sept 29 lecture

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Section 3: Membrane Structure and Function

Overview of Membrane Structure

Cellular membranes are essential components of all living cells, providing structure, protection, and regulation of transport. The plasma membrane is described as a fluid mosaic of lipids and proteins, allowing for dynamic movement and selective permeability.

Fluid Mosaic Model: The membrane consists of a double layer of phospholipids with embedded proteins, carbohydrates, and cholesterol, creating a flexible and varied structure.
Selective Permeability: Membranes allow certain substances to pass while restricting others, maintaining homeostasis.
Key Components: Phospholipids, integral and peripheral proteins, glycoproteins, glycolipids, and cholesterol.
Example: The plasma membrane of animal cells regulates the entry and exit of ions, nutrients, and waste products.

Prefixes and Suffixes in Membrane Biology

Understanding common prefixes and suffixes helps in interpreting biological terminology related to membranes.

Prefix	Meaning
Cyto-	Cell
Glyco-	Sugar
Exo-	Outside
Endo-	Inside, within
Hyper-	High
Hypo-	Low
Iso-	Same

Suffix	Meaning
-osis	Process, condition, disease

Passive and Active Transport

Transport across membranes is vital for cellular function. It can occur passively, without energy, or actively, requiring energy input.

Passive Transport: Movement of substances down their concentration gradient (from high to low concentration) without energy input. Includes diffusion and facilitated diffusion.
Active Transport: Movement of substances against their concentration gradient (from low to high concentration), requiring energy, usually from ATP.
Example: The sodium-potassium pump uses ATP to move Na+ out of the cell and K+ into the cell, maintaining electrochemical gradients.

Equation for Active Transport Rate:

Additional info: The above equation is a general rate law; for membrane transport, the rate often depends on transporter availability and substrate concentration.

Cotransport and Coupled Transport

Cotransport involves the simultaneous movement of two substances across a membrane, often coupling the downhill movement of one with the uphill movement of another.

Cotransporter: A membrane protein that facilitates the coupled transport of two solutes.
Mechanism: The diffusion of one solute down its concentration gradient provides the energy for the transport of another solute against its gradient.
Example: Plants use H+/sucrose cotransport to load sucrose produced by photosynthesis into cells in leaf veins.

Diagram Description: The image shows a proton pump creating a gradient, which is then used by a cotransporter to move sucrose into the cell against its concentration gradient.

Additional info: ATP is used indirectly to establish the proton gradient, which then powers cotransport.

Bulk Transport: Exocytosis and Endocytosis

Large molecules and particles are transported across the plasma membrane via bulk transport mechanisms, which require energy.

Exocytosis: The process by which cells export large molecules (e.g., proteins, polysaccharides) by packaging them in vesicles that fuse with the plasma membrane.
Endocytosis: The process by which cells import substances by engulfing them in vesicles formed from the plasma membrane.
Types of Endocytosis:
- Phagocytosis: "Cellular eating"; the cell engulfs large particles or cells.
- Pinocytosis: "Cellular drinking"; the cell takes in extracellular fluid and dissolved solutes.
- Receptor-mediated endocytosis: Specific molecules are taken in after binding to receptors on the cell surface.
Example: Insulin secretion by pancreatic cells (exocytosis); cholesterol uptake via LDL receptors (receptor-mediated endocytosis).

Section 4: A Tour of the Cell

Microscopy and Cell Study Techniques

Biologists use various types of microscopes and biochemical methods to study cell structure and function.

Light Microscopy (LM): Uses visible light and lenses to magnify specimens; allows observation of living cells.
Electron Microscopy (EM): Uses electron beams for much higher resolution; reveals organelles and cell ultrastructure.
Transmission Electron Microscopy (TEM): Shows internal structures of thin cell sections.
Scanning Electron Microscopy (SEM): Provides 3D images of cell surfaces.
Cell Fractionation: Technique to separate cell components by size and density using centrifugation.

Important Parameters:

Magnification: Ratio of image size to actual size (e.g., 1000X).
Resolution: Minimum distance two points can be distinguished (e.g., 200 nm for LM).
Contrast: Difference in brightness between parts of the image, often enhanced by staining.

Prokaryotic vs. Eukaryotic Cells

Cells are classified as prokaryotic or eukaryotic based on their internal structure.

Feature	Prokaryotic Cells	Eukaryotic Cells
Domains	Bacteria, Archaea	Eukarya
Nucleus	No (nucleoid region)	Yes (membrane-bound)
Organelles	Absent	Present (membrane-bound)
Size	Smaller	Larger

Common Features: Plasma membrane, cytoplasm, DNA, ribosomes.
Surface Area to Volume Ratio: Limits cell size; cells must be large enough to contain necessary components but small enough for efficient exchange with the environment.

Key Organelles and Their Functions

Eukaryotic cells contain specialized organelles that compartmentalize functions.

Nucleus: Contains genetic material (DNA); controls cell activities.
Ribosomes: Sites of protein synthesis.
Endoplasmic Reticulum (ER): Network for protein and lipid synthesis; rough ER has ribosomes, smooth ER does not.
Mitochondria: Site of cellular respiration; converts energy from nutrients into ATP.
Chloroplasts: Found in plant cells; site of photosynthesis.

Example: Muscle cells have many mitochondria to meet high energy demands.

Surface Area to Volume Ratio Calculations

The efficiency of cellular processes is influenced by the surface area to volume ratio.

Formula for Surface Area of a Rectangular Prism:

Formula for Volume:

Surface Area to Volume Ratio:

Additional info: Cells with higher SA:V ratios are more efficient at exchanging materials with their environment.