Biochemistry - Cytoskeleton & Vesicular Transport

Question 1

Microtubule functions

Answer 1

Used in mitosis, intracellular transport, movement of cilia and flagella.

Question 2

Actin functions

Answer 2

cell shape, call movement, muscle contraction, ATP bound, polar.

Question 3

Actin monomers

Answer 3

G-actin

Question 4

Actin structure

Answer 4

2 chains of F-actin

Question 5

Microtubule Structure

Answer 5

Long, hollow cylinders made up of polymerised α- and β-tubulin dimers. The tubulin dimers polymerize end to end in protofilaments, the building-blocks. Thirteen protofilaments associate laterally. Diameter: 25-15 nm.

Question 6

Microtubule Monomers

Answer 6

a and b-tubulin

Question 7

Intermediate Filament Structure

Answer 7

8 protofilaments joined end to end with staggered overlaps, 8-12 nm. No polarity.

Question 8

Intermediate Filament Monomers

Answer 8

Cytokeratins, vimentin, nuclear lamin, neurofilament

Question 9

Intermediate Filament Functions

Answer 9

structural support, provides strength to cells.

Question 10

Amyotrophic lateral sclerosis (ALS)

Answer 10

Abnormal accumulation and assembly of neurofilaments causes progressive loss of motor neurons. Intermediate filament failure.

Question 11

Linkage between epithelial intermediate filaments

Answer 11

Desmosomes

Question 12

G-actin

Answer 12

Horseshoe-shaped actin monomers, with an ATP binding site in the center.

Question 13

F-Actin

Answer 13

The filamentous form of actin.

Question 14

Intracellular Movement mediated by…

Answer 14

Actin + Myosin I and II

Question 15

Myosin I

Answer 15

functions as a monomer, moving along actin filaments, carrying a variety of cargoes (e.g. membrane vesicles). Requires ATP, and NOT involved in muscle contraction.

Question 16

Myosin II

Answer 16

In muscles, it converts chemical energy (e.g. ATP) to mechanical energy, thus generating force and movement.

Question 17

Microfilaments (Actin) epithelial anchoring

Answer 17

Cell periphery, anchored to adherens junctions (between cells) and focal adhesions (cell-ECM)

Question 18

Intermediate filaments (Keratin) anchoring

Answer 18

Located throughout cytoplasm, anchored to desmosomes (cell-cell) and hemidesmosomes (cell-ECM)

Question 19

Microtubule (Tubulin) anchoring

Answer 19

Anchored to microtubule organizing centers (MTOC). (centrioles, basal bodies).

Question 20

Microtubule Organizing Centers (MTOC)

Answer 20

anchoring points surrounded by diffuse granular material (pericentriolar material) that serve as points of nucleation at minus end with plus end extending out towards membranes where growth and shrinkage occurs.

Question 21

Colchicine

Answer 21

Inhibits microtubule polymerization by binding both a- and b-tubulin. Alters motility of immune cells (neutrophils) to reduce inflammation associated with gout.

Question 22

Vincristine/vinblastine

Answer 22

Causes tubulin to aggregate inside the cell (decreasing concentration of available tubulin heterodimers). Used in cancer treatment to block tumor cell proliferation.

Question 23

Paclitaxel (Taxol)

Answer 23

Promotes stabilization of microtubules; cells become “stuck” in mitosis due to inability to depolymerize microtubules. Used in cancer treatment to block tumor cell proliferation.

Question 24

Kinesin

Answer 24

microtubule-dependent motor protein that transports vesicles towards the plus end (cell periphery).

Question 25

Dynein

Answer 25

microtubule-dependent motor protein that carries its cargo towards the minus ends, anchored at centrosomes near center of cell.

Question 26

Axonemal microtubules

Answer 26

The central shaft of cilia and flagella. Bending possible by sliding of one past the other.

Question 27

Kartagener syndrome

Answer 27

Characterized by the absence of dynein in flagella (sperm) and cilia (respiratory tract). It results in male sterility and in chronic respiratory infection.

Question 28

axonemal dynein.

Answer 28

Allows axonemal microtubules to move back and forth.

Question 29

cis-Golgi network (CGN)

Answer 29

Cisternae closest to the ER. Vesicles containing newly-synthesized lipids/proteins from the ER continuously arrive and fuse with cisternae.

Question 30

trans-Golgi network (TGN):

Answer 30

Cisternae furthest from ER where proteins and lipids are packaged in transport vesicles that bud off.

Question 31

Golgi functions

Answer 31

Post-translational modification (processing) of proteins and the sorting of proteins to final intracellular or extracellular destinations.

Question 32

KDEL

Answer 32

a sequence in the amino acid structure of a protein which keeps it from secreting from the endoplasmic reticulum (ER).Three letter code is: Lys-Asp-Glu-Leu. (disulfide isomerase, used in ER for insulin protein processing, has one.)

Question 33

Constitutive exocytosis

Answer 33

the default pathway, operates in all cells. Examples include plasma proteins (albumin), membrane proteins (E.g., Na+-K+-ATPase), and membrane lipids (sphingolipids).

Question 34

Regulated exocytosis

Answer 34

Occurs in specific cells/tissues, and ALWAYS mediated through calcium signaling. Proteins selected in TGN are diverted into secretoryvesicles near membrane nutil signal stimulated secretion. Examples include hormones (insulin, glucagon), neurotransmitters (epinephrine, acetylcholine), and digestive enzymes.

Question 35

Lysosomes

Answer 35

sites of intracellular degradation of macromolecules contain acid hydrolases with pH ~5.0, a pH maintained by H+-ATPase in membrane. Receive cargo from ER-golgi system as well as endocytic vesicles.

Question 36

mannose-6-phosphate

Answer 36

A post-transcriptional tag for proper sorting to the lysosome. In TGN, proteins with this tag bind ot MP6 receptor, which moves to endosome, shere lysosomal proteins are released. Proteins inactivated until ATP-H+ase pumps H+ into and drops pH to 4-5.

Question 37

I-cell disease

Answer 37

a deficiency of the enzyme that adds the M-6-P moiety to the lysosomal proteins. Leads to an accumulation of undegraded macromolecules. Pathology: developmental delays, short trunk dwarfism, lethal by ~ 7 years (heart failure or respiratory tract infections.)

Question 38

Causes of storage disorder diseases

Answer 38

…dysfunction of lysosomal hydrolases, proteins involved in vesicular traffic, AND biogenesis of lysosomes.

Question 39

microtubule catastrophe

Answer 39

At low tublin-GTP concentrations, growth rate slows, allowing GTP hydrolysis to catch up, creating an unstable tip that favors depolymerization.