Cells

• Plasma membrane

  Made up of phospholipids, proteins, and cholesterol
• Plasma membrane

  • Main functions are transport, protection and communication
• Phospholipids


  Have a hydrophilic head and hydrophobic tail
• Small lipid soluble molecules


  Can passively diffuse across the plasma membrane
• Cholesterol


  Maintains the membrane fluidity
• Types of membrane proteins

  • Integral
  • Peripheral
• Integral membrane proteins


  Anchored to the membrane and may span most to all of the membrane
• Peripheral membrane proteins


  On the outside or inside of the membrane
• Membrane proteins

  • For transport, adhesion, cell recognition, and relaying information
• Components of the cytoskeleton

  • Microtubules
  • Microfilaments
  • Intermediate filaments
• Microtubules


  Hollow tube made of tubulin helices, resist compression, important for motility
• Microfilaments


  Made of actin subunits, resist tension, form the cortical network
• Intermediate filaments


  Made of keratin, resist tension, anchor organelles and are important in cell adhesion
• Euchromatin


  DNA that is used less often so it is less tightly bound
• Heterochromatin


  DNA that is used more often so it is more tightly bound
• Nucleolus


  Where rRNA and ribosomal subunits are made
• Nucleus

  • Inner surface is lined by the nuclear pores and nuclear lamina, which maintains its spherical shape
• Nuclear pores


  Made of nucleoporins, allow mRNA, tRNA and ribosomal subunits to move out of the nucleus
• Components of the endomembrane system

  • Endoplasmic reticulum
  • Golgi complex
  • Vesicles
• Endomembrane system

  • Modifies, packages, and moves proteins and lipids
• Smooth ER

  Stores Ca2+, synthesises lipids, metabolises carbohydrates, and detoxifies
• Rough ER

  Covered in ribosomes which are involved in protein synthesis
• Vesicle transport

  1. Vesicles from the ER arrive at the cis face of the Golgi and leave at the trans face

  2. Vesicles move via motor proteins "walking" along microtubules
• Simple diffusion


  Requires no energy and moves substances down their concentration gradient
• Facilitated diffusion


  Moves substances down their concentration gradient through channels/carriers
• Active transport


  Requires ATP to move substances against their concentration gradient using a transport protein
• Types of endocytosis

  • Pinocytosis
  • Phagocytosis
• Pinocytosis


  Uptake of solutes from ECF
• Phagocytosis


  Uptake of "food" particles to be digested
• Types of exocytosis

  • Constitutive
  • Regulated
• Constitutive exocytosis

  Releases proteins to the ECM
• Regulated exocytosis


  Releases signals such as hormones and neurotransmitters
• Lipid-soluble signals


  Released as they are made
• Water-soluble signals


  Released via regulated exocytosis and can be stored
• Vesicle fusion

  Tethered and docked in place, then primed and fused to plasma membrane, signal is released and vesicle is retrieved
• Cell communication coordinates body and cell functions
• Signalling pathways

  • Need specificity which is achieved by direct contact, selective receptor expression, and degradation of signal molecule
• Modes of signalling

  • Juxtacrine
  • Paracrine
  • Autocrine
  • Endocrine
• Juxtacrine signalling

  Requires direct cell to cell contact and may be mediated by gap junctions
• Gap junctions


  Made up of connexins and allow small molecules to move back and forth between cells, allowing very rapid communication