Plasma Membranes, Transport, and Enzymes

Vocabulary flashcards for key terms related to plasma membranes, transport mechanisms, and enzymes.

Plasma Membrane

The cell membrane that defines the cell's borders and keeps it functional.

Selectively Permeable

The membrane allows some materials to freely enter or leave the cell, while others require specialized processes.

Fluid Mosaic Model

Describes the plasma membrane structure as a mosaic of components, including phospholipids, cholesterol, proteins, and glycolipids, giving the membrane a fluid character.

Phospholipid

Molecule consisting of glycerol, two fatty acids, and a phosphate-linked head group, a main fabric of the membrane.

Cholesterol

Lipid comprised of four fused carbon rings, situated alongside the phospholipids in the membrane's core, helps in maintaining fluidity.

Integral Proteins

Proteins that integrate completely into the membrane structure.

Peripheral Proteins

Proteins on the membranes' exterior and interior surfaces attached either to integral proteins or to phospholipids.

Glycoproteins and Glycolipids

Carbohydrates on the cells’ exterior surface bounded to proteins or lipids.

Glycocalyx

Carbohydrate components of both glycoproteins and glycolipids on the cell’s exterior surface.

Passive Transport

A naturally occurring phenomenon that does not require the cell to exert any of its energy to accomplish the movement of substances from an area of higher concentration to an area of lower concentration.

Diffusion

The movement from high concentration to low concentration.

Concentration Gradient

The difference in concentration in two areas.

Selective Permeability

Plasma membranes that allow some substances to pass through, but not others.

Diffusion

A passive process of transport where a single substance moves from a high concentration to a low concentration area until the concentration is equal across a space.

Equilibrium

Condition in which the substance has no net movement.

Facilitated Diffusion

Materials diffuse across the plasma membrane with the help of membrane proteins.

Transport Proteins

Transmembrane proteins that function as either channels or carriers for facilitated transport.

Aquaporins

Channel proteins that allow water to pass through the membrane at a very high rate.

Ion Channels

Channel proteins that allow specific ions to diffuse across the membrane down their concentration gradients.

Carrier Protein

Protein that binds a substance and triggers a change of its own shape, moving the substance across the membrane.

Osmosis

The diffusion of water through a semipermeable membrane according to the water’s concentration gradient across the membrane.

Tonicity

Describes the concentration of impermeable solutes in a solution.

Osmolarity

Describes the solution’s total solute concentration.

Hypotonic

Fluid has lower tonicity than another

Hypertonic

Fluid having a higher tonicity than another solution

Isotonic

The extracellular fluid has the same osmolarity as the cell

Osmoregulation

Mechanism that living things have to control the effects of osmosis.

Active Transport

Require the cell’s energy, sometimes in the form of adenosine triphosphate (ATP) to move a substance into the cell against its concentration gradient.

Primary Active Transport

Moves solutes across a membrane using ATP as an energy source.

Secondary Active Transport

Does not directly require ATP; instead, it uses alternative sources of energy.

Na+-K+ ATPase

Functions to maintain high intracellular K+ concentrations and low intracellular Na+ concentrations.

Endocytosis

Moves particles, such as large molecules, parts of cells, and even whole cells, into a cell.

Phagocytosis

The process by which a cell takes in large particles, such as other cells or relatively large particles

Exocytosis

Expel material from the cell into the extracellular fluid.

Exergonic Reactions

Reactions that release free energy

Endergonic Reactions

Chemical reactions that absorbs energy

Activation Energy

The small amount of energy input necessary for all chemical reactions to occur

Adenosine Triphosphate (ATP)

A small, relatively simple molecule that contains the potential for a quick burst of energy that can be harnessed to perform cellular work

Enzymes

Catalysts produced by living organisms

Active Site

The location within the enzyme where the substrate binds.

Enzyme-Substrate Complex

Complex formed when an enzyme binds its substrate, lowers the reaction’s activation energy and promotes its rapid progression.

Molecular Regulation of Enzymes

Regulation in ways that either promote or reduce their activity

Competitive Inhibition

A type of inhibition in which the inhibitor competes with the substrate molecule by binding to the enzyme’s active site.

Noncompetitive Inhibition

An inhibitor molecule binds to the enzyme in a location away from the active site and still manages to block substrate binding to the active site

Cofactors

An inorganic ion, such as iron and magnesium ions, required for optimal enzyme activity regulation

Coenzymes

An organic helper molecules, with a basic atomic structure comprised of carbon and hydrogen, which are required for enzyme action

Feedback Inhibition

Using a reaction product to regulate its own further production