Cell Biology

• Nucleus


  The brain of the cell, the center of the cell where everything that a cell is kind of really begins in all centers around
• Nuclear envelope


  • Outer layer
  • Inner layer
• Outer layer of nuclear envelope

  Where ribosomes are found
• Inner layer of nuclear envelope

  Contains a protein structure called lamins that binds to DNA and histone proteins, controls cell division
• Nuclear pores


  Dispersed throughout the nuclear envelope, allow for transport of ions, proteins, nucleotides in and out of the nucleus
• Nucleolus


  Site of rRNA synthesis, where ribosomes are made
• Chromatin


  Made up of DNA and histone proteins, can be in euchromatin (loose, for expression) or heterochromatin (tight, towards nuclear envelope)
• Functions of the nucleus

  1. DNA replication

  2. Transcription to make different types of RNA (mRNA, tRNA, rRNA)
• Rough endoplasmic reticulum (rough ER)


  Filamentous membranous structure with ribosomes on the surface, site of protein synthesis and folding, performs glycosylation
• Smooth endoplasmic reticulum (smooth ER)

  Lacks ribosomes, site of lipid synthesis (fatty acids, phospholipids, cholesterol)
• Rough ER


  Packages synthesized, folded and glycosylated proteins into vesicles to transport to Golgi apparatus
• Lipid synthesis


  Primary function of enzymes associated with this process
• Lipids synthesized


  • Fatty acids
  • Phospholipids
  • Cholesterol
• Cholesterol


  Can become steroid hormones like testosterone, progesterone, estrogen
• Lipid synthesis process


  1. Precursor molecules taken up into smooth endoplasmic reticulum

  2. Enzymes use precursors to synthesize lipids

  3. Lipids packaged into vesicles

  4. Vesicles sent to Golgi or cell membrane
• CYP450 enzymes


  Very important for detoxification, located in smooth endoplasmic reticulum
• Glucose 6-phosphate metabolism


  1. Glucose 6-phosphate transported into smooth ER

  2. Enzyme on smooth ER removes phosphate to produce glucose
• Smooth endoplasmic reticulum


  Stores calcium, has pumps to release calcium into cytosol when needed
• Golgi apparatus


  Important packaging organelle that receives vesicles from rough and smooth ER
• Cis Golgi


  Side of Golgi where vesicles from ER enter
• Trans Golgi


  Side of Golgi where modified molecules exit in vesicles
• Functions of Golgi


  • Receives vesicles from ER
  • Modifies proteins and lipids via glycosylation and phosphorylation
  • Packages modified molecules into vesicles
  • Sends vesicles to lysosomes, cell membrane, or for secretion
• Cell membrane


  Selectively permeable barrier that allows different types of transport
• Components of cell membrane

  • Phospholipid bilayer
  • Cholesterol
  • Integral and peripheral proteins
• Phospholipid bilayer


  Hydrophilic heads facing outwards, hydrophobic tails facing inwards
• Cholesterol


  Regulates fluidity of cell membrane
• Lysosomes


  Contain hydrolytic enzymes that break down proteins, lipids, nucleic acids
• Hydrolytic enzymes in lysosomes include proteases, lipases, nucleases
• Vesicular transport


  Moving things from outside the cell to inside the cell
• Cell membrane


  • Acts as a barrier for particular types of transport processes
• Lysosomes


  Spherical organelles that contain hydrolytic enzymes
• Hydrolytic enzymes in lysosomes

  • Proteases (break down proteins)
  • Nucleases (break down nucleic acids)
  • Lipases (break down lipids)
  • Glucosidases (break down carbohydrates)
• Autophagy


  Lysosomes break down worn-out organelles
• Autolysis


  Lysosomes break down all macromolecule components of severely damaged cells
• Peroxisomes


  Organelles that contain enzymes like catalase and oxidase to break down free radicals and hydrogen peroxide
• Peroxisomes


  • Important for fatty acid metabolism, lipid synthesis (including plasmalogens in myelin), and a small amount of alcohol metabolism
• Mitochondria


  The 'powerhouse' of the cell, site of ATP synthesis via oxidative phosphorylation and other metabolic processes
• Mitochondrial components


  • Outer membrane
  • Inner membrane (cristae)
  • Matrix
• ATP synthesis in mitochondria

  1. Oxidative phosphorylation

  2. Substrate phosphorylation
• Metabolic processes in mitochondria

  • Krebs cycle
  • Heme synthesis
  • Urea cycle
  • Gluconeogenesis
  • Ketogenesis