BIOCELL GEN Lecture 7

• 1. Which of the summary statements below best describes the results of the following reaction?

  C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy?


  C6H12O6is oxidized and O2is reduced
• 1. A typical eukaryotic cell has enough available ATP to meet its needs for about 30 seconds. What is likely to happen to an individual when they exhaust their ATP supply?

  2. Catabolic processes will be activated to generate additional ATP
• 1. Glycolysis results in the net production of which of the following sets of molecules per glucose molecule??

  2. 2 NADH, 2 pyruvate, and 2 ATP
• 1. Inhibition of which of the following metabolic pathways would result in decreased rates of CO2 production??

  2. oxidation of pyruvate to acetyl CoA and the citric acid cycle
• 1. If glucose is the sole energy source for cellular respiration in an animal, what proportion of the carbon dioxide exhaled is derived from oxidation of pyruvate to acetyl CoA??

  2. 1/3
• 1. For each mole of glucose (C6H12O6) oxidized by cellular respiration, how many moles of CO2 are released in the citric acid cycle??

  2. 4
• 1. Which of the following statements best describes the relationship between photosynthesis and cellular respiration??


  Photosynthesis stores energy in complex organic molecules; cellular

  respiration releases energy from complex organic molecules
• 1. Which of the following observations would be the best indicator that an organism lacks photosystem II??

  2. It does not produce O2 in the light
• The Two Stages of Photosynthesis
• The Endomembrane System
• Endomembrane System


  • Collection of membranes inside & surrounding eukaryotic cells
  • Plasma membrane (lecture 3)
  • Nuclear envelope (lecture 4)
  • Endoplasmic Reticulum (lecture 7)
  • Golgi Apparatus (lecture 7)
  • Lysosomes (lecture 8)
  • Vacuoles (lecture 8)
  • Related either by physical contact or by transfer of vesicles (sacs made of membrane)
• Functions of the Endomembrane System


  • Storage & trafficking (vesicles for protein and lipids trafficking)
  • Metabolism (Biosynthesis of lipids, Degradation of lipids, Protein modification)
  • Detoxification
• Protein Trafficking within the Endomembrane System


  1. Sorting signals direct the movement (either retention or exit from a compartment)

  2. Gated transport (Via protein channels or pores, e.g.: nuclear import and export)

  3. Transmembrane transport (Via protein translocation channels, e.g.: protein entry into the ER)

  4. Vesicular transport (Via membrane-bound intermediates, e.g.: transport from ER to Golgi)
• Vesicular Trafficking within the Endomembrane System
• The Secretory and Endocytic Pathways
• Possible evolution of the endomembrane system in eukaryotic cells
• ER and NE co-evolved
• Endoplasmic Reticulum


  • 3 functionally distinct but interconnected regions: Smooth ER (SER), Rough ER (RER), Nuclear envelope
• Trafficking


  Movement of molecules within the cell
• Functions of the Endomembrane System

  • Trafficking
  • Metabolism
  • Biosynthesis of lipids
  • Degradation of lipids
  • Protein modification
  • Detoxification
• Sorting signals


  • Direct the movement (either retention or exit from a compartment)
• Types of transport


  • Gated transport
  • Transmembrane transport
  • Vesicular transport
• Gated transport


  Via protein channels or pores (e.g. nuclear import and export)
• Transmembrane transport


  Via protein translocation channels (e.g. protein entry into the ER)
• Vesicular transport


  Via membrane-bound intermediates (e.g. transport from ER to Golgi)
• Protein trafficking within the Endomembrane System

  1. Vesicular trafficking

  2. Secretory pathway

  3. Endocytic pathway

  4. Backflow

  5. Engulfment (autophagy)
• ER and nuclear envelope co-evolved
• Endoplasmic Reticulum (ER)


  • Smooth ER (surface lacks ribosomes)
  • Rough ER (surface covered with ribosomes)
  • Transitional ER (exit/entry site)
• Endoplasmic Reticulum


  • Gr. 'within' + 'shape', Lat. 'little net'
  • Complex and diverse morphology: flattened sacs, reticular sheets, tubules
  • Continuous with outer nuclear membrane
  • Lumen continuous with nuclear intermembrane space
• Smooth ER


  • Extensively developed in many cells: muscle, kidneys, steroid producing endocrine cells
  • Synthesis of steroid hormones
  • Sequestering Ca2+ ions
  • Detoxification in liver
  • Synthesis of membrane lipids only on cytosolic side
• Adverse drug interactions can occur due to inhibition or induction of some P450 enzymes in the smooth ER
• Rough ER


  • Protein synthesis by bound ribosomes
  • Protein translocation (transmembrane and water-soluble)
  • Protein modification, folding, quality control and export
• Co-translational translocation


  Primary mechanism of protein entry into the ER in mammalian cells
• Signal sequence/signal peptide


  Tag on proteins for the endomembrane system, recognized by signal recognition particle (SRP)
• Glycosylation


  Modification of most proteins synthesized in the rough ER, used as a marker for protein folding quality control
• Transitional ER


  • Site of exit from the ER and entry into the secretory pathway
  • Specialized for production of COPII transport vesicles
  • In mutual feedback with the Golgi apparatus
• Golgi Apparatus


  • Flattened membranous sacs called cisternae
  • Distinct 'structural directionality' or 'polarity'
  • Receives newly synthesized proteins from the ER and modifies them
  • Sorts and ships materials into transport vesicles
• Vesicular transport


  Transport vesicles bud off from one compartment and fuse with another, carrying cargo and membrane
• Coat proteins


  Different coat proteins are used for different steps in vesicle traffic, selecting different cargo and shaping the transport vesicles
• The endoplasmic reticulum and the Golgi apparatus are strictly communicating organelles that play a vital role in the metabolism and trafficking within the cells