Honors Bio Ch 4

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Microscopy

  • Hooke (1665)

  • Van Leeuwenhoek (1674)

    • Amazing array of life within a droplet of water → animalcules

Microscopy Types:

  • Light microscopy:

    • Shines light through samples

      • Very tiny (living) organisms

      • View slices of larger ones

    • Often requires staining of specimen

    • Limited magnification power due to the nature of light

  • Electron microscopy:

    • Bombards a specially treated sample with a beam of electrons

      • Changed electron patterns interpreted into visible images

      • Better magnification capacity

      • 2 types:

        • Scanning EM:

          • Reveals surface features of specimens

        • Transmission EM:

          • Examines slices making internal details visible

Cell Theory:

  • All living things are made of one or more cells

  • The cell is the basic structural and functional unit of life

  • New cells come from existing cells


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Characteristics of all cells:

  • Genome: information within DNA

    • Prokaryotes single circular chromosome

    • Eukaryotes multiple linear chromosomes

  • Ribosomes: exist as separate subunits until they join for translation

    • Composed of rRNA and proteins

  • Cytoplasm: describes both the area within a cell and the material found there


  • Eukaryotes: Cytoplasm:

    • Eukaryotic cytoplasm includes both:

      • Organelles: 

        • Highly specialized part of a cell with a unique structure and function

      • Cytosol:

        • Cellular fluid/ cell solution

  • Plasma Membrane: a cell’s perimeter/ border composed of a phospholipid bilayer


Membranes

  • Membranes are also a part of many eukaryotic organelles

  • Composed of:

    • Phospholipids ≈ (60%)

    • Associated proteins ≈ (40%)

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  • Fluid mosaic model

    • “Mosaic” → wide variety of different proteins suspended in “sea” of phospholipids

    • “Fluid”→ molecules flow past one another

  • Membranes are dynamic!!!!

  • Membranes create isolated compartments!!!!


Eukaryotes: Nucleus:

  • Border → nuclear envelope: double layer of membrane

    • Perforated by numerous nuclear pores that are each lined with a ring of “guard proteins”

  • Genome in chromatin form (used during interphase)

  • Nucleolus/ nucleoli: dark spot(s) within → area of intense activity where ribosomes are made

Eukaryotes: “ER”:

  • Endoplasmic reticulum:

    • Intricate network of membrane folds - has distinct internal environment with unique materials

    • Isolated from cytoplasms

    • ER membranes may be continuous with nuclear envelope

    • 2 types:

      • Smooth ER → lacks ribosomes

        • Lipid production

        • Detoxification of poisons

          • E.g. liver cells have more smooth er because they are in charge of detoxification of blood

      • Rough ER → studded with ribosomes

        • production/ processing of certain types of proteins

        • Numerous docks on surface for temporary ribosome attachment

        • Ribosome subunits all start out “free” - only joining up and becoming “fixed” to the RER when translating specific types of proteins ~ destined to

        • Ribosomes that are docked at the RER are translating proteins destined to:

          • To be embedded within a membrane (a membrane protein)

          • To be secreted from a cell

          • To be delivered to particular proteins

        • ~ requires ribosomes to detect the type of protein being translated:

          • certain proteins have a signal early in their aa chain - telling the ribosomes to dock at the RER 

          • If aa chain lacks signal - ribosomes continue translation- remaining free

            • These proteins are destined to function in the cytoplasm (ex microtubules)

        • As docked ribosomes continue translating - proteins get threaded inside the RER

        • Within the RER the protein is folded and modified in the unique RER environment

        • Complete proteins are packaged into a vesicle → membrane bound “bubble” for transport elsewhere

        • Vesicle formation = budding out

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Eukaryotes: Golgi Apparatus:

  • Golgi: series of flattened membrane bound pouches- each with own unique internal environment

    • Vesicles from RER fuse with 1st Golgi pouch on “receiving” side- releasing contents inside

    • Proteins move pouch to pouch where they may be uniquely modified

    • All proteins will be modified with a molecular “ID tag” to indicate their final destination in the cell

