher concentration to an area of lower concentration. osmosis diffusion of water from high to low concentration Isotonic equal concentration of water and concentration of dissolved substances; no net water movement hypertonic more solute concentration; water moves across a membrane toward hypertonic solution hypotonic lower solute concentration; water moves across a membrane, away from hypotonic solution facilitated transport Diffusion using channels/carrier proteins. channel proteins provided by transport proteins; have a hydrophilic channel that certain molecules or ions can use as a tunnel carrier proteins provided by transport proteins; bind to molecules and change shape to shuttle them across the membrane facilitated transport/diffusion diffusion with the aid of transport proteins (channel/carrier) energy requiring transport requires ATP because molecules move against their concentration gradients or are too large to cross by diffusion - active transport- Na/K pump, bulk transport- phagocytosis, pinocytosis, exocytosis active transport membrane proteins use ATP to move molecules from low to high concentration What does the sodium-potassium pump move and how does ATP help? 3 Na⁺ out, 2 K⁺ in; ATP provides energy for shape change of the pump. bulk transport moves large particles via vesicles in ER - exocytosis and endocytosis exocytosis moves materials out of cell using vesicles - vesicles from ER > golgi > plasma membrane, fuse w/membrane to release contents ex: neurotransmitters, hormones, cell wall components Phagocytosis "cell eating"; engulfs large particles into a food vaccule which is fused w/lysosomes for digestion > brings in large particles pinocytosis "cell drinking"; engulfs extracellular fluids and dissolves solutes > brings in fluids what increases membrane fluidity unsaturated fatty acid tails; they introduce kinks which prevents the fatty acid chains from packing tightly together - this space lets membrane remain flexible how does temperature affect membrane fluidity Higher temperatures increase fluidity, while lower temperatures decrease it. what acts as a buffer for membrane fluidity cholesterol a cell placed in hypertonic solution will shrivel/shrink a cell placed in a hypotonic solution will expand/swell saturated fatty acid tails affect on fluidity decrease it because tails are straight so: tighter packing = less movement = more rigid membrane. why can small nonpolar molecules cross the membrane easily, while ions cannot? nonpolar molecules dissolve in the hydrophobic lipid tails, but ions are repelled by the nonpolar core. what factors affect membrane fluidity most Saturated vs. unsaturated fatty acid tails & cholesterol content Facilitated diffusion vs. active transport Facilitated diffusion moves substances DOWN their gradient using proteins; active transport moves them AGAINST the gradient using ATP. Which transport method does a neuron use to release neurotransmitters into the synapse? exocytosis why is the ECM important It stabilizes tissue structure and helps maintain cell shape. Why can't glucose cross the lipid bilayer directly, and how does it enter the cell? Too large and polar; facilitated diffusion via carrier proteins ATP hydrolysis breaking down ATP to ADP by adding water - releases energy metabolism sum of total chemical reactions in the body; manages cells materials and energy resources chemical reaction process that forms or breaks the chemical bonds holding atoms together, convert reactants to products exergonic reactions chemical reaction that releases energy sponaneous;y - G < 0: negative; reaction will proceed without input of additional energy - products have lower free energy then reactants △G change in free energy; is a measure of the energy available to do useful work in a system, and it determines whether a reaction will be spontaneous. endergonic reactions chemical reactions that require an input of energy; absorb energy, nonspontaneous - G > 0: positive, reaction will not occur unless energy is added - products have higher free energy then reactions catabolic reactions breakdown of complex molecules to release energy (exergonic) - ex: cellular respiration, glycogen breakdown anabolic reactions build larger molecules from smaller ones; require energy (endergonic) - ex: photosynthesis, fatty acid synthesis relationship between catabolism and