CELL ORGANIZATION Flashcards
Microtubules
Structure: alpha & beta tubulin; non-branching, rigid, hollow tubes; polar ends
Function: Intracellular transport
Cell motility
Mitotic Spindle (chromosome attachment & mvmt during cell division)
Rigid intracellular skeleton (maintain cell shape and polarity)
Proteins: Dynein & Kinesin
Notes: MTOC (Microtubule organizing centers) direct/organize MT polymerization
GTP dependent
Centrioles
Structure: 9 triplets of MT arranged around a central axis (9+0 arrangement)
Function: Organize the centrosome
Form the basal body
Mitotic spindle formation (when centrosome form)
Notes: Mitotic spindles aligns during cell division
Cilia
Structure: MT-based with a 9+2 structural arrangement
Pair of Dynein arms as motor proteins
Function: Move fluid and particles along epithelial surfaces
Notes: Anchored to the cell by basal body
Primary cilia (9+0 arrangement) are located b/t main cilia and basal body
Intermediate Filaments
Structure: Rope-like, made from non-polar subunits
Essential for integrity of cell-cell & cell-ECM junctions
Function: Stabilize cell structure
Resist physical forces (Desmosomes & Hemidesmosomes)
Types: Acidic & Basic Cytokeratins - found in epithelial cells
Vimentin - found in mesoderm-derived cells
Vimentin-like - in desmin-muscle cells, glial fibrillary acid protein-glial cell
Neurofilaments - structural support for nerve cells
Lamins - Lamin A & B found in nucleus
Beaded Filaments - found in eye lens
Actin Filaments/Microfilaments
Structure: G-Actin (free) & F-Actin (polymerized in a filament, ATP dependent)
Polarized structures: (+) : fast growing, (-) : slow growing
Single filaments, bundles or networks
Function: Make up structural core of Microvilli & Stereocilia
Anchorage
Cell motility
Notes: Cell motility: 1) Protrusion where actin polymerized at (+) end and sticks out lamellipodia 2) Attachment where focal adhesion anchor actin cytoskeleton to ECM 3) Contraction where tail and middle cell body move forward
Microvilli
Structure: Membrane bound cytoplasmic projections anchored to the terminal web & cross-linked by villin
Function:
Notes:
Sterocilia
Structure: Long microvilli
Made of actin bundles that are are anchored to the terminal web
Usually found in sensory hair cells of the inner ear
Function:
Notes:
Lipfusion
Structure: Membrane bound pigments in neurons and cardiac muscle cells
Inclusion
Function: “wear & tear pigment” accumulates over time
Notes: Brownish-gold pigment generally seen in non-dividing cells
Hemosiderian
Structure: Membrane bound pigments found in spleen, from broken down RBCs
Inclusion
Function: Iron storage complex found in cytoplasm
Notes: Brown pigment
Melanin
Structure: Membrane bound pigment found in skin cells
Inclusion
Function: Absorbs UV light rays to protect the body
Notes: Brown pigment
Glycogen
Structure: Non-membrane bound
Inclusion
Function: Storage form of glucose
Notes: Through catabolism it releases glucose for energy
Lipid
Structure: Non-membrane bound, spherical droplets of triglyceride
Inclusion
Function: Energy storage
Source of short carbon chains for membrane synthesis
Notes: Lipidoses-lipid storage dx where lipid droplets accumulate in abnormal amounts and locations
Nuclear Envelope
Structure: Inner nuclear membrane (faces nucleoplasm)
Outer nuclear membrane (faces cytoplasm, continuous with ER)
Has nuclear pores
Function: Regulates the passage of macromolecules likes pores and RNA
Notes:
Nuclear Lamina
Structure: Thin, sheet-like meshwork beneath inner nuclear membrane
Made of intermediate filaments - Lamin A & B
Function: Acts as scaffolding for nuclear envelope, chromatin, and nuclear pores
Notes: Disassembles during mitosis
Clinical correlation: Hutchinson-Gilford Progeria Syndrome (HGPS)
Nuclear Pore Complex (NPC)
