Chapter 2 - Medium

Cell Membranes, Enzyme Function, and Regulation

• Facilitated diffusion is a type of passive transport through protein channels without cellular energy expenditure
• The fluid mosaic model attributes a dynamic and selective barrier function to cell membranes
• Enzymes lower the activation energy of a reaction by providing an alternative pathway with lower energy
• Covalent modification in enzyme regulation involves attaching or removing a phosphate group from an enzyme
• The 'fluid' aspect of the fluid mosaic model suggests that membrane components can move laterally within the layer
• Coenzymes like NADH primarily function as carriers of electrons or specific chemical groups in enzymatic reactions
• Enzymes regulate their activity through covalent modification, such as phosphorylation or dephosphorylation
• The fluidity of the membrane allows for flexibility and dynamic rearrangement of membrane components
• Membrane proteins, including ion channels and carrier proteins, play unique roles in cellular processes
• Transport mechanisms across cell membranes maintain cellular homeostasis through facilitated diffusion and active transport
• The fluid mosaic model describes cell membranes as dynamic structures providing a selective barrier
• Enzymes catalyze reactions by providing an alternative pathway with lower activation energy

Biology Concepts Summary

• Active transport across cell membranes involves movement of substances against their concentration gradient, from lower to higher concentration, requiring energy typically in the form of ATP.
• Passive transport describes movement of substances from higher to lower concentration without using energy.
• Cholesterol in cell membranes maintains fluidity and stability, modulating the tightness of the phospholipid bilayer.
• Coenzymes are non-protein compounds that assist enzymes in their catalytic activity, often acting as carriers for chemical groups or electrons during reactions.
• Feedback inhibition in metabolic pathways regulates enzyme activity to avoid overproduction of the end product, maintaining metabolic balance.
• The fluid mosaic model describes the cell membrane as a flexible, dynamic structure composed of a phospholipid bilayer with embedded proteins, emphasizing its fluid nature and mosaic-like arrangement of molecules.
• Integral proteins are embedded within the cell membrane and can span its entire width, crucial for various cellular functions including transport and signaling.
• An example of passive transport across a cell membrane is the movement of substances from higher to lower concentration without using energy.
• Other options for active transport mechanisms include direct protein synthesis on the cell membrane or storage of genetic information for cellular processes.
• Cholesterol does not primarily act as a channel for ions, serve as the primary energy source for membrane functions, or play a role in the synthesis of nucleic acids.
• Coenzymes are not primary substrates that enzymes act upon, proteins that bind to an enzyme to increase its activity, or a type of enzyme that breaks down proteins.
• Feedback inhibition does not speed up the reaction at the beginning of a pathway, prevent the pathway from producing its final product, or replicate the enzymes involved in the pathway.