    • Completed proteins get packaged into new vesicles and shipped from the “departure” side of the Golgi

    • Can also accumulate specialized proteins and package together- forming certain organelles: vacuoles and lysosomes

Vacuoles:

  • Vacuoles: membrane bound pouches used for the storage of various materials

    • E.g. food, water, toxins, ions, pigments

  • Central Vacuole: plants only- stores H20, ions, and other solutes

  • Contractile Vacuole: temporary H20 storage- only to squish it out later

  • Food Vacuole: stores food for later digestion- formed by phagocytosis: uptake of “food” from outside the cell “cellular eating”

Lysosomes:

  • Lysosomes: membrane bound pouches full of hydrolytic enzymes that can break down biomolecules

  • Internal pH ~ 5 as the enzymes only function in an acidic environment

  • Fuse with food vacuoles releasing enzymes to facilitate digestion

  • Can also fuse with old/ damaged or unused organelles → autophagy

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The Endomembrane System

  • Includes all eukaryotic organelles that either directly or indirectly share/ exchange membrane

  • All domain eukarya has an endomembrane system

  • Sideability

  • Everything is DYNAMIC!!!

    • Smooth er

    • Rough er

    • Vesicle

    • Golgi

    • Lysosomes

    • Vacuoles

    • Nuclear envelope

Mitochondria and chloroplasts:

  • Unique observations

    • Have membranes- but are not part of the endomembrane system

    • Accomplish the majority of metabolic activity in eukaryotes (re food and energy)

  • Unique commonalities

    • Each has 2 membrane layers

      • Inner: similar to prokaryotic plasma (bacteria) membranes

      • Outer: features similar to membranes of a eukaryotic food vacuole

    • Both have their own DNA:

      • Single circular chromosome

      • Genes lack introns

    • Both have their own ribosomes/ tRNAs

    • Both grow, replicate their DNA, and divide similar to binary fission

    • If either is removed - eukaryotic cells cannot make more of them

Endosymbiotic Theory:

  • These organelles are the result of an ancient “endosymbiotic” relationship with specialized prokaryotes that had the same unique metabolic activities

  • Ancient predator cell engulfed a prey cell (phagocytosis), forming a food vacuole

  • Captured prey were not digested 

  • Prey continued living inside the predator - eventually dividing

  • Predator cell divided and some prey ended up in their daughter cells

  • Relationship was mutually beneficial - providing both survival advantages

  • Over billions of years - the ancient prey eventually became “dependent” organelles

Mitochondria:

  • Mitochondria:

    • Perform cellular respiration: process in which food molecules are broken down with using oxygen to release energy 

    • C6H12O6 + 6O2 → 6O2 + 6H2O + energy

Chloroplasts:

  • Chloroplasts: 

    • perform photosynthesis: process in which food molecules are made using light energy Co2 and H2O

    • 6CO2+ 6H2O + energy → C6H126O2

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Eukaryotes: Cytoskeleton

  • Cytoskeleton: network of various protein fibers with aa variety of roles

    • Helps determine cell shape and involved in any shape changes

      • Ex. amoeba rearranging around its food

      • Proteins gliding past each other

    • Involved in chromosome movement during nuclear division

      • Nonkinetochore microtubules 

    • Anchors organelles and is involved in any movement/ relocation

    • Construct cell features involved in movement of the entire cell or fluids around the cell:

      • Cilia: numerous, short, hair-like projections from the cell’s surface - “sweep recover” action

      • Flagella: few, long, tail-like structures that move side to side to propel cells forward

Eukaryotes: Cell Walls: 

  • Cell walls: outermost structures for:

    • Plants (cellulose)

    • Fungi (chitin) 

    • Certain protists (varies)

  • Provide protection and support/ reinforcement of cell structure

Eukaryotes: Extra Cellular Matrix:

  • Extracellular matrix: intricate network of protein fivers outside animal cells

    • Primarily made of collagen (& elastin)

    • Tethered to anchor proteins in the plasma membrane

    • Lashes neighboring cells together- creating cohesive sheets of tissue

    • Can relay information across the membrane and to neighboring cells