anabolism Catabolism provides energy for anabolism ATP cells main high energy currency - adenine + ribose + 3 phosphate groups - made during cellular respiration ADP low energy; created when ATP releases energy (hydrolysis) - 2 phosphate groups enzymes biological catalysts that speed reactions by lowering activation energy - are highly specific and can be reused specificity of enzymes each enzyme binds a particular substrate at its active site substrates the specific reactants that an enzyme binds to substrate-enzyme process enzyme binds to specific substrate at its active site > forms temporary enzyme-substrate complex > binding lowers the activation energy, allowing the substrate to be transformed into a new product, which is then released, leaving the enzyme unchanged and ready to catalyze another reaction. activation energy the minimum amount of energy required to start a chemical reaction chemical work the making and breaking of chemical bonds ex: building macromolecules, synthesizing proteins) transport work the pumping of substances across membranes ex: Na/K pump mechanical work physical movement of the cell or its parts ex: muscle contraction induced fit model enzyme model where the substrate induces the enzyme to alter its shape slightly so it fits better (active site is flexible) cofactors non organic helper molecules, often metal ions, that stabilize enzyme structure or participate directly in catalysis ex: Mg coenzymes organic molecules, usually from vitamins, that act as electron carriers or functional group carriers ex: NAD+ and FADex inhibition process where an inhibitor substance binds to an enzyme and decreases its activity by slowing or stopping the reaction - important for toxicology, designing medicine, and regulating metabolism competitive inhibition inhibitor resembles substrate and competes to bind to active site, blocking real substrate from binding; adding substrate can overcome it noncompetitive (allosteric) inhibition inhibitor binds elsewhere on the enzyme; alters enzyme shape so that the substrate cannot bind; cant be overcome feedback inhibition type of enzyme regulation where final product of a metabolic pathway binds and inhibits an enzyme earlier in its pathway to prevent cell from wasting energy or making excess product Factors affecting enzyme speed substrate concentration, temperature, pH how does substrate concentration affect enzymatic speed enzyme activity increases with concentration because more substrate molecules collide with enzyme molecules - at max speed, adding substrate has no affect how does temperature affect enzymatic speed increased temp. increases kinetic energy, making the reaction faster because molecules collide frequently - too high of a temp = enzyme denatures, changing shape, which slows and stops reaction how does pH affect enzymatic speed alters enzyme shape and charge distribution, which can either slow down or completely stop reaction ATP synthesis during cellular respiration is powered by: Exergonic reactions, like glucose breakdown, release energy used to synthesize ATP. exergonic vs endergonic energy Exergonic = reactants have more energy → energy is released Endergonic = products have more energy → energy must be added Why do heavy metals inhibit enzymes via noncompetitive inhibition? heavy metals bind to other parts of enzyme, not active site, changing the shape. Adding more substrate doesn't help (noncompetitive inhibition) autrotroph organism that can make its own food - preform photosynthesis ex: plants, algae heterotroph consume organic molecules made by autotroph's - preform cellular respiration ec: animals, fungi, most bacteria Photosynthesis equation 6CO2 + 6H2O ------> C6H12O6 + 6O2 sunlight > CO2, H2O > photosynthsis converts those to organic molecules in chloroplast > releases Organic molecules and Oxygen Photosynthesis captures sunlight to produce O2 and organic molecules in chloroplasts in the form of sugar - generates glucose glucose A simple sugar that is an important source of energy (stores energy) cellular respiration equ. C6H12O6 + 6O2 > 6CO2 + 6H2O + ATP mitochondria > organic moleculesand oxygen generates ATP > heat energy released as waste products: CO2, H2O relationship between cell respiration & photosynthesis They are opposite processes: photosynthesis stores energy in glucose, while cellular respiration