Plasma membrane, cytoskeleton and transport WK2 Flashcards
Describe the structure and function of plasma membrane (have diagram look over)
-Border of cell separating internal and external environments
-selective, differentially, permeable lipid bilayer
-Controls entry and exit ions, e.g. Na+, K+, Ca+
-Passive/active control of substance into cell
Describe membrane lipids. Mention phospholipids
-75% of membrane lipids are phospholipids
-Amphipathic molecules arranged in bilayer
-Hydrophilic (polar) phosphate heads face H2O on each side of membrane
-Hydrophobic fatty acid tails directed towards centre
What are two types of membrane lipids? Describe them in the bilayer
Cholesterol
-Holds phospholipids still, can stiffen membrane
Glycolipids
-Phospholipids with short carbohydrate chains on extracellular face
-Contributes to glycocalyx-carbohydrate coating on cell surface
Describe integral membrane proteins
penetrate membrane
-Transmem proteins pass through
-Hydrophilic regions contact cytoplasm + extracellular
-Hydrophobic regions pass through lipid of membrane
-Some drift in membrane other anchored to cytoskeleton
Describe peripheral membrane proteins
adhere to one face of membrane
-do not penetrate membrane
-usually tethered to cytoskeleton
Provide functions of protein membranes
-Anchoring proteins (support)
-Recognition proteins (self)
-Secondary messenger systems-communicate within cell receiving chem message
-Enzymes: catalyse reactions
-Receptor proteins: bind chem signals
-Carrier proteins: bind solutes and transfer them across membrane
-Cell-adhesion molecules: mechanically link cell to extracellular material
-Channels: allow hydrophilic solutes and water to pass through membrane
Define pumps, cell-adhesion molecules and cell-identity markers
Pumps- carriers that consume ATP
Cell-identity marker: glycoproteins acting as identification tags
Cell-adhesion molecules: mechanically link cell to extracellular material
Define the types of channels
Ligan gated- respond to chem messengers
-Voltage gated- respond to charge changes
-Mechanically gated- respond to physical stress on cell
Describe structure and functions of glycocalyx
Fuzzy coat external to plasma membrane
-Protection, Immunity to infection, Defence against cancer, Transplant compatibility
Describe the process of a secondary-messenger system
-Chem message binds to surface receptor
-Receptor activate G protein (intracellular protein that obtains energy from GTP
-G protein relays signal to adenylate cyclase which converts ATP to cAMP
-cAMP activate cytoplasmic kinases
-Kinases add phosphate group to other enzymes turning some on/off
-Up to 60% of drugs work through G proteins and second messengers (medicinal etc)
Describe structure and function of microvilli
-Made of microfilaments (provide strength and anchor microvilli to cell)
.Increase SA
.Increase exposure to extracellular fluid
.Absorb materials from extracellular fluid
Describe structure and function of cilia
-Made of microtubules (movement)
-Hair-like processes, beat freely in saline layer at cell surface (mucous on top)
-nonmotile cilium on most cells monitor nearby conditions e.g. sensory cells of nose
.Balance (inner ear) light detection (retina)
.Motile cilia- respiratory tract, reproductive tract, ventricles of brain
.Beat in waves to sweep material across surface in one direction
.Axoneme-core of motile cilium
.2 central microtubules surrounded by ring of 9 pairs that anchor cilium to cell
Describe structure and function of cytoskeleton
Network of protein filaments and cylinders
-Determines cell shape
-Supports structure
-Organises cell contents
-Direct movement of materials within cell
-Contributes to movement of cell as whole
Composed of: microfilaments, intermediate fibers, microtubules
Define functions of microfilaments, intermediate fibers, microtubules. Organise from thinnest to thickest walls.
Microfilaments:
-Forms terminal web
Intermediate filaments:
-within skin cells, made of protein keratin
-Give cell shape, resists stress
Microtubules:
-Maintain cell shape, hold organelles, make axonemes of cilia and flagella; form mitotic spindle
Differentiate between active, passive and carrier-mediated membrane transport
-membrane is selectively permeable
Passive mechanisms require no ATP
-Random molecular motion of particles provides necessary energy
-Filtration, diffusion, osmosis
Active mechanisms consume ATP
-Active transport and vesicular transport
Carrier-mediated mechanisms
-use membrane protein to transport substances across membrane
Describe/define filtration
Particles driven through membrane by physical pressure
-Allows delivery water/nutrients to tissues
-Allows removal of waste from capillaries in kidneys
Describe simple diffusion
Net movement of particles from high conc to lower
- from constant, spontaneous molecular motion
-Molecules collide/bounce off each other
-Substances diffuse down their conc gradient
-Doesn’t require membrane
What factors effect diffusion rate through membrane
-Temp: increase motion of particles
-Molecular weight: larger molecules move slower
-Steepness of concentrated gradient: increase difference= increase rate
-Membrane SA: increase= increase rate
-Membrane permeability: increase= increase rate
Define osmosis. Effect of aquaporins. What are some real world examples of osmotic imbalance
Net flow of H2O through selectively permeable membrane
-From more concentrated to less
-Osmotic imbalance underlie diarrhea, constipation, edema
-More aquaporins in cell=increase speed as enhance osmosis
Define what is meant by specificity in carrier mediate transport
-Transport proteins specific for particular solutes
-Solute (ligan) binds to receptor site on carrier protein
-Solute released unchanged on other side of membrane
Define what is meant by saturation in carrier mediated transport
-solute conc rises, rate of transport rises till transport maximum (Tm) reached
-Tm: rate at which all carriers are occupied
What are the three types of carriers
-Uniport: carries one types of solute e.g. Ca+ pump
-Symport: carries two/more solutes simultaneously in same direction e.g. Sodium glucose transporters
-Antiport: carries two/more solutes in opposing directions (counter) e.g. Na+-K+ pumps remove Na bring in K
Define and list the three mechanisms of carrier-mediated transport
Facilitated diffusion
-Solute particle enters channel of membrane protein
-Solute binds to receptor site where carrier changes conformation
-carrier releases solute on other side of membrane (no ATP)
Primary active transport
-Carrier moves solute through membrane up to its conc gradient
- use ATP e.g. Ca pump/Na K pump)
Secondary active transport
-Carrier moves solute through membrane but uses ATP indirectly
E.g. Sodium-glucose transporter (symport)
Describe process of Na K pump
-Each cycle consumes 1 ATP and exchanges 3 Na for 2 k
-k conc kept higher, Na conc lower within cell
Half of daily calories used for Na K pump
Function of Na K pump
-Maintains Na conc gradient allows for secondary active transport
-Regulates solute conc, thus osmosis and cell vol
-Maintains neg. charged resting membrane potential
-Produces heat
Describe vesicular transport and it’s types
Moves large particles through membrane in vesicles-enclosures of membrane
Endocytosis- processes that bring material into cell
Phagocytosis-engulfs large particles
Membrane caves in then pinches off pinocytic vesicle
Pinocytosis-takes in ECF containing molecules useful to cell
Receptor-mediated endocytosis-particles bind to specific receptors on plasma membrane
Exocytosis-discharging material from the cell
