The Cell Membrane - Transport, well detaild explenation, that include diagrams and and visual elements that will help you to undestands fully how it works, it is formed, and all topic related.
Membranes:
• Lipid Bilayer of diglycerides (phospholipids) held together by hydrophobic forces
o Hydrophilic head group (glycerol)
o Hydrophobic fatty acid tails
§ Some saturated + unsaturated (mpt – determined by saturation level & tail length)
• Imbedded Proteins: proteínas Incrustadas
o Peripheral:
§ Associated with the polar head groups
§ Easily removed from the membrane by Δ pH or Δ [salt]
o Integral:
§ Embedded in the membrane
§ Span the width of the membrane
§ Membrane must be destroyed to remove it.
• Done by adding detergent (small amphipathic molecules)
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, How Substances Cross Cell Membranes:
• Membrane controls the flow of materials in/out of the cell.
• Either passive or active processes:
o Passive:
§ Diffusion
• Simple Diffusion – movement of small, uncharged, non-polar
and lipid-soluble substances directly through the lipid bilayer.
(O2, CO2, N, Ethanol, Glycerol, Steroids, fat soluble vitamins)
• Facilitated Diffusion – where specific molecules diffuse across
membranes, through specific transport
proteins.(Carrier/channel)
- Factors Affecting Rate of Diffusion:
o Concentration gradient
o Molecular size
o Temperature (faster @ higher temps)
o Electric or Pressure gradient
§ Passive Transport Proteins – facilitate the diffusion of specific chemicals (glucose/amino acids/nucleotides/ions)
through the membrane that would otherwise not pass through the bi-lipid layer.
• 2 Types:
o #1 Passive Carrier Proteins: SITIO de unión a
las proteínas
§ Discriminates between solutes based on the shape of the protein’s binding
- site.
§ - then transfers single molecules across the membrane by changing its conformation. (similar to a
turnstile)
§ Has a high affinity for its substrate.
§ - are therefore very effective at low substrate conc.
§ Transfer rate is inhibited by temperature.
§ Uniporters: single solute à down the conc. gradient.
b
Bicapa
lipídica
centro de acoplo
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