Cell Membrane Structure and Functions

Cell Membrane

Structure:

• Phospholipid bilayer: composed of two layers of phospholipid molecules with hydrophilic (water-loving) heads and hydrophobic (water-fearing) tails
• Embedded proteins: integral proteins (transmembrane) and peripheral proteins (attached to surface)
• Cholesterol: helps maintain fluidity and stability

Functions:

• Selective permeability: regulates what enters and leaves the cell
• Protection: acts as a barrier against external environment
• Cell signaling: involved in cell-cell communication and signaling pathways
• Cell recognition: allows cells to recognize and interact with each other

Permeability:

• Semipermeable: allows certain molecules to pass through while keeping others out
• Passive transport: movement of molecules down concentration gradient (diffusion, osmosis)
• Active transport: movement of molecules against concentration gradient using energy

Membrane Transport:

• Simple diffusion: movement of molecules from high to low concentration
• Facilitated diffusion: assisted by transport proteins (e.g., channels, carriers)
• Active transport: uses energy to pump molecules against concentration gradient (e.g., ATP-powered pumps)

Membrane Fluidity:

• Fluid mosaic model: membrane is a dynamic, fluid structure with proteins and lipids moving laterally
• Temperature: affects membrane fluidity (increased temperature increases fluidity)
• Cholesterol: helps maintain fluidity by filling gaps between phospholipid tails

Cell Membrane Structure

• Phospholipid bilayer consists of two layers of phospholipid molecules with hydrophilic heads and hydrophobic tails
• Embedded proteins include integral proteins (transmembrane) and peripheral proteins (attached to surface)
• Cholesterol helps maintain fluidity and stability of the membrane

Cell Membrane Functions

• Selective permeability regulates what enters and leaves the cell
• Acts as a barrier against external environment for protection
• Involved in cell-cell communication and signaling pathways for cell signaling
• Allows cells to recognize and interact with each other for cell recognition

Membrane Permeability

• Semipermeable, allowing certain molecules to pass through while keeping others out
• Passive transport involves movement of molecules down concentration gradient through diffusion and osmosis
• Active transport uses energy to move molecules against concentration gradient

Membrane Transport Mechanisms

• Simple diffusion involves movement of molecules from high to low concentration
• Facilitated diffusion is assisted by transport proteins like channels and carriers
• Active transport uses energy to pump molecules against concentration gradient, e.g., ATP-powered pumps

Membrane Fluidity

• Fluid mosaic model describes the membrane as a dynamic, fluid structure with moving proteins and lipids
• Temperature affects membrane fluidity, with increased temperature increasing fluidity
• Cholesterol helps maintain fluidity by filling gaps between phospholipid tails

Mitochondrial Structure

• Mitochondria have two main parts: outer membrane and inner membrane, with the inner membrane being highly folded to form cristae, increasing the surface area for cellular respiration
• Mitochondrial matrix, the region inside the inner membrane, is where the citric acid cycle and fatty acid oxidation take place
• Mitochondrial DNA (mtDNA) is found in the mitochondrial matrix

Cellular Respiration

• Cellular respiration, the process of generating energy from glucose, occurs in mitochondria
• Glucose is converted into pyruvate in the cytosol during glycolysis
• Pyruvate is then converted into acetyl-CoA, producing ATP, NADH, and FADH in the citric acid cycle
• Electron transport chain, occurring in the mitochondrial inner membrane, uses NADH and FADH to produce ATP

ATP Synthesis

• ATP synthesis takes place in the mitochondrial inner membrane during the electron transport chain
• Energy from NADH and FADH is used to create a proton gradient across the inner membrane
• The proton gradient drives the production of ATP through chemiosmosis, catalyzed by ATP synthase
• ATP synthase generates ATP from ADP and Pi

Mitochondrial Function

• Mitochondria are the primary site of energy production in eukaryotic cells
• Mitochondria regulate cell growth, division, and apoptosis (programmed cell death)
• Mitochondrial dysfunction can lead to diseases such as neurodegenerative disorders and metabolic disorders

Mitochondrial Inheritance

• Mitochondrial DNA is inherited solely from the mother, as only egg cells contribute mitochondria to the fertilized egg
• Mitochondrial DNA is susceptible to mutations due to its lack of protection by the nuclear membrane
• Mitochondrial DNA mutations can lead to mitochondrial diseases, often inherited in a maternal pattern
• Mitochondrial DNA is used in forensic science and evolutionary biology to study genetic relationships and ancestry