Cell Membrane and Membrane Transport

Question 1

What is the role of the cell membrane as a selective barrier?

Answer 1

The cell membrane controls the movement of molecules in and out of the cell, acting as a selective barrier to maintain homeostasis.

Question 2

How do amphipathic molecules and hydrophobic interactions affect membrane fluidity and cholesterol’s role?

Answer 2

Amphipathic molecules, like phospholipids, have hydrophilic heads and hydrophobic tails that interact with each other to form membranes. Cholesterol helps maintain membrane fluidity by stabilizing the membrane at high temperatures and increasing fluidity at low temperatures.

Question 3

What are diffusion and osmosis?

Answer 3

Diffusion is the movement of molecules from an area of high concentration to an area of low concentration. Osmosis is the diffusion of water across a semi-permeable membrane.

Question 4

When is active transport required across the membrane instead of diffusion?

Answer 4

Active transport is required when molecules need to be moved against their concentration gradient, from low to high concentration, and requires energy.

Question 5

What are the functions of the main types of transport proteins in membranes?

Answer 5

Transport proteins include transporters (move ions or molecules), receptors (detect environmental signals), enzymes (facilitate chemical reactions), and anchors (maintain cell structure).

Question 6

What is the experimental approach for identifying membrane transport mechanisms?

Answer 6

Experimental data can identify membrane transport mechanisms through observations of movement of molecules across membranes and the analysis of cell homeostasis in response to changes in the environment.

Question 7

What is the structure of the cell membrane?

Answer 7

The plasma membrane is made up of two layers of phospholipids, each containing a hydrophilic head and hydrophobic fatty acid tails, forming a bilayer structure.

Question 8

What is the evolution of the cell membrane?

Answer 8

The cell membrane evolved to allow limited molecular traffic, with early membranes being leaky or impervious to life molecules. Over time, membranes became more sophisticated, allowing controlled molecular movement.

Question 9

How do Van der Waals forces contribute to the dynamics of cell membranes?

Answer 9

Lipids in the membrane interact via Van der Waals forces between the fatty acid tails, allowing lipids to move within the membrane and contribute to membrane fluidity.

Question 10

How does temperature affect membrane fluidity?

Answer 10

The length and saturation of fatty acid chains affect membrane fluidity. Longer chains and fewer double bonds reduce fluidity. Cholesterol helps stabilize fluidity at both high and low temperatures.

Question 11

What is the role of cholesterol in membrane fluidity?

Answer 11

Cholesterol stabilizes membrane fluidity by reducing movement at high temperatures and preventing tight packing of lipids at low temperatures.

Question 12

What are integral and peripheral membrane proteins?

Answer 12

Integral membrane proteins are permanently attached to the membrane, often spanning the bilayer, while peripheral proteins are temporarily associated with the membrane or integral proteins through non-covalent interactions.

Question 13

What are the types of membrane proteins and their functions?

Answer 13

Transporters move ions and molecules across the membrane, receptors detect environmental signals, enzymes catalyze chemical reactions, and anchors help maintain cell structure.

Question 14

What is the difference between micelles, bilayers, and liposomes?

Answer 14

Micelles are spherical structures with one hydrophobic tail per lipid. Bilayers form the basic structure of the cell membrane, with hydrophilic heads outward and hydrophobic tails inward. Liposomes are bilayer structures that form spontaneously in neutral pH environments.

Question 15

What is facilitated diffusion?

Answer 15

Facilitated diffusion is the movement of molecules across a membrane through a transmembrane protein, such as a channel or carrier, without energy input.

Question 16

How do amphipathic molecules arrange themselves in water?

Answer 16

Amphipathic molecules spontaneously arrange into structures where the hydrophilic heads face outward toward water and the hydrophobic tails are shielded inside.

Question 17

What is passive transport?

Answer 17

Passive transport is the movement of substances across a cell membrane by diffusion, without requiring energy.

Question 18

What is membrane transport?

Answer 18

Membrane transport is the movement of molecules from areas of higher to lower concentration, facilitated by the selectively permeable cell membrane.

Question 19

How does the cell membrane contribute to homeostasis?

Answer 19

The cell membrane is selectively permeable, allowing some molecules to pass freely while preventing others, maintaining cellular balance and homeostasis.

Question 20

Why can’t ions and charged polar molecules easily pass through the cell membrane?

Answer 20

The hydrophobic interior of the cell membrane prevents ions and charged polar molecules, as well as large macromolecules like proteins, from crossing.

Question 21

Which molecules can freely move across the membrane?

Answer 21

Gases such as oxygen (O2) and carbon dioxide (CO2) can move freely across the membrane due to the hydrophobic interior.

Question 22

Can water pass through the cell membrane?

Answer 22

Water can pass the bilayer to a limited extent, but is facilitated by specific membrane proteins, like aquaporins.

Question 23

What is passive transport?

Answer 23

Passive transport is the movement of molecules from higher to lower concentration without the need for energy input, relying on random thermal motion.

Question 24

What is diffusion?

Answer 24

Diffusion is the net movement of molecules from areas of higher to lower concentration due to their random thermal motion.

Question 25

What types of molecules can move via diffusion?

Answer 25

Hydrophobic molecules like triacylglycerol can move across the membrane via simple diffusion.

Question 26

What is facilitated diffusion?

Answer 26

Facilitated diffusion is the movement of molecules across a cell membrane through a transmembrane protein, such as a channel or carrier protein.

Question 27

What is the function of channel proteins in membrane transport?

Answer 27

Channel proteins provide an opening between the inside and outside of the cell, allowing specific molecules to pass through. Some channels are gated, opening in response to chemical or electrical signals.

Question 28

What are aquaporins?

Answer 28

Aquaporins are specialized channel proteins that allow water to move more readily across the cell membrane by facilitated diffusion.

Question 29

How do carrier proteins work?

Answer 29

Carrier proteins bind to specific molecules, undergo a conformational change, and transport the molecules across the membrane, alternating between conformations that expose different sides of the membrane.

Question 30

What is osmosis?

Answer 30

Osmosis is the net movement of a solvent, such as water, across a selectively permeable membrane towards the side with higher solute concentration.

Question 31

What causes water to move during osmosis?

Answer 31

Water moves toward the side with higher solute concentration, as the water concentration decreases when solute concentration increases.

Question 32

When does osmosis stop?

Answer 32

Osmosis continues until the concentration gradient is balanced, or until another opposing force prevents further movement of water.

Question 33

What is osmotic pressure?

Answer 33

Osmotic pressure is the pressure required to prevent the movement of water across a membrane via osmosis. It is proportional to the solute concentration.

Question 34

How does active transport differ from passive transport?

Answer 34

Active transport moves molecules from lower to higher concentration, against the electrochemical gradient, requiring an energy input (usually from ATP).

Question 35

What is primary active transport?

Answer 35

Primary active transport directly uses ATP to drive the movement of ions or molecules against their concentration gradient.

Question 36

What is secondary active transport (cotransport)?

Answer 36

Secondary active transport uses the electrochemical gradient created by primary active transport to move molecules across the membrane without directly using ATP.