Cell Membrane Structure Quiz

Cell Membrane Structure

• Cell Membrane - Acts as a barrier between the intracellular and extracellular fluid.
• Membrane Lipids - The primary component of the cell membrane, including phospholipids, fatty acids, and cholesterol.
  • Phospholipids: Made up of phosphate groups and sphingosines, which are negatively charged and hydrophilic (water-loving).
    • Outer Membrane: Composed of phospholipids like phosphatidylcholine and sphingomyelin.
    • Inner Membrane: Composed of phospholipids like phosphatidylserine and phosphatidylethanolamine.
  • Fatty Acids: Hydrophobic (water-hating) hydrocarbon chains that extend from the phosphate head.
    • Saturated Fatty Acids: Straight chains with no double bonds.
    • Unsaturated Fatty Acids: Have double bonds, giving them a kinked structure.
  • Cholesterol: Embedded within the membrane, affecting its fluidity.
• Membrane Proteins: Found within the membrane, either spanning it completely (integral) or loosely attached (peripheral).
  • Integral Proteins:
    • Transmembrane Proteins: Extend across the entire membrane, often acting as ion channels or carrier proteins.
  • Peripheral Proteins: Have a weak interaction with the membrane, mainly through hydrogen bonding.
• Glycocalyx: A network of glycoproteins and glycolipids on the outer surface of the cell.

Cell Membrane Functions

• Glycocalyx:
  • Water Regulation: Helps control water movement in and out of the cell to prevent dehydration.
  • Antigenic Function: Plays a crucial role in immune system recognition of host cells versus foreign cells.
    • MHC Class 1 Complex: A specific glycocalyx structure on host cells that the immune system uses to identify them as "self."
    • Blood Typing: The specific glycoproteins and glycolipids on red blood cells determine blood type, allowing our immune system to distinguish between compatible and incompatible blood donations.
• Membrane Lipids:
  • Fluidity: The ability of the cell membrane to adapt its shape and movement. This is influenced by:
    • Temperature: Higher temperatures increase fluidity, while lower temperatures decrease fluidity.
    • Cholesterol: Plays a crucial role in maintaining the membrane's fluidity.
• Membrane Proteins:
  • Transport: Facilitates the movement of substances across the cell membrane, often in a selective manner.
  • Cell Signaling: Transmits signals from the exterior of the cell to the interior, influencing cell behavior.
  • Enzymatic Activity: Can catalyze biochemical reactions within the cell.
  • Cell Adhesion: Connects the cell to other cells or the extracellular matrix.
  • Cell Recognition: Recognizes and interacts with other cells or molecules.

Cell Membrane Fluidity

• Cell membrane fluidity is impacted by temperature, cholesterol, and fatty acid types.

• Higher temperatures lead to increased fluidity as phospholipids move apart.

• Low temperatures with little cholesterol lead to decreased fluidity as phospholipids compact.

• High cholesterol increases membrane rigidity as it acts like glue to hold phospholipids together.

• Unsaturated fatty acids increase cell membrane fluidity due to kinks in their structure, causing phospholipids to spread apart.

• Saturated fatty acids decrease cell membrane fluidity as they pack tightly together without kinks.

Membrane Lipid Transport

• Simple diffusion allows for the transport of small, nonpolar, lipid-soluble molecules across the cell membrane.

• Lipid soluble molecules dissolve in the hydrophobic core of the cell membrane and easily move across.

• Lateral diffusion is the movement of phospholipids within the cell membrane laterally.

• Transverse diffusion is the movement of phospholipids from the outer to inner cell membrane or vice versa.

• Flippases and floppases are enzymes that facilitate transverse diffusion.

Membrane Protein Functions

• Membrane proteins allow the transport of large, polar, water-soluble molecules across the cell membrane that are unable to diffuse through the membrane's hydrophobic core.

• Membrane proteins act as channels or carriers for these molecules.

• Peripheral proteins are involved in exocytosis and endocytosis, processes that involve the movement of molecules into and out of the cell.

• Membrane proteins can act as receptors for hormones and activate signaling pathways within the cell.