releases energy from glucose. how does cellular respiration work, what're the steps glucose is oxidized, 6O2 is reduced 1. glycolysis 2. pyruvate oxidation 3. citric acid cycle 4. oxidative phosphorylation redox reactions A reaction where one molecule is oxidized (loses electrons) and another is reduced (gains electrons). - oxidation, reduction, reducing agent, oxidizing agent redox reactions in cellular respiration electrons are transferred to gradually break down glucose and produce ATP. During these reactions, glucose is oxidized (loses electrons) and oxygen is reduced (gains electrons) - this is what allows electrons to move through ETC, releasing energy to make ATP oxidation loss of electrons - reducing agent: electron donor reduction gain of electrons - oxidizing agent: electron acceptor oxidation and reduction relationship always happen together: one mol. loses electrons while another gains them Which molecules carry electrons in redox reactions during respiration? NAD⁺ and FAD (become NADH and FADH₂ when reduced). In cellular respiration, what happens to glucose in terms of redox? Glucose is oxidized (loses electrons and hydrogen). In cellular respiration, what happens to oxygen in terms of redox? Oxygen is reduced to form water (gains electrons and hydrogen). Why do redox reactions release energy? Electrons move from high-energy molecules to lower-energy acceptors, releasing energy the cell can use. substrate-level phosphorylation Anaerobic process where ATP is made directly by transferring a phosphate group from a substrate to ADP using kinase Where does substrate-level phosphorylation occur? In glycolysis (cytoplasm) and the citric acid cycle (mitochondrial matrix). How is substrate-level phosphorylation different from oxidative phosphorylation? Substrate-level makes ATP directly using an enzyme; oxidative phosphorylation makes ATP indirectly using the ETC + ATP synthase. anaerobic respiration Respiration that does not require oxygen; uses a final electron acceptor instead aerobic respiration Process that requires oxygen; most efficient ATP-producing catabolic pathway kinase role in substrate-level phosphorylation the enzyme transfers a phosphate from a substrate to ADP to produce ATP what is the end product of substrate level phosphorylation 2 ATP in glycosis and 2 ATP in citric acid cycle catabolism in anaerobic resp. catabolic pathways extract energy by oxidizing fuels and using energy to make ATP; glucose is catabolized to make ATP goal of cellular respiration extract energy from glucose by oxidizing it and transfer electrons to NADH/FADH2 to make ATP Glycolysis: First step of Cell Resp. A metabolic pathway that begins break down of glucose into pyruvate, producing small amounts of ATP and NADH, and does not require oxygen. - substrate level phosphorylation occurs here end products of glycolysis 2 pyruvate 2 ATP net (4 made − 2 used) 2 NADH in glycolysis, how does glucose turn from a 6-carbon sugar into 2 pyruvate? Glucose is phosphorylated (6C) → split into 2 3-carbon G3P → each G3P becomes pyruvate (3C). result: 2 pyruvate, each with 2 carbons what are the 2 phases of glycolysis Energy investment phase and energy payoff phase. What happens in the energy investment phase of glycolysis? The cell uses 2 ATP to add phosphates to glucose and make it unstable to prepare it for splitting What happens in the energy payoff phase? 4 ATP and 2 NADH are produced and 2 pyruvate are formed How does glycolysis begin? A 6-carbon glucose molecule enters and is phosphorylated using ATP. What does "sugar splitting" mean in glycolysis? The 6-carbon molecule is split into two 3-carbon molecules (G3P). What does dehydrogenase do? An enzyme that removes electrons + H from molecules and transfers them to NAD⁺ (or FAD). How does NAD⁺ become NADH? Dehydrogenase adds 2 electrons + 1 H⁺ to NAD⁺ → forming NADH, an electron carrier. Why is NADH important? It carries high-energy electrons to the electron transport chain to help make ATP. Pyruvate Oxidation: 2nd step of cell resp. Conversion of pyruvate (3C) into acetyl-CoA (2C) + CO₂, linking glycolysis to the citric acid cycle that occurs in the mitochondrial matrix What are the main products of pyruvate oxidation per pyruvate? -1 acetyl-CoA -1 CO₂ -1 NADH Which enzyme complex carries out pyruvate oxidation? Pyruvate dehydrogenase complex (PDC). Why is