cells191 2-5 lectures

• Characteristics that define life


  • Cellular organisation: membrane bound organelles
  • Reproduction: parent to offspring
  • Metabolism: storing and releasing fuels
  • Homeostasis: maintaining internal environment
  • Heredity: passing on genetic information
  • Response to stimuli: environmental changes
  • Growth and development
  • Adaptation through evolution: changing over generations

  
• Microns


  Used for cells and organelles
• Eukaryotes


  10-100 microns
• Prokaryotes


  Less than 5 microns
• Mitochondria


  1. 10 microns
• Chloroplasts


  1. 5 microns
• Nanometres


  Used for internal structures
• Requirements of natural selection


  • Variation: individuals vary
  • Inheritance: parents pass on their genetic traits to offspring
  • Selection: some variations reproduce more than others
  • Time: successful variations accumulate over generations
• All living things have the same common ancestor
• Endosymbiosis


  Mitochondria are the result of endocytosis of aerobic proteobacteria. Chloroplasts are the result of endocytosis of photosynthetic cyanobacteria.

  
• Evidence for endosymbiosis


  • Similar size and physiology to prokaryotes
  • Double membrane (inner similar to prokaryotes)
  • Semiautonomous organelles (self replication)

  
• Phylogenetic tree


  Tree diagram representing evolution shows how closely/distantly related organisms are

  
• 3 domains of life


  • Bacteria
  • Eukarya
  • Archaea
• Building blocks (monomers) -> Macromolecules -> Supramolecular assemblies e.g. membranes, ribosomes, chromatin -> Organelles e.g. nucleus, mitochondria
• Macromolecules


  Organic biological molecules necessary for life formed by building blocks that are covalently bonded together
• Carbohydrates, nucleic acids and proteins are polymers. Lipids are NOT polymers.
• Carbohydrate building blocks


  • Monosaccharides e.g. hexose, pentose
  • Disaccharides e.g. maltose, lactose, sucrose
  • Oligosaccharides: 3-10 units
  • Polysaccharides: 10+ units e.g. starch, glycogen, cellulose
• Carbohydrate functions


  • Recognition (cell communication)
  • Energy storage e.g. starch, glycogen
  • Structure e.g. cell wall
• DNA


  Double stranded double helix, phosphodiester bonds
• RNA


  Single stranded spiral
• Nucleic acid functions


  • Genetic code
  • Transcription
  • Translation
• Protein building blocks


  • Amino acids (20 types, differ by R group)
• Protein functions


  • Protective e.g. antibodies
  • Regulatory e.g. hormones
  • Structure e.g. collagen
  • Storage e.g. carrier protein
  • Contractile e.g. muscle
  • Catalytic e.g. enzymes
  • Transport e.g. haemoglobin
  • Toxic
• Lipids


  Not a polymer, hydrophobic (dissolves in nonpolar solvents), heterogenous e.g. triacylglycerols, steroids, fats, hormones
• Lipid functions


  • Regulation e.g. hormones, cholesterol
  • Energy
  • Structure e.g. phospholipid membrane, cholesterol
• Key organelles in eukaryotic cells


  • Mitochondria
  • Nucleus
  • Smooth and Rough ER
  • Lysosomes

  
• Importance of organelles


  Cell has requirements that it must meet to be functioning: manufacturing cellular materials, obtaining raw material, removal of waste, generate required energy, control all of these processes
• Importance of organelles


  Provide different environments in the cell, allow for development of concentration gradients, keep incompatible processes apart, facilitate packaging and modification of cellular products
• Plasma membrane


  Lipid bilayer composed of hydrophilic heads and hydrophobic tails, main function is to control what can enter/exit the cell, secondary functions are to limit cell size and optimise surface area to volume ratio
• Plasma membrane components


  Hydrophilic heads allow cell to exist in hydro environment, hydrophobic tails aid in controlling what can cross easily into the cell, cholesterol stabilises the membrane, saturated/unsaturated tails determine how tightly the membrane is packed

  
• Passive transport: Diffusion


  Passive movement of a substance down its concentration gradient, must be small, neutral and hydrophobic, moving from high to low concentration, no energy required
• Passive transport: Facilitated diffusion


  Passive movement of a substance down its concentration gradient, molecules are normally large, charged and hydrophilic, requires channel and carrier membrane proteins, osmosis is a form of facilitated diffusion
• Active transport


  Requires input of ATP, moves substance against concentration gradient, uses transport proteins
• Co-transport


  Indirectly active, uses transport proteins and pumps, the movement of one substance down its concentration gradient is used to move another substance against its concentration gradient into the cell
• Membrane protein functions


  • Signal transduction
  • Cell recognition
  • Intercellular joining
  • Linking cytoskeleton and extracellular matrix
  • Transport
• Endomembrane system


  A membrane system connected directly, or through vesicular transport, includes the nuclear membrane, endoplasmic reticulum, Golgi apparatus, plasma membrane, vesicles, vacuoles, and lysosomes, does not include mitochondria and chloroplasts

  
• Smooth endoplasmic reticulum (sER)


  Responsible for carbohydrate metabolism, lipid synthesis, and detoxification of drugs and poisons, storage of Ca+ ions (myocytes), extensive in cells highly active in these processes
• Rough endoplasmic reticulum (rER)

  Heavily involved in protein synthesis: presence of ribosomes, secreted and membrane-bound proteins enter the lumen and are marked for transport to the cis-Golgi, proteins are shuttled to the cis-Golgi and further processed, delivered from the trans-Golgi to the plasma membrane for secretion or retention on the membrane
• Golgi apparatus


  Series of cisternae and associated vesicles, polarity, movement from cis to trans, post office of the cell, receives, sorts, and ships proteins from the rER
• Golgi apparatus functions


  • Glycosylation: addition (or modification) of carbohydrates to proteins
  • Sorting: addition of molecular markers directing the proteins to the correct vesicles before leaving the trans-Golgi
  • Directing vesicle traffic: addition of molecular markers to departing vesicles to direct them to the proper destinations