• Membrane proteins can link cells together by forming cell junctions.

• Membrane proteins can catalyze enzymatic reactions both inside and outside the cell.

• Membrane proteins facilitate cell communication between cells through channels called gap junctions.

• Membrane proteins can attach cells to the extracellular matrix.

• Hemidesmosomes are examples of structures that attach cells to the extracellular matrix.

Fluid Mosaic Model

• The cell membrane is characterized as a fluid mosaic model.

• It consists of a lipid bilayer, comprised of two layers of phospholipids, with embedded proteins.

• The phospholipid heads are hydrophilic, water-loving, and face the extracellular fluid and cytoplasm.

• The phospholipid tails are hydrophobic, water-fearing, and face each other in the center of the bilayer.

Cell Membrane Structure

• The cell membrane acts as a barrier between the inside (intracellular) and outside (extracellular) of a cell.
• The primary component is membrane lipids, which include phospholipids, fatty acids, and cholesterol.
• Phospholipids consist of a phosphate group and sphingosines, which are negatively charged and attracted to water (hydrophilic).
• The outer membrane is made of phospholipids like phosphatidylcholine and sphingomyelin.
• The inner membrane is made of phospholipids like phosphatidylserine and phosphatidylethanolamine.
• Fatty acids are hydrocarbon chains without an affinity for water (hydrophobic) which extend from the phosphate head.
• Saturated fatty acids have no double bonds, giving them a straight chain structure.
• Unsaturated fatty acids have one or more double bonds, giving them a bent or kinked structure.
• Cholesterol is embedded in the membrane and affects its fluidity.
• Membrane proteins are found within the membrane and can either span it completely (integral) or be loosely attached (peripheral).
• Integral proteins can be transmembrane proteins, which extend across the entire membrane, often acting as ion channels or carrier proteins.
• Peripheral proteins have a weak interaction with the membrane, mainly through hydrogen bonding.
• Glycocalyx is a network of glycoproteins and glycolipids that is found on the outer surface of the cell and contributes to several cell functions.

Cell Membrane Functions

• Glycocalyx plays a role in
  • Water Regulation by controlling water movement in and out of the cell.
  • Antigenic Function by being crucial for immune system recognition of self vs non-self cells.
  • MHC Class 1 Complex is a specific glycocalyx structure on host cells that is recognized by the immune system.
  • Blood Typing as the specific glycoproteins and glycolipids on red blood cells determine blood type, allowing our immune system to distinguish between compatible and incompatible blood donations.
• Membrane Lipids contribute to
  • Fluidity by allowing the cell membrane to adapt its shape and movement, influenced by temperature and cholesterol.
• Membrane Proteins support
  • Transport of substances across the membrane, often in a selective manner.
  • Cell Signaling by relaying signals to the cell's interior, influencing cellular behavior.
  • Enzymatic Activity by catalyzing biochemical reactions within the cell.
  • Cell Adhesion by connecting cells to other cells or the extracellular matrix.
  • Cell Recognition by recognizing and interacting with other cells or molecules.

Cell Membrane Fluidity

• Temperature affects membrane fluidity: higher temperatures increase fluidity, and lower temperatures decrease fluidity.
• Cholesterol plays a crucial role in regulating cell membrane fluidity: it maintains fluidity at high temperatures and increases rigidity at low temperatures.
• Fatty acid types also affect membrane fluidity: unsaturated fatty acids increase fluidity due to their kinked structure, while saturated fatty acids decrease fluidity due to their tightly packed, straight structure.

Membrane Lipid Transport

• Simple diffusion allows small, nonpolar, lipid-soluble molecules to easily pass across the membrane's hydrophobic core.
• Lateral diffusion refers to the movement of phospholipids within the plane of the membrane, moving side to side.
• Transverse diffusion is the movement of phospholipids from one leaflet of the membrane to the other leaflet.
• Enzymes called flippases and floppases facilitate transverse diffusion by assisting in flipping phospholipids between membrane leaflets.

