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chapter 7- Membrane structure and function - Coggle Diagram
chapter 7- Membrane structure and function
7.1-Cellular membranes are fluid mosaics of lipids and proteins
Main components: lipids, proteins, and carbohydrates.
Phospholipids are the most common lipids in membranes.
A phospholipid is amphipathic
Hydrophilic head (water-loving)
Hydrophobic tail (water-fearing)
The Fluid Mosaic Model
The membrane is a fluid bilayer of phospholipids with proteins floating
Fluidity of Membranes
Membranes are not rigid; they are held together by weak hydrophobic interactions.
Phospholipids move quickly side to side
Proteins move slower, some anchored by the cytoskeleton or extracellular matrix
Factors affecting fluidity:
Temperature:
High temp → more fluid
Low temp → can solidify
Unsaturated tails: keep membranes more fluid ex: Cold-water fish → more unsaturated tails
Cholesterol: acts as a fluidity buffer
Membrane Proteins
Phospholipids = structure, but proteins = function.
two main types:
Integral proteins: embedded in the bilayer (many are transmembrane);
hydrophobic regions
made of
nonpolar
amino acids
.
Peripheral proteins: attached to the surface (not embedded)
Functions: transport, enzymic activity, signal transduction, and cell-cell recognition.
Membrane Carbohydrates and Cell Recognition: Found on the outer surface of the plasma membrane; short; branched chains of sugar
ex:Example: Blood types (A, B, AB, O) differ in their surface carbohydrates.
attach to
Lipids → glycolipids
Proteins → glycoproteins
7.2-Membrane structure results in selective permeability
Selective permeability some substances can cross more easily than others.
fluid mosaic model
explains how this selectivity works through the combined roles of lipids and proteins.
Cells constantly exchange materials with their environment:
Take in: sugars, amino acids, nutrients, and O₂
Release: waste products and CO₂
Regulate ions: Na⁺, K⁺, Ca²⁺, Cl
*
Transport Proteins-**specific molecules and ions cross the membrane w/o touching hydrophobic interior
Channel Proteins: act like channels or proteins; ex: Aquaporins
Carrier proteins:Hold onto a molecule and change shape to move it across, extremely specific. EX; Glucose transporter in red blood cells
7.3- Passive transport is diffusion of a substance across a membrane with no energy investment
Diffusion- movement of molecules from high to low concentration until equilibrium is reached.
Facilitated Diffusion (Passive Transport Aided by Proteins)
Passive transport-No energy required
Osmosis: Diffusion of free water molecules from a low to high concentration
Tonicity: The ability of a solution to cause a cell to gain or lose water.
Isotonic: no net movement,
Hypertonic: water leaves cell, cell shrivles. Ex Saltwater (hypertonic) kills freshwater animals
Hypotonic: water enters cells, cells swell ex freshwater (hypotonic) would burst animal cells without regulation.
7.5-Bulk transport across the plasma membrane occurs by exocytosis and endocytosis
Endocytosis (Enter the Cell)-
ex: cholerstrol uptake
3 Types of endocytosis
Phagocytosis – “Cell eating”; cell engulfs large particles or cells.
Pinocytosis – “Cell drinking”; cell takes in droplets of extracellular fluid.
Receptor-Mediated Endocytosis – Uses receptors to bring in specific molecules.
Exocytosis (Exit the Cell)
ex:Pancreatic cells release insulin by exocytosis.
Membrane Recycling
Endocytosis and exocytosis occur constantly to:
Renew the plasma membrane
Balance membrane loss and addition
7.4-Active transport uses energy to move solutes against their gradients
**Active transport moves substances against their concentration gradients; from low to high
Membrane Potential
-all cells have voltage; Inside of the cell = negative relative to the outside.
Electrochemical Gradient
Chemical gradient (concentration difference).
Electrical gradient (charge difference).
Electrogenic Pumps-
Pumps that generate voltage across the membrane.
Cotransport (Coupled Transport)-downhill diffusion of one solute to drive the uphill transport of another
.
Ex: Example in plants: H⁺/sucrose cotransporter