CELLS, continued

There are 2 basic kinds of cells.
 Prokaryotic and eukaryotic.
  Delineates life’s three basic kinds of organisms.
   Archaeans and Eubacteria -- prokaryotes.
   Plants, animals, fungi, protists -- Eukaryotes.

Prokaryotic cells:
 Generally small, 1-10 micrometers, or um, in diameter (but some much larger).
    What's a micrometer?
 DNA not bounded by a special membrane.
 DNA circular, not associated with specialized histone proteins.
 Cell organization relatively simple.
  A few specialized membranes, but no true organelles.
 The most ancient cells known, about 3.5 billion years.

Eukaryotic cells:  (Fig. 3.4, Stern et al.)
 Cells much larger: 5-100 um, or larger (ostrich egg...)
 DNA housed in discrete nucleus, bounded by a nuclear envelope.
 DNA associated with histone proteins to comprise CHROMATIN
  (what we recognize as chromosomes).
 Cell organization highly compartmentalized into organelles that house discrete processes.
  Regulate exchange between cell processes.
  Makes metabolism very efficient.

Parts of a ‘typical’ plant cell:
 Cell wall
 Protoplast -- 80-90% water
      Nucleus
      Cytoplasm
               (Fig. 3.4)
Cell wall
 Protects the cell from dessication, pathogens.
 Provides structural strength to plant.
 Non-living, but dynamic. Contains enzymes.
 Relatively porous.
 Walls of adjacent cells held in common -- a continuum.
 Composed of complex polysaccharides and proteins; also, 'secondary' metabolites such as lignin, plus cutin or suberin.
 Main polysaccharide is cellulose.
  Long chains of glucose. Many chains associated together as MICROFIBRILS.  Crystalline structure. (Figs. 3.6A,B)
  Microfibrils in the wall usually have discrete orientations that help determine the wall’s structural properties and cell shape.
 Cementing, matrix polysaccharides such as pectins and hemicelluloses.
   Lignin and proteins too.
  Analogy to reinforced concrete.
 

Other than the chloroplast, the cell wall is probably the single most  important feature in the evolution of plants.
  Allowed success on dry land. HOW????

Protoplast is bounded by a PLASMA MEMBRANE, OR PLASMALEMMA.
 Flexible. Has fluid properties.   (Fig. 3.7).
 Boundary of living part of cell. Like a fence.
 Very thin. Around 7 nanometers, or nm. Can only see it with an electron microscope. What's a nanometer?
  Looks like a railroad track. It’s a lipid bilayer.
 Controls exchange in and out of cell.
 Site of cellulose synthesis.

Plant cells are linked by thin channels called PLASMODESMATA.
 Channels are lined by the plasma membrane.
 Cytosol is continuous through them.
       NOTE: Cytosol is the non-structured part of the cell's cytoplasm. Think of chicken soup: it consists of broth, plus all sorts of chunks like carrots, dumplings, peas etc. Cytosol is like the broth, and organelles, e.g. nucleus and chlorplasts, are the clumps.
 Transport ions and macromolecules like RNA and viruses.
 They are dynamic. Their structure and size are regulated physiologically and developmentally.
        Protoplast is bounded by a PLASMA MEMBRANE, OR PLASMALEMMA.
 Flexible. Has fluid properties.   (Fig. 3.7).
 Boundary of living part of cell. Like a fence.
 Very thin. Around 7 nanometers, or nm. Can only see it with an electron microscope. What's a nanometer?
  Looks like a railroad track. It’s a lipid bilayer.
 Controls exchange in and out of cell.
 Site of cellulose synthesis.

Plant cells are linked by thin channels called PLASMODESMATA.
 Channels are lined by the plasma membrane.
 Cytosol is continuous through them.
 Small molecules, ions and large macromolecules like RNA can move thru them. Even viruses.
 They are dynamic. Their structure and size are regulated physiologically and developmentally.

Vacuoles  (Fig. 3.14)
 Single membrane bound sacs.
 Comprise up to 90% of cell volume.
  Filled with an aqueous solution containing inorganic ions such as K+, Ca2+, Cl-
  Also sugars and a variety of other organic compounds, including pigments such as ANTHOCYANINS.
    Why are anthocyanins important to plants????
  Vacuoles also contains crystals of various kinds, especially
 
  Functions:
   Storage
   Turgor regulation
    What’s turgor? Osmosis?
   Growth
    Turgor pressure provides the force necessary for
     cell growth.
   Enlarging a sac with water is a ‘cheap’ way to grow.
     Important for plants for which nitrogen is in
      relatively short supply.
   Recycling.
    Vacuoles are a digestive organelle.
     Break down proteins etc.
   Color Display -- e.g. flowers.
    Anthocyanin pigments.
     What is the function of flower colors?

Cytoplasm
 Soluble phase, or CYTOSOL.
  Analogy: the broth phase of chicken soup.
  An aqueous solution of proteins, sugars etc.
 The soup also contains ‘chunks’, or ORGANELLES.

The largest chunk is the nucleus. (Fig. 3.8)
Generally one nucleus per cell.
 Bounded by a double membrane, called an ENVELOPE.
  Envelope has hundreds of nuclear pores.
 Nucleus is the ‘Control Center’ of the cell.
 Nucleoplasm, or nuclear sap, contains chromatin.
  Extended threads of DNA associated with proteins. Each thread is a chromosome.
   Humans have how many threads, or chromosomes, per body cell?

Another group of organelles bounded by an envelope:
Plastids.
 THE ‘type’organelle of plants!! THE SEAT OF PHOTOAUTOTROPHY.
A general category of oval to lens shaped organelles.
 Surrounded by a double membrane envelope.
 The most prominent plastid is called the CHLOROPLAST.
            (Fig. 3.11)
  Main function is photosynthesis.
  Up to 100 chlorplasts per cell in leaves.
  Generally, around 4-6 um in length.