Phospholipid Bilayer and Cell Membrane Transport

Flashcard study set covering cell membrane structure, phospholipid properties, components, factors affecting fluidity and permeability, transport mechanisms, and tonicity.

Where are the phospholipids that form cell membranes synthesized within eukaryotic cells?

Phospholipids are synthesized in the smooth Endoplasmic Reticulum.

What term describes a molecule, such as a phospholipid, that has both hydrophilic and hydrophobic properties?

Amphipathic

What specific region forms the hydrophilic head of a phospholipid molecule?

A strong phosphate group (along with glycerol) forms the hydrophilic head region.

How do amphipathic phospholipids arrange themselves when placed in water?

Their hydrophilic heads face outward to mix with water, while their hydrophobic tails face inward toward each other to stay away from water, forming a bilayer.

What are the four primary components of biological cell membranes?

1. Phospholipid bilayer, 2. Cholesterol molecules embedded among the tails, 3. Various embedded or loosely attached proteins, and 4. Sugar chains attached to the outer surface.

What structural role does cholesterol play within the cell membrane?

Cholesterol embeds between the hydrophobic phospholipid tails to fill gaps and stabilize hydrophobic interactions.

How does the amount of embedded cholesterol affect membrane fluidity and permeability?

Having less cholesterol in the membrane results in higher membrane fluidity and permeability.

How do unsaturated phospholipid tails alter membrane properties compared to saturated tails?

Unsaturated tails have kinks that force them to pack loosely, which increases membrane fluidity and permeability.

How do phospholipid tail length and environmental temperature influence membrane permeability?

Shorter phospholipid tails make the membrane narrow and increase permeability, while higher temperatures increase both fluidity and permeability.

Which class of molecules can easily pass directly through the phospholipid bilayer without protein assistance?

Small nonpolar molecules (such as $O_2$, $CO_2$, $N_2$, and steroids).

Why are charged ions unable to directly cross the phospholipid bilayer without transport proteins?

Biological membranes are completely impermeable to charged ions (such as $Na^+$, $K^+$, and $Cl^-$) due to the hydrophobic interior of the phospholipid bilayer.

What is the difference in energy requirement between simple/facilitated diffusion and active transport?

Diffusion moves substances down their concentration gradient (from high to low concentration) without requiring energy, whereas active transport moves substances against their concentration gradient (from low to high concentration) using energy.

How do channel proteins and carrier proteins differ in the types of cargo they transport?

Channels transport ions and small polar molecules (such as water), whereas carriers transport larger polar molecules (such as sugars).

What is the specific name of the channel protein that facilitates the rapid diffusion of water across cell membranes?

Aquaporin

What direction does water move when a cell is placed in a hypertonic solution, and what happens to the cell?

Water moves out of the cell via osmosis toward the higher solute concentration outside, causing the cell to shrink.

What direction does water move when a cell is placed in a hypotonic solution, and what happens to the cell?

Water moves into the cell via osmosis toward the higher solute concentration inside, causing the cell to swell.

How does an isotonic solution affect cell shape and water movement?

An isotonic solution has an equal solute and water concentration relative to the cell interior, resulting in equal movement of water in and out, so the cell maintains its normal shape.