Topic 2: Cell Physiology I Flashcards
The Cell Membrane
- Phospholipid Bilayer
- Membrane Proteins
- Membrane Carbohydrates
Phospholipid Bilayer
- continuous layer around the cell
- barrier to water soluble substances – NOT to small molecules (O2 & CO2) and lipid soluble molecules
Membrane Proteins
- Transport Proteins
- Receptor Proteins
- Enzymes
- Joining Proteins
- Identifying Proteins
Transport Proteins
- Channels
- Carrier Proteins
Channels
- form pore in membrane
- selectively permit channel-mediated facilitated diffusion of water & specific ions
- Can be:
- -gated: can open or close – when signaled
- -non-gated (= leakage channels): always open
Carrier Proteins
- bind solute + carry it across membrane
- allow protein carrier-mediated facilitated transport OR active transport
Receptor Proteins
- can bind specific extracellular molecules (= ligands) e.g. hormones, neurotransmitters (nt)
- e.g. glucose uptake:
- -insulin binds to receptor on skel. muscle or adipose tissue
- -triggers movement of more glucose transporters to cell membrane
- -⇑ glucose movement from blood into cells
Enzymes
- control chemical reactions on outer or inner surface
- e.g. acetylcholinesterase
- e.g.2: Na+/K+- ATPase - all cells have these
Joining Proteins
- control anchor cell membrane to cytoskeleton or an adjacent cell
- junctional proteins between cells forming:
- -desmosomes, tight junctions, and gap junctions
- extracellular fibers (usually glycoproteins)
Identifying Proteins
e. g. Major Histocompatibility Complex (MHC) proteins
- on surface of all cells except rbc
- identify cell as “self” (part of the body) – not foreign
Membrane Carbohydrates
- glycoproteins and glycolipids
- differs for every cell type - allow cells to recognize type e.g. sperm recognizes egg
Membrane Transport
movement of material between the intra and extra cellular fluids
Solute vs Solvent
- substance dissolved in a solution
- Solvent – substance solute is dissolved in e.g. water
-Types of transport
- Passive Transport
- Active Processes
Passive Transport
- no energy required (no ATP)
- movement from a high to low concentration (i.e. down its conc. gradient)
- the greater the difference in concentration = the more molecules want to move
Passive Transport Types
Solute movement: -Simple diffusion -Facilitated diffusion -Facilitated transport Solvent movement: -Osmosis
Simple diffusion
- solute diffuses directly through cell membrane bilayer
- small and lipid soluble molecules (O2, CO2, etc.)
Facilitated diffusion
-ions diffuse through membrane via protein channels
Facilitated transport
- large, charged or water soluble molecules
- diffuse across membrane using a specific carrier protein – must bind to protein to be transported
e. g. glucose into liver or skeletal muscle
d) Osmosis
- movement of H2O across a semipermeable membrane (permeable to H2O) due to [H2O] difference (H2O moves down it’s concentration gradient) via pores (channels) or across the membrane bilayer
- note:
- [solute] depends on the number of ions or molecules not the type
high [H2O]
low [solute] (dilute solution)
low [H2O]
high [solute] (concentrated solution)
Osmotic Pressure
- pressure that must be applied to prevent movement of H2O from a pure H2O solution (S1) across a semipermeable membrane into another solution (S2)
- the greater [solute] in solution the greater OP and lower [H2O] ⇒ water will want to move in (down gradient)
- OP is used as a measure of the [solute] of a solution
- high OP = high [solute] (low [H2O])
Tonicity
- response of a cell immersed in a solution
- depends on [solute] (and permeability of cell membrane to solute)
Tonicity classification
- Hypotonic solution
- Hypertonic solution
- Isotonic solution
Hypotonic solution
- ECF has lower OP (higher [H2O]) than ICF (cytosol)
- cell swells (takes in water) + may burst
- swelling can rupture cell = lysis
- if rbc = hemolysis
Hypertonic solution
- ECF has higher OP (lower [H2O]) than ICF (cytosol)
- cell shrinks (loses H2O)
Isotonic solution
- ECF and ICF have equal OP
- cell neither swells nor shrinks
- rbc - all [solutes] within equals a 0.9% saline solution (= normal saline)
Tonicity uses
- injecting 10% sucrose solution (hypertonic) will move water to blood stream
e. g. use to ⇓ brain edema (swelling)
Osmosis role in [Solute] regulation
- Concentration of solutes in body fluids must be maintained within narrow limits or cells will die
e. g. If body loses H2O (e.g. sweat) ⇒ ⇑ [blood] ∴ blood OP ⇑ ⇒ fluid moves from tissues to blood - response = thirst and ⇓ renal H2O loss which leads to ⇓ urine production
Major body fluids
- extracellular fluids=blood plasma, interstitial fluid
- intracellular fluid
Bulk Flow
- movement of fluid (+ solutes) due to a pressure gradient (high pressure to low pressure)
e. g. cell membrane, blood vessel wall (= blood pressure)
e. g. Capillary – if blood has higher pressure than ISF, fluid flows out of the capillary (= filtration)
hydrostatic pressure
Pressure of a fluid pressing against a surface
Active Processes
Require energy (ATP)
Active Process types
- Active Transport
- Vesicular Transport
Active Transport
- substances move against conc. gradient (low to high)
- always protein carrier-mediated
Active Transport types
- Primary (1°) Active Transport
- Secondary (2°) Active Transport
Primary (1°) Active Transport
- molecular pumps - ATP breakdown is directly part of transport process
e. g. Na+/K+-ATPase Pump – 3 Na+ out of cell and 2 K+ in per ATP
Secondary (2°) Active Transport
- cotransport (use of ATP is indirect)
e. g. glucose entry at small intestine - 2 steps: - Na+ gradient established by Na+/K+-ATPase (ATP use step)
- glucose & Na+ both must bind to carrier and are cotransported into the cell ⇒ Na+ moving down its concentration gradient drives in glucose against its concentration gradient (transport step)
Vesicular Transport
substance is surrounded by a membrane within a cell (vesicle)
Vesicular Transport types
- Endocytosis
- Exocytosis
Endocytosis
- movement into a cell
- phagocytosis or pinocytosis
Phagocytosis
- large items into cell (e.g. bacteria)
- = “cell eating”
Pinocytosis
- fluids (+ dissolved substances)
- = “cell drinking”
Exocytosis
- movement out of cell
- vesicles containing hormones, enzymes, neurotransmitters, etc.
- fuse with cell membrane releasing contents into ECF (triggered by a rise in cytosolic Ca++)
