Biology, Chap.#5: The Working Cell

Fluid Mosaic

A discription of membrane structure, depicting a cellular membrane as a mosaic of diverse protein molecules embedded in a fluid bilayer made of phospholipid molecules

Selective permeability

allow some substances to cross more easily than others


The tendency for particles of any kind to spread out evenly in an available space, moving from where they are more concentrated to regions where they are less concentrated

Concentration gradient

An increase or decrease in the density of a chemical substance in an area.

Passive transport

The diffusion of a substance across a biological membrane, without any input of energy


The diffusion of water across a selectively permeable membrane, a type of passive transport


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

Isotonic solution

A solution having the same solute concentration as nother solution, thus having not effect no passage of water in or out of the cell.

Hypotonic solution

A solution with a solute concentration lower than that of the cell. The cell gains water, swelles and may burst like an overfulled balloon.

Hypertonic solution

A solution with a higher solute concenration. The cell shrivels and can die from water loss


Control of water balance

Facilitated diffusion

When one of these proteins makes it possible for a substance to move down its concentration gradient


Rapid diffusion of water into and out of certain cells, such as plant cells, kidney cells, and red blood cells is made possible by them

Active transport

A cell has to expend energy to move a solute against its concentration gradient-that is, across a membrane toward the side where the solute is more concentrated.


A process a cell uses to export bulky materials such as proteins or polysaccharides


A cell takes in substances. A depression in the plasma membrane pinches in and forms a vesicle enclosing material that had been outside the cell. There are 3 types


A cell engulfs a particle by wrapping extensions called pseudopodia around it and packaging it within a membrane-enclosed sac large enough to be called a vacuole.


The cell "gulps" droplets of fluid into tiny vesicles. It takes in any and all solutes dissolved in the droplets

Receptor-mediated endosytosis

Receptor proteins for specific molecules are embedded in regions of the membrane that are lined by a layer of coat proteins.


The capacity to perform work

Kinetic energy

The energy of motion. Work is performed when an object is moved against an opposing force, such as gravity or friction


Thermal energy, is a form of kenetic energy associated with the random movement of atoms or molecules

Potential energy

Stored energy that an object possesses as a result of its location or structure.

Chemical energy

Refers to the potential energy available for release in a chemical reaction


study of energy transformation that occur in a collection of matter

First law of thermodynamics

The energy in the universe is constant. Energy can be transferred and transformed, but it cannot be created or destroyed

Second law of thermodynamics

During every energy transfer or transformation, some energy becomes unusable-unavailable to do work. The law is that energy conversions increase the entropy (disorder) of the universe.


A measure of disorder, or randomness

Exergonic reaction

A chemical action that releases energy.

Cellular respiration

A chemical process that uses oxygen to convert the chemical energy strored in fuel molecules to a form of chemical energy that the cell can use to perform work

Endergonic reactions

Yield products that are rich in potential energy


The total of an organism's chemical reactions.

Metabolic pathway

A series of chemical reactions that either builds a complex molecule or breaks down a complex molecule into simpler compounds.

Energy coupling

The use of energy released from exergonic reactions to drive essential endergonic reactions

ATP (adenosine triphosphate)

Powers nearly all forms of cellular work. Consists of adenine, a nitrogenous base, and ribose


The transfer of a phosphate group, usually from ATP, to a molecule.

Energy of Activation

The amount of energy needed to push the reactants over an energy barrier, or "hill," so that the "downhill" part of the reaction can begin


Proteins that function as biological catalysts


A specific reactant on which an enzyme acts. Each enzyme recogizes only the specific substrate or substrates of the reaction it catalyzes

Active site

The part of an enzyme molecule where a substrate molecule attaches (by means of weak chemical bonds); typically, a pocket or groove on the enzyme's vaccine

Induced fit

The active site changes shape slightly so that it embraces the substrate more snugly, like a firm handshake


A nonprotein molecule or ion that is required for the proper functioning of an enzyme. Often inorganic, nonprotein helpers such as zinc, iron, or copper


An organic molecule serving as a cofactor. Most vitamins function as coenzymes in important metabolic reactions

Competitive inhibitor

Reduces an enzyme's productivity by blocking substrates from entering the active site

Noncompetitive inhibitor

Does not enter the active site. Instead, it bind to the enzyme somewhere else, and its binding changes the shape of the enzyme so that the active site no longer fits the substrate

Feedback inhibition

Whereby a metabolic control in which a product of a metabolic pathway acts as an inhibitor of an enzyme within that pathway

Steroid cholesterol helps

wedge into the bilayer, helps to stabilize the membrane at warm temperatures but also helps keep the membrane fluid at lower temperatures

Function of membrane proteins...

Some give the membrane a stronger framework (integrins) and glycoproteins are involved in cell-cell recognition

Many carbohydrates function as...

Id. tags that are recognized by other cells

Many membrane proteins are..

enzymes, they may work as a team to carry out sequential steps in a pathway

Some proteins function as...

receptors for chemical messengers from other cells

Signal transduction

The binding of the messenger to the receptor triggers a chain reaction involving other proteins, which relay the message to molecules that perform specific functions inside the cell


As a plant cell loses water, it shrivels, and its plasma membrane pulls away from the cell wall


Extensions of a cell that help with phagocytosis

3 main types of cellular work

chemical, mechanical, transport

ATP become ADP

Through hydrolysis, an H is removed and energy is release with the break of the chemical bond