Membrane Transport, Energy, and Glycolysis

Flashcards covering membrane transport mechanisms, thermodynamics, enzyme kinetics, and the fundamentals of glycolysis.

Cell membrane (Plasma membrane)

A fundamental defining feature of cells that acts as a boundary defining the space of the cell, separating its internal contents from the external environment.

Selectively permeable

The property of the cell membrane that lets some molecules in and out freely while preventing other molecules from passing through at all.

Diffusion

The net movement of substances from areas of higher to lower concentration due to the constant random motion of molecules.

Passive transport

Occurs when molecules move across a cell membrane by diffusion as a result of differences in concentration between the inside and outside of the cell.

Facilitated diffusion

Movement of molecules through a membrane transporter, either via channel proteins or carrier proteins.

Channel protein

A type of membrane transporter that provides an opening between the inside and outside of the cell through which certain molecules can pass based on shape and charge.

Carrier Protein

A membrane transporter that binds to and then transports specific molecules across the cell membrane.

Aquaporins

Specific channel proteins that allow water to move much more rapidly across the cell membrane by facilitated diffusion than by simple diffusion.

Osmosis

The net movement of a solvent like water across a selectively permeable membrane from regions of higher water concentration to lower water concentration.

Osmotic Pressure

The tendency of a solution to draw water in by osmosis; it increases as the solute concentration of the solution increases.

Active Transport

The uphill movement of substances against a concentration gradient, requiring an input of energy either directly or indirectly.

Contractile vacuoles

Organelles that take up excess water from inside the cell and expel it into the external environment by contraction.

Turgor Pressure

Pressure that develops because the cell wall resists being stretched and pushes back on the interior of the cell when water enters.

Metabolism

The collection of all the chemical reactions occurring within a cell.

Gibbs Free Energy ($G$)

The amount of energy available to do work in a system, determined by the enthalpy and entropy.

Gibbs Free Energy Equation

$$\Delta G^{\circ} = \Delta H^{\circ} - T \Delta S^{\circ}$$

Activation energy ($E_a$)

The initial energy input necessary to reach the transition state; it determines the rate of a chemical reaction.

Exergonic reactions

Chemical reactions with a negative $\Delta G$ ($\Delta G < 0$) that release free energy.

Endergonic reactions

Chemical reactions with a positive $\Delta G$ ($\Delta G > 0$) that require an input of free energy.

pH

A measure of proton ($H^+$) concentration defined by the equation $pH = -\log [H^+]$.

Negative feedback

A regulatory mechanism where the final product of a pathway inhibits the first step of the reaction to maintain homeostasis.

Allosteric enzymes

Enzymes whose activity is regulated by molecules that bind at sites other than their active sites.

Chemical Equilibrium

The state where the rate of the forward reaction equals the rate of the reverse reaction and the concentrations of reactants and products remain constant.

Energetic coupling

A process where a spontaneous reaction (negative $\Delta G$) drives a non-spontaneous reaction (positive $\Delta G$), requiring a net negative $\Delta G$.

ATP Hydrolysis

The exergonic process of breaking down ATP into ADP and Inorganic phosphate ($P_i$) using water, which releases energy for the cell to use.

Transition State

A highly unstable intermediate state between reactants and products that has a large amount of free energy.

Active Site

The specific region of an enzyme where substrates bind to form an enzyme-substrate complex.

Cofactors

Non-protein substances, which can be inorganic or organic, that assist enzymes in catalyzing reactions.

Denature

The process by which an enzyme unfolds at very high temperatures, causing it to lose its ability to catalyze chemical reactions.

Glycolysis

The anaerobic process of 'splitting sugar' where a 6-carbon glucose molecule is split into two 3-carbon molecules of pyruvate, producing a net of 2 ATP and 2 NADH.

Substrate-level phosphorylation

The mechanism by which ATP is produced directly during glycolysis.