Cell membranes and transport 1.3 Flashcards
What is the structure of cell membranes?
-Appears under the electron microscope as a double line
-Barrier is 7-8nm across
-Made of phospholipids, proteins & other macromolecules
What is the function of cell membrane?
-Separates living cell from non-living surroundings
-Takes up nutrients, secretes chemicals, allows cell recognition
-Selectively permeable to water and some solutes
What are Phospholipids?
-Hydrophilic Phosphate head
-Hydrophobic Phosphate tail
-Arranged as a Bilayer
What theory did Singer and Nicolson propose?
Membrane proteins are inserted into the Phospholipid bilayer (The ‘fluid mosaic’ model)
Why is the word ‘fluid used’ in the Singer and Nicolson theory?
Lipids and membrane proteins can move laterally or sideways through the membrane
Why is the word ‘mosaic’ used in the Singer and Nicolson theory?
It is made up of many different parts such as proteins, glycoproteins, phospholipids, glycolipids, and in some cases cholesterol & lipoproteins
What is the glycocalyx?
A carbohydrate coating that covers the outside of many cells, particularly bacteria
What is the function of extrinsic proteins?
-Eukaryotic: recognition of cell
-Bacterial: protective coat from host factors
-Can be glycosylated to make glycocalyx
-Cell surface identity marker (antigen)
What is the function of intrinsic proteins?
-Penetrate lipid bilayer, usually across the whole membrane
-Transport proteins
-Channel proteins and carrier proteins (transmembrane)
How does temperature affect permeability?
-Low temperature=low kinetic energy, the membrane is rigid
-High temperature=high kinetic energy, forms gaps
-Above 45 degrees C membrane denatures
How does ethanol affect permeability?
Ethanol can dissolve non-polar phospholipids. If ethanol concentration is high enough, membrane dissolves completely
How does detergents affect permeability?
Reduces surface tension and disperses the phospholipids in membrane, permeability increases
How does NaCl affect permeability?
Na+ ions will bond to Oxygen atoms in phosphate heads, increasing rigidity
What can the rate of diffusion be affected by?
-Temperature
-Thickness of membrane
-Size of a molecule
-Lipid solubility
-Concentration gradient
What molecules can diffuse directly?
-Lipid soluble
-Non charged
-Vitamine A,D, & E
What molecules use protein channels?
-Not lipid soluble
-Charged
-Large
What are the three methods of facilitated diffusion?
-Channel protein
-Carrier protein
-Co-transport
What is exocytosis?
Substances leaving the cell after being transported through the cytoplasm in a vesicle (needs ATP)
What is endocytosis?
Substance being engulfed by infolding membrane
What is pinocytosis?
endocytosis of liquid materials (smaller vesicles)
What is phagocytosis?
endocytosis of solids
destroys bacteria
digests cell debris
Amoeba use this method to feed
Describe co-transport
1) Sodium and glucose is deposited into cell via a carrier protein
2)Sodium is pumped out of cell by active transport. Potassium is pumped in
3) Glucose leaves cell via facilitated diffusion
What molecules use carrier proteins?
large sugars and amino acids
What molecules use channel proteins?
Charged substances
How does temperature affect membrane permeanility?
-Low temperature, Low KE, membrane is rigid
-Temperature increase, KE increases, gaps form
-Above 45c, proteins denature, fully permeable
How does ethanol affect permeability?
Dissolves non polar substances like the phospholipids, increasing permeability
How does detergent affect permability?
reduces surface tension, creating gaps, increasing permeability
How does NaCl affect permeability?
Na+ ions bond to oxygen in the phospholipid heads, making membranes rigid, decreasing permeability
