9/1/20111Membranes are a fluid mosaic of phospholipids and proteinsMembrane proteins have specific functions9/1/20112Membranes form spontaneously, a critical step in the origin of lifePassive transport is diffusion across a membrane with no energy investmentOsmosis is the diffusion of water across a membrane9/1/20113Water balance between cells and its surroundings is crucial to organismsTransport proteins may facilitate diffusion across membranesCells expend energy in the active transport of a solute against its concentration gradient9/1/20114Exocytosis and endocytosis transport large molecules across membranes Cells transform energy as they perform work9/1/20115Two laws govern energy transformations• First law of thermodynamics: Energy can be transferred and transformed, but it cannot be created or destroyed.• Second law of thermodynamics: Energy conversions increase the Entropy of the universe.• Entropy: A measure of disorderChemical reactions either release or store energyExergonic reactionEndergonic reactionATP shuttles chemical energy and drives cellular work9/1/20116ATP powers cellular workPhosphorylationEnzymes speed up the cell’s chemical reactions by lowering energy barriersA specific enzyme catalyzes each cellular reaction9/1/20117Enzyme inhibitors block enzyme action and can regulate enzyme activity in a
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