gen bio 2 test 2

Prokaryotic cells lack a membrane-bound nucleus and membrane-bound organelles, contain circular DNA in a nucleoid region, have 70S ribosomes, and divide by binary fission; eukaryotic cells have a true nucleus enclosed by a double membrane, linear chromosomes, membrane-bound organelles such as mitochondria and ER, 80S ribosomes, a complex cytoskeleton, and divide by mitosis or meiosis, allowing compartmentalization and increased regulatory control.

Plant cells contain a cellulose cell wall, chloroplasts for photosynthesis, a large central vacuole, and plasmodesmata for cell-to-cell communication, whereas animal cells lack a cell wall and chloroplasts, have smaller vacuoles, possess lysosomes for intracellular digestion, and rely on an extracellular matrix for structural support.

Microfilaments are thin (7 nm) actin polymers involved in cell shape and motility; microtubules are hollow 25 nm tubulin tubes that function in intracellular transport, mitotic spindle formation, and cilia/flagella movement; intermediate filaments (10 nm) are rope-like fibers composed of proteins such as keratin that provide tensile strength and mechanical stability without polarity.

Proteins with signal peptides are translated by ribosomes bound to the rough ER, co-translationally inserted into the ER lumen for folding and modification, packaged into transport vesicles, sent to the cis-Golgi for further modification (e.g., glycosylation), processed through medial and trans Golgi cisternae, sorted into vesicles, and transported by motor proteins along microtubules to destinations such as the plasma membrane, lysosome, or extracellular space.

The plasma membrane consists of a phospholipid bilayer with hydrophilic heads facing outward and hydrophobic tails inward; integral proteins span the bilayer, peripheral proteins attach to one surface, cholesterol is embedded among phospholipid tails to regulate fluidity, and carbohydrate chains attached to proteins (glycoproteins) or lipids (glycolipids) extend extracellularly for cell recognition.

Diffusion is the passive movement of solutes down their concentration gradient (e.g., O₂ entering cells); osmosis is the diffusion of water across a semipermeable membrane toward higher solute concentration (e.g., water balance in kidney cells); facilitated diffusion uses membrane proteins to move polar molecules down their gradient without ATP (e.g., glucose transport via GLUT carriers).

The hydrophobic core of the phospholipid bilayer repels charged and polar molecules because removing their hydration shells and placing them in a nonpolar environment is energetically unfavorable, creating a high activation energy barrier that transport proteins help overcome.

Small nonpolar molecules (O₂, CO₂) cross most rapidly due to compatibility with the hydrophobic core; small uncharged polar molecules (H₂O) cross more slowly; large polar molecules (glucose) cross very slowly; ions (Na⁺, Cl⁻) cross least efficiently due to charge and hydration shell constraints.

Membranes with unsaturated fatty acids and shorter tails are more fluid and permeable due to reduced tail packing; saturated, longer tails increase rigidity; cholesterol buffers fluidity by preventing tight packing at high temperatures and preventing excessive fluidity at low temperatures.

Passive transport moves substances down their concentration gradient without ATP, often via channels (aqueous pores) or carriers (conformational change proteins); active transport requires energy, typically ATP, and uses pumps (e.g., Na⁺/K⁺ ATPase) to move substances against their gradient, establishing electrochemical gradients.

ATP serves as the cell’s primary energy currency; coupled reactions link an exergonic reaction (like ATP hydrolysis) to an endergonic one so the overall ΔG is negative; phosphorylation adds two closely spaced negative charges, increasing electrostatic repulsion and raising free energy, making the molecule more reactive.

Two reactions can be coupled successfully if the sum of their ΔG values is negative, meaning the energy released by the exergonic reaction exceeds the energy required by the endergonic reaction.

Reactants are the starting energy level, activation energy is the energy difference between reactants and the peak (transition state), and products are the final energy level; energy peaks at the transition state because bonds are unstable and partially broken/formed; if products are lower in energy than reactants the reaction is exergonic, if higher it is endergonic.

The active site is the region where substrates bind and catalysis occurs; enzymes lower activation energy by orienting substrates, stabilizing the transition state, straining bonds, or providing a favorable microenvironment; specificity arises from precise 3D structure and chemical compatibility; enzymes speed reactions by lowering activation energy but do not alter overall ΔG.

Reaction rate typically increases with temperature until denaturation occurs and forms a bell-shaped curve with pH reflecting the enzyme’s optimal environment; the optimal pH and temperature indicate the natural cellular conditions in which the enzyme evolved to function.

Competitive inhibitors resemble substrates and bind the active site, increasing Km but not altering Vmax; non-competitive inhibitors bind elsewhere and decrease Vmax without changing Km; allosteric inhibitors bind regulatory sites, inducing conformational changes that alter enzyme activity and often regulate metabolic pathways.

Glycolysis converts glucose to pyruvate producing ATP and NADH; pyruvate oxidation forms acetyl-CoA and NADH; the citric acid cycle generates NADH, FADH₂, and CO₂; oxidative phosphorylation uses NADH and FADH₂ to create a proton gradient that drives ATP synthesis; energy is transferred from glucose to electron carriers to a proton gradient and finally to ATP.

Fermentation regenerates NAD⁺ from NADH by reducing pyruvate to lactate or ethanol, allowing glycolysis to continue producing a small amount of ATP without oxygen.

Inhibiting components of the ETC prevents proton gradient formation, halting ATP production and causing NADH accumulation; inhibiting ATP synthase prevents proton flow, increasing the gradient and slowing electron transport.

Altering a step leads to accumulation of upstream intermediates, reduced downstream products, decreased NADH/FADH₂ production, impaired ATP synthesis, and potentially increased fermentation and lactic acid buildup.

In photosynthesis, water is oxidized (loses electrons) to form O₂, and carbon in CO₂ is reduced (gains electrons) to form glucose; reduction stores energy in high-energy C–H bonds of glucose.

PSII splits water producing O₂ and a proton gradient; PSI generates NADPH; the Calvin cycle uses ATP and NADPH to fix CO₂ into glucose via rubisco; light energy is converted into chemical energy stored in ATP and NADPH and ultimately in glucose.

Carbon dioxide from the air enters the tree’s leaves, and the carbon atoms are used to build sugars that become wood, so the tree’s mass comes mostly from carbon taken out of the air.

Photosynthesis uses CO₂, H₂O, and light to produce glucose and O₂, storing energy in chemical bonds; cellular respiration uses glucose and O₂ to produce CO₂ and H₂O, releasing energy to make ATP.

Photosynthesis occurs only in cells with chloroplasts (e.g., plant leaf cells), while cellular respiration occurs in nearly all eukaryotic cells with mitochondria, including both plant and animal cells.