Bct-L03 Cell Membranes

Front 1

Explain the formation of phospholipid bilayersin an aqueous environment

Back 1

Phospholipids are amphipathic- they have a polar/hydrophilic phosphate head with hydrophobic aliphatic fatty acid chains which may be saturated or unsaturated

Front 2

What are the properties of the membrane?

Back 2

• Selectively permeable
  
• Impermeable to macromolecules, biochemical intermediates.
  
• Permeable to water molecules and a few other small, uncharged molecules like oxygen and carbon dioxide, nutrients, waste products.
  
• Transfer of information (signal transduction).
  

Front 3

Lipid bilayers are permeable to...

Back 3

Water, some small uncharged molecules.

Front 4

Define Simple diffusion

Back 4

Simple Diffusion: the movement of molecules and small particles across the semi-permeable membrane driven by adifference in the concentration of molecules on either side.

Front 5

Define Osmosis

Back 5

Osmosis: the net movement of water molecules across a semi-permeable membrane driven by a difference inconcentration of solute on either side. The membrane must be permeable to water but not to the solute molecules

Front 6

Active Transport

Back 6

the movement of a molecule across a membrane against its concentration gradient driven by ATPhydrolysis or another form of metabolic energy

Front 7

Facilitated diffusion

Back 7

the movement of hydrophilic (charged) molecules down their concentration gradient throughprotein pores that hide the ionic charges from the hydrophobic core of the lipid bilayer. Proteins (or proteinassemblies) offer a water-filled channel. The channel can be ‘gated’- specific, i.e. a particular molecule may modify itsstructure, opening the channel allowing the substance to pass through the membrane e.g. drugs.

Front 8

Lipid bilayers are impermeable to...

Back 8

Cations (K+, Na+, Ca2+) but some do leak through, down the concetration gradient.  Anions (Cl-, HCO3-)  Small hydrophilic molecules like glucose  Macromolecules like proteins and RNA

Front 9

Function of membrane proteins

Back 9

1. increase fluidity

2. Transport (Sodium-Glucose transport)

3. Transmission of signals

4. Anchors to link intracellular actin filaments to extracellular matrix proteins (anchors the membrane to macromolecules on either side)

5. Receptors for hormones and growth factors- detect chemical signals in the cell’s environment, and relay them to the cells interior

6. Cell recognition and adhesion

7. Electron carriers in cellular respiration and photosynthesis in mitochondria and chloroplasts 8. Enzymes

Front 10

Explain the movement of Na+ and K+ ions across the cell membrane against a concentration gradient

Back 10

Via electrostatic repulsion move ions across a membrane, which can pull water with it via osmotic attractions. The osmotic equilibrium is established by electrogenic transfer of Na+ out of the cell through a kinase sensitive pump that undergoes conformational changes.

Front 11

Describe how glucose is transported

Back 11

uses a facilitated diffusion, where by a molecule binds to a specific transporter which functions by a flip-flop mechanism.

Front 12

Describe how amino acids are transported

Back 12

Uses coupled transporters- symporters and antiporters

Move in the opposite direction to Na+ using ATP hydrolysis

Front 13

Explain how external chemical signals can be sensed at the interior of a cell.

Back 13

Some use exocytosis, e.g. hormones.

lipid-soluble molecules that cross membranes. signals rely on trans-membrane receptors.

Front 14

What is the neuromuscular junction

Back 14

The Neuromuscular junction or synapse is a highly complex structure involving pre- and post-synaptic membranes,pre-synaptic vesicles, invagination of the post-synaptic membrane, receptors and enzymes.

Front 15

Which terms does neuromuscular synaptic transmission involve?

Back 15

t-tubule, sarcoplasmic reticulum, dihydropiridine receptors, myofilaments, toponin, ADP, mysoin head, ATPase, actin filament