Topic 2: Cell Physiology Flashcards
Phospholipid Bilayer
- Continuous layer around cell
- Barrier to water soluble substances - NOT to small molecules and/or lipid soluble molecules (e.g. O2 and CO@)
Membrane Proteins
1) Transport Proteins
a) Channels
b) Carrier Proteins
2) Receptor Proteins
3) Enzymes
4) Joining Proteins
5) Identifying Proteins
Channels (Transport Proteins) (Membrane Proteins)
- Form pore in membrane
- Selectively permit channel- mediated facilitated diffusion of specific ions
- Can be:
1) Gated: can open or close -in response to stimuli
2) Non-gated (= leakage channels): always open
Carrier Proteins (Transport Proteins) (Membrane Proteins)
- Blind solute + carry it across membrane
- Allow protein carrier-mediated facilitated transport OR active transport
- E.g. glucose transporters
Receptor Proteins (Membrane Proteins)
- Can bind specific extracellular molecules (=ligands) e.g. hormones, neurotransmitters (nt)
- e.g. glucose uptake:
1) insulin binds to receptor on skel. muscle or adipose tissue
2) triggers movement of more glucose transporters to cell membrane
3) Increased glucose movement from blood into cells
Enzymes (Membrane Proteins)
- Control chemical reactions on outer or inner surface
- e.g. 1: acetylcholinesterase
e. g. 2: Na+/K+ - ATPase - all cells have this
Joining Proteins (Membrane Proteins)
- Anchor cell membrane to cytoskeleton or an adjacent cell
1) Junctional proteins between cells forming: - Desmosomes, tight junctions, gap junctions
2) Extracellular fibres (usually glycoproteins)
Identifying Proteins (Membrane 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
- Differ for every cell type - allow cells to recognize type e.g. sperm recognizes egg
Membrane Transport
- Movement of material between the intra- and extracellular fluids
- Types of Transport:
1) Passive Transport
2) Active Transport
Solute
Substance dissolved in a solution
Solvent
Substance solute is dissolved in e.g. water
Passive Transport
- No energy required (no ATP)
- Movement form high to low concentration (i.e. down its concentration gradient)
- The greater the difference in concentration = more and faster the molecules will move
Types of Passive Transport
- Types:
1) Simple Diffusion (solute movement)
2) Facilitated Diffusion (solute movement)
3) Facilitated Transport (solute movement)
4) Osmosis (solvent movement)
5) Bulk Flow
Simple Diffusion (solute movement)
- Solute crosses through the cell membrane bilayer - small, lipid soluble (O2, CO2, etc)
Facilitated Diffusion (Solute movement)
- Ions diffuse through membrane via protein channels
Facilitated Transport (solute movement)
- Large, charged or water-soluble molecules
- Move across membrane using a specific carrier protein - MUST BIND to protein to be transported
- e.g. glucose into liver or skull. muscle cells
Osmosis (solvent movement)
- Movement of H2O across a semipermeable membrane (permeable to H20) due to [H2O] difference (water moves down its concentration gradient) via pores (channels) or across the membrane bilayer
Osmosis Note
- High [H20] = low [solute] - dilute solution
- low [H2O] = high [solute] - concentrated solution
- [Solute] depends on the number of ions or molecules, not the type
Osmotic Pressure (OP)
- Pressure that must be applied to prevent movement of H2O from pure H2O solution (S1) across a semipermeable membrane into another solution (S2)
Osmotic Pressure Step 1
If S2 has high [salt] (low[H2O]) then H2O will move into it –> requires pressure to stop it moving into S2
- the greater [salt] in S2, the greater the OP and lower [H2O] –> more water will move in (down its gradient) –> more P needed to stop it moving
Osmotic Pressure Step 2
If S2 also = pure H2O –> no required to prevent H2O movement (no gradient) - S2 OP = 0
