BIOL 1020 Chapter 7

Fluid Mosaic Model

Amphipathic

membranes that have both a hydrophilic and hydrophobic region

• hydrophobic tails

• hydrophilic heads

Glycoproteins

Embedded with the membrane and have a sugar molecule attached

• used for cell recognition and signaling

Integral Proteins

penetrate fully through the membrane

Peripheral Proteins

loosely bounded to the surface of membrane or part of an integral protein

Functions of Proteins

• transport

• signaling

• cell-to-cell recognition

• intercellular joining

• attachment to cytoskeleton

Passive Transport

Diffusion (net movement) across a membrane from high to low concentration

• no energy

• gradient represents potential energy

Osmosis

the diffusion of free water across a selectively permeable membrane

• water moves from areas of high solute concentration to low

Osmotic Pressure

tendency of water to move into the solution

Tonicity

the ability of a surrounding solution to cause a cell to gain or lose water

• compares two solutions

Isotonic

• Same osmotic pressure

• no net movement of water

Hypertonic

• higher osmotic pressure

• water flows into a solution

Hypotonic

• lower osmotic pressure

• water flows out of a solution

Turgor Pressure

the force within plant cells where water inside cell pushes the membrane against the cell, keeping cell rigid by providing structural support

Turgid

• very firm plant cell

• healthy state

• kept by being in a hypotonic solution

Flaccid

• limp

• happens when plant is in an isotonic solution

Plasmolysis

• cell membrane pulls away from wall

• leads to cell death

• occurs in a hypertonic solution

Facilitated Diffusion

polar molecules and ions travel through membrane with the help of a transport protein

• ions and large molecules (glucose)

• no energy

Active Transport

• uses energy to pump solute against its gradient

• allows cell to maintain internal concentrations

• sodium potassium pump

Sodium Potassium Pump

• active transport via ATP

• linked co-transport

• cell moves 3 Na⁺ out and 2 K⁺ in

• ions are transported down their concentration gradient

• causes an electrochemical gradient

Charge of the cytoplasmic side

relatively negative

Electrochemical Gradient

The two forces that drive diffusion of ion

• chemical force: ion’s gradient

• electrical force

Proton Pump

electrogenic pump where protons (H+) are transported out of the cell

Cotransport

the coupling of “down hill” diffusion of one substance to the “uphill” transport of another against its own gradient

• uses a co-transporter

Exocytosis

Fusion of vesicles with plasma membrane that results secretion of molecules outside of the cell

• often packaged from Golgi

Endocytosis

Cell takes in molecules by forming new vesicles from plasma membrane

Phagocytosis

• “cell eating”

• cell engulfs large particles by extending pseudopodia around and packing it within a membranous sac

Pinocytosis

• “cell drinking”

• smaller molecules (fluid) is gulped up into tiny vesicles

Receptor-mediated endocytosis

specialized types of pinocytosis that acquires bulk quantiles of specific substances

• receptor proteins bind to molecules, causing protein to change shape