Cell membrane

• The cell membrane is composed of phospholipids, cholesterol, proteins, and carbohydrates.
• Phospholipids are amphiphilic molecules with hydrophobic tails and polar heads that form the bilayer structure of the cell membrane.
• Cholesterol helps maintain fluidity and stability of the membrane by interacting with phospholipid tails.
• Proteins play various roles such as transporting substances across the membrane, acting as receptors or enzymes, and providing structural support.
• Proteins play various roles such as transport, signaling, adhesion, and enzymatic functions.
• Carbohydrates (glycoproteins) serve as recognition markers on the surface of cells and can be involved in cell-cell interactions.
• Plasma membranes surround all living cells and regulate the exchange of materials between the inside and outside of the cell.
• Membranes in plants contain more lipids than animal membranes due to the presence of waxes and cutin.
• Glycolipids are lipids attached to carbohydrate chains and also function as recognition markers.
• Plasma membranes surround all living cells and regulate the movement of materials into and out of the cell.
• Factors of diffusion:

  • concentration gradient
  • temperature
  • thickness of surface
  • surface area
  • size of diffusing molecule
  • nature of molecule ( polar/ non polar)
• Permeability Factors:

  • temperature ( molecules diffuse quickly, increase fluidity, denature proteins)
  • organic solvents e.g. ethanol (dissolve phospholipid bilayer, more porous)
• Examples of lipid soluble substances:

  • co2
  • viramin a
  • o2
• Lips soluble substances dissolve + diffuse through the membrane
• Water soluble substances do not dissolve + cannot pass through the membrane
• Active transport is when substances move against their concentration gradients using energy from ATP hydrolysis
• Carrier protein binds with substance on one side of membrane
• Passive transport is when no energy is required to move substances across the plasma membrane
• Facilitated diffusion uses carrier proteins to allow water-soluble substances to cross the membrane
• Carrier protein binds to substance at high conc outside cell
• ATP hydrolyses to ADP + Pi
• examples of water soluble substances:

  • ions
  • amino acids
  • glucose
• Facilitated diffusion is the movement of molecules across a membrane with the help of a channel/ carrier protein

  • more rapid than simple diffusion
  • affected by number of transport proteins
  • affected by steepness of concentration gradient
• Active Transport requires ATP, which powers pumps that actively move substances against their concentration gradients.
• Examples of active transport include sodium (Na+) pump, potassium (K+) pump, calcium (Ca2+) pump, chloride (Cl-) pump, glucose transporter, amino acid transporters, and iron transporter.
• Co-transport is the movement of molecules across a membrane in both directions
• Endocytosis involves the uptake of large particles into cells through invagination of the plasma membrane forming vesicles
• Phagocytosis is the process whereby cells engulf larger objects such as bacteria or dead cells
• Pinocytosis is the process whereby cells take up fluid from outside the cell
• Pinocytosis is the process whereby small amounts of fluid are taken up from outside the cell
• Exocytosis is the reverse of endocytosis - it is the release of materials out of the cell
• Exocytosis is the release of materials out of the cell by fusion with the plasma membrane
• The Golgi apparatus modifies, sorts and packages proteins made by ribosomes
• Lysosomes contain hydrolytic enzymes that break down macromolecules
• Examples of endocytosis are pinocytosis and phagocytosis
• Phagocytosis involves engulfing large particles such as bacteria or dead cells
• In exocytosis, vesicles fuse with the plasma membrane and their contents are released outside the cell
• Pinocytosis involves engulfing small molecules dissolved in water