Test 2

• Plasma membrane


  Separates the internal cytoplasm from the external environment of the cell, it also allows incompatible chemical reactions

  
• Phospholipid bilayer


  • External surface/cytoplasmic surface lined with hydrophilic polar heads
  • Nonpolar-hydrophobic-fatty acid tails sandwiched in between
• Cholesterol


  Lipid in animal plasma membranes that modifies and fluidity of the membrane

  
• Components of the plasma membrane


  • Lipid component (phospholipid bilayer)
  • Protein molecules
  • Peripheral: found in the inner membrane surface
  • Integral: partially of wholly embedded (transmembrane) in the membrane. Held by cytoskeleton and the Extracellular Matrix (ECM)

  
• Extracellular Matrix (ECM)


  • Only found in animal cells
  • Supports the plasma membrane
  • Facilitates communication between cells

  
• Carbohydrate chains


  • Glycoproteins: Proteins with attached carbohydrates chains
  • Glycolipids: lipids with attached carbohydrate chains
• Carbohydrate chains exist only on the outside of the ECM which makes it asymmetrical
• Functions of membrane proteins


  • Channel proteins
  • Carrier proteins
  • Cell recognition proteins
  • Receptor proteins
  • Enzymatic proteins
  • Junction proteins
• Channel proteins


  Allow passage of molecules through the membrane freely, responsible for passive transport
• Carrier proteins


  Combine substances to be transported across the plasma membrane to enter or exit the cell, often requires ATP, actively moving molecules through the membrane called Active transport

  
• Cell recognition proteins


  Glycoproteins and glycolipids serve as surface receptors for cell recognition and identification (cellular fingerprint), helps the body to recognize foreign substances

  
• MHC (major histocompatibility complex)


  Glycoproteins that are different in everyone, so organ transplants are difficult to achieve, determines organs transplant acceptance or rejection
• Receptor proteins


  Serve as binding or attachments sites, have a specific shape so that specific molecules can bind to them, binding molecules can influence the cell

  
• Enzymatic proteins


  Many enzymes are embedded in membranes, which attract reacting molecules to the membrane surface, catalyses a specific reaction
• Junction proteins


  Form various types of junctions between animal's cells, signalling molecules that pass-through gap junctions allow the cilia of cells lining the respiratory tract to beat at the same time, tight junctions in the animal cells can form a specific function
• Permeability of the plasma membrane


  They are selectively permeable, inhibits passage of other materials such as polar molecules, small, non-charged molecules freely cross the membrane by passing through the phospholipid bilayer, by regulating chemical traffic across its plasma membrane, a cell controls its volume and its internal ionic and molecular composition

  
• Water moves across the plasma membrane (proteins called aquaporins speed up the transport of water in the membrane)
• The movement of ions and polar molecules across the membrane is often assisted by carrier proteins

  
• Passive Transport


  • no ATP
  • Diffusions/facilitated transport
  • Follow the concentration gradient (high to low)
• Active Transport


  • When there is no gradient
  • Requires carrier protein
  • Move through the membrane against the concentration gradient
  • Requires energy in form of ATP
  • Exocytosis/endocytosis
• Diffusion


  Solvent (the liquid you mix in) – Solute (the dissolved solid), net movement is always high to low, equilibrium happens when the NET movement stops, solute concentration is uniform (no gradient)
• Factors affecting passive transportation (diffusion)


  • Temperature
  • Molecule size
  • Concentration
  • Electrical and pressure gradients of the two regions
• Materials that may move through membranes freely by simple diffusion


  • CO2
  • O2
  • Small lipid-soluble molecules

  
• Passive transport


  • H2O (aquaporin)
  • Glucose
  • Many small ions
  • Some amino acids
• Osmosis


  Focuses on solvent (water) movement rather than solute, diffusion of water across the selectively permeable membrane, net movement of water is toward low water (high solute concentration), water can diffuse both ways, but the solute can't, osmotic pressure is the pressure that develops due to osmosis
• Types of solutions


  • Isotonic
  • Hypotonic
  • Hypertonic
• Isotonic


  Solute and water concentrations are equal on both sides of cellular membrane, no gain or loss of water by the cell, physiological or normal saline consists of 0.9% NaCl in water, which is isotonic to RBC (red blood cells)
• Hypotonic


  Concentrations of solute in the solution is lower (more water) than inside the cell, more water molecules outside the cell, if cells are placed in a hypotonic solution, they will get swollen (get bigger), in plants we say (turgor pressure), in animals (lyse) where the rupture
• Cells that are usually found in hypotonic solutions use various mechanisms such as Protozoans living in freshwater environment have (contractile vacuoles) to get of excess water, well-developed kidneys in freshwater fish to excrete large volume of diluted urine, plants cells osmotic pressure to their advantage
• Hypertonic


  Concentration of solute is higher (less water) in the solution than inside the cell, the concentration of water molecules outside the cell is more, the cell has more wate concentration than the outside environment, cells placed in hypertonic solution will shrink: Crenation in animal cell, Plasmolysis in Plants cells
• Saltwater is hypertonic to the cells of freshwater organisms, central vacuole in plants lose water and the plasma membrane pulls away from the cell wall, Plasmolysis occurs in plants when the soil/water around them contains high concentration of salts/fertilizers, marine animals cope in various ways though, sharks either increase or decrease urea in blood, fishes excrete salts through their gills
• Facilitated Transport


  Movement of molecules cannot pass directly through the membrane lipids (like glucose and amino acid), these molecules must combine with specific carrier proteins to move across the membrane (follow concentration gradient)(H to L)(no energy)

  
• Active Transport


  Movement of molecules against their concentration gradient (L to H), movement facilitated by specific carrier proteins, requires expenditure of energy in the form of ATP
• Macromolecules transport


  Transported into or out of the cell inside vesicles via bulk transport, requires energy (ATP), formation of vesicles are called exocytosis/endocytosis

  
• Exocytosis


  Vesicles formed from Golgi apparatus fuse with plasma membrane and secrete contents like hormones-neurotransmitters-digestive enzymes, the secretion is regulated when plasma membrane receives a signal

  
• Mechanisms of Endocytosis


  • Phagocytosis
  • Pinocytosis
  • Receptor mediated endocytosis
• Phagocytosis


  Large-solid materials taken in (like bacterium or viruses), cell eating, human white blood cells engulfing debris or viruses, vacuole may fuse with lysosomes, degrading the ingested material
• Pinocytosis


  Formed around a liquid / very small particles "cell drinking", cells takes in macromolecules like polypeptides, vesicles from around a liquid or very small particles, cells do not shrink size why? Because the loss of the plasma membrane due to pinocytosis is balanced by the occurrence of exocytosis
• Receptor-Mediated Endocytosis


  Specific from of pinocytosis using receptor proteins and a coated pit, targeted intake of specific macromolecules that bind to plasma membrane receptors, forming coated vesicles at the plasma membrane, coated pits are regions lined with a fibrous protein, coating on the vesicle detaches, and the uncoated vesicle then fuses with a lysosome for degradation of its content, selective exchange of substances (e.g., between maternal and fatal blood) and is more efficient than basic pinocytosis, defects in this system can lead to diseases such as familial hypercholesterolemia, in hypercholesterolemia, LDL receptors fail to bind in the coated pits, preventing cholesterol uptake, excess cholesterol accumulates in the circulatory system, increasing the risk of heart attacks and atherosclerosis

  
• Types of Endocytosis


  • Phagocytosis
  • Pinocytosis
  • Receptor-Mediated endocytosis