Chapter 3A Human Physiology

Eukaryotic Cell Overview

  • Organelles: membrane-bound structures that perform specific functions
  • Cytoplasm: everything inside cell membrane except the nucleus
  • Cytosol: fluid inside the cell membrane but outside of the organelles

Plasma Membrane

  • Plasma membranes act as a selective barrier
    • Selective barrier: The function of the plasma membrane as it is surrounding whole cell, organelles, nucleus
    • Helps with compartmentalization
    • Movement of molecules between compartments
    • Selectivity
    • Regulation
  • The plasma membrane also senses chemical messengers and helps with cell signaling
  • The plasma membrane functions as cellular support
    • Cellular Support: The plasma membrane function that anchors the cells to adjacent cells and the extracellular matrix (ECM)
    • Glycoproteins in ECM bind to proteins in plasma membrane
    • Provide sites for transmission of forces
    • The plasma membrane also acts as a double layer of phospholipids
    • Few chemical bonds link the phospholipids
    • Helps with fluid structure
    • Cholesterol adds stability to the cell membrane
Proteins in the Cell Membrane
  • Integral proteins: Proteins imbedded within the cell membrane
    • Integral proteins are amphipathic
    • Transmembrane proteins: A subunit of integral proteins that form channels, transmitting cell signals from the extracellular fluids to the intracellular fluids
  • Peripheral Proteins: Proteins attached to inside or outside the cell membrane, but do not transverse the whole membrane; helps with enzyme activity and cell shape
  • Glycocalyx: This is a layer made of glycoproteins & carbohydrates used for cell recognition,
Cell Membrane Junctions
  • Cell Membrane Junctions: Physical connections between cells
  • Desmosomes: Membranes of adjacent cells linked by strong fibers in isolated spots
    • Important in areas subjected to stretch
    • Holds cells firmly together, structural support
  • Tight Junctions: Membranes joined with no space between them, connections go all the way around the cell; restricts molecular diffusion between cells
    • Paracellular Pathways: A passive transport process that results in the transport of substances across an epithelium by passing through the intercellular spaces in between epithelial cells.
    • Transcellular Pathways: A carrier-mediated, energy-dependent, active transport mechanism,
  • Gap Junctions: Protein channels that link the cytosol of adjacent cells; allows small molecules & ions to pass between cells & rapid cell communication

 

Cellular Organelles

 

  • Cellular Organelles: Plasma membrane-bound structures that perform specific cellular functions
  • Nucleus: Largest cellular organelle, stores DNA
    • Cells without a nucleus include skeletal muscle and red blood cells
    • A nucleus stores genetic information in the from of DNA, the blueprints of protein synthesis
    • Nucleolus: Part of the nucleus, site of ribosomal RNA synthesis
    • Chromatin: Part of the nucleus, is the DNA
    • Nuclear evelope: Encases the nucleus and allows mRNA to pass into cytoplasm, also called pores
  • Ribosomes: An organelle that builds proteins by connecting amino acids; many of these in a cell
    • Free ribosomes: Ribosomes that release proteins into cytosol
    • Bound ribosomes: Ribosomes that are attached to the ER and release proteins into the ribosome
  • Endoplasmic Reticulum: A large continuous space encoled my membranes, has a rough and a smooth type
    • Rough ER: Contains ribosomes, involved in packaging of proteins
    • Smooth ER: Responsible for protein synthesis, Ca2+ handling
  • Golgi Apparatus: A series of flat membraned sacs that deal with protein modification & packages proteins into vesicles
    • Vesicle: A small sac that moves stuff into and out of a cell
    • Intracellular transport
    • Secretory vesicles: Vesicles that fuse with the cell membrane and release contents (proteins) to the extracellular fluid
  • Mitochondria: Produces the cell’s energy (ATP) and has inner & outer membranes and a matrix
    • The mitochondria consumes oxygen and produces CO2, heat, and water
  • Lysosomes: Contain acidic fluid and digestive enzymes used to break down bacteria, damaged \n cells, and cellular debris
  • Peroxisomes: Contains enzymes that oxidize organic molecules like lipids and alcohol
  • Cytoskeleton: Generally made of proteins, this is NOT a membrane-closed organelle but helps maintain and change cell shrape
  • Cytosol is the fluid in a cell, but the cytoplasm is all of the cell contents