Exam II

Question 1

Name four types of intermediate filaments.

Answer 1

Nuclear, vimentin-like, epithelial, axonal

Question 2

nuclear, components and location

Answer 2

nuclear lamina, lamins A, B,C

Question 3

Vimentin-like, components and location

Answer 3

vimentin - many cells of mesenchymal origin
desmin - muscle
glial abrillary acidic protein - glial cells (astrocytes and some Schwann cells)
Peripherin - some neurons

Question 4

Epithelial

Answer 4

type I keratins (neutral/basic), epithelial cells and their derivatives

Question 5

Axonal

Answer 5

neurofilament proteins - neurons

Question 6

how is a microtubule built?

Answer 6

-building block is heterodimer of alpha and beta tubulin proteins
-each tubulin subunit has a GTP binding site. The GTP bound to beta tubulin can be hydrolyzed, but the GTP bound to alpha can’t be exchanged.
-tubulin heterodimers form protofilaments by linear polymerization. There is intrinsic polarity and heterodimers point in the same direction.
microtubule is stabilized by side or lateral binding of tubulin subunits such that 13 protofilaments fomr the side walls of the hollow microtubule

Question 7

five conditions required for favorable microtubule assembly

Answer 7

1. sufficient concentration of subunits
2. warm temp
3. low calcium levels
4. GTP
5. MAPs

Question 8

Is GTP required for microtubule assembly?

Answer 8

no. GTP is thought to change the conformation of the beta tubulin protein.

Question 9

What is the MTOC? What is at the core?

Answer 9

microtubule organizing centers, aka centrosomes. have two centrioles at right angles in center.

Question 10

what is the effect of colchicine on the cytoskeleton?

Answer 10

It is an antimitotic drug because it causes microtubules to disassemble.

Question 11

what is the make up of centrioles?

Answer 11

centrioles have two halves positioned at right angles to each other at the cell center. each half contains 9 triplet microtubules arranged around a hollow core. The centrioles cap the minus ends of microtubules so that plus end assembly can continue rapidly.

Question 12

what is a gamma tubulin?

Answer 12

a unique form of tubulin at centrosomes that is known to nucleate new microtubules by binding and stabilizing the minus ends. It forms unique “ring” structures called the gamma tubulin ring comnplex. gammg-TuRC nucleates new MTs by presenting a row of gamma tubulin subunits to recruit and bind to the minus ends of MTs.
gamma-TuRCs are part of pericentriolar material, not the centrioles themselves.

Question 13

What are MAP proteins?

Answer 13

can crosslink, cap, segregate and alter the dynamic properties of MTs. MAP2 and Tau are two examples.

Question 14

How is Tau related to Alzheimer’s?

Answer 14

it forms the insoluble paired helical filaments that are present in alzheimer’s brain tissue. Neurofibrillary tangles or NFTs are a sign of the disease. The NFTs are mainly made up of clumps of highly insoluble hyperphosphorylated tau protein that fill and choke the neuron. Hypothesis: tau abnormalities destabilize MTs so neurons more likely to die when tau dissociates from the MTs.

Question 15

How do MAPS influence the rate of catastrophe and rescue of MTs?

Answer 15

some binds to MTs and “pry” the protofilaments apart. (kinesin related proteins, catastrophe factors). Other MAPS have a stabilizing effect.

Question 16

Taxol?

Answer 16

binds and stabilizes microtubules

Question 17

colchicine, calcemid

Answer 17

binds subunits and prevents the MT polymerization

Question 18

vinblastine, vincristine

Answer 18

binds subunits of MT and prevents their polymerization

Question 19

Nocodazole

Answer 19

binds subunits of MT and prevents their polymerization

Question 20

What kind of motors do cilia and flagella have? membranes/organelle traffic?

Answer 20

axonemal/cytosolic

Question 21

three motility examples that use MTs

Answer 21

1. cilia and flagella movement (axonemal)
2. transport of membrane vesicles in the cytoplasm (cytosolic)
3. the alignment and separation of chromosomes during mitosis and meiosis by the action of the mitotic spindle apparatus

Question 22

what cells are ciliated in humans?

Answer 22

epithelial cells of trachea and parts of the reproductive system

Question 23

cilia movement vs. flagella

Answer 23

beat/sinusoidal

Question 24

axoneme? what is it made of?

Answer 24

core of a cilia or flagella
9 outer doublet MTs and 2 single MTs in center
subfiber A in outer doublet is complet MT with 13 protofilaments but subfiber B only has ten.
junction between A and B tubules strengthned by tekin
central pairs of MTs connected by periodic bridges and surrounded by fibrous inner sheath
inner and outer arms, ciliary dynein protein complex.
dynein arm extends from A subfiber of outer doublet to the B fiber of next adjacent outer doublet.
crosslinkers that hold axoneme together include: links made from nexin that join outer MT doublets in elastic straplike fashion and radial spokes that extend from inner MTs.

Question 25

what is the mechanism of ciliary motility?

Answer 25

microtubule sliding
activated dynein arm walks towards the minues end of the adjacent doublet using ATP hydrolysis. conformational changes and energy from force by ATP hydrolysis enables the dynein arms to push adjacent outer doublet towards the tip of the cilium

Question 26

two major branches of dynein family

Answer 26

axonemal or ciliary
cytoplasmic

ciliary: 1-3 heavy chains make heads to bind ATP. tails bind cargo.
cytoplasmic: heavy-chain homodimers, with two large motor domains as heads. important for membrane vesicle trafficking on MTs.

Question 27

what is a basal body?

Answer 27

each axoneme is continuous with one.
at base of cilia
has 9 triple MT arrangement. 2 at bottom continue into cilia. third starts at transition point, and two others are added. thought to be nucleating agent for cilia.

Question 28

what is Primary Ciliary Dyskinesias: Kartagener syndrome

Answer 28

inherited primary ciliary diskinesia. immotile cilia syndrome results from defective, nonproductive cilia that occur bedcause of mutations in the dynein complex proteins.
symptoms
1. chronic respiratory tract problems
2. infertility
2. situs inversus

Question 29

In what direction do kinesins go? cytosolic dyneins?

Answer 29

kinesins: plus end
cytosolic dyneins: minus end
in most animal cells, minus ends of cytoplasmic MTs are proximal to MTOC and plus end at distal end.

neurons: distal axon always +. dendrites vary.

Question 30

processive walking movement of kinesin-1

Answer 30

heads swing over each other in sequence

Question 31

how does cytoplasmic dynein bind to its cargo?

Answer 31

not directly. It uses the dynactin complex as an adaptor. Dynactin is a group of proteins that include the actin-related protein ARP1, spectrin, ankyrin, and numerous other proteins.