Structure and Function of Plasma Membranes

Flashcards covering the structure and function of plasma membranes, including components like phospholipids and proteins, fluid mosaic model details, transport mechanisms (passive and active), osmosis, tonicity, and bulk transport.

What are the four primary functions of the plasma membrane?

Defining the outer border of cells and organelles, managing what enters and exits the cell, receiving external signals and initiating cellular responses, and adhering to neighboring cells.

Who proposed the Fluid Mosaic Model, and in what year?

S.J. Singer and G.L. Nicolson proposed it in 1972.

What are the three components of a phospholipid molecule?

Two fatty acid chains (nonpolar), a glycerol molecule, and a phosphate group (polar).

What is the physical difference between saturated and unsaturated fatty acids in phospholipids?

Saturated fatty acids have all single $C-C$ bonds and are saturated with $H$, while unsaturated fatty acids have at least one double $C=C$ bond.

How is the phospholipid bilayer arranged?

Polar heads face outward toward the aqueous environment and hydrophobic tails face inward, away from water.

What is the difference between integral and peripheral proteins?

Integral proteins are integrated completely into the bilayer, while peripheral proteins occur only on the membrane surfaces.

Where are carbohydrates located on the plasma membrane and what is their function?

They are located on the exterior surface (forming glycoproteins or glycolipids) and function in cell-cell recognition and attachment.

Which glycoprotein on T cells is recognized by HIV as "self"?

The CD4 receptor glycoprotein.

How does cholesterol affect membrane fluidity?

It acts as a fluidity buffer, keeping membranes fluid when cold and preventing them from becoming too fluid when hot.

According to the Second Law of Thermodynamics, what happens to the entropy of an isolated system over time?

The entropy (amount of disorder) is always increasing.

What does it mean for a plasma membrane to be selectively permeable?

It allows some molecules to pass through but not others, which allows the cytosol solutions to differ from extracellular fluids.

Which molecules are able to diffuse directly through the lipid bilayer?

Only small nonpolar molecules, such as $O_2$, $CO_2$, and lipid hormones.

Name four factors that affect diffusion rates.

Concentration gradients, mass of the molecules, temperature, and solvent density (also solubility, surface area, distance travelled, and pressure).

What are the two types of facilitated transport proteins?

Channel proteins and carrier proteins.

What are aquaporins?

Channel proteins that are specific to the transport of $H_2O$.

How do carrier proteins function during transport?

They bind to a specific substance, change shape, and carry it to the other side of the membrane.

Define osmosis.

The diffusion of water across a membrane from an area of higher water concentration to one of lower water concentration.

What is osmolarity?

The total solute concentration of a solution, including both permeable and non-permeable solutes.

Describe what happens to a cell in a hypertonic extracellular fluid.

The extracellular fluid has a higher osmolarity than the cytosol, causing water to leave the cell.

What is turgor pressure?

The pressure exerted by the plasma membrane against the cell wall, which is critical for the growth and function of plants, fungi, and bacteria.

What is plasmolysis?

The process where the plasma membrane detaches from the cell wall when a plant cell is in a hypertonic solution.

How do freshwater protists like paramecia manage water balance?

They use contractile vacuoles to pump excess water out of their cells so they do not burst.

What is the difference between primary and secondary active transport?

In primary active transport, $ATP$ provides the energy; in secondary active transport, an electrochemical gradient provides the energy.

Identify the three types of carrier proteins used as pumps in active transport.

Uniporters (carry one molecule/ion), Symporters (carry two different substances in the same direction), and Antiporters (carry two different substances in different directions).

What is the specific movement of ions in the $Na^+-K^+$ pump?

It moves 3 $Na^+$ out of the cell and 2 $K^+$ into the cell using 1 $ATP$.

Define the three types of endocytosis.

Phagocytosis (cellular eating/engulfing particles), Pinocytosis (cellular drinking/taking in fluid), and Receptor-mediated endocytosis (targeted uptake of specific substances).

What occurs during exocytosis?

Vesicles containing substances fuse with the plasma membrane, releasing their contents to the exterior of the cell.