Module 4 Cellular Processes Flashcards
In general, do hydrophobic or hydrophilic molecules diffuse passively in the cell membrane?
Hydrophobic (non-polar) Water is polar and an exception to this rule (though the diffusion is slow)
What is the membrane structure?
Thin, 8nm flexible and sturdy barrier that surrounds the cytoplasm of the cell.
The fluid mosaic model describes membrane structure (sea of lipids).
What is the composition of the membrane? (%)
Made of 50% lipid and 50% protein.
How are the membrane components held together? (what type of bonds?)
Held together by hydrogen bonds.
What is the function of the membrane?
Functions as a barrier to entry/exit of polar (hydrophilic) substances; proteins are ‘gatekeepers’ that regulate traffic.
What is the fluid mosaic model of membrane?
Describes the membrane as a flexible, ‘sea-like’ structure of lipids and proteins held together by hydrogen bonds.
What is the function of the fluid mosaic model?
Allows the membrane to act as a selective barrier—preventing entry of polar substances while allowing dynamic control through embedded proteins (‘gatekeepers’).
Which lipid causes asymmetry in the membrane structure?
Glycolipids (on the outer leaf of the membrane).
Why do glycolipids contribute to membrane asymmetry?
They are only found on the outer leaflet and are involved in cell recognition, adhesion, and immune response.
What 3 types of lipid molecules are in the lipid bilayer of the cell membrane?
Phospholipids, Cholesterol, Glycolipids.
What is the relationship between cholesterol, glycolipids, and phospholipids in the bilayer?
Cholesterol and Glycolipids are scattered among the double (back to back) row of phospholipid molecules.
What is the percentage of phospholipids in the bilayer?
~75%.
Which parts of the phospholipids are non-polar and polar?
Non-polar & Hydrophobic: the tails (core of layer); Polar & Hydrophilic: the heads (outer).
What makes a species amphipathic?
Having both non-polar and polar regions.
What makes the leaflets asymmetrical?
Membranes are fluid and thus lipids can move dynamically in the membrane leaflet making this dynamic movement asymmetric.
What is the equation Pw = Pd + Pf?
Pw is the permeability of water, Pd through lipid bilayer and Pf through water channel
In osmosis, if one side of the membrane has a high concentration of solute, does water move towards it?
Yes
Cells use what percentage of resting energy to maintain concentration and electrical gradients?
~30%
What is the concentration gradient?
When non-charged molecules will diffuse down their concentration gradients
What is the electrical (chemical) gradient?
-When ions are influenced by the difference in electric charge across a membrane. (High concentration of negative ions will cause a positive ion to cross).
-This can act as a ‘storage’ for energy
What factors can increase the rate of diffusion across a cell membrane?
-Temperature (higher=faster)
-Size of molecule (smaller=faster)
-Concentration (the greater the difference in concentration=faster)
-Surface Area (bigger surface area=faster)
-Distance of diffusion (short distance for molecules to travel=faster)
True or false: Membrane proteins mediate the transport of substances across the membrane that cannot permeate the hydrophilic core of the lipid bilayer
False it mediates the transport of substances across the membrane that cannot permeate the HYDROPHOBIC core
What is the membrane permeable and impermeable to?
Permeable to:
-Non-polar uncharged molecules (O2, N2, benzene)
-Lipid soluble molecules (steroids, fatty acids, some vitamins) diffuse down concentration gradient
-Small uncharged polar molecules (water, glycerol, CO2, urea)
Impermeable:
-Large uncharged polar molecules (glucose, amino acids)
-Ions (Na+, K+, Cl-, Ca2+, H+)
Finish the acronyms: Membrane proteins can act as…
-RP
-CIM
-L
-E (can catalyse reactions)
-IC (2 classes, 2 mechanisms)
-TP (2 classes, 2 mechanisms)
-Receptor proteins
-Cell Identity Markers
-Linkers
-Enzymes
-Ion Channels
-Transporter proteins
Fill in the blanks: Integral proteins are (hydrophobic/hydrophilic/amphipathic), they have (hydrophobic/hydrophilic) regions that span the (hydrophobic/hydrophilic) core of the lipid bilayer. These regions usually consist of (polar/non polar) coiled into (sheets/helices)
Integral proteins are (amphipathic), they have (hydrophilic) regions that span the (hydrophobic) core of the lipid bilayer. These regions usually consist of (non polar) coiled into (helices)
What is fluidity in the lipid bilayer determined by?
-Length of lipid tail (longer the length of the tail, the less fluid the membrane)
-Number of double bonds (more double bonds increases fluidity)
-Amount of cholesterol (more decreases fluidity)
Integral proteins are (hydrophobic/hydrophilic/amphipathic)?
Integral proteins are (amphipathic)
