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The Working Cell (chapter 5)

STUDY
PLAY
selective permeability
A property of biological membranes that allows some substances to cross more easily than others and blocks the passage of other substances altogether
Diffusion
Is passive transport. Solutes naturally diffuse from high to low concentrations, and the cell does not have to expend any energy. Small, non-polar molecules can easily cross a cell through simple diffusion (fig 5.3)
passive transport
The diffusion of a substance across a biological membrane with no expenditure of energy.
Osmosis
is the diffusion of water. Water tends to diffuse toward high solute concentrations, remember, "water follows salt." (fig 5.4)
Tonicity
The ability of a solution surrounding a cell to cause that cell to gain or lose water. Hypotonic, hypertonic, and isotonic.
hypotonic
Referring to a solution that, when surrounding a cell, will cause the cell to take up water.
hypertonic
Referring to a solution that, when surrounding a cell, will cause the cell to lose water.
isotonic
Referring to a solution that, when surrounding a cell, has no effect on the passage of water into or out of the cell.
Facilitated diffusion
requires a transport protein to cross(FACILITATE) the cell membrane. However, it is still passive transport (no energy required). Water, sugars, amino acids, and many ions cross the membrane this way.
Active transport
____________ requires energy from the cell, and can push solutes "uphill" against their concentration gradients (fig 5.8). The sodium-potassium pump is a protein that "actively transport" ions across the cell membrane.
Exocytosis and endocytosis
are also active transport. These involve physical engulfing (endo-) or ejection (exo-) of materials in vesicles (fig 5.9)
Potential energy
is stored energy. The energy stored in the chemical bonds of organic molecules is a form of ____________.
(water behind a dam possesses ____________).
Kinetic energy
is energy released or set into motion. Heat, transport, and movement are forms of ____________.
Consume energy
All cells _______________, typically by breaking down organic molecules to release their chemical energy, and then storing or using that energy in other forms
Second law of thermodynamics
no energy conversion is perfectly efficient, and some energy is always lost as heat.
Exergonic
chemical reactions release energy (catabolism).
Endergonic
chemical reactions require an input of energy (anabolism).
metabolism
The totality of an organism's chemical reactions. The sum of an organism's chemical reactions is the ______.
ATP (adenosine triphosphate)
is the universal energy "currency" of the cell; energy released from splitting (hydrolysis) of ______ powers all cellular work. Energy released from break-down of sugars (exergonic) is used to re-charge (phosphorylate) the cell's stock of ATP. (fig 5.12A,B,C)
hydrolysis
a chemical reaction that breaks bonds between two molecules by the addition of water; process by which polymers are broken down and an essential part of digestion.
exergonic reaction
an energy-releasing chemical reaction in which the reactants contain more potential energy that the products. The reaction releases an amount of energy equal to the difference in potential energy between the reactants and the products.
phosphorylation
The transfer of a phosphate group, usually from ATP, to a molecule. Nearly all cellular work depends on ATP energizing other molecules by _________.
Enzymes
are large, complex proteins that function as catalysts. As such, they speed up or facilitate biochemical reactions, but are not themselves consumed in the reaction (fig 5.13, 5.14)
Cofactors
A non-protein molecule or iron that is required for the proper function. Many enzymes require helper(COPILOT) pieces called cofactors. Vitamins are organic cofactors also known as coenzymes. Cofactors can also be mineral ions, like zinc, iron, magnesium, etc.
feedback inhibition
A method of metabolic control in which a product of a metabolic pathway acts as an inhibitor of an enzyme within the pathway.

Competitive/noncompetitive inhibitors of enzymes, concept of "feedback inhibition" (fig 5.15A,B)
Competitive inhibitors
A substance that reduces the activity of an enzyme by binding to the enzyme's active site in place of the substrate. A _____________s structure mimics that of the enzyme's substrate.
Noncompetitive inhibitor
A substance that reduces the activity of an enzyme without entering an active site. By binding elsewhere on the enzyme, a _____________ changes the shape of the enzyme so that the active site no longer effectively catalyzes the conversion of substrate to product.