Membranes and membrane transport

Question 1

What is the Fluid Mosaic Model?

Answer 1

Describes the structure of biological membranes as a dynamic arrangement of phospholipids, proteins, cholesterol, and carbohydrates.

Question 2

What are the key components of the Fluid Mosaic Model?

Answer 2

Phospholipid bilayer, membrane proteins (integral & peripheral), cholesterol, carbohydrates

Question 3

What are the functions of membrane proteins?

Answer 3

Transport, receptors, enzymes, cell adhesion, structural support.

Question 4

What are integral and peripheral membrane proteins?

Answer 4

Integral: Embedded within the bilayer.

Peripheral: Attached to the surface of the membrane.

Question 5

What types of membrane proteins are involved in transport?

Answer 5

Transport proteins (e.g., channels, carriers), pumps for active transport.

Question 6

What is cholesterol’s role in membranes?

Answer 6

egulates membrane fluidity and permeability.

At high temperatures: Reduces fluidity.

At low temperatures: Increases fluidity.

Question 7

What does “amphipathic” mean for phospholipids?

Answer 7

Phospholipids have a hydrophilic (water-loving) head and a hydrophobic (water-fearing) tail.

Question 8

What is selective permeability?

Answer 8

The membrane allows certain molecules to pass while blocking others based on size, charge, and polarity.

Question 9

What substances can diffuse through the membrane?

Answer 9

Non-polar molecules, fat-soluble molecules, small uncharged polar molecules (like water).

Question 10

What substances cannot diffuse through the membrane?

Answer 10

Ions and large polar molecules.

Question 11

What is simple diffusion?

Answer 11

Movement of molecules from high to low concentration without energy use, aiming for equilibrium.

Question 12

What factors affect the rate of diffusion?

Answer 12

Temperature, concentration gradient, molecule size.

Question 13

What is facilitated diffusion?

Answer 13

Passive transport through protein channels or carriers for molecules that can’t diffuse directly through the bilayer.

Question 14

What is osmosis?

Answer 14

Net movement of water molecules from low solute concentration to high solute concentration across a semi-permeable membrane.

Question 15

What are aquaporins?

Answer 15

Protein channels that facilitate the movement of water across the membrane.

Question 16

What is primary active transport?

Answer 16

Transport that directly uses ATP to move substances against their concentration gradient. Example: Sodium-potassium pump.

Question 17

What is secondary active transport?

Answer 17

Uses energy stored in electrochemical gradients (from primary active transport) to move substances. Example: Sodium-glucose cotransporter.

Question 18

How does active transport work?

Answer 18

ATP hydrolysis changes the shape of the transport protein, allowing molecules to move against the concentration gradient.

Question 19

What is endocytosis?

Answer 19

Process where the cell membrane engulfs material to bring it into the cell, forming a vesicle.

Question 19

What are the types of endocytosis?

Answer 19

Phagocytosis: Engulfing large particles (e.g., immune cells).

Pinocytosis: Uptake of extracellular fluid.

Receptor-mediated endocytosis: Specific uptake of molecules through receptor binding.

Question 20

What is exocytosis?

Answer 20

Process of releasing materials from the cell via vesicle fusion with the membrane.

Question 21

What is the role of glycoproteins and glycolipids?

Answer 21

Involved in cell recognition, communication, and immune responses.

Question 22

What is the difference between glycolipids and glycoproteins?

Answer 22

Glycolipids: Carbohydrates attached to lipids.

Glycoproteins: Carbohydrates attached to proteins.

Question 23

What is the role of glycoproteins and glycolipids in the immune system?

Answer 23

They act as antigens to help target foreign substances.

Question 24

What is the role of membrane proteins in cell-to-cell communication?

Answer 24

Facilitate signaling and interactions between cells.

Question 25

What are the types of membrane transport proteins?

Answer 25

Channel proteins: Allow specific ions or molecules to pass. Carrier proteins: Bind to molecules and transport them across the membrane.

Question 26

What are the different types of transport proteins?

Answer 26

Uniporters: Move one type of molecule. Symporters: Move two types of molecules in the same direction. Antiporters: Move two types of molecules in opposite directions.

Question 26

What is the function of structural proteins in membranes?

