MCP 1-10

Question 0

Properties of Intermediate Filaments

Answer 0

• No structural polarity
• Not useful as motility tracks
• High tensile strength

Question 1

4 Types of Intermediate Filaments

Answer 1

1. Keratins
2. Vimentin-family
3. Neurofilament proteins
4. Nuclear lamins

Question 2

Structure of Intermediate Filaments

Answer 2

• Monomers: rod-like proteins with small globular ends
• Associate into homo- or hetero-dimers via tetrameric intermediates (don’t require cofactors, relatively stable)
• Dimers –> large bundles w/out structural polarity

Question 3

Keratins

Answer 3

• Cytoplasmic
• Epithelial cells, hair, nails, etc.
• Diverse family of proteins, co-assemble to form mixed filaments
• Main function = provide strength
• Essential for the body surface barrier function of skin

Question 4

Vimentin Family

Answer 4

• Cytoplasmic
• Vimentin: in cells of mesodermal origin
• Desmin: in muscle cells - holds together adj. myofibrils
• GFA (Glial Fibrillary Acidic Protein): in astrocytes and glial cells (CNS support cells)

Question 5

Neurofilaments

Answer 5

• Cytoplasmic
• In neurons: 3 subunits co-assemble into filaments that extend along axon
• Provide axon extensions with tensile strength

Question 6

Nuclear Lamins

Answer 6

• nuclear
• meshwork on inner surface of nuclear membrane of all cells
• most dynamic IF (disassemble/reassemble during mitosis - regulated by phosphorylation/dephosphorylation)

Question 7

Medical issues related to IF

Answer 7

• Progeria (premature aging): caused by Lamin A mutation
• Cancer diagnosis/treatment: type of IF proteins made can reveal tissue type of origin. Keratin typing esp. useful in identifying epithelial cancers
• Keratin mutations cause skin blister disease

Question 8

Microtubule Properties

Answer 8

• dynamic
• structural polarity
• motility tracks
• Dyneins and kinesins: motors that move organelles/chromosomes along microtubules

Question 9

Microtubule structure

Answer 9

• Hollow tube with a wall of 13 rows of subunits (alpha/beta dimers, contain GTP binding sites)
• Overall polarity: dimers all assemble in the same orientation along each row of MT
• Assembly requires Mg2+ and GTP

Question 10

Microtubule Assembly

Answer 10

• DYNAMIC INSTABILITY
• Requires GTP, Mg2+, and a critical subunit concentration
• Assembly/disassembly both on + side
• Tubulin binds GTP
• Beta tubulin assembled in dimers can hydrolyze its GTP-> GDP
• Assembly faster than hydrolysis = growth
• Assembly slower than hydrolysis = unstable, shrink rapidly
• Unstable MT rescued by binding new GTP dimers at end, resume growth

Question 11

Anti-microtubule drugs

Answer 11

1. Colchicine: blocks MT assembly by binding free tubulin, therapeutic for gout. Also anti-mitotic: disrupt mitotic spindle of dividing cells
2. Anti-cancer (chemotherapy) agents:
   - Vinblastine/vincristine (block MT assembly, anti-mitotic, kills dividing cells);
   - Taxol: binds/stabilizes MTs and arrests dividing cells in mitosis

Question 12

Microtubule Organizing Centers (MTOCs)

Answer 12

• centrosome = paired centrioles and surrounding material
• negative end attached to MTOC
• nucleating sites where + ends easily add, made of gamma tubulin

Question 13

Microtubule Maturation

Answer 13

• no longer show dynamic instability
• post-translational modifications: acetylation and detryosination of alpha tubulin contributes to stability
• ex. in cilia and nerve axons

Question 14

Microtubule-associated proteins

Answer 14

• may be stabilized by capping proteins or microtubule-associated proteins (MAPs) - decrease probability of disassembly
• proteins change surface of the microtubule for interaction with other cellular proteins
• ex. MAP2 and tau in nerve cells

Question 15

Dynein

Answer 15

• microtubule motor, carries heavy cargo (i.e. nucleus. Golgi, vesicles, MTs in mitotic spindle)
• Uses ATP hydrolysis to do mechanical work
• Move toward - end
• “inward” transport (e.g. recycled membrane)
• one and three headed - cilia and flagella
• keeps Golgi near the nucleus
• two headed - cytoplasmic dyenins

Question 16

Kinesins

Answer 16

Microtubule motor, carries cargo (ER network. mitotic/meiotic spindles, small vesicles (synaptic vesicles))
+ end directed motility
Uses ATP hydrolysis
Two headed ATPases
Outward transport (e.g. neurotransmitters)
Stretches the ER from nuclear out toward MT + ends

Question 17

Primary Ciliary Dyskinesia (PCD) aka Kartagener’s Syndrome

Answer 17

• Mutations affecting ciliary motility - defective motile cilia
• Causes infertility (males), respiratory infections, developmental asymmetry defects

Question 18

Polycystic Kidney Disease (PKD)

Answer 18

• mutations affecting ciliary membrane receptors
• caused by lack of receptors in membrane of non-motile cilia (needed for sensory systems and during limb development)
• loss of these cilia = wide range of symptoms