BIO 1305 Chapter 7: Membrane Structure and Function

Passive transport

Diffusion of a substance across a membrane with no energy investment.

Active transport

Uses energy to move solutes against their gradients.

phospholipids

Membranes are composed mainly of ____________________.

amphiphatic

Phospholipids are _________________ molecules, containing hydrophobic and hydrophilic regions.

hydrophobic interactions

Membranes are held together mainly by weak _______________________.

Fluidity

____________________ affects both permeability and movement of transport proteins.

Cholesterol

A membrane component in animal cells that has variable effects on membrane fluidity at different temperatures.

Proteins

Determine most of the membrane's functions.

Peripheral proteins

Proteins bound to the surface of the membrane.

Integral proteins

Proteins that penetrate the hydrophobic core.

Transmembrane proteins

Integral proteins that span the membrane.

Glycolipids

Carbohydrates bonded to lipids.

Glycoproteins

Carbohydrates bonded to proteins.

selective permeability

Membranes exhibit _______________________; some substances cross more easily than others.

Hydrophobic (nonpolar) molecules

Dissolve in the lipid bilayer and pass through the membrane rapidly.

Hydrophilic (polar) molecules

The hydrophobic interior of the membrane impedes the passage of ____________________________.

transport proteins

Hydrophilic substances cross membranes more quickly passing through ______________________.

Channel proteins

Have a hydrophilic channel that certain molecules or ions can use as a tunnel.

Carrier proteins

Bind to molecules and change shape to shuttle them across the membrane.

lipid bilayer and transport proteins

Selective permeability of a membrane is dependent on both the ______________________ and the specific ____________________ in contains.

Aquaporins

Channel proteins that greatly increase the rate of passage of water molecules.

Diffusion

Movement of particles of any substance so that they spread out evenly into the available space from an area of higher concentration to lower concentration.

concentration gradient

In passive transport (diffusion), substances diffuse down their _______________________, the region along which the density of a chemical substance increases or decreases.

Osmosis

The diffusion of free water (water molecules not clustered around another substance) across a selectively permeable membrane.

lower, higher

Free water molecules diffuse across a membrane from the region of ____________ solute concentration to the region of ___________ solute concentration.

Tonicity

The ability of a surrounding solution to cause a cell to gain or lose water; dependent on the concentration of solutes in the solution that cannot cross the membrane.

Isotonic solution

Occurs when a solution's solute concentration is the same as that inside the cell.

Hypertonic solution

Occurs when the solute concentration is greater outside the cell than inside the cell.

shrink

In a hypertonic solution, cells _________________.

Hypotonic solution

Occurs when the solute concentration outside the cell is less than that inside the cell.

swell

In a hypotonic solution, cells ________________.

turgid

A plant cell in a hypotonic solution takes up water and swells until the inelastic wall exerts back a pressure on the cell. At this point the cell is _________________ (very firm), the healthy state for most plant cells.

flaccid

Plant cells become _____________ (limp) in an isotonic solution, and the plant wilts.

lose

Plant cells ___________ water in a hypertonic environment.

plamolysis

In a hypertonic environment, plant cells shrivel and the membrane pulls away from the cell wall in multiple locations, a phenomenon called __________________. As a result, the plant will wilt and may die.

Facilitated diffusion

A process where transport proteins speed the passive movement of molecules across the plasma membrane.

Gated channels

Ion channels that open or close in response to a stimulus.

shape change

Carrier proteins undergo a subtle ________________________ that moves the solute binding site across the membrane.

ATP hydrolysis

Active transport requires energy, usually in the form of ________________________, to move substances against their concentration gradients.

carrier transport

All proteins involved in active transport are ________________________.

Membrane potential

The voltage across a membrane.

Voltage

Created by differences in the distribution of positive and negative ions across a membrane.

Cations

_______________ are transported into the cells (the inside of the cell is negative in charge).

Anions

______________ are transported out of the cells, as the inside of the cell is negative relative to the outside.

Electrochemical gradient

Two combined forces that drive the diffusion of ions across a membrane.

Electrogenic pump

A transport protein that generates voltage across a membrane, storing energy that can be used for cellular work.

Sodium-potassium pump

The main electrogenic pump in animals.

Proton pump

The main electrogenic pump in plants, fungi, and bacteria, which actively transports hydrogen ions out of the cell.

Cotransport

Occurs when active transport of a solute indirectly drives transport of other substances.

Exocytosis

Process where transport vesicles migrate to the membrane, fuse with it, and release their contents outside the cell.

Endocytosis

Process where macromolecules are taken into the cell in vesicles.

Phagocytosis

Type of endocytosis where a cell engulfs a particle by extending pseudopodia around it and packing it in a membranous sac called a food vacuole.

Pinocytosis

Type of endocytosis where molecules are taken up when extracellular fluid is "gulped" into tiny vesicles.

Receptor-mediated endocytosis

Type of endocytosis where vesicle formation is triggered by solute binding to receptors.