Calculating Water Potential
Ψ = Ψs + Ψp
Calculating Solute Potential
Ψs = -iRCT
The # of particles the molecule will make in water
Molar Conentration (from experimental data)
Pressure Constant = 0.0831 liter bar/mole K
Temperature in degrees Kelvin = 273 + C° of solution
Lipids (phospholipids, cholesterol), proteins, carbohydrate groups.
Made of glycerol, two fatty acid tails, and a phosphate-linked head group.
→A phospholipid bilayer involves two layers of phospholipids with their tails pointing inward
Lipid composed of four fused carbon rings
→Found alongside phospholipids in the core of the membrane.
Primary Active Transport
Directly uses a source of chemical energy (e.g., ATP) to move molecules across a membrane against their gradient
Secondary Active Transport
Uses an electrochemical gradient – generated by active transport – as an energy source to move molecules against their gradient
→Does not directly require a chemical source of energy such as ATP
The Sodium-Potassium Pump Cycle
Moves Na+ out of cells and K+ into them
1. The pump is open to the inside of the cell and binds/takes up 3 Na+ ions
2. Once the Na+ ions bind, the pump is triggered to hydrolize ATP. One P-group is attached to the pump, and then phosphorylated. ADP is released as a by-product.
3. Phosphorylation causes the pump to change form so that it then faces the exterior of the cell. Like this, the pump no longer has an affinity for Na+ ions, and 3 are released.
4. Facing this direction, the pump now has an affinity for K+ ions. It binds 2 of them which triggers the release of the P-group attached to the pump.
5. With the P-group gone, the cell once again changes form and then faces towards the interior of the cell.
6. The pump is now back to step 1, and the cycle repeats.
The sodium-potassium pump acts primarily by building up a high concentration of potassium ions inside the cell, which makes potassium’s concentration gradient very steep. The gradient is steep enough that potassium ions will move out of the cell (via channels), despite a growing negative charge on the interior. This process continues until the voltage across the membrane is large enough to counterbalance potassium’s concentration gradient. At this balance point, the inside of the membrane is negative relative to the outside. This voltage will be maintained as long as K+concentration in the cell stays high
may be engulfed when no longer needed
cells with genetic damage are replaced
defense against infection
signals trigger caspases to carry out apoptosis
Hypotonic vs Isotonic vs Hypertonic
Isotonic solution: Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane
Hypertonic solution: Solute concentration is greater than that inside the cell; cell loses water
Hypotonic solution: Solute concentration is less than that inside the cell; cell gains water
Cells without cell walls will shrivel in hypertonic solution and lyse (burst) in a hypotonic solution
Phospholipids are ampipathic because of their hydrophilic, polar heads and hydrophobic, nonpolar tails.
The hydrophilic heads of phospholipids in a membrane bilayer face outward, contacting the watery fluid both inside and outside the cell. Since water is a polar molecule, it readily forms electrostatic interactions with the phospholipid heads.
Phospholipids tuck their fatty acid tails away in the interior of the membrane, where they are shielded from the surrounding water.
The hydrophobic core of the plasma membrane helps some materials move through the membrane, while it blocks the movement of others
Polar molecules can easily interact with the outer face of the membrane, where the negatively charged head groups are found, but they have difficulty passing through its hydrophobic core
While small ions are the right size to slip through the membrane, their charge prevents them from doing so. Instead, they must be transported by special proteins.
Larger charged and polar molecules, like sugars and amino acids, also need help from proteins
where rRNA & ribosomes are synthesized
regulates protein traffic+metabolic functions
holds chromatin, surrounded by nuclear envelope
Rough: makes proteins Smooth: synthesizes lipids, stores Ca++, detoxifies drugs/poisons
processes, packages, & secretes substances
powerhouse of the cell
storage & pumping out water
absorbs light & synthesize sugar
maintains cell shape, flow, positioning
organize spindle fibers (cell division)
protects, maintains shape, regulates water intake
break down fatty acids to be used for forming membranes and as fuel for respiration, transfer hydrogen from compounds to oxygen to create hydrogen peroxide and then convert hydrogen peroxide into water
Osmosis & Tonicity
Osmosis is the movement of water through a semi-permeable membrane from a region of high concentration to a region of low concentration, tending to equalise the concentrations of the water.
Osmosis is passive transport, meaning it does not require energy to be applied.
The ability of an extracellular solution to make water move into or out of a cell by osmosis is know as its tonicity.
A solution's tonicity is related to its osmolarity, which is the total concentration of all solutes in the solution.
A substance moves from an area of high concentration to low concentration until its concentration becomes equal throughout a space
Molecules diffuse across the plasma membrane with assistance from membrane proteins, such as channels and carriers
A concentration gradient exists for these molecules, so they have the potential to diffuse into (or out of) the cell by moving down it. However, because they are charged or polar, they can't cross the phospholipid part of the membrane without help. Facilitated transport proteins shield these molecules from the hydrophobic core of the membrane, providing a route by which they can cross.
Channel proteins span the membrane and make hydrophilic tunnels across it, allowing their target molecules to pass through by diffusion
Very selective and will accept only one type of molecule for transport
Aquaporins are channel proteins that allow water to cross the membrane very quickly, and they play important roles in plant cells, red blood cells, and certain parts of the kidney
Play an important role in electrical transmission along membranes (in nerve cells) and in muscle contraction (in muscle cells)
Change their shape to move a target molecule from one side of the membrane to the other
Will change shape in response to binding of their target molecule, with the shape change moving the molecule to the opposite side of the membrane
Provide hydrophilic molecules with a way to move down an existing concentration gradient (rather than acting as pumps)
Types of Cell Communication
monitors bacteria population density & controls gene expression
produced & used by same cell
physically touching cells (gap junctions, plasmodesmata)
adjacent (not touching) cells (synapses, growth factors)
for all tissues, long distance (hormones)
Prokaryote vs Eukaryote
no internal membranes/organelles
DNA forms chromosomes
anaerobic or aerobic metabolism
no cytoskeleton present