CELL ORGANIZATION

Question 1

Microtubules

Answer 1

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

Question 2

Centrioles

Answer 2

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

Question 3

Cilia

Answer 3

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

Question 4

Intermediate Filaments

Answer 4

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

Question 5

Actin Filaments/Microfilaments

Answer 5

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

Question 6

Microvilli

Answer 6

Structure: Membrane bound cytoplasmic projections anchored to the terminal web & cross-linked by villin
Function:
Notes:

Question 7

Sterocilia

Answer 7

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:

Question 8

Lipfusion

Answer 8

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

Question 9

Hemosiderian

Answer 9

Structure: Membrane bound pigments found in spleen, from broken down RBCs
Inclusion
Function: Iron storage complex found in cytoplasm
Notes: Brown pigment

Question 10

Melanin

Answer 10

Structure: Membrane bound pigment found in skin cells
Inclusion
Function: Absorbs UV light rays to protect the body
Notes: Brown pigment

Question 11

Glycogen

Answer 11

Structure: Non-membrane bound
Inclusion
Function: Storage form of glucose
Notes: Through catabolism it releases glucose for energy

Question 12

Lipid

Answer 12

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

Question 13

Nuclear Envelope

Answer 13

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:

Question 14

Nuclear Lamina

Answer 14

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)

Question 15

Nuclear Pore Complex (NPC)

Answer 15

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:

Question 16

Nucleolus

Answer 16

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

Question 17

Nucleosome

Answer 17

Structure: macromolecular complex - 2 loops DNA wrapped around 8 histones
Function: fundamental structural unit of chromatin
Notes:

Question 18

Ribsomes

Answer 18

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)

Question 19

Endoplasmic Reticulum (ER)

Answer 19

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

Question 20

Golgi Apparatus

Answer 20

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

Question 21

Lysosomes

Answer 21

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

Question 22

Proteasomes

Answer 22

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

Question 23

Peroxisomes

Answer 23

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

Question 24

Mitochondria

Answer 24

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

Question 25

Centrosome

Answer 25

Structure: pair of perpendicular centrioles

Function: organize microtubules

Question 26

Centromere

Answer 26

Site of kinetochore formation

Heterochromatin

Question 27

Kinetochore

Answer 27

Where mitosis spindle forms

Question 28

Retrograde vesicles transport

Answer 28

Transport from golgi to rER

Involves COP-I coated vesicles

Question 29

Anterograde vesicles transport

Answer 29

Transport rER to Golgi

Involves COP-II coated vesicles