MCB and Biomembranes Flashcards
What are the roles of biological membranes?
- Form boundary around all cells- helps maintain structural integrity
- Aids establishment of conc. gradient (membranes are fluid and selectively permeable)
- Compartmentalisation
- Communication and transport
- Organelles can also have specialised membranes
Describe the phospholipid bilayer
- All eukaryotic bio membranes have similar phospholipid bilayers
- Driven by the hydrophobic edict due to hydrophobic tails and hydrophilic heads
Describe lipids
- Spontaneously associate to exclude water from hydrophobic regions (energetically favourable)
- Includes fatty acids, waxes, glycerol and triacylglycerols, phospholipids and cholesterol
- Lipid structure varies and involved in compartmentalisation, energy storage and cell signalling
Describe phospholipids
- They are amphipathic
- Partly polar and partly non-polar
- 2 OH groups in glycerol moiety linked to fatty acids, 3rd phosphorylated
- Phosphate linked to a variety of small polar alcohol head groups (e.g. choline, serine etc,)
- Naming phosphatidyl- variable head group
What is the cytosolic face?
Membrane face that faces the cytoplasm
What is the ectoplasmic face?
Faces outside the cell or inward toward organelle
What are flippases?
Enzymes that aid the ‘flip-flop= movement of lipid, and maintains asymmetry- natural for ‘programmed cell death’
What is the signature phospholipid of the mitochondria?
Cardiolipin
What is the name of carbohydrates presented on the outside of the cell?
Glycolipids (blood-type determining antigens)
What is another example of membrane lipids?
Cholesterol
What are sphingolipids?
- Sphingosine instead of glycerol as carbon backbone to create sphingomyelins
- Most common sphingomyelin has choline polar head group
- Enriched in the myelin sheath that surrounds neuron axons
What is the liquid crystalline phase?
- Lipids within bio membranes contain mobile fatty acid chains (c-16 to 22)
- Unsaturation prevents tightly packed acyl chains, resulting in mobility
- Lipids move around plane of bilayer
- Essential for membrane proteins that require fluidity to operate and interact
How do you label?
(Number of carbons: number of double bonds’n’-placement of double bond)
What receptors are directly involved in the propagation of signals?
- G-protein couple receptors (most diverse type of membrane receptor)
- Nuclear receptors (Sensing steroid and thyroid hormones)
What are the precursors of signalling molecules and cellular messengers?
- Sphinogsine-1-phosphate
- Diacylglycerol
- Inositol phosphates
- Prostaglandins
- Steroid hormones
Describe membrane composition and regions
- Protein to lipid ratios differs among bio membranes
- Patches of varied lipid density, essential for signalling
- Cholesterol enriched areas from lipid rafts, interaction between saturated tails of sphingolipids with cholesterol stabilises fluid phase
- Increased stability
- Cholesterol transport, endocytosis and signal transduction with lipid rafts
What is an integral membrane protein?
Deeply embedded in the bilayer
What is a peripheral membrane protein?
Associated to lipids or other proteins within the membrane
What is a transmembrane protein?
- Integral proteins that traverse the membrane
- Composed of amino acids with non-polar side chains
- Often interact with he hydrophobic lipid tails and form complex structure, e.g. pores
What types of molecules can diffuse across the membrane?
Small non-polar or uncharged polar molecules
What types of molecules undergo facilitated diffusion across the membrane?
Larger polar molecules and require a transporter
Transporters are substrate specific and catalyse passive movement
What is a uniport?
Transporter where molecule goes in one direction
What is a symport?
Transporter where two things go in together (co-transport)
What is an antiport?
Transporter where one thing goes in whilst one goes out
What is the rate of transporter diffusion dependent on?
- Transporter concentration
What type of transport is used in sodium-potassium pumps?
- Primary active transport
- Creates a potential difference
- Requires energy
What is secondary active transport?
Molecules are moved through a membrane anti port as a result of the diffusion of another substance
- ATP not directly used
- Energy stored in ion gradients is used to power secondary transporters
What are two examples of diseases linked to membranes?
- Menkes- X-linked lethal disorder, copper transporting ATPase defective
- Wilson’s- another copper ATPase, failure to excrete copper from liver into bile- toxic accumulation
