MODULE 1: Principles of Cell Function Flashcards
Phospholipid
- amphipathic molecule
- lipid tail made of of carbons and hydrogens
- non polar –> hydrophobic
- phosphate head is charged –> hydrophilic
Viscous Membrane
- single carbon-carbon bonds
- fits together and packed tightly
- saturated tails
- increasing temp decreases viscosity
- cholesterol stops membrane become too viscous/fluid
Fluid Membrane
- double carbon-carbon bonds creating kinks
- not tightly packed
- unsaturated tails
- increasing temp increases fluidity
- cholesterol stops membrane become too viscous/fluid
Structure of proteins
- peptide bonds
- alpha helix or beta sheets
- N terminus = NH2 group
- C terminus = COOH group
- additional side chains
- charged/polar chains are hydrophilic
- uncharged/non-polar chains are lipidphilic
6 Major Functions of Membrane Proteins
- transport
- enzymatic activities
- signal transduction
- cell-cell recognition
- intercellular joining
- attachment to cytoskeleton and extracellular matrix
Selective Permeability
Lipid bilayers NOT permeable to:
- ions
- small hydrophilic molecules (glucose)
- macromolecules (proteins & RNA)
Permeable to:
- hydrophobic, non-polar, uncharged small molecules
Passive Transport
Diffusion of a substance across membrane with no energy arrangement
Occurs with time due to random motion of molecules becoming equally distributed
Moves to eliminate concentration gradient
Osmosis
Diffusion of water through selectively permeable membrane into another aqueous compartment containing solute with higher concentration
Water wants to reach equilibrium
Sugars, ions, proteins and nutrients are osmotically active
Tonicity
Ability of solution to cause cell to gain/lose water
Isotonic / Hypertonic / Hypotonic
Isotonic: solute concentration is same as inside cel, no net water movement
Hypertonic: solute concentration is greater than inside cell, cell loses water (shrink)
Hypotonic: solute concentration less than inside cell, cell gains water (swell/pop)
Facilitated Diffusion
Passive Transport aided by proteins
Transport proteins speed up passive movement
Channel proteins provide hydrophilic corridors that allow a specific molecule or ion to cross membrane (aquaporins, ion channels)
Transport Proteins
Allow passage of hydrophilic substances across membrane
Carrier proteins bind to specific molecule and changes shape to shuttle it across membrane
Passive vs Active Transport
passive: down concentration gradient
active: against concentration gradient
Electrogenic Pump
- active transport
- transport protein that generates voltage across membrane to pump ions through
- sodium-potassium is major electrogenic pump of animal cells
- plants, fungi and bacteria use proton pump
Cotransport
Active transport of a solute indirectly drives transport of another solute
Bulk Transport
exocytosis - vesicle fuses with membrane to release contents
endocytosis - vesicle pinches off from membrane containing particles
Phagocytosis
- endocytosis
- engulfing large particles by forming food vacuole
Pinocytosis
- endocytosis
- absorbing molecules from solution
- cells drinking
Receptor-mediated Endocytosis
special coated segment of membrane with specific receptors combine with certain molecules from surroundings
Paracrine Signalling
- secreting cells acts on nearby target cell
- discharges molecules of local regulator into extracellular fluid
- local sigalling
Synaptic Signalling
- nerve releases neurotransmitters into synapse
- stimulates target cell
- local/long distance signalling
Hormonal Signalling
- specialised endocrine cells secrete hormones into blood
- reach all body cells
- long distance signalling
Autocrine Signalling
- cells release compound which acts on receptors on same cell
- most localised signalling
Stages of Cell Signalling
- Reception - signalling molecule attaches to receptor
- Transduction- relay molecules in a signal transduction pathway
- Response - activation of cellular response (gene activation, enzyme stimulation, rearrange cytoskeleton)
G protein coupled receptor
- signal molecule/1st messenger binds to extracellular receptor
- receptor made of amino acid chain
- 7 transmembrane domains
- couples with a G protein attached to inside of membrane
- G protein reacts with something else inside cell to produce large yield of another compound/2nd messenger
- 2nd messenger produces response within cell
- happens within one second
- can control the activity of enzymes, ion channels and intracellular signal transduction pathways
Tyrosine Kinase Linked Receptor
- tyrosine is an amino acid
- kinase is an enzyme that initiates phosphorylation
- phosphorylation results in conformational change, protein-protein interactions, change in cellular location
- phosphorylation produces response within cell
Steroid Receptors
- steroid moves into cell via diffusion (lipidphilic)
- hormone receptor complex moves into nucleus
- binds to DNA to activate genes
- produces new proteins
- takes hours/days
Insulin Receptor
- tyrosine kinase linked receptor
- 1 transmembral domaine
- binds to two receptors to create bridge
- results in phosphorylation
- glucose transporters move outside cell
- glucose taken from blood to cell