Answer 26

Maintain the shape and support the membrane structure.

Question 26

What is the function of cell adhesion proteins?

Answer 26

Help cells stick together to maintain tissue structure.

Question 27

What are the effects of temperature on membrane fluidity?

Answer 27

Higher temperature: Increases fluidity. Lower temperature: Decreases fluidity.

Question 28

How does the presence of cholesterol affect membrane fluidity?

Answer 28

High temperatures: Reduces fluidity. Low temperatures: Increases fluidity.

Question 28

How do phospholipid fatty acid tails affect membrane fluidity?

Answer 28

Saturated tails: Pack tightly, reducing fluidity. Unsaturated tails: Pack loosely, increasing fluidity.

Question 29

What is membrane permeability?

Answer 29

The ability of the membrane to allow molecules to pass through it.

Question 29

What types of molecules are highly permeable to the membrane?

Answer 29

Small nonpolar molecules (e.g., CO₂, O₂), and lipophilic molecules.

Question 29

What molecules have low membrane permeability?

Answer 29

Large polar molecules (e.g., glucose) and ions.

Question 30

What is the thickness of the cell membrane?

Answer 30

Typically 7-10 nm.

Question 31

Why is cholesterol’s fluidity control important?

Answer 31

Cholesterol's ability to adjust membrane fluidity helps maintain proper membrane function across a range of physiological temperatures, preventing the membrane from becoming too rigid or too fluid.

Question 31

Why does cholesterol affect membrane fluidity?

Answer 31

At higher temperatures: Cholesterol reduces membrane fluidity by interacting with phospholipids and stabilizing the membrane, preventing excessive movement. At lower temperatures: Cholesterol increases fluidity by preventing phospholipids from packing too tightly, ensuring the membrane remains flexible.

Question 32

What are ion pumps?

Answer 32

Ion pumps are membrane proteins that use ATP to actively transport ions across the membrane against their concentration gradient.

Question 33

What is the function of the sodium-potassium pump?

Answer 33

The sodium-potassium pump maintains the cell’s electrochemical gradient by pumping 3 Na⁺ ions out of the cell and 2 K⁺ ions into the cell, which is essential for maintaining resting potential.

Question 34

What is active transport using protein pumps?

Answer 34

Active transport uses energy (usually ATP) to move molecules against their concentration gradient.

Question 35

How does a protein pump work?

Answer 35

Molecules bind to a specific site on the pump. ATP is hydrolyzed, releasing energy. The pump changes shape, moving the molecule across the membrane, and resets for the next transport cycle.

Question 36

What are the types of protein pumps?

Answer 36

Uniporter: Moves one molecule/ion in one direction. Symporter: Moves two molecules/ions in the same direction. Antiporter: Moves two molecules/ions in opposite directions.

Question 37

What is secondary active transport?

Answer 37

Secondary active transport uses the energy created by primary active transport to move molecules against their concentration gradient without directly using ATP. Example: Glucose-sodium cotransporter uses Na⁺ gradient to absorb glucose.

Question 38

What are facilitated diffusion channels?

Answer 38

Channel proteins help ions and polar molecules move across the membrane via facilitated diffusion, which does not require energy.

Question 39

Why does water move through membranes easily?

Answer 39

Water molecules are small and can fit through the gaps in the lipid bilayer, or they may pass through aquaporins (water channels).

Question 40

What are aquaporins?

Answer 40

Aquaporins are water-specific protein channels that facilitate the transport of water molecules across the membrane.

Question 41

Where are aquaporins found?

Answer 41

Tissues with high water permeability, such as kidney tissue, cornea of the eye, and epithelial cells of salivary and sweat glands.

Question 42

What is the difference between simple diffusion and facilitated diffusion?

Answer 42

Simple diffusion: Movement of molecules across the membrane from high to low concentration without the need for a transport protein. Facilitated diffusion: Molecules move through a membrane via transport proteins (channel or carrier) without energy use.

Question 43

What is the difference between active transport and facilitated diffusion?

Answer 43

Active transport: Moves molecules against their concentration gradient using ATP. Facilitated diffusion: Moves molecules along their concentration gradient without energy input, using proteins.