PHYS335: Lab 2

Nucleus

part of the cell where DNA/RNA are kept and the location of the transcription process

Cytoplasm

part of the cell that contains cytosol and organelles (i.e. intracellular fluid, membrane bound organelles, and fluid within them)

Cytosol

intracellular fluid EXCLUDING organelles

Plasma membrane

separates extracellular fluid and intracellular with a selective layer comprised of a lipid bilayer; has selective gate-keeping and barrier properties

Lipid bilayer

the plasma membrane is one of these; a double layer of lipids containing embedded proteins

Phospholipid

amphipathic; hydrophilic head and hydrophobic tail

Integral protein

protein in lipid bilayer that has substantial interaction with hydrophobic tail and is stable (ex: transmembrane protein)

Peripheral protein

protein of lipid bilayer that only interacts with hydrophilic head group of bilayer

Cholesterol

plays important role in lipid bilayer by keeping phospholipids together (packs tightly while maintaining fluid mosaic model)

• Diffusion (directly though lipid bilayer, protein channel, of water)

• mediated transport systems (facilitated diffusion, primary active transport, secondary active transport)

• vesicular transport (endocytosis/exocytosis)

How can solutes be moved across plasma membrane?

Diffusion

random thermal motion of molecule from region of high concentration to lower concentration

best for moving substances within cell cytoplasm, to/from capillaries, and amongst cells

CANNOT saturate

Net flux

pertaining to diffusion, total movement down a concentration gradient, though some solute may randomly move from low concentration to high

Diffusion equilibrium

pertaining to diffusion, when net flux = 0, but diffusion is still occurring

Increase

As permeability of a substance increases, diffusion rates ___.

Increase

As membrane surface area increases, diffusion rates ___.

Increase

As the concentration gradient across a membrane increases, diffusion rates __.

Increase

As temperature increases, diffusion rates ____.

Decrease

As molecular weight/size increases, diffusion rates __.

Decrease

As membrane thickness/distance diffused increases, diffusion rates ___.

Hydrophobic core; hydrophobic and nonpolar substances diffuse easily

What part of the plasma membrane determines selective permeability?

Ion channel

have water filled hydrophilic core from linear amino acid sequence folds

selectivity controlled by linear amino acid sequence; can gate (open/closed)

Facilitated diffusion

increase concentration of solute in ECF increases probability of binding to high affinity site (ex: glucose entry into most body cells)

energy supplied by solute concentration, certain shape-based (binding site) selectivity, and CAN saturate

Primary active transport

net flux against concentration gradient, required energy provided by hydrolysis of ATP (ex: Na+/K+ ATPase pump found in every cell)

certain selectivity, CAN saturate

1. Na+ binds 3 high affinity binding sites at the same time as ATP association

2. ATP is hydrolyzed, ADP diffuses away

3. Hydrolysis reaction causes confirmation change to pump Na+ out into ECF

4. K+ binds 2 high affinity sites as phosphate released

5. Final confirmation change occurs, pumping K+ into ICF

How does the Na+/K+ ATPase pump work?

• ICF = 15mM Na, 150 mM K

• ECF = 145mM Na, 5mM K

What is Na/K gradient in mM?

Na+/K+ ATPase pump; kidney

___ regulates ICF Na/K concentration, __ regulates ECF Na/K concentration.

Secondary active transport

energy from concentration gradient utilized to move a second solute (usually paired with Na+)

net flux against concentration gradient (ex: glucose/amino acid movement with Na+)

NO ATP use, certain selectivity, CAN saturate

Cotransport

pertaining to secondary active transport, Na+ and other solute moving in same direction

ex: glucose, amino acids

Countertransport

pertaining to secondary active transport, Na+ and other solute moving in different directions

ex: Ca2+, H+

Osmosis

net movement of water across a membrane through aquaporins; always towards MORE solute

Tonicity

describing ECF relative to ICF with regards to nonpenetrating solutes

Nonpenetrating solute

hydrophilic, cannot cross plasma membrane

Isotonic solution

solution that has no change in cell volume

Hypertonic solution

solution in which cell shrinks

Hypotonic solution

solution in which cell swells

Endocytosis

vesicular transport entering cell (ex: protein complex of thyroid cell)

requires energy, many membrane proteins, and allows bulk movement

Exocytosis

vesicular transport exiting cell (ex: exiting chemical messengers of nerve cells)

requires energy, many membrane proteins, and allows bulk movement