Body Composition and Cell Membranes Flashcards
Vertebrate Body Composition
- ECF
- Specialized compartments of ECF
- Intracellular fluid
- ECF: body fluid that surrounds cells (the internal environment)
- protects most cells from external environment
- regulating ECF = regulation of internal enviro
- many specialized ECF compartments – lymph, cerebrospinal fluid, synovial fluid, serous fluid
- Intracellular fluid: separate from extracellular fluid by plasma membrane
Divisions of Total Body Water
Total body water= Intracellular fluid (66%) + Extracellular Fluid (33%)
Extracellular fluid = Plasma (20% ECF - has glucose, albuminum and electrolytes) + Interstitial fluid (80% ECF - surrounds cells & gets into tissue)
Body Composition
-Main components and other smaller constituents
- 66% water
- 16% fat
- 16%protein
- Glycogen, Phosphorus, Calcium, sodium, potassium, Mg, Fe, Cl, Zn, Cu
Definitions;
- Solutes
- types of solutes (2) and features/e.g.
- Solvents
- Solution
- Osmolarity
- Solutes: Substances dissolved in liquid
- Electrolytes; Dissociate into charged ions in H2O, Ionic bonds, can conduct electricity, Include inorganic salts, inorganic and organic acids and bases, some proteins.
- Non-electrolytes: Do not dissociate in water, covalent bonds (much stronger), not electrically charged, mostly organic molecules.
- Solvents: liquids in which solutes dissolve (water)
- Solution: Combination of solutes dissolved in solvents
- Osmolarity: Total number of particles/litre of solution
Solute Composition of ECF & ICF
(Na, Cl, HCO3, K, Protein)
-Plamsa composition
- Most electrolytes (Na, Cl, HCO3) higher concentration outside of cell (interstitial and plasma)
- Only K and proteins are at higher concentration inside cell
- ECF (plasma and Interstitial fluid) also has high concentrations of nutrients, fatty acids, glucose and wastes
-Plasma has similar composition to interstitial fluid, but more protein
ICF/ECF boundary
- Between Plasma and Interstitial fluid = Leaky epithelium
- Between Interstitial fluid and intracellular fluid = Cell membrane
Cell membrane vs plasma membrane
Cell membrane: may refer to many different membranes w/in cell
Plasma membrane: membrane encompassing the cell
4 Functions of Plasma membrane
- Physical isolation
- Regulation of exchange with environment (controls movement of ions, gases, wastes)
- Communication between cell and environment
- Structural support
Structure of Plasma Membrane
-why fluid mosaic model
- Fluid-mosaic model
- Thin phospholipid bilayer (7-8nm)
- w/ polar P heads facing outwards and nonpolar tails inwards
- Lipids and proteins inserted throughout - can move laterally
2 Major components of Plasma membrane
-and 2 subclasses of each
*lipid:protein ratio
- Protein
i. Integral (Embedded w/in)
ii. Peripheral (Sit on edge - don’t penetrate) - Lipids
i. Phopholipids (i.e. bilayer)
ii. Cholestrol (Aids in lipophilic/hydrophobic nature)
- Rations of lipid:protein in membrane depend on type of membrane
- more metabolically active = more protein
- more cholesterol = more control of water movement
Phospholipids vs cholesterols
-Polarity, Location in bilayer, Functional role
Phospholipids; -hydrophobic tail and hydrophilic head
- two layers, heads outwards - main structural component of lipid bilayer, polarity stops flipping but allows lateral fluidity, polarity promotes membrane repair
Cholestrols (~20% membrane lipid): Completely hydrophobic
- Found in the middle of bilayer - Increases membrane flexibility, decreases water permeability, restricts migration to lipid-soluble molecules
Integral Proteins vs Peripheral proteins
- where found in membrane
- e.g.