pyruvate oxidation important? It prepares carbon for the citric acid cycle and generates NADH for ATP production. How is NAD⁺ involved in pyruvate oxidation? NAD⁺ accepts electrons and a proton from the oxidized pyruvate, forming NADH, a high-energy electron carrier. citric acid cycle: 3rd step of cellular respiration A series of chemical reactions in the mitochondrial matrix that oxidizes acetyl-CoA to CO₂ and produces ATP, NADH, and FADH₂. Where does the citric acid cycle occur? In the mitochondrial matrix of eukaryotic cells. What enters the citric acid cycle? Acetyl-CoA (2C) from pyruvate oxidation combines with oxaloacetate (4C) to form citrate (6C). Which molecules carry electrons during the citric acid cycle? NAD⁺ → NADH and FAD → FADH₂ are reduced, carrying high-energy electrons to the electron transport chain. Why is the citric acid cycle important? It completes the oxidation of glucose, generates electron carriers for ATP production, and produces CO₂ as a waste product. How does the citric cycle regenerate itself? Oxaloacetate (4C) is regenerated at the end of each cycle to combine with the next acetyl-CoA, allowing the cycle to continue. What is oxidative phosphorylation? The process in the mitochondria where ATP is produced using energy from electrons transferred through the electron transport chain. Where does oxidative phosphorylation occur? In the inner mitochondrial membrane. What is the electron transport chain (ETC)? A series of protein complexes that pass electrons from NADH and FADH₂ down the chain, releasing energy to pump H⁺ ions into the intermembrane space. How are electrons supplied to the ETC? From NADH and FADH₂, which were produced in glycolysis, pyruvate oxidation, and the citric acid cycle. What is chemiosmosis? The flow of H⁺ ions back into the mitochondrial matrix through ATP synthase, driving ATP production. How is ATP generated in oxidative phosphorylation? H⁺ ions flow through ATP synthase, which uses this proton-motive force to phosphorylate ADP → ATP. What is the final electron acceptor in the ETC? Oxygen (O₂), which combines with electrons and H⁺ to form water (H₂O), allowing electron flow and ATP production to continue. Why is oxidative phosphorylation important? It produces the most ATP per glucose (~28 ATP) and completes cellular respiration by using high-energy electrons efficiently. What happens to pyruvate during pyruvate oxidation and its products per pyruvate? What are the products of the citric acid cycle per acetyl-CoA? 3 NADH, 1 FADH₂, 1 ATP (or GTP), 2 CO₂ What is oxidative phosphorylation and what does it produce? Uses ETC + chemiosmosis to make ~28 ATP per glucose from NADH (~2.5 ATP) and FADH₂ (~1.5 ATP). What is the approximate total ATP yield per glucose from cellular respiration? ~30-32 ATP per glucose (Glycolysis: 2 ATP + 2 NADH (~5 ATP), Pyruvate oxidation: 2 NADH (~5 ATP), Citric acid cycle: 2 ATP + 6 NADH (~15 ATP) + 2 FADH₂ (~3 ATP)). what are the products of oxidative phosphorylation ATP: ~28 ATP (from NADH and FADH₂ via ETC + chemiosmosis) - Water - regenerated NAD+ and FAD (ready to accept more electrons) Approximate total ATP yield per glucose from cellular respiration? Glycolysis: 2 ATP + 2 NADH (~5 ATP) Pyruvate oxidation: 2 NADH (~5 ATP) Citric acid cycle: 2 ATP + 6 NADH (~15 ATP) + 2 FADH₂ (~3 ATP) Total: ~30-32 ATP per glucose What is NADH? A high-energy electron carrier that carries electrons from glycolysis, pyruvate oxidation, and the citric acid cycle to the electron transport chain. - reduced, electron carrying form of NAD+ What is FADH₂? Another electron carrier from the citric acid cycle that donates electrons to the ETC to help make ATP. - reduced, high energy form of FAD - comes later in the chain so it generates less ATP than NADH What is lactic acid fermentation? Anaerobic process where pyruvate is reduced to lactate by NADH → NAD⁺, allowing glycolysis to continue and produce ATP without oxygen. What is ethanol (alcohol) fermentation? Anaerobic process in yeast and some bacteria where pyruvate → acetaldehyde → ethanol, regenerating NAD⁺ for glycolysis. What is the key difference between lactic acid and ethanol fermentation? Lactic acid: pyruvate → lactate, no CO₂; Ethanol: pyruvate → ethanol + CO₂. What is gluconeogenesis? The process of making glucose from non-carbohydrate sources (like lactate, glycerol, amino