Membrane Protein Functions

• Membrane proteins assist in the transport of large, polar, water-soluble molecules across the membrane.
• They act as channels or carriers for these molecules that cannot easily pass through the hydrophobic core.
• Peripheral proteins are involved in exocytosis and endocytosis, processes that involve the movement of molecules into and out of the cell.
• Membrane proteins can act as receptors for hormones and activate signaling pathways within the cell.
• Membrane proteins can link cells together by forming cell junctions.
• Membrane proteins can catalyze enzymatic reactions both inside and outside the cell.
• Membrane proteins can facilitate cell communication between cells through channels called gap junctions.
• Membrane proteins can attach cells to the extracellular matrix through structures like hemidesmosomes.

Fluid Mosaic Model

• The Fluid Mosaic Model describes the cell membrane as a dynamic, fluid structure, consisting of a lipid bilayer with embedded proteins.
• The phospholipid heads are hydrophilic, water-loving, and face the extracellular fluid and cytoplasm.
• The phospholipid tails are hydrophobic, water-fearing, and face each other in the center of the bilayer.

Cell Membrane Structure

• The cell membrane acts as a barrier between the inside (intracellular) and outside (extracellular) of the cell.
• It's made up of three main parts: membrane lipids, membrane proteins, and the glycocalyx

Membrane Lipids

• The cell membrane's outer and inner faces are made up of phospholipids.
• The outer membrane is rich in phosphatidylcholine and sphingomyelin.
• The inner membrane has higher levels of phosphatidylserine and phosphatidylethanolamine.
• Fatty acid chains sit between the phosphate heads of phospholipids.
• Saturated fatty acids have no double bonds, making them straight chains. These pack tightly, decreasing fluidity.
• Unsaturated fatty acids have double bonds, which create kinks. These kinks increase fluidity and spacing between phospholipids.
• Cholesterol is embedded in the membrane to help maintain its stability. It regulates membrane fluidity.

Membrane Proteins

• Integral proteins span the entire cell membrane.
• Transmembrane proteins are integral proteins that cross the entire membrane and serve as channels and carriers.
• Peripheral proteins are weakly linked to the cell membrane.

Glycocalyx

• Glycoproteins and glycolipids form a network on the outer surface of the cell membrane.
• Functions:
• Regulates water movement in and out of the cell, preventing dehydration.
• Antigenic function, helping cells recognize self from non-self, crucial for the immune system and blood typing.

Membrane Lipid Function

• Membrane fluidity is the ability of the cell to adapt its shape and movement.
• Factors affecting fluidity:
• Temperature: Higher temperatures increase fluidity; lower temperatures decrease fluidity.
• Cholesterol: High cholesterol stabilizes the membrane, decreasing fluidity while low cholesterol increases fluidity, but only at lower temperatures.

Membrane Lipids and Transport

Simple Diffusion

• Small, nonpolar, and lipid-soluble molecules can pass through the membrane by simple diffusion.
• This is because they can easily dissolve in the hydrophobic fatty acid tails of the membrane.

Lateral Diffusion

• Phospholipids move freely within the membrane, shifting side-to-side.

Transverse Diffusion

• Phospholipids can flip-flop between the inner and outer leaflets, but this requires specific enzymes:
• Flippase moves phospholipids from the outer to inner leaflet.
• Floppase moves phospholipids from the inner to outer leaflet.

Membrane Proteins and Their Functions

• Transport: Transmembrane proteins facilitate the transport of large, polar, and water-soluble molecules across the membrane by acting as channels or carriers.
• Cell-to-Cell Communication: Membrane proteins can act as receptors, binding hormones and signaling molecules to trigger responses within the cell.
• Enzymatic Activity: Membrane proteins can catalyze reactions, acting as enzymes to speed up the conversion of substrates into products.
• Cell-to-Cell Attachment: Integral membrane proteins can link cells together, forming structures like:
  • Tight junctions
  • Desmosomes
  • Adherence junctions These structures provide cell-to-cell adhesion.
• Cell Attachment to Extracellular Matrix: Membrane proteins connect cells to the extracellular matrix, providing structural support and stability.
  • Examples include hemidesmosomes.