• Cell is the basic unit of life

• Cell theory - dictates that all living things are composed of cells, and all cells arise from other cells

  • “Living things” not composed of cells are things like viruses

• Most organisms consist of a single cell

  • unicellular 

  • E.g bacteria, amoeba, paramecium, yeast

• Organisms with more than one cell that work together

  • multicellular 

  • E.g plants, animals, most fungi

• Cell theory only possible through light microscopy

  • Most eukaryotic cells are 10um in dimension

  • Most prokaryotic cells are 1-3um in dimension

  • Not visible to the naked eye

Prokaryotic Cells

• Smaller and more simple than eukaryotic cells

• Unicellular

• No nucleus

  • Usually only have one circular piece of  DNA

  • Nucleoid region is sometimes visible, not properly defined entity

• Prokaryotic cell contains:

  • One or two phospholipid-based membrane(s)

  • Rigid cell wall

    • In bacteria, solid portion of cell wall is made of a polymer of amino acid sugars (peptidoglycan

    • In archaea, cell wall is more variable. Most have pseudomurein (similar to peptidoglycan but different) while others have polysaccharides and glycoproteins

  • Many have:

    • Flagella (motion)

    • Frimbriae (adherence)

    • glycocalyx/capsule (adherence and pathogen avoidance)

• Can be found in extreme environments

Eukaryotic Cells

• 5-10 times larger in any dimension

• Larger size creates issues with respect to surface to volume ration

  • As size increases, less SA to produce metabolic resources (ATP)

  • Solution = provide more membrane SA on inside of cell

• Extra structure inside allow functions to be compartmentaliized 

  • E.g Mitochondria takes care of most ATP generation (in prokaryotes, it is handled by the plasma membrane)

• Endomembrane system

  • There are membranes and membrane-bound bodies throughout the cell

  • Derives from the endoplasmic reticulum

  • Most, not all, transfer materials between them, directly or indirectly

• Nucleus

  • Defined by a double phospholipid bilayer nuclear membrane, the nuclear envelop is part of the endomembrane system

    • Several pores allow selective entry and exit of specific materials (e,g M-RNA) from nucleus

      • Controlled by protein-based pores complexes

    • Inner surface of the envelope is stabilized by filamentous nuclear lamina

  • Contians all of the chromosomes

    • Linear strands of DNA woud around heads of Histones

      • Eukaryotes have more DNA than prokayotes

  • When are wound up tightly, individual chromosomes can be seen as discrets units under light microscope

    • When wound loosely, not visible (Chromatin)

• Nucleolus

  • Dark unbound and non-discrete body within nucleus

  • Puts together ribosomal units

    • Ribosomal units compromised of rRNA and ribosomal proteins

  • Subunits are exported to the cytoplasm, where they are put together into functional proteins

• Ribosomes

  • Found either in: 

    • Free in cytosol

      • Used to make proteins for use in cytosol

    • Bound to ER

      • Used to make proteins for export out of the cell or for inclusion membranes

• Endoplasmic Reticulum (ER)

  • Memberous series of tunnels and sacs that run throughout the cell 

  • Is continuous with the outer membrane of the nucleus

  • Two types:

    • Rough ER - studded with ribosomes

      • Proteins for transport are translated and sent back into the cisternae

        • Carbohydrates attached become glycoproteins

        • Packed into vesicles that bud off from ER

      • Synthesis of proteins and lipids that become part of the ER, and other parts of the endomembrane system

    • Smooth ER - NOT studded with ribosomes

      • Synthesis of lipids, phospholipids and steroids

        • Adrenal gland cells that make steroid sex hormones have extenisve smooth ER

      • Deoxify poisons and drugs in liver cells

        • Smooth ER associated with enzymes add -OH groups to toxins

        • Makes them soluble in the cytosol and thus more easily eliminated

      • Glycogen metabolism

        • Smooth ER associated enzymes removes phosphate group from glucose, releasing it in to the blood

      • Stores calcium for muscle contraction

        • Ca^2+ pumped into the cisternae of the ER, then released into the cytosol when muscle contracts

• Golgi Apparatus

  • Flattened membranous sac, very similar to ER

  • Products of the Er are brought via vesicles, are modified and sent to other places, especially for secretion outside of cell

    • Amylase in saliva

  • Cis Fae

    • Facing towards the interior of the cell

    • Receives vesicles from the rough ER

      • Vesicles and ER fuse like two soap bubbles

    • Modifies product from ER

      • Placing saccharides onto proteins to make glycoproteins

  • Modified products end up at the trans face

    • Packaged  into new vesicles, and pinched off

    • Vesicles containing products for secretion from the cell then fuse with the plasma membrane and are released

  • Some golgi-derived vesicles contain digestive enzymes and related proteins; become lysosomes

    • H ions are pumped into the lysosome form the cytosol to keep pH low

    • Lysosomes have three functions:

      • Intracellular digestion

      • Autolysis

      • Programmed cell death (apoptosis)

  • Some cells can engulf (phagocytosis) particles some plasma membrane around it and internalize it as a food vacuole (phagosome)

    • E.g white blood cells, amoebae

    • Lysosomes fuse with food vacuoles

      • Degrade the particle and pump nutrients into cytosol

  • Lysosome will engulf and destroy a cellular component when needed (autolusos) 

    • Damaged mitochondria

    • Cellular health

  • During development of multicellular organisms, some cells must be destroyed as part of normal tissue development (apoptosis)

    • E.g tissue between fingers

    • Lysosomal enzymes released, killing cell

• Vacuole

  • Large membrane-bound sacs with specific functions

    • Food vacuole

    • Contractile vacuole

      • Pumps water from cell (fresh water protozoa)

  • Central vacuole for mature plant cells

    • Enclosed by tonoplast membrane

  • Several functions

    • Storage: organic or inorganic compounds, pigments, protective chemicals

    • Sequestration of metabolic by-products

    • Takes up water to help plant cell elongate

      • Takes up space, there is little cytoplasm per unit membrane surface