1.3 cell membranes organells
Review of Macromolecules and Cell Biology
Macromolecules: Consist of monomer building blocks.
Hydrolysis: Reaction that breaks down macromolecules into monomers.
Dehydration Synthesis: Reaction that builds macromolecules from monomers.
Enzymes:
Proteins produced by cells that catalyze (speed up) chemical reactions.
Can be organized into pathways for efficiency.
Denaturation: Enzymes lose their functional shape outside of their tolerable environmental conditions, which inhibits their activity.
Inhibitors: Substances that can reduce the activity of enzymes.
Negative Feedback Example: When the product of a reaction pathway inhibits an enzyme involved in its own production.
Raises the question of survival when two necessary enzymes operate under different tolerable ranges.
Cells, Membranes, and Organelles
Basic Cell Facts:
All living organisms are composed of cells.
Cells utilize energy to perform functions necessary for life.
Cells construct the body and manage vital processes for survival.
This cell function relies on the cytoplasm being separated from the external environment.
Example: Concentration of sugar in muscle cells fuels metabolism.
Organelles (internal structures in cells) possess specialized tasks due to their compartmentalization, such as acidic environments that can destroy pathogens.
Membrane-bound Organelles:
Provide spatial organization within the cell and contain unique functions (e.g., mitochondria generate ATP).
Contrast with non-membrane-bound structures like ribosomes, which are critical for protein synthesis.
Membrane Structure and Function
Cell Membrane Functions:
Regulates internal and external substance movement:
Segregation of solutions
Homeostasis maintenance
Designed for versatility and response to conditions.
Membrane Composition:
Plasma Membrane: Contains a lipid bilayer with embedded proteins and carbohydrates.
Lipid Characteristics:
Composed primarily of carbon, hydrogen, and small amounts of oxygen.
Non-polar covalent bonds result in hydrophobic properties.
Phospholipids:
Have hydrophilic (water-attracting) phosphate heads and hydrophobic (water-repelling) tails.
Main components of cell membranes.
Phospholipid Bilayer Structure:
The arrangement prevents mixing of solutions inside and outside the cell, aiding in maintaining the necessary internal chemistry.
Cholesterol molecules interspersed between phospholipids enhance membrane integrity.
Reduces permeability and resists mechanical puncture.
Maintains fluidity under varying temperatures, allowing for flexibility without compromising structure.
Fluid Mosaic Model of the Plasma Membrane
Components of the Fluid Mosaic Model:
Phospholipid bilayer interspersed with cholesterol and proteins.
Glycans:
Carbohydrate side chains attached to membrane proteins or lipids, known as glycoproteins and glycolipids.
Important for cell identity, signaling, and interaction.
Transport Proteins:
Facilitate and regulate the transportation of substances across membranes.
Facilitated Diffusion:
Allows the passage of polar molecules, ions, and large molecules without energy expenditure by creating “hallways” for movement.
Example: Aquaporin, a channel specifically for water transport.
Energy Considerations:
Facilitated diffusion does not require energy, while transport against a concentration gradient requires energy (active transport).
Transport precision varies:
High Precision: Facilitated diffusion and active transport involve controlled movement of specific molecules.
Low Precision: Endocytosis and exocytosis involve bulk movement of many molecules.
Mechanisms of Transport
Endocytosis:
Bulk transport of materials into a cell.
Exocytosis:
Bulk transport of materials out of a cell (e.g., secretion of hormones).
Factors Influencing Transport:
Transport Proteins: Specific pathways for molecules.
Concentration Gradient: Difference in solute concentrations on either side of the membrane drives diffusion.
Pressure Gradient: Physical forces that affect molecule movement across membranes.
Electrical Gradient: Variations in charge affect ion movement across the membrane.
Electrochemical Gradient
Inside Cell Composition:
High concentration of potassium ions (K+) and anions (charged proteins).
Outside Cell Composition:
High concentration of sodium ions (Na+) and chloride ions (Cl-).
Implications of Gradients:
The differences in ion concentrations establish an electrochemical gradient, resulting in membrane potential measured in millivolts (mV).
Group Work and Application
Importance of Cell Organization:
Separation of labor within organelles enables the growth and functionality of larger cells, such as human cells compared to bacteria, which lack membrane-bound organelles.
Functionality of Organelles:
Each organelle's specialized functions arise from diverse enzymes adapted to specific environmental conditions necessary for their tasks.
Review Points:
Plasma membranes maintain homeostasis through a hydrophobic core that restricts permeability.
Organelles serve distinct functions fueled by individual enzymatic reactions.
Comparison of membrane structures highlights differences in organization between eukaryotic cells and prokaryotic bacteria.
Conclusion:
The cell's compartmentalization into organelles facilitates complex processes necessary for life, contrasting starkly with simpler bacterial structures.