2.3 Eukaryotic Cells
Overview
 Much more complex internal structure than prokaryotic cells
 Has a nucleus and organelles in the cytoplasm with single or double membranes
 Organelle
 Def n: Discrete structures that have specific functions
Diagrams
 Draw and label a diagram of the ultrastructure of a liver cell as an example of an
animal cell
 Includes:
 Free Ribosomes
 Appear as dark granules in the cytoplasm
 Are not surrounded by a membrane
 Similar size to attached ribosomes (20 nm in diameter)
 Synthesize protein
 Created in a region of the nucleus called the nucleolus
 Rough Endoplasmic Reticulum
 Consists of flattened membrane sacs called cisternae
 Attached to these cisternae are ribosomes
 Synthesizes protein for secretion from the cell
 Protein passes into the cisternae and is carried by vesicles which bud
off (?) and move to the Golgi apparatus
 Lysosomes
 Almost spherical with a single membrane
 Formed from Golgi vesicles
 Densely stained due to high concentrations of protein
 Contain digestive enzymes which digest macromolecules
 Works best at low pH – 5
 Can be used to break down ingested food in vesicles or to break down
organelles in the cell or even the entire cell
 “Suicide Sacs” – self death
 Golgi Apparatus
 Consists of flattened membrane sacs called cisternae (like rER)
 Curved, stacked tubes with small vesicles near ends
 NO ribosomes attached
 Looks like pita bread
 Processes proteins brought in vesicles from the rER
 Most of these proteins are then carried in vesicles to the plasma
membrane for secretion
 Mitochondria
 Double membrane with inner folding
 Inside membrane invaginated to form structures called cristae (???)
 Shape is usually spherical or ovoid
 Has own DNA and ribosomes (can have hundreds if needed)
 Produce ATP for the cell by aerobic cell respiration
 Fat is digested in mitochondria if it is used as an energy source
 Nucleus
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Double membrane with pores
Uncoiled chromosomes are spread through the nucleus (chromatin)
Often densely stained areas of chromatin around the edge of nucleus
Stores almost all the genetic material of the cell
Where DNA replication and transcription takes place
Where mRNA is modified before export to the cytoplasm
Other Structures
 Nuclear Membrane – with pores
 Nucleolus – produces ribosomes
 Smooth Endoplasmic Reticulum
 No ribosomes attached
 Contains enzymes that do some metabolism
 Sedatives like Phenobarbital and alcohol cause more smooth ER to be made
which means more enzymes. This increases tolerance, leads to more drugs.
 Ribosomes
 Two Types:
 Free – makes proteins for internal cell use
 Attached to ER – makes proteins for secretion from the cell
 Vesicles
 Small membrane sacs
 Carry proteins from ribosomes on rER to Golgi to be processed
 Then travels to plasma membrane, fuses and expels protein through exocytosis
 Only formed when needed
 Cell Wall
 Selectively permeable
 Present in plant cells ONLY
 Made of cellulose
 Contains bundles of microfibrils
 Chloroplasts
 Double Membrane
 Present in plant cells ONLY
 Contains own DNA
 Contains chlorophyll
 Belongs to a larger group called plastids
 Cytoplasm
 Entire region between nucleus and plasma membrane
 Cytoskeleton runs through it
 Cytosol – fluid in cytoplasm
 Cytoskeleton
 Network of three types of fibres:
 Microtubules
 Involved with muscles
 Made up of globular proteins called tubulin
 Responsible for shape and support of cell
 Involved in separating chromosomes during mitosis
 Microfilaments
 Intermediate fibres
 Vacuole
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Present in plant cells ONLY
Large fluid filled sac used for storage and growth
Prokaryotic Vs. Eukaryotic Cells
 Naked DNA vs. DNA associated with proteins (chromatin and histones)
 DNA in cytoplasm vs. DNA enclosed in a nuclear envelope
 No mitochondria vs. mitochondria
 70S ribosomes vs. 80S ribosomes
 Eukaryotic cells have internal membranes that compartmentalize their functions,
prokaryotes do not
Plant Cells Vs. Animal Cells
 Plant cells have cell walls, animal cells do not
 Plant cells that photosynthesize contain chloroplasts, animal cells do not
 Starch is used as a storage compound in Plant cells, glycogen is used in animal cells
 Plant cells often times have a large fluid-filled vacuole, animal cells usually do not
 Plant cells have a fixed and usually regular shape, animal cells are able to change
shape and usually rounded
Endosymbiotic Theory
 Possible origin of Eukaryotic cells
 Prokaryotes, mitochondria, chloroplasts existed separately. Prokaryotes engulfed
either one or both to live in symbiotic relationship.
 Evidence:
 Mitochondria and chloroplasts have own DNA
 Certain organelles have double membranes
 Emergent properties
Compartmentalization
 Provides different local environments that facilitate a specific metabolic function
 Incompatible processes can occur simultaneously in separate areas
 Needs membrane-bound organelles
Extracellular Components
 Def n: structures made by cells outside their plasma membranes
 E.g. Cell Wall
 Cellulose microfibrils are assembled inside the cell and passed out through
the plasma membrane to add to the thickness of the wall
 Maintains cell shape
 Allows for high pressure to build up without the cell bursting
 Prevents excessive water uptake
 Holds plant up against gravity (turgor pressure)
 Extracellular Matrix
 Formed by glycoproteins secreted by animal cells
 Consists of a protein and an attached carbohydrate
 Functions in support, adhesion, movement of cells
 Two general forms (extracellular matrix):
 Interstitial matrix is a 3D gel that surrounds cells and fills space
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 Basement membrane is a mesh-like sheet formed at the base of
epithelial tissues (tissue that covers internal/external surfaces of the
body) that perform protective, secretory, or other functions and acts as
a cellular organizer.
Serves to:
 Support single layers of thin cells which might otherwise tear or
perforate
 Cell to cell adhesion
 E.g. a basement membrane helps capillary wall cells to adhere
to alveolus wall cells
*Also be able to identify structures in electron micrographs of liver cells.
**Distinguish between rER and Golgi, check micrographs (May ‘06).
***When comparing/contrasting, give difference first, then similarities.