Term 1- Lec 9- Cytoskeleton & Vesicular Transport

Question 1

Intermediate filaments: •Size
•shape
•composition
•function

Answer 1

• 8-10 nm (middle sized fil)
• Rope-like
• Various protein filaments
• Helps to maintain structure of the cell

Question 2

Microtubules: •size
•shpe
•composition
•function

Answer 2

• 20-25 nm
• Hollow cylinder
• Polymer of tubulin dimers—∂ & ß
• Intracellular transport via motor proteins, chromosome segregation, and cilia and flagella

Question 3

Actin Filaments (Microfilaments): •size
•shape
•composition
•function

Answer 3

• 6-8 nm
• Double-stranded hilical shape
• Polymer of G-actin
• Structural, muscle contraction

Question 4

Intermediate filaments are anchored at

Answer 4

desmosomes and hemidesmosomes—sites of stress

Question 5

Intermediate filaments in epithelium

Answer 5

Keratin

Question 6

Intermediate filaments in non-epithelium

Answer 6

Vimentin

Question 7

Intermediate filaments in neurons

Answer 7

Neurofilaments

Question 8

What is the structural polarity of an intermediate filament?

Answer 8

Intermediate filaments do not have structural polarity

Question 9

Mutations in keratin genes that result in abnormal assebly of keratin filaments in epidermis:

Answer 9

Epidermolysis Bullosa Simplex (EBS)

Question 10

Mutations in neurofilaments that cause abnormal accumulation and assembly cause progressive loss of motor neurons:

Answer 10

Amyotrophic Lateral Sclerosis (ALS, or Lou Gehrig’s disease)

Question 11

Microtubules are anchored at:

Answer 11

• MTOC (centrosome, minus ends)
• Capping proteins (plus ends)
• Spindle poles
• Basal body of cilia and flagella

Question 12

Microtubules bind to which nucleotide

Answer 12

GTP—has GTP Catalytic activity

Question 13

Monomers that make up microtubules

Answer 13

∂ and ß tubulin (form heterodimers)

Question 14

What is the structural polarity of microtubules

Answer 14

1 minus and 1 plus end per microtubule

Question 15

What motor proteins are associated to Microtubules

Answer 15

• Kinesin—toward plus end (plasma membrane)

* Dynein—toward centrosome (into heart of cell)

Question 16

Describe Dynamic Instability of microtubules

Answer 16

GTP-bound heterodimers of ∂ and ß tubulin concentrations drive this. If the dimers are added faster than the previous layer can be hydrolyzed off, then the microtubule grows. Vice versa for shrinking.

Question 17

What stabilize microtubules at the + end?

Answer 17

Capping proteins

Question 18

What event polarizes a cell

Answer 18

The capping of the + end of microtubules

Question 19

What motor proteins are associated to microtubules and enzymatic activity do they exhibit?

Answer 19

Kinesin and Dynein. They both exhibit ATPase activity. Walking along the microtubules requires ATP.

Question 20

What is the motor protein in cilia and flagella?

Answer 20

Axonemal dynein

Question 21

Absence of motor protein in flagella and cilia:
• Name of the disorder
•Motor protein it is deficient of
• What are the cinical consequences

Answer 21

• Kartagener Syndrome
• Axonemal dynein is deficient
• Leads to male sterility and chronic resiratory infection

Question 22

Function of Actin filaments or microfilaments

Answer 22

• Microvilli
• Muscle contraction
• Lamellipodia and filopodia for movement

Question 23

What anchors actin filaments/microfilaments?

Answer 23

Adherens junctions and Focal adhesions

Question 24

Microfilaments bind to what nucleotide?

Answer 24

ATP—has ATP catalytic activity

Question 25

Monomers of microfilaments

Answer 25

G-actin

Question 26

Do microfilaments have structural polarity?

Answer 26

Yes, - and + ends

Question 27

Associated motor proteins with microfilaments

Answer 27

Myosin I and Myosin II

Question 28

What controls microfilament dynamic instability?

Answer 28

ATP binding and hydrolysis. ATP binding favors polymerization, ATP hydrolysis favors depolymerization

Question 29

What are the 3 structures formed by Microfilaments and where are they?

Answer 29

• Parallel bundles—Microvilli and filopodia
• Contractile Bundles—Stress fibers @ focal adhesions
• Networks—Cell cortex: determines cell shape

Question 30

Actin’s role in muscle contraction

Answer 30

Myosin II (using ATPase activity) pull actin filaments to the center of the sarcomere

Question 31

Anctin’s role in intracellular transport

Answer 31

Myosin I walks along the actin filaments toward the plus end.

Question 32

Vesicular Transport

Answer 32

Transportation of newly synthesized proteins move via vesicales along the ER-Golgi path

Question 33

Organelle specific proteins:

Answer 33

Include ER-, Golgi- and Lysosomal-specific proteins

Question 34

Plasma membrane proteins and secretory proteins:

Answer 34

Mediated through exocytosis.

Question 35

What tag assures that a protein will return to the ER?

Answer 35

KDEL

Question 36

How do ER-destined proteins return from the golgi?

Answer 36

A membrane receptor in the CIS golgi packages them and returns them in retrograde vesicles

Question 37

What type of enzymes do lysosomes contain?

Answer 37

Acid hydrolytic enzymes—nucleases, proteases, glycosidases, lipases, etc.

Question 38

What is the pH of the lumen of a lysosome, and how is it maintained?

Answer 38

Lysosomal lumen is acidic. The acidic pH is maintained by a H-ATPase, which pumps H+ into the lysosome.

Question 39

All lysosome destined proteins are marked by

Answer 39

Mannose-6-P (M6P)

Question 40

How does I-cell disease occur?

Answer 40

Deficiency of the enzyme that adds M6P to the lysosomal proteins

Question 41

Early and Late endosomes

Answer 41

Early: Conatins macromolecules that are waiting to be borken down.
Late: Contains an increasing amount of hydrolytic enzymes. As more enzymes arrive, it will become a lysosome

Question 42

Lysosomal storage diseases

Answer 42

Most involve the dysfunction of lysosomal hydrolases, impairing degradation. Some involve vesicular traffic or the biogenesis of lysosomal proteins (I-cell) causing storage disorders

Question 43

What always causes secretory granules to be released?

Answer 43

Ca2+