acids), mainly in the liver. Why is gluconeogenesis important? Maintains blood glucose levels during fasting or intense exercise when glycogen is depleted. NAD+ oxidized, electron-carrying form co-enyme that acts as an electron carrier during metabolic reactions - necessary for glycolysis to continue FAD coenzyme and electron carrier thats slightly lower in energy compared to NAD+ - accepts 2 electrons and 2 protons during citric acid cycle - becomes FADH2 fermentation Anaerobic process that regenerates NAD⁺ from NADH so glycolysis can continue producing ATP. Alcoholic (ethonal) Fermentation Pyruvate → acetaldehyde → ethanol, regenerating NAD⁺.Products: Ethanol + CO₂ + NAD⁺Example: Yeast and some bacteria. Key difference between lactic acid and ethanol fermentation? Lactic acid: pyruvate → lactate, no CO₂ Ethanol: pyruvate → ethanol + CO₂ Lactic acid fermentation produces Lactate + NAD⁺ Ethanol fermentation produces Ethanol + CO₂ + NAD⁺ Chloroplasts site of photosynthesis; mostly in meophyll cells stomata Small openings on the underside of a leaf through which oxygen exits and carbon dioxide enters light reactions in thylakoid membranes; first stage of photosynthesis, where light energy is captured by chlorophyll a and converted into chemical energy stored in the molecules ATP and NADPH What are the main reactants and products of the light reactions? Reactants: H₂O, light, NADP⁺, ADP + Pi Products: O₂, ATP, NADPH What happens in electron flow during light reactions? Light excites electrons in PSII, which are passed through the electron transport chain (ETC) → ATP is made via chemiosmosis Electrons move to PSI, get re-excited by light, and reduce NADP⁺ → NADPH Water is split to replace lost electrons, releasing O₂ What are the main steps of the Calvin cycle? Carbon Fixation: CO₂ attaches to ribulose-1,5-bisphosphate (RuBP) via rubisco, forming 3-phosphoglycerate (3-PGA) Reduction: 3-PGA is converted to G3P using ATP and NADPH Regeneration of RuBP: Some G3P regenerates RuBP using ATP to allow the cycle to continue What are the main reactants and products of the Calvin cycle? Reactants: CO₂, ATP, NADPH Products: G3P (can be used to make glucose or other carbohydrates), ADP + Pi, NADP⁺ what is the job of the calvin cycle capture CO2, turn it into G3P, a 3 carbon sugar, used to build glucose What is rubisco? Enzyme that fixes CO₂ to RuBP in the Calvin cycle Can also bind O₂, which leads to photorespiration how do light reactions and the calvin cycle cooperate light reactions produce ATP, NADPH, and release O2. the calvin cycle uses ATP and NADPH to build sugars RuBP ribulose biphosphate; a five-carbon carbohydrate that combines with CO2 to form two molecules of PGA in the first step of the Calvin Cylce What is photorespiration? Process where rubisco fixes O₂ instead of CO₂ Produces no ATP or sugar, wastes carbon and energy More common in C3 plants under hot, dry conditions How do C3, C4, and CAM plants differ? C3 plants fix CO₂ directly with rubisco in the Calvin cycle; C4 plants use PEP carboxylase to fix CO₂ into 4-carbon compounds, reducing photorespiration; CAM plants fix CO₂ at night into 4-carbon compounds, conserving water. What is the main CO₂ fixation method in C3 plants? Rubisco fixes CO₂ directly in the Calvin cycle, producing a 3-carbon compound (3-PGA). What happens if a C3 plant is in a hot, dry environment? Stomata close to prevent water loss, leading to less CO₂ entering, slowed photosynthesis, O₂ buildup, and increased photorespiration. What is the main adaptation of C4 plants to reduce photorespiration? CO₂ is first fixed by PEP carboxylase into a 4-carbon compound in mesophyll cells, then transported to bundle-sheath cells for the Calvin cycle. Why does separating steps between mesophyll and bundle-sheath cells help C4 plants? It keeps CO₂ concentration high around rubisco, reducing oxygen binding and lessening photorespiration. How do CAM plants fix CO₂ differently? CO₂ is fixed at night into 4-carbon compounds, stored in vacuoles, and released during the day for the Calvin cycle. Why do CAM plants open stomata at night instead of during the day? To conserve water in hot/dry environments while allowing CO₂ to enter for photosynthesis. What happens first when a C3 plant is put in the desert? Stomata close to prevent water loss, CO₂ decreases, photosynthesis slows, O₂ accumulates, and