- OP is used as a measure of the [solute] in a solution
- High OP = high [solute] (low [H2O]) + vice versa
Tonicity
- Response of a cell immersed in a solution
- Depends on [solute] (and permeability of cell membrane to the solute)
- Classifications:
1) Isotonic Solution
2) Hypotonic Solution
3) Hypertonic Solution
Isotonic Solution
- cell neither swells nor shrinks
- ECF and ICF have EQUAL OP
- rbc - [all solutes] in ICF = 0.9%
saline (NaCl) solution (= normal saline)
Hypotonic Solution
- Cell swells (takes in water)
- ECF has higher [H2O] (lower OP) than ICF (cytosol)
- <0.9% NaCl e.g. 0.1%
- Swelling can rupture cell = lysis
- if a red blood cell –> hemolysis
Hypertonic Solution
- Cell shrinks (loses H2O)
- ECF has lower [H2O] (higher OP) than ICF (cytosol)
- > 0.9% NaCl e.g. 1.5%
- Uses:
- injecting 10% surges solution (hypertonic) will draw water into blood from tissues
- e.g. use to lower brain edema (swelling)
Osmosis Role in Regulation of [Solute]
- Concentration of solutes in body fluids must be maintained within narrow limits or cells will die
- Major body fluids:
1) Extracellular Fluids (ECFs): - Blood Plasma
- Interstital Fluid (ICF)
2) Intracellular Fluid (ICF) - E.g. if body loses H2O (sweat) => [blood] increases
- Blood OP increases = fluid moves from tissues into blood
- Response = thirst and lower renal H2O loss which leads to decreased urine production
Bulk Flow
- Movement of fluid (+solutes) due to pressure gradient (high pressure to low pressure)
- Hydrostatic pressure = P of a fluid pressing against a surface e.g. cell membrane, blood vessel wall (= blood pressure)
Example of Bulk Flow in Capillary
- If blood has higher pressure than ISF, fluid flows out of capillary (= FILTRATION)
- If ISF is higher pressure than blood, fluid flows from ISF into capillary (= ABSORPTION) (Flowing into)
Active Processes
- Require energy (ATP)
- Types:
1) Active Transport
a) Primary Active Transport
b) Secondary Active Transport
2) Vesicular Transport
Active Transport
- Substances move against concentration gradient (low to high)
- Always protein carrier-mediated
- Theres two different types
Primary Active Transport
- Molecular pumps - ATP breakdown is a direct part of transport process i.e. ONE protein breaks ATP and transports the solute(s)
- e.g. Na+/K+-ATPase - 3 Na+ out of cell and 2 K+ in per ATP
Secondary Active Transport
- Cotransport (2 proteins involved & use of ATP is indirect) i.e. one protein breaks down ATP (creating a Na+ gradient = stored energy) and another protein transport the solute(s)
- e.g. glucose entry at small intestine - 2 steps:
1) Na+ gradient established by Na+/K+-ATPase (=ATP-use step
2) Glucose & Na+ both must bind to carrier and are cotransported into the cell –> Na+ moving down its concentration gradient drives in glucose concentration gradient (= transport step) = glucose transport is active
Example of Secondary Active Transport
- e.g. glucose entry at small intestine - 2 steps:
1) Na+ gradient established by Na+/K+-ATPase (=ATP-use step
2) Glucose & Na+ both must bind to carrier and are cotransported into the cell –> Na+ moving down its concentration gradient drives in glucose concentration gradient (= transport step) = glucose transport is active
Vesicular Transport
- Substance is surrounded by a membrane within a cell (a vesicle)
- types:
1) Endocytosis
i) Phagocytosis
ii) Pinocytosis
2) Exocytosis
Endocytosis
Endocytosis - movement into a cell i) Phagocytosis - large items into cell (e.g. bacteria) = "cell eating" ii) Pinocytosis - Fluids (+ dissolved substances) "cell drinking"
Exocytosis
Exocytosis - movement out of cell
- Vesicles containing hormone, enzymes, neurotransmitter etc.
- Fuse with cell membrane, releasing contents into ECF (triggered by a rise in cytosolic Ca2+)
