Organelle/Inclusion TEMs • This slide show reviews the images you have for study in the laboratory binder. • Images here may not be of high enough resolution to allow careful study. They are meant as reminders of key facts. • Nothing can substitute for careful examination of quality images in textbooks.
Nucleus • This TEM depicts a typical nucleus. • Usually the largest cellular organelle. • Note both euchromatin and heterochromatin. • Can you ID other organelles here?
Nucleus • This cell appears to have multiple nuclei, but it does not. Why does the nucleus look like this? • Remember that while most cells have only 1 nucleus, some do indeed have more.
Nucleus • This close-up view shows euchromatin surrounding heterochromatin. • Do not mistake these blobs of nuclear material for glycogen particles.
Nucleus • Here, both the nucleolus and nuclear pores are evident. • Pores are indicated by the small arrows. • The surrounding RER and the large nucleolus indicate biosythesis of proteins.
Nucleus • Freeze-fracture reveals the distribution of pores in the nuclear envelope. • Pores are dynamic and can open and close. • We know little about how pores are positioned.
Mitochondria/Plasma Membrane • Here, mitochondria are localized to the basal cell cytoplasm. • They associate with the basal membrane in order to provide ATP for membrane located ATP-dependent ion pumps.
Mitochondria/Glycogen • The top panel shows a cell totally filled with mitochondria. • The lower panel shows mitochondria and numerous glycogen particles.
Mitochondria • These are typical mitochondria cut in cross-section. • Remember that this diameter is about 0.5 mm and use this as a reference value.
Mitochondria • Here, mitochondria are located between the filaments in cardiac muscle. • Contrast this location with mitochondria in skeletal muscle.
Mitochondria • This is a cross-section of cardiac muscle. • The mitochondria are seen as irregularly shaped objects. • Cristae are apparent and aid identification.
Smooth ER • This cytoplasm is also entirely filled with SER. • Some RER with ribosomes is present. • “L” indicates a lysosome. • Mitochondria are also seen.
Endoplasmic Reticulum • SER fills the space between mitochondria with tubular cristae in this cell. • What is this cell likely synthesizing? • “L” indicates lipid droplets.
Endoplasmic Reticulum • Smooth ER fills much of this cytoplasm. • “LF” indicates probable lipofuchsin material or a secondary lysosome. • Can you find a bit of the nucleus in this image?
Endoplasmic Reticulum • Rough ER studded with ribosomes. • Can you determine what areas are cytoplasmic and what areas are compartmentalized?
Endoplasmic Reticulum • RER showing attached ribosomes very clearly. • Note the polysomes sectioned transversely. These look like spirals, with one shown at the arrow.
Golgi Apparatus • A poorly organized Golgi complex is located beneath a centriole. • Many of the Golgi sacs are distended, probably because they were filled with protein for secretion.
Golgi/Endoplasmic Reticulum • A Golgi complex in the center of the field is surrounded by RER and SER. • The black dots are NOT glycogen, but packaged protein. (They are membrane enclosed.)
Golgi Apparatus • This Golgi complex shows very distended saccules. • Note the extensive RER surrounding it.
Glycogen Particles • Glycogen particles, or rosettes, are seen here along with SER and mitochondria. • Glycogen is a cellular inclusion, not a membrane limited organelle.
Lysosomes • Numerous secondary lysosomes are seen in the upper half of this figure. • Two peroxisomes are seen at the bottom. How are these identified?
Lysosomes/Peroxisomes • Both lysosomes and peroxisomes are shown in these panels. • Can you determine which is which? • Do you understand their respective functions?
Secretory Vescicles • Why are these identified as secretory vesicles (granules) and not lysosomes? • Can we be positive of our identification here? • Practice by looking at other images.
Organelle Review • Images such as this allow you to see many organelles at once. • Compare relative sizes, locations, number etc. • Is this cell making protein?
Organelle Review • Review images like this in you textbooks. • Find such images in chapters we have not yet covered and just concentrate on identifying organelles. • Training your eyes takes practice.
Organelle Review • Nuclei, plasma membranes and mitochondria should be apparent to you even at this low magnification. • Locate euchromatin and heterochromatin.
Organelle Review • Here, cells are very active in protein biosynthesis. • What criteria tell you this?
Organelle Review • This is a cell similar to those shown on the preceding image. • Note the distended saccules of RER and the euchromatic nucleus.
Microtubules • Seen best in the lower panel, MTs here radiate from a centriole. • They are straight, hollow tubes made of tubulin protomers assembled into protofilaments.
Centrioles • Centrioles are composed of MTs, in triplet spirals when seen in cross-section (left). • A longitudinal section of a centriole is to the right. • Function of centrioles?
Centrioles • Centrioles exist as pairs, oriented at right angles to each other. • Centrioles are NOT membrane-limited. • Basal bodies anchoring cilia are modified centrioles.
Microtubules • “A”= anaphase. MTs help separate the chromosomes. • “C” and “D” show different sections of the area indicated in “B”. MTs are cut in cross/longitudinal section (left/right).
MTs/Intermediate Filaments • Review this image at higher magnification in the laboratory. • MTs are hollow in cross-section and 25mm in diameter. • Ifs are not hollow and only 10 nm in diameter.
Actin Microfilaments • Microvilli contain a core of actin microfilaments • These filaments are anchored in the cytoplasm • Microvilli contain NO microtubules
Actin Microfilaments • Freeze-etch of actin microfilaments in microvilli. • Their interaction with the internal terminal web is easily seen using this method.
Mitosis • Make sure that you can identify cells in interphase, prophase, metaphase, anaphase and telophase.
Prophase • A cell in late prophase with the chromosomes not quite yet forming a true metaphase plate. • Could you have determined these were chromosomes and not, for example, mitochondria?
Metaphase • A good metaphase plate seen in transverse section using the TEM at low magnification. • You can get an impression of the MTs forming the spindles fibers here as well.
Telophase • A cell in telophase with a clear cleavage furrow (arrows). • Telophase is rapid and cells at this stage are difficult to find. • Anaphase is a much more lengthy process.
Conclusion • You should be able to identify all organelles and inclusions at the level of the electron microscope. • Some organelles and inclusions should be visible and identified using the LM. • Knowledge of molecular composition will also allow you to ID these structures. • Know the stages of mitosis.