Integral: tightly bound in phospholipid layer, Extend into/through layers
-includes membrane channels and transporters
Peripheral: Attach loosely to integral proteins or phospholipid head, can be removed w/out disrupting flexibility
-Include enzymes and structural proteins
*many different types of proteins in a phospholipid bilayer
4 Functions of Membrane Proteins
- Structure: connect membrane and cytoskeleton to maintain shape of cell
- collagen in ECM
- Enzymes: catalyse reactions on internal or external surface of cell
- brush border peptidases in gut
- Receptors: activate biochem pathways in response to binding of ligands (transmitters, hormones)
- e.g. insulin binding to insulin receptor
- Transporters: Membrane proteins are responsible for regulating what gets in and out of cell
- allow molecules that could not diffuse across cell membrane to enter
Glycocalyx
- what it is
- where found
- why it’s important
- Carbohydrate-containing molecules, w/ branching sugar groups
- Found on extracellular membrane surface
- Carbohydrate chains bind to either membrane lipids or integral membrane proteins
*pattern of sugars is cell-type specific -> important for cell recognition
Membrane Heterogeneity
e.g. Lipid rafts and Homeoviscous adaptation
- Is significant structural variation between diff. regions of same membrane
e. g. Lipid rafts: thickened regions of membrane containing higher density of cholesterol, glycolipids and intergal proteins
- form spatially-segregated, functional micro-compartments w/in cell
e. g. Homeoviscous adaptation: Many factors change membrane fluidity - can change membrane fluidity by changing lipid composition
Structures made from Bilayer (2)
-Extra uses for one of extra structures
- Micelle: sphere: no internal fluid component
- Liposome: sphere with small cavity; can be filled with hydrophilic substance
Center of liposomes filled w/ drugs, antibodies or DNA fragments
- can reduce toxicity and improve efficacy of drug
- liposomes w/ multiple shells can release drugs in pulsatile manner
Diffusion
- defn
- driving force
- type of gradient
- what rate depends on
- Diffusion: movement of molecules from area of higher concentration to one of lower concentration of the molecule
- molecules above 0 K have constant state of motion
- driving force for diffusion is kinetic energy = electrochemical gradient
- rate depends on magnitude of concentration difference
7 properties of diffusion
- Move from area of higher concentration to lower concentration
- Is a passive process
- Net movement until concentration is equal everywhere
- Diffusion is rapid over short distances, but much slower over long distances
- Directly related to temperature (higher temp = faster diffusion)
- Inversely related to molecule size
- Can occur in an open system or across a partition
Simple Diffusion
- definition
- what kind of molecules can transverse
- water - can it pass through
- Simple Diffusion: Diffusion directly across phopholipid bilayer of a membrane
- Size and lipid solubility/polarity determine movement across a membrane (hydrophilic molecules tend to be lipophobic)
- Very small/lipid-soluble substances can cross directly
- Larger/less lipid soluble molecules excluded from transfer
- Size and lipid solubility/polarity determine movement across a membrane (hydrophilic molecules tend to be lipophobic)
- water (altho polar) can cross some membranes due to small size -> but membranes w/ high cholesterol content is impermeable
Simple diffusion
-3 things that dictate rate
- Rate directly proportional to surface area of the membrane (larger SA, greater diffusion)
- Rate inversely proportional to thickness of membrane (thicker = slower)
- Rate depends on ability of molecule to pass through the membrane lipid layer
Simple Diffusion; Fick’s Law
-Describes the diffusion coefficient of a solute that is influenced by its structural properties
dQs/dt = Ds x A x dC/dX
Rate of diffusion of solute per unit time = diffusion coefficient of solute x diffusion area x concentration gradient
Mediated transport - Types of carriers
- definition
- 3 types
- Mediated transport for molecules that are too polar to dissolve in bilayer and pass through
1. Uniport carriers: transport only one kind of substrate in one direction
2. Symport carriers: Move two or more substrates in the same direction across the membrane
3. Antiport carriers: Move substrates in opposite directions - symport and antiport = cotransporters
3 types of proteins involved in Mediated transport
-few features of each
- Ion channels: H20 filled channels linking ICF/ECF compartments
- formed by aa cylinders
- allows movement of H20 and specific ions (via selective electrical charge)
- Membrane channels have regions that act as gates
- Porins: larger channels that move larger molecules
- aquaporins rapidly move water molecules
- Permeases: bind a substrate, causes a very temporary conformational change - releases the substrate into the other side
- e.g. glucose, a.a.
- also called carrier proteins
* all allow facilitated diffusion
2 types of proteins involved in Facilitated diffusion
- Channel proteins: H20 filled channels linking ICF/ECF compartments
- Carrier proteins: No direct connection between ICF/ECF (slower, but more discriminatory)
3 Factors that determine Rate of Facilitated Diffusion
- The transport rate of individual carriers (e.g. glucose transporters - 10 000/sec)
- The number of carriers or channels in the membrane
- Magnitude of the concentration (or electrochemical) gradient of the transported substance
3 Properties of Facilitate diffusion
- Specificity: ability to only move one molecule or family of molecules (e.g. 6C or 5C sugars)
- Competition: relates to affinity of molecule binding to the transporter
- glucose and galactose transported on same protein, but higher affinity for glucose
- Competitive Inhibition: maltose blocks glucose transport in small intestine (maltose = 2 x glucose -> blocks transporter)
- Saturation: when transporters are functioning at maximum capacity
Active Transport
- definition
- 2 factors that rate depends on
- Active Transport: moves molecules across a membrane against a concentration gradient
- requires input of energy in form of ATP’s high-energy phosphate bonds
- Rate depends on;
i) Rate of pump
ii) Number of pumps in the membrane
Primary Active Transport
- what it is
- e.g. and what results
- Primary active transport: Utilizes energy in the form of ATP
- Na-K pump most important (crucial to maintain electrochemical gradients)
- Both Na and K move against their concentration gradients
- [K] high, [Na] low inside (opposite true for extracellular fluid)
- pumps 3 Na out and 2 K into cell per ATP hydrolysed
- inside of cell becomes less positive
Steps of Na/K pump
- 3 Na and 1 ATP bind to protein pump (causes a change in conformation of pump)
- ADP released, cause change in pump’s shape (P attached to pump still)
- 3 Na released as 2 K bind to pump
- P released from pump, causing change in pump’s shape and release of 2 K
- Process recommences
Secondary Active transport
- what it is
- what usu driven by
- Couples the kinetic energy of one molecule moving down its concentration gradient, to the movement of another molecule moving against its concentration gradient
- one molecule drags other across
- can be symport or antiport
- most driven by Na conc gradient
- as Na enters cell, it brings molecule/s w/ it or exchanges w/ molecules exiting cell
2 types of electrochemical gradients
- Chemical Gradients
- Electrical gradients (ions)
Secondary Active Transport
-Na-Glucose linked tranport
- When carrier open to ECF, has high-affinity binding site for Na and low-affinity site for glucose
- Sodium bind to his surface due to high conc of Na outside
- Proteins often change shape when their chemical enviro changes
- Na binding created a high affinity binding site for glucose, its unbinding can cause the loss of that affinity and glucose is released (inside of cell)
Transepithelial Transport
- Movement of molecules across two membranes
- uses passive and active transport
Epithelial exchange
- features
- Basolateral and apical
- e.g.