Structure: Spans inner & outer membrane
A nucleoporin made up of >50 proteins
Function: Transport of molecules b/t nucleus & cytoplasm
Passive transport: ions & molecules <9nm
Active transport: Molecules >9nm
Notes:
Nucleolus
Structure: 3 zones - fibrillar center (FC), fibrillar material (F), & granular mat (G)
Function: site of ribosomal production - rRNA is transcribed & ribosomal subunits are assembled
Notes: FC - pale stained because no rRNA is transcribed
F - darkest stained area because transcription of rRNA
GM - dark stained because initial ribosomal subunit assembly occurs
Nucleosome
Structure: macromolecular complex - 2 loops DNA wrapped around 8 histones
Function: fundamental structural unit of chromatin
Notes:
Ribsomes
Structure: 2 rRNA subunits: 30S (small) + 70S (large) in prokaryotes
40S (small) + 60 (large) in eukaryotes
Function: protein synthesis (translation)
Notes: found in membrane-bound ribosomes (rER) and free ribosomes (cytoplasm)
Endoplasmic Reticulum (ER)
Structure: Interconnected network of branching tubules, look like flattened sacs
Parts are continuous with the cytoplasm
Function: Smooth ER - synthesizes lipids and detoxification, gather calcium
Rough ER - synthesizes protein for plasma membrane, lysosomes, secretion
Notes: Smooth ER in cells specialized in lipid met & cells that synth/secrete steroids
Rough ER in cells specialized in protein synth & initial protein folding
Golgi Apparatus
Structure: Flat sacs stacked on top of each other
located next to the nucleus and centrosome
Contains cis face (entry) and trans face (exit)
Function: Sorting and packaging for vesicle transport
Notes: Well developed in secretory cells
Don’t usually stain well compared to other organelles
Lysosomes
Structure: Membrane-enclosed compartments filled with hydrolytic enzymes (acidic hydrolases)
Function: Controlled intracellular digestion of macromolecules
Pathways for lysosomal digestion - phagocytosis, endocytosis, autophagy
Clinical Features: Lysosomal Storage Diseases - Tay-Sachs Disease: accumulation of undigested GM2 ganglioside, disruption of normal cell functioning, and death of neurons in brain and spinal cord
Proteasomes
Structure: Large protein complexes that are ATP dependent
Function: Mediate protein degradation without the need of lysosomes
Notes: Destroy abnormal proteins and short-lived regulatory proteins by covalently tagging them with ubiquitin to initiate the process
Peroxisomes
Structure: Small organelles (.5 micrometers)
Function: Degrade toxic oxygen molecules
Detoxification of ingested alcohol
Important for fat metabolism
Notes: Synthesized by free ribosomes found in the cytoplasm
Clinical features: Zellweger syndrome - problem with importing peroxisomal proteins
Mitochondria
Structure: Inner & Outer Membranes
Intermembrane space
Matrix
Function: Generate ATP
Outer membrane - porins allow passage of small molecules, contains
Phospholipase and Acetyl CoA Synthase
Inner membrane - cristae folds, performs oxidation rxns., synthesize ATP,
regulate metabolite transport
Intermembrane space - enzymes used for ATP generation,
Cytochrom C matrix - oxidation of pyruvate, fatty acids, and citric acid cycle;
includes mitochondrial DNA, ribosomes, and tRNA; storage site for Ca+2
Notes: Site of Citric Acid Cycle, Oxidation Phosphorylation, and Beta-Oxidation of FAs
Associated diseases: MERRF (Myoclonic Epilepsy with Raffed Red Fibers)
Leber Hereditary Optic Neuropathy
Centrosome
Structure: pair of perpendicular centrioles
Function: organize microtubules
Centromere
Site of kinetochore formation
Heterochromatin
Kinetochore
Where mitosis spindle forms
Retrograde vesicles transport
Transport from golgi to rER
Involves COP-I coated vesicles
Anterograde vesicles transport
Transport rER to Golgi
Involves COP-II coated vesicles
