Cells

Cards (55)

  • Robert Hooke (1665) first described cells, built one of the primitive microscopes to look at a thin slice of pork
  • Antonie van Leeuwenhoek was the first to observe living cells in water (animalcules)
  • Matthias Schleiden (1838) stated that all plants are composed of individual units called cells
  • Theoder Schwann (1839) - discovered the Schwann cell, which is a glial cell that surrounds and protects nerve fibers
  • The Modern Cell theory
    • Cells are the smallest complete living things
    • All organisms are composed of one or more cells
    • Cells arise only from preexisting cells through cell division
    • All existing cells are descendants of the first cells formed early in evolutionary history
  • Cell membrane / plasmalemma
    Physical barrier separating the inside of the cell from extracellular fluid
  • Functions of the cell membrane
    • Physical isolation
    • Regulation of exchange with the environment
    • Sensitivity to the environment
    • Structural support
  • Membrane lipids
    Mostly found at the surface of the cell membrane, forming a phospholipid bilayer
  • Membrane lipids
    • Contain cholesterol and other steroids, small quantities of other lipids, proteins, and glycolipids
    • Cholesterol makes the plasma membrane less fluid and less permeable
  • Examples of membrane proteins
    • Anchoring proteins
    • Recognition proteins
    • Enzymes
    • Receptor proteins
    • Carrier proteins
    • Channels
  • Membrane carbohydrates
    Form a layer known as the glycocalyx
  • Functions of the glycocalyx
    • Lubrication and protection
    • Anchoring and locomotion
    • Specificity in binding
    • Recognition
  • Cytoplasm
    The material between the plasma membrane and the membrane that surrounds the nucleus
  • Subdivisions of the cytoplasm
    • Cytosol
    • Organelles
    • Inclusions
  • Cytoskeleton
    • Internal protein framework that gives the cytosol strength and flexibility
    • Made up of microfilaments, intermediate filaments, and microtubules
    • Determines where key enzymatic reactions take place and where specific proteins are synthesized
  • Centrosome and centrioles
    Region of cytoplasm located next to the nucleus, form the basal bodies found at the base of some cellular extensions
  • Ribosomes
    Responsible for protein synthesis, consist of two subunits (small and large)
  • Proteasomes
    Contain protein-digesting enzymes that remove and recycle damaged or denatured proteins
  • Endoplasmic reticulum (ER)

    • Network of intracellular membranes continuous with the nuclear envelope
    • Smooth ER - synthesis of phospholipids, cholesterol, glycerides, glycogen
    • Rough ER - fixed ribosomes synthesize, modify, and package proteins
  • Golgi apparatus
    • Modifies and packages secretions
    • Adds or removes carbohydrates to/from proteins
    • Renews or modifies the plasma membrane
    • Packages enzymes within vesicles (lysosomes)
  • Lysosomes
    Vesicles that provide an isolated environment for potentially dangerous chemical reactions, contain digestive enzymes
  • Peroxisomes
    Smaller than lysosomes, break down fatty acids and other organic compounds, generate hydrogen peroxide
  • Mitochondria
    Produce energy in the form of ATP, have double membrane, contain their own DNA and ribosomes
  • Nucleus
    Control center of cellular operations, surrounded by double nuclear membrane, contains chromatin and nucleolus
  • Protein synthesis
    1. DNA in nucleus transcribes mRNA
    2. mRNA leaves nucleus to ribosome
    3. Ribosomes assemble protein from amino acids brought by tRNA
  • Cell diffusion
    How materials get across the plasma membrane without damaging it or reducing its effectiveness as a barrier
  • Plasma membranes are selectively permeable, permitting the free passage of some materials and restricting the passage of others based on size, electrical charge, and other factors
  • Protein synthesis
    The process of making a particular protein
  • Protein synthesis
    1. The code to make a particular protein lies on a DNA molecule in the nucleus
    2. mRNA copies the code from the DNA (transcription) with the assistance of RNA polymerase (enzyme)
    3. mRNA leaves the nucleus through a nuclear pore towards the cytoplasm to a ribosome
    4. Ribosomes will assemble the protein from the amino acids
    5. tRNA will collect all the amino acids from the cytoplasm to match the amino acids brought by mRNA (translation)
    6. Line up all the amino acids forming a polypeptide chain
  • Plasma membrane permeability
    Property of the plasma membrane that determines precisely which substances can enter or leave the cytoplasm
  • Plasma membranes are selectively permeable permitting the free passage of some materials and restricts the passage of others based on size, electrical charge, molecular shape, lipid solubility, etc.
  • Passive processes

    Move ions or molecules across the plasma membrane with no expenditure of energy by the cell
  • Active processes
    Require that the cell expend energy, generally in the form of ATP
  • Diffusion
    • Passive; tends to eliminate concentration gradients
  • Factors influencing diffusion
    • Distance
    • Ion and molecule size
    • Temperature
    • Concentration Gradient
    • Electrical Forces
  • Channel mediated diffusion
    More complicated for ions and water-soluble compounds, which are not lipid soluble; must pass through a membrane channel
  • Osmosis
    Diffusion of water across selectively permeable membranes
  • Types of osmolarity
    • Isotonic
    • Hypotonic
    • Hypertonic
  • Abnormal cell growth and division characterize tumors and cancer
  • Agents that cause mutation (mutagens)
    • Radiation
    • Chemicals
    • Bacteria and viruses
    • Alcohol
    • Estrogen