photorespiration increases. What happens when a C4 or CAM plant is put in the desert? C4 plants concentrate CO₂ in bundle-sheath cells, continuing photosynthesis with less photorespiration; CAM plants take in CO₂ at night, store it, and use it during the day, conserving water. What is the linear (noncyclic electron flow) pathway? PS II > ETC II > ATP > PS I > ETC I > NADPH. What is chlorophyll a? Main photosynthetic pigment in plants, algae, and cyanobacteria. What light does chlorophyll a absorb? Mostly blue-violet and red light. What role does chlorophyll a play in photosynthesis? Directly participates in the light reactions by transferring excited electrons to the ETC. What is chlorophyll b? Accessory pigment that absorbs blue and orange light. What does chlorophyll b do? Transfers energy to chlorophyll a and helps broaden the spectrum of light a plant can use. What are carotenoids? Accessory pigments that absorb blue and green light. What colors do carotenoids reflect? Yellow, orange, or red. How do carotenoids protect chlorophyll? By quenching excess energy and protecting chlorophyll from photooxidative damage. What is an accessory pigment? Pigments like chlorophyll b or carotenoids that help capture light energy and pass it to chlorophyll a. What is the function of accessory pigments in photosynthesis? Expand the range of usable light for photosynthesis. cell signaling allows cells to detect and respond to environmental or internal cues - signals are communicated via ligands which bind to receptors on or inside target cells What are the 3 main steps of cell signaling? Reception, Transduction, Response What happens in reception? A ligand binds to a receptor on the cell surface or inside the cell. What happens in transduction? The signal is converted into a cellular response. What happens in the response step? The cell reacts with changes in gene expression, enzyme activation, cytoskeleton rearrangement, and secretion. What is direct contact signaling? Signals pass through gap junctions or surface molecules between neighboring cells. What is paracrine signaling? Local signals affect nearby cells. What is synaptic signaling? Neurons release neurotransmitters into a synapse to communicate with a target cell. What is endocrine signaling? Hormones travel through the bloodstream to affect distant cells. What is a hydrophilic ligand? Polar, cannot cross the membrane, binds cell-surface receptors. What is a hydrophobic ligand? Nonpolar, can cross the membrane, binds intracellular receptors. What is the difference between hydrophilic and hydrophobic ligands? Hydrophilic: cell-surface receptor → cascade → response; Hydrophobic: intracellular receptor → often directly changes gene expression. What are intracellular receptors? Located in cytoplasm or nucleus, bind hydrophobic ligands like steroid hormones. What are cell-surface receptors? Located on the plasma membrane, bind hydrophilic ligands, trigger signal transduction pathways. What is a ligand-gated ion channel? Opens when a ligand binds, allowing ions to flow in/out, triggering a response. What is a receptor tyrosine kinase (RTK)? Ligand binds, receptors dimerize, autophosphorylation activates signaling proteins. What is a G-protein coupled receptor (GPCR)? Ligand binds, activates G-protein, triggers secondary messengers like cAMP. What does cAMP do? Activates protein kinase A (PKA), phosphorylates proteins, leading to a cellular response. What does Ca²⁺ do as a secondary messenger? Triggers muscle contraction, secretion, enzyme activation, and apoptosis. What is apoptosis? Programmed cell death that removes damaged/unnecessary cells without inflammation. What are the steps of apoptosis? Signal received, caspases activated, cell shrinks, forms apoptotic bodies, fragments engulfed by phagocytes. What receptor type does a neurotransmitter bind on the next cell? Ligand-gated ion channel. What type of receptor and secondary messenger is involved when adrenaline binds to a heart cell? GPCR activates G-protein, produces cAMP, increases heart rate. How does a steroid hormone trigger a response? Binds intracellular receptor, receptor-hormone complex acts as a transcription factor. What receptor and process is activated when a growth factor binds to a cell? Receptor tyrosine kinase (RTK) dimerizes and autophosphorylates, triggering cell division. How