A.S Bio - Cell Structure

• Nucleus


  The brain of the cell, the center where everything begins and centers around
• Nuclear envelope


  • Outer layer - where ribosomes are found
  • Inner layer - contains lamins that bind to DNA and histones, control structure and cell division
• Nuclear pores


  Proteins dispersed throughout the nuclear envelope that allow transport in and out of the nucleus
• Nucleolus


  Site of rRNA synthesis, which combines with proteins to form ribosomes
• 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)

  Contains ribosomes, site of protein synthesis, protein folding, and glycosylation
• Smooth endoplasmic reticulum (smooth ER)

  Lacks ribosomes, site of lipid synthesis (fatty acids, phospholipids, cholesterol)
• The smooth ER contains enzymes for lipid synthesis, including fatty acids, phospholipids, and cholesterol</b>
• Cholesterol synthesized in the smooth ER can be used to make steroid hormones
• 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 ER

  2. Enzymes in smooth ER use precursors to synthesize lipids

  3. Lipids packaged into vesicles

  4. Vesicles sent to Golgi or cell membrane
• Golgi apparatus


  Important packaging organelle
• Golgi apparatus


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


  • Phospholipid bilayer with cholesterol and proteins
  • Acts as a selectively permeable barrier
• Phospholipid bilayer


  Phospholipid heads are polar/hydrophilic, fatty acid tails are non-polar/hydrophobic
• Cholesterol


  Regulates fluidity of cell membrane - more cholesterol = less fluidity
• Cell membrane proteins


  • Can act as transporters, enzymes, or linker proteins between cells
• Lysosomes


  Contain hydrolytic enzymes that break down proteins, lipids, and other molecules
• Hydrolytic enzymes in lysosomes

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


  • Contain catalase and oxidase enzymes to break down hydrogen peroxide
  • Involved in fatty acid metabolism and lipid synthesis
  • Involved in a small amount of alcohol metabolism
• Mitochondria


  The powerhouse of the cell, site of ATP synthesis
• Components of mitochondria


  • Outer membrane
  • Inner membrane (cristae)
  • Mitochondrial matrix
• ATP synthesis in mitochondria

  1. Oxidative phosphorylation

  2. Substrate phosphorylation
• Metabolic processes in mitochondria

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


  Inherited from mother
• Ribosomes


  Organelles that synthesize proteins
• Components of ribosomes


  • Large subunit
  • Small subunit
• Ribosomes


  Made up of rRNA and proteins
• Locations of ribosomes


  • Membrane-bound (on rough ER)
  • Cytosolic (free)
• Function of ribosomes


  Translate mRNA into proteins
• Locations of ribosomes


  • Bound to rough endoplasmic reticulum (membrane-bound ribosomes)
  • Freely circulating in cytosol (cytosolic or free ribosomes)