Term 1- Lec 9- Cytoskeleton & Vesicular Transport Flashcards
Intermediate filaments: •Size
•shape
•composition
•function
- 8-10 nm (middle sized fil)
- Rope-like
- Various protein filaments
- Helps to maintain structure of the cell
Microtubules: •size
•shpe
•composition
•function
- 20-25 nm
- Hollow cylinder
- Polymer of tubulin dimers—∂ & ß
- Intracellular transport via motor proteins, chromosome segregation, and cilia and flagella
Actin Filaments (Microfilaments): •size
•shape
•composition
•function
- 6-8 nm
- Double-stranded hilical shape
- Polymer of G-actin
- Structural, muscle contraction
Intermediate filaments are anchored at
desmosomes and hemidesmosomes—sites of stress
Intermediate filaments in epithelium
Keratin
Intermediate filaments in non-epithelium
Vimentin
Intermediate filaments in neurons
Neurofilaments
What is the structural polarity of an intermediate filament?
Intermediate filaments do not have structural polarity
Mutations in keratin genes that result in abnormal assebly of keratin filaments in epidermis:
Epidermolysis Bullosa Simplex (EBS)
Mutations in neurofilaments that cause abnormal accumulation and assembly cause progressive loss of motor neurons:
Amyotrophic Lateral Sclerosis (ALS, or Lou Gehrig’s disease)
Microtubules are anchored at:
- MTOC (centrosome, minus ends)
- Capping proteins (plus ends)
- Spindle poles
- Basal body of cilia and flagella
Microtubules bind to which nucleotide
GTP—has GTP Catalytic activity
Monomers that make up microtubules
∂ and ß tubulin (form heterodimers)
What is the structural polarity of microtubules
1 minus and 1 plus end per microtubule
What motor proteins are associated to Microtubules
- Kinesin—toward plus end (plasma membrane)
* Dynein—toward centrosome (into heart of cell)
Describe Dynamic Instability of microtubules
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.
What stabilize microtubules at the + end?
Capping proteins
What event polarizes a cell
The capping of the + end of microtubules
What motor proteins are associated to microtubules and enzymatic activity do they exhibit?
Kinesin and Dynein. They both exhibit ATPase activity. Walking along the microtubules requires ATP.
What is the motor protein in cilia and flagella?
Axonemal dynein
Absence of motor protein in flagella and cilia:
• Name of the disorder
•Motor protein it is deficient of
• What are the cinical consequences
- Kartagener Syndrome
- Axonemal dynein is deficient
- Leads to male sterility and chronic resiratory infection
Function of Actin filaments or microfilaments
- Microvilli
- Muscle contraction
- Lamellipodia and filopodia for movement
What anchors actin filaments/microfilaments?
Adherens junctions and Focal adhesions
Microfilaments bind to what nucleotide?
ATP—has ATP catalytic activity
Monomers of microfilaments
G-actin
Do microfilaments have structural polarity?
Yes, - and + ends
Associated motor proteins with microfilaments
Myosin I and Myosin II
What controls microfilament dynamic instability?
ATP binding and hydrolysis. ATP binding favors polymerization, ATP hydrolysis favors depolymerization
What are the 3 structures formed by Microfilaments and where are they?
- Parallel bundles—Microvilli and filopodia
- Contractile Bundles—Stress fibers @ focal adhesions
- Networks—Cell cortex: determines cell shape
Actin’s role in muscle contraction
Myosin II (using ATPase activity) pull actin filaments to the center of the sarcomere
Anctin’s role in intracellular transport
Myosin I walks along the actin filaments toward the plus end.
Vesicular Transport
Transportation of newly synthesized proteins move via vesicales along the ER-Golgi path
Organelle specific proteins:
Include ER-, Golgi- and Lysosomal-specific proteins
Plasma membrane proteins and secretory proteins:
Mediated through exocytosis.
What tag assures that a protein will return to the ER?
KDEL
How do ER-destined proteins return from the golgi?
A membrane receptor in the CIS golgi packages them and returns them in retrograde vesicles
What type of enzymes do lysosomes contain?
Acid hydrolytic enzymes—nucleases, proteases, glycosidases, lipases, etc.
What is the pH of the lumen of a lysosome, and how is it maintained?
Lysosomal lumen is acidic. The acidic pH is maintained by a H-ATPase, which pumps H+ into the lysosome.
All lysosome destined proteins are marked by
Mannose-6-P (M6P)
How does I-cell disease occur?
Deficiency of the enzyme that adds M6P to the lysosomal proteins
Early and Late endosomes
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
Lysosomal storage diseases
Most involve the dysfunction of lysosomal hydrolases, impairing degradation. Some involve vesicular traffic or the biogenesis of lysosomal proteins (I-cell) causing storage disorders
What always causes secretory granules to be released?
Ca2+
