Export Campbell Biology: Chapter 7

Plasma membrane

The boundary that separates the living cell from its surroundings

Selective permeability

_________ ____________ is a characteristic of cell membranes that means what passes in and out is regulated. It allows some substances to cross the membrane more easily than others.

Amphipathic

Having characteristics of being hydrophobic and hydrophilic, such as a phospholipid.

Phospholipid

The basic structural component and most abundant lipid of cell membranes is ____________.

Fluid Mosaic Model

Describes a membrane as a fluid structure with a "mosaic" of various proteins embedded in it.

Osmosis

The diffusion of water across a selectively permeable membrane.

Diffusion

A passive process that involves the movement of substances or molecules from high solute concentration to low. It is also the tendency for molecules to spread out evenly into the available space.

Active transport

Uses energy (usually in the form of ATP) to move solutes against their concentration gradients and to maintain concentration gradients that differ from their surroundings, i.e. sodium-potassium pump.

Electrogenic pump

An ion transport protein that generates voltage across a membrane.

Endocytosis

The cell takes in macromolecules by forming vesicles from the plasma membrane.

Phagocytosis

Also known as cellular eating. A cell engulfs a particle in a vacuole.

Pinocytosis

Also known as cellular drinking. Molecules dissolved in droplets are taken up when extracellular fluid is "gulped" into tiny vesicles.

Receptor-mediated endocytosis

Special receptor proteins catch molecules and bring them into the cell against a concentration gradient

Exocytosis

Transport vesicles migrate to the

membrane, fuse with it, and release their contents outside the cell

Cotransport

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

Peripheral proteins

Proteins bounded to the surface of the membrane.

Integral proteins

Proteins that penetrate the hydrophobic core.

Transmembrane proteins

Proteins that span the membrane.

What are the 6 major functions of membrane proteins?

Transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, and attachment to the cytoskeleton and extracellular matrix (ECM)

Hydrophobic (nonpolar) molecules

Can dissolve in the lipid bilayer and pass through the membrane rapidly, such as hydrocarbons.

Hydrophilic molecules

Do not cross the membrane easily, such as ions and polar molecules.

Transport proteins

Allow passage of hydrophilic substances across the membrane.

Channel protein

A type of transport protein that has a hydrophilic channel that certain molecules or ions can use as a tunnel.

Aquaporins

Channel proteins that facilitate the passage of water.

Carrier protein

A type of transport protein that binds to molecules and changes shape to shuttle them across the membrane.

Passive transport

The diffusion of a substance across a membrane with no energy investment.

Concentration gradient

The region along which the density of a chemical substance increases or decreases.

Tonicity

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

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.

Osmoregulation

The control of solute concentrations and water balance that is a necessary adaptation for life in such environments.

Turgid

A plant cell in a hypotonic solution swells until the

wall opposes uptake; the cell is now turgid (firm).

Flaccid

If a plant cell and its surroundings are isotonic,

there is no net movement of water into the cell;

the cell becomes flaccid (limp).

Plasmolysis

A process in which plant cells lose water in a hypertonic environment, making the membrane pull away from the cell wall and causing the plant to wilt.

Facilitated diffusion

Transport proteins speed the passive movement of molecules across the plasma membrane. I describe the passive assistance of a transport protein to move substances from high solute concentration to low. I require no energy expenditure, instead using transport proteins to pass through membranes. What am I?

Ion channels

Channel proteins that facilitate the diffusion of ions.

Gated channel

A type of ion channel that opens or closes in response to a stimulus.

Electrochemical gradient

Two combined forces that drive the diffusion of ions across a membrane: A chemical force (the ion's concentration gradient) and an electrical force (the effect of the membrane potential on the ion's movement).

Sodium-potassium pump

The major electrogenic pump of animal cells

Proton pump

The main electrogenic pump of plants, fungi, and bacteria

What is the purpose of electrogenic pumps?

To help store energy that can be used for cellular work

Bulk transport

Occurs by exocytosis and endocytosis and requires energy

How do small molecules and water enter or leave the cell?

Through the lipid bilayer or via transport proteins

How do large molecules, such as polysaccharides and proteins, cross the membrane?

In bulk via vesicles

What are the 3 types of endocytosis?

Phagocytosis, pinocytosis, and receptor-mediated endocytosis