Endosomes, Lysosomes, Cytoskeleton and Cytoplasmic Inclusions

-located close to plasma membrane
-involved in receptor recycling
-transport of early endosomes to late endosomes takes place through endosomal carrier vesicles

-Lie close to Golgi or nucleus
-Receive materials for digestion
-arise from early endosomes or fuse with hetero/autophagosomes

1. Take material in via endocytoses in clathrin coated pit
2. loses clathrin joins w/ early endosome (pH=6) which sorts contents
3.early endosome bring material to late endosome (pH=5.5)
4.Hetero/autophagosomes can join w/late endosomes forming lysosome (pH=5)

-formed from late endosomes
-pH=5-6 maintained by ATP driven H+ pump
-Contain hydrolytic enzymes i.e. nuclease, proteases, lipases
-like small stomachs
-special membranes to protect from enzymes
- membrane prevents leakage but allow digested materials to diffuse into cytosol
-permeability may change
-end products of lysosomal digestion are residual bodies or cleared out

-small, vary in size and shape
-electron-dense contents usually contain crystallin and cylindrical bodies
-contain catalase but no acid-phosphatase, produce H2O2
-location: liver cells, kidney tubules
-fxns: perform oxidative reactions, energy is then used for metabolic processes or is dispersed as heat, detox ethanol
-a role in gluconeogenesis

consists of:
microfilaments, intermediate filaments, microfilaments, associated intercalated proteins.
-dynamic
-microfilaments, microtubules have similar structure in all cells, but intermediate filaments vary in composition from cell to cell.
-fxns:
contractions, rigidity, mechanical strength, give shape to cell, intercellular transport/movement, chromosomal migration.

-actin filaments:
8nm, G and F actin form helices, only 1/2 cellular actin is found in filamentous form, crosslinked by actin binding proteins into parallel bundles and gel like networks
-myosin:
14nm
slide along each other during muscle contraction

-helical array of tetramers formed by elongated filamentous protein monomers
-10nm
-abundant in cells subjected to mechanical stress
-fxns:
provide mechanical strength to cell, shape, make different cells unique
-in 6 major types:
keratin, desmin, vimentin, glial filaments, neurofilaments and nuclear lamins

-hollow tubules
-25nm
-protofilaments formed of alpha tubulin and beta tubulin subunits (13 of these combine to form a microtubule)
-polarity
positive: polymerizing and growing
negative: depolymerizing
-fxns of MAPs (microtubule-associated proteins):
prevent depolarization and mediate interactions w/ other cell components, dyneins and kinesins are MAPs
fxns:
centrioles pull chormosomes apart, provide binding sites for MAPs, mediate organelle, and vesicle movement, structural components of basal bodies, maintenance of shape in erythrocytes and platelets

-barely visible w/ LM
-consist of 2 centrioles at right angles to each other
-0.1microm
-components of 9 groups of triplets (1 complete, 2 incomplete)

-present in liver, heart and skeletal muscle cells
-stained w/ bests caramine or PAS
forms:
-alpha particles assemble as groups in rosette config
-beta particels are individual units

-in adipose cells, hepatocytes and sterid producing cells
-non-membrane bound droplet
-imp. energy resource

Melanin:
-dark brown to black
-membrane bound melanosomes in melanocytes
-may be transferred to keratinocytes
Hemosiderin:
-due to hemoglobin degradation
-golden brown due to iron, formed of ferritin
-location:
spleen, liver, bone marrow, hemal nodes
Lipofuscin:
-aging pigment in cardiac cells, neurons
-residual product of lysosomal activity