Dialysis and Molecular Diffusion Quiz

Phospholipid Structure

• The head of a phospholipid is made of a glycerol molecule attached to a phosphate group.
• The phosphate group is often linked to another molecule, such as choline or ethanolamine.
• The head is hydrophilic (water-attracting).

Cell Membrane Structure

• Cell membranes are primarily composed of phospholipids.
• A phospholipid bilayer forms, with water-attracting heads facing outward toward the surrounding fluid and water-repelling tails facing inward away from the water.

Carbohydrate Function in Cell Membranes

• Carbohydrates in cell membranes function in cell recognition and communication.
• They are commonly attached to proteins or lipids, forming glycoproteins or glycolipids.
• This aids in cell recognition (distinguishing self-cells from foreign cells).
• Facilitates cell-to-cell communication.
• Provides protection, acting as a barrier against harmful substances.

Protein Function in Cell Membranes

• Proteins in cell membranes perform diverse functions.
• Transport substances in and out of the cell.
• Receive external signals and transmit them inside the cell.
• Maintain cell shape.
• Help in cell recognition.
• Facilitate chemical reactions (act as enzymes).

Isotonic, Hypertonic, and Hypotonic Solutions

• These solutions affect water movement in and out of cells.
• Isotonic: Solute concentration outside the cell is equal to that inside, so water movement is balanced.
• Hypertonic: Solute concentration outside the cell is higher than inside, causing water to leave the cell and shrink.
• Hypotonic: Solute concentration outside the cell is lower than inside, causing water to enter the cell and potentially swell.

Osmosis vs. Diffusion

• Osmosis is the movement of water across a semi-permeable membrane, from an area of low solute concentration to high.
• Diffusion is the movement of molecules from an area of high concentration to low, in air, liquids, or across a membrane (not limited to water).

Reverse Osmosis

• Reverse osmosis is a purification technique using high pressure to force water across a semi-permeable membrane separating dissolved substances from pure water.
• This process is used in water purification, wastewater treatment, and for producing fresh water from seawater.

Osmosis Examples

• Absorption of water by plants: Plant roots absorb water from the soil through osmosis.
• Salting vegetables: Applying salt to vegetables causes water to move out of the cells, resulting in shrinkage.
• Kidney function: Osmosis regulates the balance of water and salts in the body by filtering blood and reabsorbing water.

Dialysis

• Dialysis is a medical process used to remove waste, excess water, and toxins from the blood when the kidneys are not functioning properly.
• Two types: hemodialysis (blood filtered by a machine) and peritoneal dialysis (using the abdomen as a filter).

Types of Diffusion

• Simple Diffusion: Molecules move from high to low concentration across a membrane without energy.
• Facilitated Diffusion: Molecules move from high to low concentration with the help of transport proteins, no energy required.
• Osmosis: Water moves from low solute concentration to high across a membrane.
• Active Diffusion: Molecules move against their concentration gradient using energy (ATP).

Cell Membrane Function

• Selective Permeability: Regulates what enters and leaves the cell.
• Protection and support: Protects cell contents and maintains shape.
• Communication: Receives signals from the environment.
• Cell Recognition: Helps cells recognize each other.
• Anchoring cytoskeleton: Connects the membrane to the cell's internal structure.
• Transport: Facilitates movement of materials across the membrane.

Cell Membrane Composition

• Phospholipids: Form the bilayer structure of the membrane.
• Proteins: Located on or within the membrane; aid in transport and cell communication.
• Carbohydrates: Attached to proteins or lipids; aid in cell recognition.
• Cholesterol: Increases membrane flexibility and stability.

Cell Membrane Proteins

• Types: Peripheral (surface), Integral (spanning), Glycoproteins (carbohydrate-attached).

Fluid and Flexible Cell Membrane

• Phospholipid bilayer arrangement allows for movement and flexibility.
• Cholesterol helps maintain stability and flexibility at various temperatures.

Main Functions of Proteins in Cell Membranes

• Transport: Move substances across the membrane.
• Reception: Receive chemical signals.
• Structural Support: Anchors, supports membrane structure.
• Cell Recognition: Help cells identify each other

Six Common Functions of Membrane Proteins

• Transport: Move substances across the membrane.
• Receptor: Receive chemical signals.
• Structural Support: Anchors, supports membrane structure.
• Cell Recognition: Identify other cells (glycoproteins).
• Enzyme Activity: Catalyze chemical reactions on the membrane surface.
• Intercellular Joining: Link cells together.

Main Purpose of Cell Membrane

• Regulate movement of substances to maintain internal balance (homeostasis) and protect the cell from harmful substances. Function in cell communication and recognition.

Membrane Solubility

• Membranes are insoluble in water due to their phospholipid structure (hydrophilic head, hydrophobic tail). This structure creates a barrier to water, key to membrane function.

Cell without a Cell Membrane

• Loss of protection from harmful substances.
• Inability to regulate material entry/exit.
• Cell contents become damaged and leak out.
• Loss of communication abilities.
• Inability to perform essential cellular functions.

Phospholipid Functions

• Form the cell membrane.
• Maintain membrane stability and function.
• Control passage of materials across the membrane.
• Organize and distribute membrane proteins.

Osmosis: Active or Passive

• Osmosis is a passive process. Water moves from low solute concentration to high across a semi-permeable membrane without energy.

Sodium-Potassium Pump

• Active transport process requiring energy (ATP).
• Moves sodium ions out of and potassium ions into the cell against their concentration gradients (low to high).

Active vs. Passive Transport

• Active transport requires energy (ATP) to move substances against their concentration gradient.
  • (Example: Sodium-Potassium pumps)
• Passive transport does not require energy to move substances with their concentration gradient.
  • (Examples: Diffusion and osmosis)

Factors Affecting Diffusion Rate

• Concentration Gradient: The larger the difference, the faster the rate.
• Temperature: Higher temperatures increase the rate.
• Molecular Size: Smaller molecules diffuse faster.
• Membrane Properties: Membrane permeability affects the rate.
• Medium Type: The medium affects the diffusion rate (e.g., water vs. air).