is Ca²⁺ released for muscle contraction? Released from ER, binds proteins like troponin, triggers contraction. What happens when a damaged cell activates apoptosis? Caspases are activated, cell shrinks, forms apoptotic bodies, fragments engulfed. What type of ligand and receptor is involved in a paracrine signal? Hydrophilic ligand binds cell-surface receptor. How does a plant hormone work after diffusing across the membrane? Binds intracellular receptor, regulates gene transcription. What are housekeeping genes? Genes that are always expressed in a cell to maintain basic cellular functions. Why are housekeeping genes important experimentally? They serve as controls in experiments measuring gene expression, since their transcription levels are stable across conditions. What is an operon? A cluster of genes under a single promoter, transcribed together as one mRNA. What are the main components of an operon? Promoter, operator, structural genes, and regulatory proteins. What is CRP (cAMP receptor protein)? An activator protein that enhances RNA polymerase binding when cAMP levels are high. Is the lac operon inducible or repressible? Inducible; normally off and turned on in the presence of lactose. How does lactose activate the lac operon? Lactose binds the repressor, causing it to release the operator, allowing transcription. Will the lac operon be active in a glucose-rich medium with lactose? No, glucose lowers cAMP, making CRP inactive and reducing transcription. What enzymes does the lac operon produce? β-galactosidase, permease, and transacetylase. Is the trp operon inducible or repressible? Repressible; normally on and turned off when tryptophan is abundant. How does tryptophan regulate the trp operon? Tryptophan binds the repressor, activating it to stop transcription. Is the trp operon active in a bacterial cell with low tryptophan? Yes, the repressor is inactive, allowing transcription to occur. How does histone acetylation affect transcription? It relaxes chromatin, leading to increased transcription. How does DNA methylation affect transcription? It condenses chromatin, leading to decreased transcription. What are transcription factors? Proteins that bind DNA or other proteins to regulate gene expression. What is alternative splicing? The process of splicing pre-mRNA in different ways to produce multiple protein isoforms. What is epigenetics? Heritable changes in gene expression without altering the DNA sequence. What mechanisms are likely used to rapidly express stress-response genes? Histone acetylation and transcription factors that recruit RNA polymerase. What mechanism is responsible for permanently silencing a gene in a differentiated cell? DNA methylation and/or histone deacetylation. What allows one gene to produce multiple proteins? Alternative splicing, which includes/excludes different exons. What happens to the lac operon if a bacterium is in lactose but no glucose? Lactose binds the repressor, making it inactive, allowing transcription. What happens to the trp operon if tryptophan is high? Tryptophan binds the repressor, blocking RNA polymerase and stopping enzyme production. How does a steroid hormone affect transcription? It binds an intracellular receptor, forming a complex that acts as a transcription factor. What epigenetic changes might occur to shut down unnecessary metabolic genes? DNA methylation and histone deacetylation to condense chromatin. consider this pathway: epinephrine > G protein-coupled receptor > G protein >adenylyl cyclase > cAMP Identify the second messenger cAMP (photosynthesis > cellular respiration diagram) what do "4" and "5" represent, respectively? - outputs of photosynthesis > cellular respiration oxygen and glucose/sugar What condition must occur for a repressible operon (e.g., trp operon) to be transcribed? Tryptophan is low, RNA polymerase binds to the promoter and repressor is inactive. What are DNA methylation and histone acetylation examples of? Epigenetic phenomena. What type of molecules are least likely to diffuse through the phospholipid bilayer of a cell membrane? Small ions. What is the process that produces ATP during cellular respiration and photosynthesis whereby energy is released as H+ ions flow down their concentration gradient through channel proteins? Chemiosmosis. What is the role of GTP in GPCR? Activates G protein