Cell Biology






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Prokaryotic_Cells Structure_of_the_Cell_Membrane Energy_and_Biology
Eukaryotes Cell_Transport Enzymes











Prokaryotic Cells

  1. Bacteria & Archaebacteria

  2. Small, relatively simple structure

  3. DNA not enclosed in nucleus









  1. •Single cells (protists) or multicellular organisms

  2. •DNA contained in nucleus

  3. •Contain organelles:  Specialized structures with specific functions in the cell

  4. •Animal and plant cells have some differences!



Animal Cell

Plant Cell


Eukaryotic Cell Parts


Nucleus: The Headquarters


  1. •DNA protected within membrane-bound nucleus

    •Control center – information contained in DNA

  2. Chromatin = DNA wrapped with protein

  3. •Many cell organelles are connected through a network of membranes within cell

    •Endomembrane system is a collection of membranous organelles that manufactures and distributes cell products

Smooth Endoplasmic Reticulum (ER): Production of Lipids

  1. •Smooth ER

  2. Synthesizes lipids

  3. Processes toxins and drugs in liver cells

Rough Endoplasmic Reticulum: Production of Proteins

•Ribosomes on the surface of the rough ER •produce proteins that are:

  1. •     released from cell (secreted) 

  2. •     inserted into membranes or

  3. •     transported in vesicles to other organelles


Golgi apparatus: Packaging & Shipping (UPS)

  1. The Golgi apparatus finishes, sorts and ships cell products

  2. Stacks of membranous sacs receive and modify ER products then ship them to other organelles or the cell surface


    Lysosomes: Clean-up Crew

    1. •Lysosomes breakdown materials in cell

    2. •Sacs of enzymes that digest food, macromolecules and damaged cell parts

    3. •Lysosomes in white blood cells destroy bacteria

      Lysosomes also recycle damaged organelles


      Lysosomal Storage Diseases

      •Abnormal enzymes in lysosomes cannot break down large molecules -->

      •Build up toxic levels in cell

      •Damage nerves, liver, other organs

      •>40 Lysosomal storage diseases

      •Due to defective gene coding for the enzyme

      •(examples:  Tay Sachs, Gaucher, etc.)




      Vacuoles: Storage

      Vacuoles function in the general maintenance of the cell

      •Plant cells contain a large central vacuole which has lysosomal and storage functions

      •Some protists have contractile vacuoles that pump out excess water


      The various organelles of the endomembrane system are interconnected structurally and functionally





See Textbook Website or CD for animation of protein synthesis in endomembrane system.





Energy Converting Organelles

Chloroplasts: Solar converters

•Chloroplasts convert solar energy (sunlight) to chemical energy (sugars)

•Found in plants and some protists


Mitochondria: Powerhouse of the Cell

Mitochondria harvest chemical energy from food








Cytoskeleton and Related Structures

Cytoskeleton: Network of protein fibers

  1. The cell’s internal skeleton helps organize its structure and activities

  2. Cilia and flagella move when microtubules bend

    •Eukaryotic cilia and flagella on the surface of some cells allow movement




    1. Cell surfaces protect, support, and join cells

    2. •Cells interact with their environments and each other via their surfaces.

    3. •Animal cells are embedded in an extracellular matrix which binds cells together in tissues

    4. •Plant cells are supported by rigid cell walls made largely of cellulose and connect by connecting channels

      •called plasmodesmata.












Structure of the Cell Membrane


Structure Function
Phospholipid bilayer Basic structure of cell membrane; phospholipids arranged with hydrophilic phosphate heads in contact with cytoplasm and extracellular matrix; lipid tails align to form a hydrophobic interior
Cholesterol Allows membrane to be flexible
Transport Proteins Act as channels or gates to regulate what enters and exits the cell.
Receptor & Signal Proteins Mechanism by which cell interior communicates with environment
Glycoproteins Used for identification (e.g., blood type)

Cell Transport


Diffusion works by:

nDifference in concentration of molecules

nMolecules move from high concentration --> low concentration


Continue to move until the molecules are evenly distributed

Diffusion across a selectively permeable membrane

nMembrane will allow some molecules into cell by simple diffusion

nSmall, nonpolar molecules

nGases (CO2, O2) n(some water)


Passive transport in cells

Substances move from high concentration --> low concentration

Does not require Energy


simple diffusion (small nonpolar molecules & gases)

facilitated diffusion (some ions, sugars, amino acids)

osmosis (water)


Osmosis = diffusion of water across a selectively permeable membrane

water crosses membrane, but solute dissolved in water does not because it is too large or too polar

  • Water moves from area of high water concentration to low water concentration
  • Water moves from area of low solute concentration to high solute concentration





No change in the amount of water in the cell in isotonic solution Water flows into cells from hypotonic solution Water flows out of cells in hypertonic solution    
Facilitated Diffusion

High concentration --> low concentration

No energy required

Special proteins help substance cross the cell membrane by creating channels in the membrane

Carrier protein in membrane changes shape as a specific molecule binds, allowing molecule to enter the cell.



Why is passive transport important?
nOxygen to body cells
nCO2 waste removed
nRemoves toxins and waste from blood
nRegulates blood pressure and volume
nFacilitated diffusion
nNutrients from food enter body
nCells get supplies they need
nCommunication between cells



Active Transport

n       Cell needs something that is not abundant
(low concentration)

n       Transport molecules from
low concentration high concentration

n       Like pedaling a bike uphill – molecules move against concentration gradient

n       Requires ENERGY (ATP)


Click to see Sodium Potassium Pump (with sound effects!)

n       Na+ pumped out of the cell

n       K+ pumped into the cell

n       ATP involved

n       Used in nerve cells to create an electrical charge that is used by nerve cells to communicate



n       Cell takes in particles or solutes by forming vesicles which surround substance

n       Pinocytosis –Cell drinking

n       Phagocytosis – Cell eating


n  Membrane folds in, trapping liquid in vesicle.

n  Vesicle pinches off, enters cell.

n  Energy required.

n  Click here to see Pinocytosis

Phagocytosis – cell eating

n  Pseudopods (false feet) surround particle to form a vesicles

n  Vesicle is taken into cell

n  Click here to see Phagocytosis




n       Vesicle with cell products or waste moves to cell membrane.

n       Vesicle fuses with cell membrane.

n       Contents of vesicle released from cell.


Comparison of Passive and Active Transport

Passive Transport

Active Transport

No energy required

Energy required

High --> Low concentration

Low --> High concentration

Nonpolar molecules            

Polar molecules

Small molecules                                               

Large molecules                    






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Mitosis video

Shoe mitosis