- Surface of epithelium facing lumen is apical (mucosal) surface
- bottom part of cells in contact with ECF = Basolateral (serosal) surface
- have tight junctions that act as cement - molecules MUST go through cells
- bottom part of cells in contact with ECF = Basolateral (serosal) surface
- Transporting epithelial cells are polarised (apical and basolateral surfaces have different transportation properties due to uneven distribution of membrane proteins on surfaces)
- allows directional transport of material
e. g. Na/K ATPase found in basolateral membrane, while Na-Glucose symporter found in apical membrane
Movement of molecules using Protein across epithelia
-2 steps
- If molecule can be transported through protein channel/carrier protein, usu 2 step process;
1) An uphill step requiring energy
2) Downhill step in which molecules move passively down concentration gradient
*e.g. transport of glucose across an epithelium
3 transport systems involved in Transporting across epithelia (using e.g of glucose)
- what is required to happen for glucose to be continually absorbed
- Osmotic gradient - its role
1) Active transport: of Na across basolateral surface by Na-K ATPase pump
2) Secondary Active transport of glucose with Na from lumen into cell at apical membrane
3) Facilitated diffusion of gluocse across basolateral surface and into the ECF (eventually into blood supply)
- removal of Na necessary for continued glucose absorption (Na-glucose symporter relies on low intracellular Na)
- Osmotic gradient is another feature of epithelial solute transport -> water transport often said to be secondary to solute transport
Osmosis
- definition
- 2 factors affect energy lvl
- Osmosis: The movement of water from areas of high concentration to areas of low concentration through a selectively permeable membrane
- 2 most important factors affecting energy level in H2O;
- Amount of solutes dissolved in water
- Physical pressure/tension exterted on water (hydrostatic pressure)
Osmosis
-Water concentration and solute concentration
- Water conc and solute conc are inversely related
- the no. of solute particles determines conc of H2O
- in osmosis, water moves across membrane to dilute area of higher solute concentration (presence of solutes reduces H2O concentration)
Osmolarity vs osmolality
*eqn for osmolarity
- Osmolarity: osmoles (total concentration of all solute particles) per litre of solute (Osm/L)
- Osmolality: Osmoles per kg of solution (Osm/kg)
- largely interchangeable, but osmolality not used for us
Osmolarity = Molarity (M) x no. of particles/molecules w/in solution
*says nothing about the NATURE of particles in solution
Total solute conc of ICF and ECF in living cells
-280-300 mM
Membrane permeability on Osmosis and diffusion
- Membrane where solutes can move through = no change in water level in U tube
- Impermeable membrane to solutes = water movement only and water lvl changes in U tube (explains why osmotic pressure has units of mmHg (like gravity))
Three rules of Osmotic pressure
1) OP increases as solute conc increases
2) OP depends on total solute conc (NOT molecular identities)
3) OP greater in solutions w/ ionised molecules
Describing Osmolarity in relation to cells
- Iso-osmotic: solution equivalent on both sides of cell
- Hyper-osmotic: greater osmolarity in surrounding solution than that of cells
- Hypo-osmotic: Less osmolarity in surround solution than that of cells
Osmolarity vs Tonicity
- Osmolarity: Takes into account the total conc of penetrating solutes and non-penetrating solutes
- has absolute values
- Tonicity: Takes into account the total concentration of only non-penetrating solutes
- solutions tonicity is not affected by the concentration of permeable solutes
- always compares a cell and a solution (has no absolute values)
Tonicity;
-Hypertonic, isotonic and Hypotonic
- Hypertonic: In this solution, cells lose H2O and shrink (crenate)
- cells have lower concentration of impermeable solutes than solution
- Isotonic: H2O moves out and in of cell at same rate
- Hypotonic: Cells swell and will eventually burst -> cells have high conc of impermeable solutes than solution
