Cell Membrane Structure and Transport Flashcards

A comprehensive set of practice questions covering cell membrane functions, the fluid mosaic model, transport mechanisms (diffusion, osmosis, active/bulk transport), and cell signaling based on the provided lecture notes.

What is the 'fluid mosaic model' of the cell membrane?

A model describing the membrane as 'fluid' because phospholipids and proteins move by diffusion, and 'mosaic' because proteins of various shapes and sizes are scattered within it.

How do phospholipids orient themselves in a bilayer?

Hydrophilic heads face outwards toward the water inside and outside the cell, while hydrophobic tails point inward toward each other, held by hydrophobic interactions.

How does the saturation of fatty acid tails affect membrane fluidity?

The more unsaturated (kinked) the tails, the more fluid the membrane is, as kinks leave more space between tails and result in fewer hydrophobic interactions.

What determines the thickness and fluidity of the membrane in relation to fatty acid tails?

The length of the fatty acid tails; shorter tails result in a thinner and more fluid membrane.

What are transmembrane proteins?

Intrinsic (integral) proteins that span the entire thickness of the membrane.

What are the primary functions of proteins in the cell surface membrane?

Transport (carrier and channel proteins), cell receptors and antigens for recognition/adhesion, enzymes for digestion, and structural support by attaching to the cytoskeleton.

What is the function of glycolipids and glycoproteins?

Stabilization of the membrane via hydrogen bonds with water, serving as cell receptors/antigens for signaling and adhesion, and forming a sugary coat called the glycocalyx.

How does cholesterol affect membrane fluidity at low temperatures?

It increases fluidity to prevent the membrane from being broken in cold temperatures.

What are the three factors listed that affect the fluidity of the membrane?

1. Temperature (higher temperature increases fluidity); 2. Cholesterol (regulates fluidity); 3. Fatty acid chains (unsaturated and shorter chains increase fluidity).

What is a ligand in cell signaling?

A biological molecule that binds specifically to another molecule, such as a cell surface membrane receptor.

Describe the process of transduction in cell signaling.

The process of converting a signal from one method of transmission to another.

What occurs when a receptor undergoes a conformational change during signaling?

The receptor spans the membrane and activates a G-protein, which activates a second messenger, leading to an enzyme cascade that amplifies the signal.

Which molecules move via simple diffusion through the phospholipid bilayer?

Hydrophobic (non-polar) molecules like oxygen and carbon dioxide, and small polar molecules like water.

How does facilitated diffusion differ from simple diffusion?

It utilizes transport proteins (channels or carriers) to move polar molecules passively through the membrane, as they cannot pass through the hydrophobic core.

What is the specific function of channel proteins in facilitated diffusion?

They possess water-filled pores lined with hydrophilic $R$-groups to allow charged ions to diffuse through the membrane.

Define osmosis in terms of water potential.

The net movement of water molecules from a less negative (higher) water potential to a more negative (lower) water potential down a water potential gradient.

Why do plant cells not burst when placed in a solution with higher water potential?

The cellulose cell wall has high tensile strength which prevents the cell from bursting.

Define active transport.

The movement of molecules or ions through transport proteins across a cell membrane against their concentration gradient, using energy from $ATP$.

What is the difference between phagocytosis and pinocytosis?

Phagocytosis is the bulk movement of solids into a cell (engulfing), while pinocytosis is the uptake of liquids.

How are vesicles moved during exocytosis?

A Golgi vesicle buds from the Golgi body and rolls over the cytoskeleton until it reaches and fuses with the cell surface membrane.

How does surface area to volume ratio change with increasing size?

Surface area to volume ratios decrease as size increases.

Which two factors are inversely proportional to the rate of diffusion?

Diffusion distance and the size of the molecule.