Cell Membranes, Transport, and Geometric Consequences of Size

Flashcards covering cell membrane structure, various transport mechanisms (diffusion, permeation, active transport), and the geometric challenges faced by organisms of different sizes.

Cell Membrane Assembly

Tends to self-assemble with water-loving (hydrophilic) heads facing outward and hydrophobic tails facing inward.

Lipophilic

Fat-loving; describes substances that can interact well with fatty molecules, allowing them to pass through the cell membrane.

Integral Proteins

Proteins embedded within the cell membrane, which can either respond to chemical signals or transport substances across the membrane.

Diffusion (across membrane)

The process by which small, uncharged, lipophilic molecules move quickly and easily across the cell membrane without assistance.

Channel Protein

A type of integral protein that creates a specific pathway for substances, such as ions or water, to move through the cell membrane. Does not transport large molecules.

Permeation

The term used to describe the movement of substances through a channel protein.

Aquaporin

A specific type of channel protein that facilitates the passage of water molecules across the cell membrane, allowing osmosis to occur.

Carrier Protein

A type of integral protein that binds to a specific molecule on one side of the membrane, changes its shape (conformation), and transports the molecule to the other side (usually down a concentration gradient).

Active Transport

The process of moving substances across the cell membrane against their concentration gradient, which requires an input of energy (energetically unfavorable).

Pumps

Carrier proteins specifically involved in active transport, moving substances against their gradient.

Uniform Pump

A type of active transport pump that moves only one substance at a time against its concentration gradient.

Antiport

A specific type of co-transport where two different substances move in opposite directions across the cell membrane.

Secondary Active Transport

A transport mechanism that moves a substance against its concentration gradient by coupling its movement with the movement of another substance down its electrochemical gradient, rather than directly using ATP. The gradient for the 'downhill' substance is maintained by primary active transport.

Geometric Consequences of Getting Bigger

The unavoidable changes in properties (like diffusion distance and surface area to volume ratio) that occur as an organism or cell increases in size due to basic geometric principles.

Diffusion Distance

The length a substance must travel from the cell membrane to the center of a cell; this distance increases as cell size increases.

Surface Area to Volume Ratio

A ratio that decreases as an organism or cell increases in size, because volume increases faster than surface area. This impacts the efficiency of material exchange with the environment.

Evolutionary Adaptations for Size

Changes in an organism's shape (e.g., flattening, sphere-like) or increased complexity (e.g., circulatory systems) that evolve to overcome the challenges associated with a decreasing surface area to volume ratio as organisms get larger.